Thermal Therapy & Focused Ultrasound I
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 82

14:00         4390.     Real Time MR Thermometry for Monitoring Focused Ultrasound in the Liver

Andrew B. Holbrook1,2, Juan M. Santos3,4, Elena Kaye1,3, Viole Rieke1, Kim Butts Pauly1

1Radiology, Stanford University, Stanford, CA, USA; 2Bioengineering, Stanford University, Stanford, CA, USA; 3Electrical Engineering, Stanford University, Stanford, CA, USA; 4HeartVista, Inc., Los Altos, CA, USA

We have integrated a high speed, high resolution pulse sequence with referenceless MR thermometry to produce temperature images of high intensity focused ultrasound ablations in real time for therapies in the liver. The sequence was tested in a moving phantom. Maximum temperatures were compared to an identical sonication in a stationary phantom, and the system’s real time reconstruction was also tested. The moving phantom temperature data showed good agreement with the stationary phantom, as did its shape. Finally, in-vivo tests in a patient abdomen were performed to verify that minimal “temperature” rises from phase noise and blood flow occurred.

14:30         4391.     Localized FFT Phase-Correction Algorithm for Improved Real-Time PRF Shift Thermometry

R. Jason Stafford1, Axel J. Krafft2, Roger Jason McNichols3, Ashok Gowda3, Michael Bock2, John D. Hazle1

1Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA; 2Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 3BioTex, Inc., Houston, TX

MR-guidance of thermal therapy using the proton resonance frequency technique is susceptible to error from background variations in the magnetic field, particularly those caused by motion. Several techniques for suppressing these background errors so that useful thermometry can be performed have been presented in recent years. This work is concerned with a technique that uses iterative Fourier extrapolation into the treatment zone in order to obtain an estimate of the background and remove it.

15:00         4392.     A Fast Thermal Imaging Sequence for Focused Ultrasound Ablation of the Liver

Yuval Zur1

1GE Healthcare, Tirat Carmel, Israel

We developed a restricted FOV gradient echo EPI sequence for focused ultrasound ablation of the liver during free respiration. The scan time is ~50 msec with spatial resolution of 1.8 by 1.8 mm. A low SAR b1 insensitive broad band RF pulse is employed to suppress signal out of the FOV. The images are filtered along the time axis and SNR improves by ~2.9. The filtering enables us to acquire up to 3 slices simultaneously, or improve spatial resolution by using the UNFOLD technique.

15:30         4393.     MR-Guided Focused Ultrasound Ablation of the Rat Liver

Randy L. King1, Viola Rieke2, Kim Butts Pauly2

1Bioengineering, Stanford University, Stanford, CA, USA; 2Radiology, Stanford University, Stanford, CA, USA

>HIFU is being developed for the minimally invasive treatment of primary and metastatic liver cancer. We examined the feasibility of the rat model for the study of HIFU treatment of the liver. Our results show that it is possible to localize thermal lesions to the liver of the rat by sonicating through the ribs with no skin burns. We also demonstrate the ability of MR to thermally monitor and localize the lesions resulting from such a treatment.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 82

13:30         4394.     A Novel Application for MR Thermometry: Post Mortem Interval Estimation in Forensic Medicine

Sara Maria Sprinkhuizen1, Hedwig A. Tromp2, Chris J. Bakker1, Jessica D. Workum1, Hendrik de Leeuw1, Max A. Viergever1, Lambertus Wilhelmus Bartels1

1Image Sciences Institute, University Medical Center, Utrecht, Netherlands; 2Dept. Pathology/Toxicology, Netherlands Forensic Institute, The Hague, Netherlands

The exact time point of death (the post-mortem interval, PMI) is of great importance in the legal and criminological field. Currently, the nomogram of Henssge is used worldwide for PMI estimation. The rectal temperature used as input for the nomogram is a single point measurement, spatially as well as temporally. It is hypothesized that absolute, spatiotemporal temperature data acquired using MRS techniques improves the outcome of the PMI estimation. The goal of this work was to assess the feasibility of MRS based MRT to map absolute temperatures in post-mortem situations.

14:00         4395.     Fast Temperature Measurement Using a 2DRF Pulse Enables Both Reduced-FOV Imaging and Fat Suppression

Chang-Sheng Mei1,2, Jing Yuan1, Nathan J. McDannold1, Lawrence P. Panych1

1Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA; 2Department of Physics, Boston College, Chestnut Hill, MA, USA

During thermal ablation, the region of heating can be much smaller than the image FOV, resulting in waste of scan time to cover regions away from the heated zone. In addition, temperature estimation is problematic when the PRF method is used in tissues that contain both water and fat. We propose a technique that uses a 2DRF pulse to excite a reduced volume and to suppress fat. Focused ultrasound heating experiments were conducted where the reduced-FOV was selected to contain the focal spot. The observed temporal resolution increased by 2.3 fold without temperature error due to the presence of fat.

14:30         4396.     Online Phase-Collection Based Correction of MR Thermometry for Breast HIFU Ablation: Evaluation Under Various Respiratory Motion Susceptibility Conditions in Phantom.

Matthieu Lepetit-Coiffe1, Baudouin Denis de Senneville1, Philippe Lourenco de Oliveira1, Charles Mougenot1, Bruno Quesson1, Jean Palussiere1, Chrit Moonen1

1Laboratoire IMF CNRS UMR 5231 / Universite Bordeaux 2, Bordeaux, France, Metropolitan

An online phase-atlas based correction was evaluated regarding temperature accuracy improvement under various frequency and amplitude of respiratory motion conditions simulated thanks to a home made phantom. Fixed acoustic power and duration of High Intensity Focused Ultrasound (HIFU) was delivered during real time MR temperature acquisition in the respiratory mimicking phantom; Temperature maps were corrected with the proposed correction and results compared to temperature maps acquired under same HIFU delivery conditions without any perturbations.

15:30         4397.     Initial Evaluation of a Fast Chemical Shift Thermometry Technique in the Breast

Hua Ai1, Brian A. Taylor1, Andrew M. Elliott1, Huong LePetross2, John D. Hazle1, Roger Jason Stafford1

1Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; 2Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, USA

A fast chemical shift imaging technique for real-time temperature imaging in the breast was investigated. The uncertainty in temperature was evaluated by measuring the proton resonant frequency shift between lipid and water at various points across the breast. Temperature uncertainty over 20s was about 3.0~3.6°C. Calculated frequency difference is 13.8% percent lower than the expected quadrature sum of two frequencies, indicating that temperature uncertainty was consistently reduced by subtraction of lipid peak while the improvement was largely limited by low SNR. Moderate compression of breast is needed to minimize motion and hence temporal uncertainty in temperature.

 


 
MR-Guided Interventions II: Devices, Sequences & Applications
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 83

13:30         4398.     Increased Applicability of a Manipulator to Assist MR Guided Microwave Ablation of Liver Tumors and Clinical Experiences of 14 Cases

Shigehiro Morikawa1, Toshiro Inubushi1, Shigeyuki Naka2, Koichiro Murakami2, Yoshimasa Kurumi2, Tohru Tani2, Hasnine Akter Haque3, Junichi Tokuda4, Nobuhiko Hata4

1Biomedical MR Science Center, Shiga University of Medical Science, Ohtsu, Shiga, Japan; 2Department of Surgery, Shiga University of Medical Science, Ohtsu, Shiga, Japan; 3GE Yokogawa Medical System, Hino, Tokyo, Japan; 4Brigham and Women's Hospital, Boston, MA, USA

We developed a motorized MR-compatible manipulator with synergetic remote-center-of-motion control to assist MR guided microwave ablation of liver tumors and started clinical studies using it. To increase the applicability of this manipulator, several types of adaptors of the handpiece were developed. As a result, lateral approach to tumors was enabled and liver tumors in various locations could be punctured under the assistance of this manipulator. We have already experienced 14 clinical cases with liver tumors. All cases were successfully treated without any complications. Nowadays, this manipulator is routinely used in this procedure.

14:00         4399.     Automatic Passive Tracking of an Manually Steerable Instrument Holder for MR-Guided Interventions Applied in LITT

Axel Joachim Krafft1, Florian Maier1, Patrik Zamecnik, André de Oliveira1,2, Jürgen Walter Jenne3,4, Roger Jason Stafford5, Kamran Ahrar6, Axel Winkel7, Wolfhard Semmler1, Michael Bock1

1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 2Siemens AG, Erlangen, Germany; 3Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 4Mediri GmbH, Heidelberg, Germany; 5Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA; 6Interventional Radiology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA; 7Invivo Germany GmbH, Schwerin, Germany

The increasing complexity of MR-guided interventions demands high SNR and short image acquisition times. Therefore, a rising number of such procedures is performed in closed-bore MR scanners where patient access is severely restricted. Consequently, safe, accurate, and continuous instrument monitoring and guidance is a mandatory pre-requisite. A combination of an automatic passive tracking technique and a manually steerable instrument holder is proposed to meet the requirements of percutaneous interventions. The setup was tested during LITT as an advanced minimally invasive technique. Our experiments demonstrate the potential of this approach which is suitable for a wide range of interventional applications.

14:30         4400.     A Technique for Improving 2D X-Ray to 3D MRI Registration in Fluoroscopy-Guided Orthopedic Interventions

Martijn John van der Bom1, Josien Petronella Pluim1, Matthew Gounis2, Lambertus Wilbert Bartels1

1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; 2Radiology, University of Massachusetts Medical School, Worcester, MA, USA

MRI can provide 3D insight and soft tissue contrast for real-time intra-procedural navigation. However, MRI to X-ray registration is technically challenging due to insufficient similar landmarks caused by differences in physical imaging principles. We have investigated a novel technique for improved 3D MR to 2D X-ray registration. A simulated CT is generated from multispectral MRI data using a k-nearest neighbor classification method. This simulated CT than provides sufficient landmarks for MRI to X-ray registration. Classification was based on MR sequences commonly used in clinical practice. Validation in ex vivo experiments shows that this method is accurate and reliable.

15:00         4401.     Validation of a Vasculature-Based Co-Registration Technique of X-Ray and MR Images for the Guidance of Cardiovascular Interventions

Perry Radau1, Andriy Smatukha2, Peter Jones1, Regis Vaillant3, Alexander J. Dick4, Graham A. Wright1

1Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; 2Applied Science Laboratory, General Electric Healthcare, Toronto, ON, Canada; 3Applied Science Laboratory, General Electric Healthcare, Buc, France; 4Cardiology, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

Combined X-ray and MRI (XMR) guidance of interventions has been shown to offer considerable benefits by providing soft-tissue and functional information and real-time visualization of devices. This study presents and validates a software solution, FluoroFusion, which does not require hardware calibrations, optical tracking, or external markers. Phantom images were successfully fused with 3D error of 1.7 ± 0.7 mm and range 0.1-3.7 mm, from 14 trials utilizing two X-ray views each. In a study with patient data the accuracy was similar based on qualitative visual assessment. Its use requires minimal workflow adjustment or operator time. Images from any stand-alone MRI and X-ray systems could be used with Fluorofusion.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 83

13:30         4402.     Automatic Slice Positioning of the Interventional Guidewire Using Passive Paramagnetic Markers

Sunil Patil1, Oliver Bieri1, Permi Jhooti1, Klaus Scheffler1

1Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland

In this work, a novel method for passive real-time tracking of paramagnetic markers is proposed, termed Projection Reconstruction Imaging using echo-Dephasing (PRIDE). PRIDE is based on the acquisition of projections along all three physical (X, Y, and Z) axes, enabling a real-time positional update of the slice to the detected guidewire location. PRIDE exploits paramagnetic marker-related gradients along each projection to give rise to peak signal corresponding to marker position. Our initial in-vitro and in-vivo results indicate that PRIDE can be successfully used for real-time slice positioning.

14:00         4403.     Multiparametric Monitoring of Chemical Ablatons Using a Rapid Chemical Shift Imaging Technique

Brian A. Taylor1, Andrew M. Elliott1, John D. Hazle1, Roger Jason Stafford1

1Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA

The potential for monitoring chemical ablations with a high spatiotemporal resolution CSI technique is demonstrated ex vivo. Results demonstrated the ability to dynamically detect the chemical shift of the methyl group in ethanol and separate it from the water component. Additionally, dynamic T1-weighted images and quantitative T2* maps provided additional information which correlated with the agent location as observed on post-injection T1-weighted images. If a reference standard of known concentration is kept in the image, the amplitude of each chemical shift could possibly provide a quantitative means to monitoring the progress of therapy and better relate to outcome.

14:30         4404.     A Reliable Real Time Liver Motion Tracking for Application in Magnetic Resonance Guided High Intensity Focused Ultrasound Therapy

Dattesh D. Shanbhag1, Rekha Tranquebar1, James C. Ross2

1Imaging Technologies, GE Global Research, Bangalore, Karnataka, India; 2Department of Radiology, Surgical Planning Laboratory, Boston, MA, USA

Bias error analysis for liver feature tracking using an automated thin-plate spline algorithm is presented. The mean errors observed with automated algorithm were 1.8 mm and 2.9 mm with a maximum bias of 3.5 mm and 5mm, along the S-I and R-L respectively. The analysis shows that automated tracking could reliably replace the tedious manual tracking of features during the MRgFUS therapy procedure.

15:00         4405.     Compressed Sensing for Highly Accelerated 3D Visualization of 19F-Catheters

Carsten Oliver Schirra1, David Brunner2, Jochen Keupp3, Reza Razavi1, Tobias Schaeffter1, Sebastian Kozerke1,2

1Division of Imaging Sciences, King's College London, London, UK; 2Institute for Biomedical Engineering, Univeristy and ETH Zurich, Zurich, Switzerland; 3Philips Research Europe, Hamburg, Germany

Short response times and RF safety are essential in MR-guided interventions and numerous techniques have been proposed to address these issues.

 


 
Thermal Therapy & Focused Ultrasound II
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 84

14:00         4406.     The Influence of Background Gradients in Multi Gradient-Echo MR Thermometry

Sara Maria Sprinkhuizen1, Chris J. Bakker1, Lambertus Wilhelmus Bartels1

1Image Sciences Institute, University Medical Center, Utrecht, Netherlands

In multi gradient-echo (mGE) based MR thermometry (MRT), multiple gradient-echo images are acquired. The mGE signal contains spectral information of the substances involved, which can be post-processed into temperature data. Our study shows the impact of background gradients on the mGE based MRT technique. Such gradients shift the acquired echoes, and therefore alter the spectral properties of the mGE signal. This leads to errors in the temperature data, regardless of the post-processing technique used. A correction method is presented which largely adjusts for this effect.

14:30         4407.     Temperature Error Reduction During MRI Guided HIFU Treatment

Xiaodong ZHOU1,2, Qiang HE1,2, Qiang ZHANG2, Cheng NI1,2

1College of life science and technology, Tongji University, Shang hai, China; 2Siemens Mindit Magnetic Resonance Ltd., Shenzhen, Guangdong, China

We propose a method to remove ultrasound applicator susceptibility temperature error based on PRF-shift phase difference method during MRgHIFU. With this method reference image is not necessary to acquire repetitively when applicator moves position. Therefore tissue cooling down time between reference imaging can be saved. MRgHIFU treatment is simplified and total treatment time is much reduced.

15:00         4408.     Practical Thoughts on Using Repeated Bipolar Gradients for MR-ARFI

Jing Chen1,2, Kim Butts Pauly2

1Electrical Engineering, Stanford University, Stanford, CA, USA; 2Radiology, Stanford University, Stanford, CA, USA

MR-ARFI is a novel method for monitoring HIFU treatments. We have previously shown how to improve the accuracy and precision of MR-ARFI by using the repeated bipolar gradients to encode the displacement. In this work, two practical aspects in the in vivo application of MR-ARFI are analyzed. The bulk motion sensitivity is considered, and a list of optimized encoding width for different tissue types is provided.

15:30         4409.     Measurements of Kinetic Stability, Blood-Brain Barrier Permeability and Cytotoxicity for Two Thulium Based Contrast Agents

Daniel Coman1,2, Margarita Gattas-Sethi1, Hubert K.F. Trubel3,4, Peter Herman1,5, Fahmeed Hyder2,6, Garry Kiefer7, Francesco d’Errico6

1Department of Diagnostic Radiology, Yale University, New Haven, CT, USA; 2Quantitative Neuroscience with Magnetic Resonance (QNMR), Yale University, New Haven, CT, USA; 3Bayer HealthCare Research Center, Wuppertal, Germany; 4Department of Pediatrics, HELIOS-Klinikum Wuppertal, University Witten/Herdecke, Wuppertal, Germany; 5Semmelweis University, POB 448, H-1446, Budapest, Hungary; 6Departments of Diagnostic Radiology and Biomedical Engineering, Yale University, New Haven, CT, USA; 7Macrocyclics, Dallas, TX 75235, USA

In the last decade, a new non-invasive method for temperature and pH determination was developed based on temperature and pH dependencies of the 1H chemical shifts emanating from TmDOTP5-. More recently a similar temperature-sensitive probe was introduced, based on temperature dependence of the methyl 1H chemical shift of TmDOTMA-, which is pH independent. Our results show that these two agents are kinetically stable, they cross the blood-brain barrier, they clearly show the lack of any acute toxicity effects on Chinese hamster lung cells and they demonstrate that the brain’s activity is unaffected by their presence in the extracellular space.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 84

13:30         4410.     Real-Time Non-Subtraction Thermal Ablation Monitoring In-Vivo Using RE-TOSSI

Jamal Jon Derakhshan1,2, Sherif G. Nour1,2, Simi Paul2, Stephen R. Yutzy1,2, Jeffrey L. Sunshine2, Mark A. Griswold1,2, Jeffrey L. Duerk1,2

1Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA; 2Radiology, University Hospitals of Cleveland, Cleveland, OH, USA

Thermal ablation treatment monitoring in real-time has been challenging in MRI. Some techniques require a pre-treatment image for baseline subtraction which can cause severe distortions in temperature/thermal dose maps if motion occurs between acquisition of the baseline and subsequent imaging assessment. In a study involving 26 laser ablations in the paraspinal and tongue base muscles of 11 pigs at 1.5 T, RE-TOSSI, a new SSFP based pulse sequence with 5 second temporal resolution, is shown to directly visualize growing thermal ablation lesions (as compared to post ablation contrast enhanced images) with high CNR and resolution without requiring a pre-treatment image.

14:00         4411.     Dynamics and Distributions of Temperature Changes During Pharyngeal Selective Brain Cooling by 1H CSI

Daniel Coman1,2, Hubert K.F. Trubel3,4, Peter Herman1,5, Fahmeed Hyder2,6

1Department of Diagnostic Radiology, Yale University, New Haven, CT, USA; 2Quantitative Neuroscience with Magnetic Resonance (QNMR), Yale University, New Haven, CT, USA; 3Bayer HealthCare Research Center, Wuppertal, Germany; 4Department of Pediatrics, HELIOS-Klinikum Wuppertal, University Witten/Herdecke, Wuppertal, Germany; 5Semmelweis University, POB 448, H-1446, Budapest, Hungary; 6Department of Diagnostic Radiology and Biomedical Engineering, Yale University, New Haven, CT, USA

Pharyngeal selective brain cooling (pSBC) has been suggested a more suitable alternative to whole body cooling to decrease brain temperature. Temperature distributions in rat brain can be obtained within minutes by using a new exogenous temperature-sensitive probe, TmDOTMA-. The pharyngeal brain cooling rate constants and the recovering rate constants were calculated from the temperature variation over time. The recovering rate constants show a distribution which is slightly more dispersed than that of the cooling rate constants. Our results indicate that pSBC rate constants are tightly dependent on the local net heat contribution, measured indirectly by the recovering rate constants.

14:30         4412.     Feasibility Study of a New System for MR-Guided Scanned Focused Ultrasound Hyperthermia in Small Animals

Robert Staruch1, Rajiv Chopra

1University of Toronto, Toronto, ON, Canada

In order to facilitate hyperthermia-mediated drug delivery studies in small animal models, a motorized MR-guided transducer positioning system has been developed for focused ultrasound heating of rapidly scanned circular trajectories between 5 and 20mm in diameter. With this system, the temperature artifacts during simultaneous scanning and imaging were small enough to allow controlled heating, and good spatial and temporal temperature control (+/- 1 degree C) were achieved by applying multiple single-point controllers along the circular trajectory.

15:00         4413.     Computer Simulation and Temperature Measurement for MR Hyperthermia Therapy Using Coaxial-Slot Antenna

Tae Hyung Kim1, Kee Chin Tan1, Song I. Chun1, Ki Sueng Choi1, Yong Hee Han1, Chi Woong Mun1

1Biomedical engneering, Inje Univ., Gimhae, Kyungnam, Korea

Hyperthemia therapy combined with Magnetic Resonance Imaging (MRI) has several advantages for the treatment of small tumor. High Frequency Ultra Sound (HIFU) method has been commonly used for heating source. HIFU method, however, has some drawbacks. For this, coaxial-slot antenna driven by 2.45GHz ¥ì-wave was proposed. The coaxial-slot antenna was designed by computer simulation. To optimize the design of antenna, reflection parameter(S11) and SAR distribution in muscle model at the center frequency, 2.45§×, were analyzed using HFSS s/w. The temperature was measured to test heating performances of hand-made coaxial-slot antenna based on the distance from the heating point and power using agarose gel phantom. The SAR distribution has similar trends on both computer simulation and temperature measurement experiment. In this study suggest that coaxial-slot antenna is a useful heating source for MR hyperthemia therapy.

 


 
MR-Guided Interventions I: Devices, Sequences & Applications
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 85

13:30         4414.     Design and Preliminary Clinical Studies of an MRI-Guided Transrectal Prostate Intervention System

Axel Krieger1, Peter Guion2, Csaba Csoma1, Iulian I. Iordachita1, Anurag K. Singh2,3, Aradhana Kaushal2, Cynthia Menard4, Gabor Fichtinger1,5, Louis L. Whitcomb1

1Johns Hopkins University, Baltimore, MD, USA; 2NCI - NIH-DHHS, Bethesda, MD, USA; 3Roswell Park Cancer Institute, Buffalo, USA; 4Princess Margaret Hospital, Toronto, Canada; 5Queen's University, Kingston, Canada

This paper reports on the development and preliminary clinical studies of a new system for MRI guided transrectal prostate interventions. This system employs a novel hybrid tracking method which reduces procedure time and simplifies deployment on different scanners while achieving millimeter needle placement accuracy. Transrectal MRI guided prostate interventions such as biopsies and gold marker placements inside a high-field MR scanner are reported in initial clinical trials, demonstrating accurate and fast needle targeting of the complete clinical target volume.

14:00         4415.     Comparison of Two Real Time Tracking Methods for a Robotic Assistance System

Jaane Rauschenberg1, André De Oliveira2, Florian Maier1, Wolfhard Semmler1, Michael Bock1

1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany; 2Siemens AG, Erlangen, Germany

Passive markers such as contrast-agent filled spheres provide a cost-effective and reliable method to localize devices in an MR system. In this work two real time methods are evaluated that track the position of a robotic assistance system with passive markers. A fully automatic localization algorithm with sub-pixel precision, a combination of a phase-only cross correlation with a center-of-mass algorithm, is compared to a direct coordinate exchange between robot and MR. Slice positions and orientations are evaluated in a phantom experiment yielding a similar angular precision of about 1.3° for the needle axis.

14:30         4416.     MRI-Guided Monitoring of Cement Injection in Vertebral Bodies

René Schilling1, Hermann Josef Bail2, Florian Wichlas2, Christian Jürgen Seebauer2, Jens Rump1, Ulf Teichgräber1

1Department of Radiology, Charité Universitätsmedizin Berlin, Berlin, Germany; 2Center for Musculoskeletal Surgery, Charité Universitätsmedizin Berlin, Berlin, Germany

At last years’ ISMRM meeting, we presented modified PMMA bone cement for interventional use in open MRI systems. In this study, we evaluated various techniques for the safe application of cement in vertebral bodies under MRI–monitoring, using a phantom with artificial leakage ducts. Although monitoring a volume with near real-time MRI is still challenging, the experimental results suggest that a fast T1FSE (1 image/ 2.4s) and a “radial-shift” technique provide sufficient detection of leakage ducts up to 3mm in diameter. The experimental filling time (85s) was markedly shorter, than the cement injection time recommended by the manufacturer.

15:00         4417.     Nd:YAG Laser Based Laparoscopic Liver Resection in a 1.0 Tesla High Field Open MRI: Evaluation of Suitable Dynamic MR Sequences for Image Guided Surgery

Sascha Santosh Chopra1, Guido Schumacher1, Sven Christian Schmidt1, Christian Seebauer2, Ioannis Papanikolaou3, Ivo Van der Voort3, Florian Streitparth4, Jens Rump4, Ulf Teichgraeber4

1Dept. of Surgery, Charité Campus Virchow-Clinic; University Medicine Berlin , Berlin, Germany; 2Dept. Trauma Surgery, Charité Campus Virchow-Clinic; University Medicine Berlin; 3Dept. Gastroenterology, Charité Campus Virchow-Clinic; University Medicine Berlin; 4Dept. of Radiology, Charité Campus Mitte; University Medicine Berlin

Aim of this study was to identify suitable interactive (dynamic) magnetic resonance (MR) sequences for real time MR guided liver dissection in a 1.0 Tesla high field open MRI Scanner. Four dynamic sequences encompassing balanced steady state free precession (bSSFP), T1W gradient echo (GRE), T2W GRE and T2W fast spin echo (FSE) were analyzed regarding the image quality, artifact susceptibility and the performance of SNR and CNR. The T2W TSE sequence (1.5 seconds/image) was considered superior due to an intraoperative SNR of 6.9 (±0.7) and CNR (vessel to parenchyma) of 5.6 (±1.7) in the interventional setting. As a proof of concept MR-guided laparoscopic liver resection was performed in two healthy house pigs using the T2W TSE sequence.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 85

13:30         4418.     An Optical and Electromagnetic Hybrid Tracking System for MR Image Guided Interventional Procedures

Shigehiro Morikawa1, Hasnine Akter Haque2, Shigeyuki Naka3, Koichiro Murakami3, Yoshimasa Kurumi3, Tohru Tani3, Toshiro Inubushi1

1Biomedical MR Science Center, Shiga University of Medical Science, Ohtsu, Shiga, Japan; 2GE Yokogawa Medical System, Hino, Tokyo, Japan; 3Department of Surgery, Shiga University of Medical Science, Ohtsu, Shiga, Japan

In MR guided interventional procedures, an optical or electromagnetic tracking system has been used for image plane control. The optical tracking system precisely works in the strong magnetic fields, but line of sight must be maintained. An electromagnetic tracking system, which utilizes gradient pulses during data collection, can be used in any directions and even in covered area, but it requires continuous MR image acquisitions and its accuracy depends on the location. To take advantages of two sensor systems complementarily, we have developed a hybrid tracking system of them and enabled seamless navigation in MR guided interventional procedures.

14:00         4419.     Dual MRI-Tracking/SJM NavX Electro-Physiology Catheters for Navigation Inside an MRI: Initial Experience

Ehud Schmidt1, Jeremy D. Dando2, Robert D. Darrow3, Daniel Kacher1, Laurence M. Epstein4, Ferenc Jolesz1, Charles L. Dumoulin5, Vivek Y. Reddy6

1Radiology, Brigham and Womens Hospital, Boston, MA, USA; 2Atrial Fibrillation Division, St. Jude Medical, Minnetonka, MA, USA; 3GE Global Research, Niskayuna, NY, USA; 4Cardiology, Brigham and Womens Hospital, Boston, MA, USA; 5Radiology, Cincinnati Children’s Hospital, Cincinnati, OH, USA; 6Cardiology, University of Miami, Miami, FL, USA

An MRI-compatible Electro-Physiology catheter was constructed with positional tracking elements using both MRI Tracking micro-coils and St Jude NavX non-MRI, Voltage based, tracking. The catheter was tested in a Left Atrial Phantom inside an MRI. Simultaneous low-receiver bandwidth (+16 and +32 KHz) MR Tracking at 20 fps and Navx Tracking at 12 fps was possible. High Bandwidth (+128 KHz) Real-time MR Imaging disturbed the NavX tracking, but intermittent use of imaging and NavX tracking was possible, since the Navx system returned to the same position after each MRI scan.

14:30         4420.     Tracking System for Real-Time MR-Guided Percutaneous Interventions at 1.5T

R. Jason Stafford1, Barry Fetics2, Amir Roth2, Christine Lorenz3, Axel J. Krafft4, Michael Bock4, Kamran Ahrar5

1Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA; 2Robin Medical, Inc., Baltimore, MD, USA; 3Siemens Medical Solutions, Inc., Baltimore, MD; 4Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 5Diagnostic Radiology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA

New short bore, wide aperture 1.5T scanners make MR-guidance of percutaneous interventions in cylindrical bore scanners with real-time imaging technically feasible. A tracking system that operates within the bore of the magnet to aid in the needle or applicator placement of these procedures is needed for increasing workflow. In this report we describe our initial experience with an FDA approved active tracking system for MRI that can be used in a cylindrical bore to help plan and target needle/applicator placement in real time.

15:00         4421.     MRPen – 3D Marker Tracking for Percutaneous Interventions

Florian Maier1, Axel Joachim Krafft1, André de Oliveira2, Wolfhard Semmler1, Michael Bock1

1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 2Healthcare Sector, Siemens AG, Erlangen, Germany

In percutanous MR-guided interventions passive markers are used to delineate the position or the trajectory of rigid instruments, e.g. needles. In this work, a modified passive marker and a modified passive tracking pulse sequence are proposed. Based on the 3D position and rotation of the marker an imaging slice is automatically adjusted in real time. Measurements indicate that the marker design combined with the pulse sequence allows an accurate rotation estimation and 3D tracking of rigid instruments. Thus, the choice of an optimal needle trajectory in percutaneous interventions is highly facilitated and under manual control of the operator.

 


 
Interventional MR
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 86

14:00         4422.     Magnetic Resonance Guided Laser Thermal Therapy with Finite Element Simulation for Treatment Planning

Andrew Elliott1, Anil M. Shetty1, Roger McNichols2, David Fuentes1, John D. Hazle1, R Jason Stafford1

1Imaging Physics, M.D. Anderson Cancer Center, Houston, TX, USA; 2Biotex Inc., Houston, TX, USA

Image-guided laser induced thermal therapy using actively cooled applicators can potentially provide a minimally invasive alternative to conventional surgical interventions in regions such as the brain. Active cooling of the laser tips eliminates undesirable effects such as charring. This can be combined with real time temperature imaging feedback and use of appropriate modeling for final temperature and damage prediction. The current modeling is carried out using a finite element model of the Pennes equation which includes the effect of brain perfusion. The effect of the cooled laser tip is also simulated. Results show reasonable agreement between simulation and experiment.

14:30         4423.     Percutaneous Laser Disc Decompression (PLDD) in an Open High-Field MRI

Florian Streitparth1, Thula Walter2, Bernhard Schnackenburg3, Bernd Hamm2, Ulf Teichgräber2

1Radiology, Charité , Berlin, Germany; 2Radiology, Charité, Berlin, Germany; 3Philips Healthcare

Percutaneous laser disk decompression (PLDD) is a minimal-invasive treatment modality for lumbar disk prolapse. MR-guidance of PLDD allows not only planning and needle navigation, but also permits the monitoring of the temperature spread within the treated disc. To evaluate MR-thermometry, a 3D gradient echo sequence (GRE) was used with varying echo times in cadaveric lumbar spines to monitor the lasing procedure. Actual temperature within the disc was correlated with the calculated temperatures. Lesion sizes post-PLDD were correlated with lesion sizes on the corresponding MRI. A preferred echo time for the GRE sequence was determined for thermometric monitoring in vivo.

15:00         4424.     Real-Time Guidance and Thermal Monitoring of Interstitial Laser Ablation of Osteoid Osteomas in an Open High-Field MRI

Florian Streitparth1, Bernhard Gebauer2, Jens Rump2, Sascha Chopra2, Florian Wichlas2, Bernd Hamm2, Ulf Teichgräber2

1Radiology, Charité , Berlin, Germany; 2Radiology, Charité, Berlin, Germany

Under CT-guidance, interstitial laser ablation (ILA) in the treatment of osteid osteoma (Oo) has been successfully applied. After only one publication has described ILA of the Oo under low-field (0.23T) MR-guidance, we have evaluated the feasibility of ILA in an open high-field MRI (1.0T). 5 patients underwent ILA under open MR-guidance. All lesions were successfully localized and targeted under near real-time MR-fluoroscopy with fast turbo spin echo sequences. The laser ablation was monitored online with conventional magnitude images (T1 effect) of a gradient echo sequence. Color-coded proton resonance frequency (PRF) phase mapping data was found to be valuable.

15:30         4425.     MR-Guided Thermal Ablation in Bone Using a Rapid Chemical Shift Imaging Technique

Brian A. Taylor1, Andrew M. Elliott1, John D. Hazle1, Roger Jason Stafford1

1Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA

The rapid CSI technique is presented that can provide measurements of temperature in bone marrow at high spatiotemporal resolutions where CPD techniques are currently limited due to intravoxel lipid contamination. The technique allows a rapid acquisition without time or SNR-consuming lipid suppression and preserves the lipid signal for internal correction. Temperature calibrations seen in this study are consistent with those seen in lipid-containing materials. The ability of monitoring more than one lipid peak at high spatiotemporal resolution is demonstrated.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 86

13:30         4426.     Intravascular 3.0T MRI Using an MR Imaging-Guidwire

Yanfeng Meng1,2, Zhaoqi Zhang1, Huidong Gu3, Xing Lv4, Jue Zhang4, Jing Fang4, Bensheng Qiu2, Xiaoming Yang2

1Radiology, Beijing Anzhen Hospital, Capital Medical University, Beijing, China; 2Radiology, University of Washington, Seattle, WA, USA; 3MRI Research Team, MR Modality, GE Healthcare China, Beijing, China; 4Biomedical Engineering, Peking University, Beijing, China

Previous studies demonstrate MR imaging-guidewires (MRIG) can be used to create high-resolution vessel wall and plaque images with 1.5T MR scanners. The aim of this study was to evaluate the possibility of generating MRIG-mediated intravascular MR imaging with a 3.0T MR scanner. We first tested, in vitro, the functionality of a 0.032-in MRIG for intraluminal 3T MRI of a phantom, which demonstrated clearly the wall of the phantom tube and the MRIG itself with high SNRs. We then validated, in vivo, the feasibility of generating intravascular 3T MRI of abdominal aorta in two rabbits, which showed clearly the aortic walls when using different sequences. This study proves the capability of using the MRIG to generate high-SNR, intravascular 3.0T MRI, which may enable further MRIG-guided interventions in the 3T environment.

14:00         4427.     Tapering Improves the Forward-Looking Properties of the Interventional Loopless Antennae

Di Qian1,2, AbdELMonem M. EL-Sharkawy1, Paul A. Bottomley1,2

1Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA; 2Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA

The interventional loopless antenna has low tip sensitivity, which is exacerbated by uniform insulation. It is shown that the antenna’s current sensitivity can be redistributed distally by tapering the insulation. Electromagnetic (EM) method-of-moment analysis, experiments in phantoms and biological specimens at 3T, demonstrate that tapering can produce ~4-fold gains in the signal-to-noise ratio 1cm from the tip. Insulation tapering enhances the tip visibility for interventional MRI (iMRI) using loopless antennae without compromising the antenna’s tiny cross-sectional profile. Numerical EM analysis is a valuable design tool for improving the performance characteristics.

14:30         4428.     High Precision Measurement of Micro-Coil Locations for Real-Time Tracking Applications

Melvyn Boon King Ooi1, Sascha Krueger2, William J. Thomas3, Srirama V. Swaminathan4, Truman R. Brown1,3

1Biomedical Engineering, Columbia University, New York, USA; 2Philips Research Europe, Hamburg, Germany; 3Radiology, Columbia University, New York, USA; 4Philips Medical Systems, Cleveland, OH, USA

The ability to track the positions of multiple micro RF-coil in the MR system has been the foundation of recent advances in MR-guided medical devices, as well as motion detection and correction applications. The success of these marker-based tools is dependent upon the quality of the micro-coil position calculation. The current work presents a fully developed methodology – consisting of a short tracking pulse-sequence and micro-coil hardware – capable of high measurement accuracy and reproducibility in a temporal resolution suitable for use in real-time applications. The technique’s efficacy is validated by a series of measurements in a well-defined grid-phantom.

15:00         4429.     Interactive MR Image Scan Guidance with a Capability of Motion Compensation Using Endoscout Sensor

Hasnine Akter Haque1, Shigehiro Morikawa2, Shigeyuki Naka3, Koichiro Murakami4

1Japan Applied Science Laboratory, GE Yokogawa Medical Systems Inc., Hino, Tokyo, Japan; 2Biomedical MR Science Center, Shiga University of Medical Science, Ohtsu, Shiga, Japan; 3Department of Surgery, Shiga University of Medical Science, Ohtsu, Shiga, Japan; 4Department of Surgery,, Shiga University of Medical Science, Ohtsu, Shiga, Japan

Interactive real-time MR image guided navigation for the intervention use is a promising strategy. However, it is difficult to perform complicated surgical procedures with the guidance of Real-time MR images only. Reformatted image from the pre-acquired high-resolution interoperative image volume is commonly used for improved visibility, with an assumption that no change of patient position during surgery, which is not always possible. Here we propose a method of full automatic motion compensation technique using tiny gradient tracking sensor (Endoscout) attached to the patient.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 86

13:30         4430.     MR Compatible Phased Array HIFU Transducer for Localized Prostate Cancer Treatment; in Vitro Validation

Lorena PETRUSCA1, Rares SALOMIR1, Emmanuel BLANC2, Lucie BRASSET2, Francois COTTON3, Jean-Yves CHAPELON1

1U556, Inserm, Lyon, France; 2EDAP-TMS, Lyon, France; 3RMN Unit, CHU Lyon Sud, Lyon, France

High Intensity Focused Ultrasound (HIFU) under MRI guidance represents a minimally invasive approach for localized prostate cancer treatment. In our in-vitro study, an MR-compatible multi-element endorectal HIFU device capable of focusing the beam at different depths in the tissue is being investigated. Fast MR thermometry was made in 2 orthogonal planes simultaneously for different sonication sequences chosen based on numerical simulations: elementary lesions, lines, slices and volumes. Temperature and thermal dose maps obtained showed that a homogenous lethal dose was induced in the desired shape. Dynamic focusing strategy permits to treat patients with more complex anatomy: smaller or larger prostate.

14:00         4431.     3-D Control Over Spatial Heating Using Multi-Element Ultrasound Heating Applicators and Real-Time MR Temperature Feedback

Rajiv Chopra1,2, Kee Tang1, Matthew Asselin1, Mathieu Burtnyk1,2, MIchael Bronskill1,2

1Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; 2Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

The aim of this study was to evaluate the capability to deliver a targeted 3D pattern of thermal damage in the prostate gland using a multi-element transurethral ultrasound heating applicator operating under MR temperature control. MRI-guided transurethral ultrasound therapy was performed in 10 dogs using a five element heating applicator operating at 8.3MHz. MR thermometry was acquired in five planes centred on each transducer to measure the heating pattern in the plane of rotation of each element, and to control the treatment. The results of this study indicated that multi-planar MR thermometry enabled precise heating of a 3D region in the prostate gland.

14:30         4432.     Feasibility of Cardiac-Gated 3T MRI-Guided Myocardial Ablation with High Intensity Focused Ultrasound

Aravind Swaminathan1, Viola Rieke2, Randy Lee King2, John Pauly3, Kim Butts-Pauly2, Michael McConnell1

1Medicine, Stanford University School of Medicine, Stanford, CA, USA; 2Radiology, Stanford University, Stanford, CA, USA; 3Electrical Engineering, Stanford University, Stanford, CA, USA

3T MRI guided cardiac HIFU was performed and proved feasible in an ex-vivo study on porcine myocardium. Left ventricular septal ablation lesions could be created of varying size and with cardiac gating. Ablation was successfully monitored with MR temperature mapping.

15:00         4433.     T2-Weighted Imaging of the Left Atrium Acutely After Pulmonary Vein Isolation Demonstrates Wall Thickening and Edema.

Dana C. Peters1, Jeff Hsing1, Kraig V. Kissinger1, Beth Goddu1, Reza Nezafat1, Jason E. Taclas1, Mark E.  Josephson1, John V. Wylie1, Warren J.  Manning1

1Medicine, Cardiovascular Division, Beth Israel Deaconess Medical Center & Harvard Medical School, Boston, MA, USA

Radio frequency (RF) ablation of the left atrium (LA) to treat atrial fibrillation has a 65-80% success rate. In order to understand the acute effects of pulmonary vein isolation (PVI) in treatment of AF, the RF ablations were imaged acutely (1 day following PVI) in five patients and two healthy subjects, who served as controls. The T2-weighted sequence to visualize edema in the LA was optimized. TE values, breath-holding vs. free-breathing, and fat-suppression methods were compared. We found evidence of thickened LA wall with increased T2. This study is an important step in anatomically asessing the completeness of PVI, in the acute stage.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 86

13:30         4434.     Inductively Coupled Coils for Local SNR-Enhancement During MR-Guided Prostate Biopsy

Reiner Umathum1, Axel Joachim Krafft1, Andre de Oliveira1,2, Michael Bock1

1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany; 2Healthcare Sector, Siemens AG, Erlangen, Germany

MR-guided prostate biopsy procedures need an improved image SNR. MRS metabolic information could further help deciding from which areas samples need to be taken. As MR data quality crucially depends on local SNR, typically endorectal coils are utilized. In commercial needle holders passive markers fill the available space so that integration of a coil becomes difficult. Inductively coupled coils without direct connection to the MR system have significantly smaller space requirements. Two coil designs were examined for their ability to improve the local SNR at or near the biopsy sample area and for possible integration into commercial biopsy systems.

14:00         4435.     Active Needle for Real-Time MRI-Guided Percutaneous Procedures

Christina Elena  Saikus1, Kanishka Ratnakaya1, Anthony Z. Faranesh1, Robert J. Lederman1, Ozgur Kocaturk1

1Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA

MRI is increasingly used to guide percutaneous procedures but passive needle artifacts can often be non-specific and difficult to locate and follow under MRI. We have developed an active profiling needle that incorporates a loop antenna to provide distinct device appearance displayed on simultaneously acquired real-time images. The needle visibility and handling were evaluated during in vitro phantom imaging and in vivo real-time MRI-guided vascular access experiments in swine. Incorporating active visualization in the needle design provided clear information on needle location, insertion depth, and shaft positioning which can help safely conduct a variety of percutaneous interventional MRI procedures.

14:30         4436.     A Gd-DTPA Based Insoluble Polymer Coating Technique for Endovascular Device Visualization

Tomoka Kurita1,2, Kagayaki Kuroda3,4, Takeo Ohsaka1

1Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan; 2R & D Center, Terumo Corporation, Ashigarakami-gun, Kanagawa, Japan; 3Department of Human and Information Sciences, School of Information Science and Technology, Tokai University, Hiratsuka, Kanagawa, Japan; 4Medical Device Development Center, Foundation for Biomedical Research and Innovation, Chuo-ku, Kobe, Japan

For MR-guided endovascular procedures, the passive visualization technique of guidewires and catheters with the coating of the Gd-DTPA based polymer was developed. The guidewire and urethane tube were coated using the polymer by a dipping process and they were soaked into saline for swelling. Imaging was performed using a clinical 1.5 Tesla MRI with T1-FLAIR and FSPGR sequence. Coating devices were visible with a high signal intensity without any susceptibility artifact. The signal enhancement was maintainable and repeatable. This study shows that the MR-visible catheters and guidewires coated with the Gd-DTPA based polymer will contribute to the development of MR-guided endovascular procedures.

15:00         4437.     Optimization of Piezoelectric Motors to Enhance MR Compatiblity for Interventional Devices

Yi Y. Wang1, Mohammed Salman Shazeeb2,3, Christopher H. Sotak2,4, Gregory Scott Fischer1

1Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA, USA; 2Biomedical Engineering, Worcester Polytechnic Institute, Worcester, MA, USA; 3Medical Physics, University of Massachusetts Medical School, Worcester, MA, USA; 4Radiology, University of Massachusetts Medical School, Worcester, MA, USA

MR enables closed loop image-guided surgery, but the inability to use conventional sensors and actuators in high-filed MR limits the availability of assistive technologies for interventional procedures. We have worked to optimize the Piezo LEG piezoelectric motors so that they can be successfully used in the MR environment. Through thorough shielding, grounding and filtering, we have managed to reduce average SNR degradation to under 3% for standard T1 and T2 scan protocols; this level of compatibility surpasses previously reported results. With appropriate considerations, this technology enables high precision MR-compatible interventional devices such as the neurosurgery robot we are developing.

 


 
Relaxometry
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 87

14:00         4438.     A Fast Clinically Viable 3D T2 Mapping Technique

Ravi Teja Seethamraju1, Vladimir Jellus2, Timothy Hughes3, Mukesh G. Harisinghani4,5, Alexander Guimaraes4,5

1MR R&D, Siemens Medical Solutions, Charlestown, MA, USA; 2Siemens AG., Erlangen, Germany; 3Siemens AG, Erlangen, Germany; 4Center for Molecular Imaging Research, Boston, MA, USA; 5Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA

Though T2 mapping is desirable in many clinical applications it is not preferred due to the long acquisition times associated with the conventional Spin Echo (SE) sequence. Turbo or fast SE sequences though considerably faster than spin echo are not suitable for T2 mapping due to the stimulated echoes associated with them. Here we present an alternative technique based on DESS (Double echo steady state) to produce T2 maps.

14:30         4439.     Rapid T1 Mapping of Mouse Myocardium with Saturation Recovery Look-Locker Method

Wen Li1,2, Jia Zhong1,2, Ming Lu1,2, Mark Griswold1,2, Xin Yu1,2

1Biomedical Engineering Department, Case Western Reserve University, Cleveland, OH, USA; 2Case Center for Imaging Research, Case Western Reserve University, Cleveland, OH, USA

An ECG-triggered saturation recovery Look-Locker (SRLL) method is developed for fast cardiac T1 mapping. High temporal resolution (2.5 minutes) can be achieved without the aid of parallel imaging or EPI. In vitro validation was performed by comparing T1 measurements with that obtained from inversion-recovery method. The in vivo application of this method in delineating the kinetics of manganese-induced T1 shortening was demonstrated in mouse heart in response to intraperitoneal injection of MnCl2. These results suggest that SRLL may provide a rapid T1 mapping method for cardiac MRI using small animal models.

15:00         4440.     Improved Accuracy in T1 Mapping and Flip Angle Correction with Random Spoiling in Radial Gradient Echo Imaging

Wei Lin1, Hee Kwon Song1

1Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA

Due to its high imaging speed and SNR efficiency, spoiled gradient echo imaging plays an important role in many quantitative MR methods. However, conventional RF spoiling generates non-ideal signal intensities, particularly at short repetition times and large flip angles, which could significantly reduce measurement accuracy. We propose a novel spoiling scheme, based on random gradient moments and RF phases, in conjunction with the radial acquisition scheme, to achieve ideally spoiled image intensities for a wide range of T1, T2, TR and flip angles. Phantom experiments demonstrate significant improvement in T1 mapping and flip angle accuracy over conventional RF spoiling.

15:30         4441.     Fast High-Resolution T1 Mapping Using Inversion Recovery Look-Locker Echo-Planar Imaging at a Steady State: Optimization for Accuracy and Reliability

Wanyong Shin1, Hong Gu1, Yihong Yang1

1Neuroimaging Research Branch, National Institute on Drug Abuse, Baltimore, MD, USA

A fast T1 measurement sequence using inversion recovery Look-Locker echo-planar imaging at steady state (IR LL-EPI SS) is presented. Delay time for a full magnetization recovery is not required in the sequence, saving acquisition time significantly. Imaging parameters were optimized to minimize the bias from the imperfection of excitation pulses and to maximize the accuracy and reliability of T1 measurements. IR LL-EPI SS method preserves similar accuracy and reliability as conventional Look-Locker echo-planar imaging, while saving 20% acquisition time. Quantitative T1 mapping with 1×1×4 mm3 resolution and whole brain coverage (28 slices) can be collected in approximately 4 minutes.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 87

13:30         4442.     Accuracy of T1 and Equilibrium Magnetization Maps Using a Spoiled Gradient-Recalled Echo Sequence with Variable Flip Angles at 4.7 T, 7 T, and 9.4 T: A Gadolinium-Doped Gel Phantom Study.

Hideto Kuribayashi1, Takuya Minowa2, Yoshie Maitani2, Masaki Sekino3, Hiroyuki Ohsaki3, Masayuki Ueda4, Yasuo Katayama4

1Varian Inc., Minato-ku, Tokyo, Japan; 2Hoshi University, Shinagawa-ku, Tokyo, Japan; 3The University of Tokyo, Kashiwa, Chiba, Japan; 4Nippon Medical School, Bunkyo-ku, Tokyo, Japan

T1 calculated using a spoiled gradient-recalled echo sequence with variable flip angles (SPGR-VFA) was underestimated especially at 9.4 T and with a short TR (< 10 ms). T2* wasn't found to be the main reason of the shortened T1 from the SPGR-VFA method at 9.4 T. Variable TR measurements were found to be useful for more accurate T1map measurement. Magnetization equilibrium maps using the SPGR-VFA method were interestingly stable among the variable TRs.

14:00         4443.     Flip Angle Optimisation Using an In-Vivo T1 Distribution-Weighted Approach Based on the Cramer-Rao Lower Bound Theory for Accurate T1 Quantification

Keiko Miyazaki1, David J. Collins1, Dow-Mu Koh1,2, Martin O. Leach1, Matthew R. Orton1

1Cancer Research UK Clinical Magnetic Resonance Research Group, The Institute of Cancer Research, Sutton, Surrey, UK; 2Academic Department of Radiology, Royal Marsden Hospital, Sutton, Surrey, UK

The variable flip angle method allows accurate and efficient T1 quantification which is important in many fields of MR. Optimisation of flip angles when imaging samples with a large T1 range of values has been far from trivial and little work has been published on this subject. During the optimisation, it is important that the actual distribution of T1 values in the image sample is taken into account. We propose a novel flip angle optimisation approach, based on the Cramer-Rao lower bound (CRLB) theory, which is weighted by the probability distribution of the T1 range of interest.

14:30         4444.     Simultaneous Quantitation of T1 and T2 Using a Novel 2D Magnetization-Prepared Multi-Slice Pulse Sequence

Eric Tzguang Han1

1Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA

A novel 2D multi-slice pulse sequence uses a magnetization preparation scheme to impart varying degrees of T1- and T2- weighting in a single scan – enabling simultaneous quantitation of T1, T2, and M0. Using this new method, in vivo T1 and T2 maps of the head and knee were acquired. Measured T1 and T2 values were within published ranges.

15:00         4445.     T1-Mapping Using Two Flip Angle Spoiled FLASH-EPI Hybrid Sequences

Christine Preibisch1,2, Steffen Volz2, Ralf Deichmann2

1Abteilung für Neuroradiologie, Klinkum rechts der Isar der TU München, München, Germany; 2Brain Imaging Center, Universitätsklinikum Frankfurt, Frankfurt, Germany

Problem: Several T1-mapping methods are based on dual flip angle spoiled gradient echo sequences. We propose a FLASH-EPI hybrid readout for improving the signal-to-noise ratio (SNR).

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 87

13:30         4446.     Singleshot Measurements of T1 and Field Variation Using 2D Simultaneous Singleshot Spin-, Gradient-, and Stimulated-EPI (2D Ss-SGSTEPI)

Xianfeng Shi1, Xin Liu1, EunKee Jeong2

1Department of Physics, University of Utah, Salt Lake City, UT, USA; 2Department of Radiology, University of Utah, Salt Lake City, UT, USA

A stimulated echo is formed after three 90o RF pulses. Magnetization-preparation is accomplished immediately after the first RF pulse and the second RF pulse restores a half of prepared magnetization into the longitudinal space. Other half is remained on the transverse plane. In the conventional stimulated-echo pulse sequence, a half of the prepared magnetization is discarded. A novel imaging technique has been developed to utilize other half of the prepared magnetization at the spin-echo position and simultaneously acquire spin-, gradient-, and stimulated-EPI in a singleshot using 2D singleshot spin-/stimulated-EPI (2D ss-SGSTEPI).

14:00         4447.     Fast T1 Mapping Using a CPMG Sequence

Robert L. Greenman1, Robert V. Mulkern2

1Radiology, Harvard University Medical School and Beth Israel Deaconess Medical Center, Boston, MA, USA; 2Radiology, Harvard University Medical School and Boston Children's Hospital, Boston, MA, USA

Many pathologies are characterized by changes in the T1 relaxation rate of specific tissues. Most of the widely accepted methods of measurement of the tissue T1 values are time consuming. The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence is widely used for fast imaging where spin-echo contrast is required. We present a novel method for measuring T1 relaxation rates, based on the CPMG sequence. The results of T1 measurements of a phantom and human skeletal muscle suggest that this method may provide fast, accurate T1 information.

14:30         4448.     Apparent Change in the T1 of Lipids in Mixture

Houchun Harry Hu1, Krishna S. Nayak1

1Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA

This work investigates potential bias in the T1 spin-lattice relaxation constant between pure fat and fat in mixture with water and lean tissue. We present results obtained at 3 Tesla from fat-water emulsions, ground pork meat, and in vivo experiments that suggest the existence of this additional T1 bias in fat. We observed the apparent T1 of fats to increase from their natural, pure-form T1 (200-350 ms at 3 Tesla) by as much as two to three-fold, when fat was in relatively homogenous mixtures characterized by fat-water signal fractions of less than 40%.

15:00         4449.     Quantification of Noise Efficiency with T1 Corrected IDEAL Spoiled Gradient Echo Imaging

Curtis Nathan Wiens1, Bryan Thomas Addeman2, Shawn Joseph Kisch2, Catherine D. Hines3, Hanzhou Yu4, Jean H. Brittain4, Scott B. Reeder3,5, Charles A. McKenzie1,2

1Physics, University of Western Ontario, London, Ontario, Canada; 2Medical Biophysics, University of Western Ontario, London, Ontario, Canada; 3Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, USA; 4Applied Science Laboratory, GE Healthcare; 5Radiology, University of Wisconsin-Madison, Madison, Wiconsin, USA

Both single and multi-flip angle methods have been used to minimize the T1 bias that can cause a difference between the true fat mass fraction and the fat fraction estimated by IDEAL-SGPR. Breath-hold restrictions in abdominal imaging require that data for each flip angle have short acquisition times, and thus with lower SNR, when acquiring multiple flip angles. To examine this tradeoff, the noise efficiency of using 1-5 flip angles for fat fraction measurement was determined. Measurements in phantoms of varying water-fat fractions demonstrated that a single flip angle is the most noise efficient method to determine the fat fraction.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 87

13:30         4450.     Accurate and Efficient Mapping of Flip Angle and T1 Using Simultaneous Actual Flip Angle - Variable Flip Angle Imaging (AFI-T1)

Samuel A. Hurley1, Alexey A. Samsonov2

1Medical Physics, University of Wisconsin - Madison, Madison, WI, USA; 2Radiology, University of Wisconsin - Madison, Madison, WI, USA

The knowledge of flip angle is essential for many quantitative MRI techniques such as variable flip angle (VFA) T1 mapping. We propose a new approach, which circumvents the shortcomings of Actual Flip angle Imaging (AFI) such as T1 dependence of flip angle values for short T1/long TR regimes, and simultaneously yields T1 maps with higher precision in less imaging time. The new method (AFI-T1) exploits a synergy between AFI and VFA T1 methods arising from the similarity of the steady state spoiled gradient echo (SPGR) based pulse sequences.

14:00         4451.     Skin T1 Mapping at 1.5T, 3T, and 7T.

Joelle Karine Barral1, Nikola Stikov1, Erik Gudmundson2, P. Stoica2, Dwight George Nishimura1

1Electrical Engineering, Stanford University, Stanford, CA, USA; 2Information Technology, Uppsala University, Uppsala, Sweden

Increasing the field strength seems promising for high-resolution skin imaging but a legitimate concern is the increase in the spin-lattice relaxation parameter T1. Skin T1 maps at 1.5T, 3T, and 7T are compared and a novel non-linear least-square approach for fast and accurate T1-estimation is proposed.

14:30         4452.     Fast Three-Point Approach for Volumetric T1 Mapping

Rahul Sarkar1, Alan R. Moody1,2, General Leung1,2

1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; 2Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

A fast volumetric technique for T1 quantitation at 3T is presented. Results are validated in a phantom model and initial results are shown in a whole brain scan requiring less than 5 minutes.

15:00         4453.     Towards Whole-Brain Quantitative T1 Mapping at 3.0T for Imaging Hippocampal Sclerosis

Rebecca Sara Samson1, Mark R. Symms2, Mahinda Yogarajah2, Niels Focke2, John S. Duncan2

1Department of Neuroinflammation, UCL Institute of Neurology, London, UK; 2Department of Clinical & Experimental Epilepsy, UCL Institute of Neurology, London, UK

This study aimed to establish the normal variation in T1 measurements made using a 3D, whole-brain T1 mapping method at 3.0T with a view to applying the technique in Hippocampal Sclerosis. Measured T1 values are consistent with literature and inter- and intra-subject variation were demonstrated to be uniformly low, indicating the potential of this method for clinical applications, including imaging the hippocampus. T1 mapping in Hippocampal Sclerosis may provide complementary information to the well-established technique of T2 measurement.

 


 
Local Field Perturbations
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 88

14:00         4454.     Crushed Early Acquisition Spin Echo (CEASE): A Novel Technique for Positive Contrast and Spectroscopic Imaging of Superparamagnetic Particles

Bernard MCW Siow1, Aiqing Chen2, Gavin Clowry2, Li Sun2, Andrew M. Blamire1

1Newcastle Magnetic Resonance Centre, Newcastle University, Newcastle upon Tyne, Tyne and Wear, UK; 2Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, Tyne and Wear, UK

Imaging of iron oxide particles with T2* weighted scans provides negative contrast, however, in biological samples other hypointense regions are likely to be present. Positive contrast methods generate contrast that is more specific to iron oxide particles. Here we present a novel sequence that provides positive contrast and provides spectroscopic imaging: The CEASE sequence eliminates background signal by crushing macroscopic magnetisation and rephases spins local to the iron oxide particles. We have shown that it provides positive contrast and spectroscopic imaging in a phantom containing MPIO and an ex-vivo rat brain with stem cells that have been labelled with MPIO.

14:30         4455.     Flow-Insensitve Magnetization Preparation for T2* Contrast

Christian Stehning1, Jürgen Rahmer1, Ulrike Blume2, Tobias Schaeffter2

1Philips Research Europe, Hamburg, Germany; 2Division of Imaging Science, King's College, London, UK

A magnetization preparation pulse sequence to obtain magnetic resonance images with strong T2* weighting is described. It overcomes the need to use sequences with long echo times (TE), which are inherently sensitive to flow artifacts.

15:00         4456.     Selective Depiction of Holmium-Loaded Microspheres (HoMS) Using Susceptibility Gradient Mapping (SGM): Initial Experience in Animal Models

Peter Roland Seevinck1, Gopal Varma2, Hendrik de Leeuw1, Julien Senegas3, Tobias Schaeffter2, Chris J.G. Bakker1

1Imaging Sciences Institute, Department of Radiology , University Medical Center, Utrecht, Netherlands; 2Division of Imaging Sciences, King's College London, UK; 3Philips Research Europe, Hamburg, Germany

The potential of susceptibility gradient mapping (SGM) for the selective depiction of holmium-loaded microspheres (HoMS) in the liver in ex vivo and in vivo animal models was investigated and confirmed. It was shown that positive contrast can be optimized by varying the echo time. Although SGM is not sensitive to the origin of the induced d÷ affect, directional information (i.e. 1D and 2D SG maps) can be used to exclude macroscopic field variations along the direction of choice. This allows discriminating between T2* effects induced by paramagnetic substances (local d÷) and macroscopic field inhomogeneities.

15:30         4457.     Quantification of SPIO Using T2*  and Phase Imaging

Alexia Rodríguez-Ruano1, Marina Benito1, Cristina Santa Marta2, Gema Elvira3, Paula Montesinos1, Juan Jose Vaquero1, Augusto Silva3, Manuel Desco1,4

1Medicina y Cirugía Experimental, Hospital General Universitario Gregorio Marañón, Madrid, Spain; 2Dept. Física Matemática y Fluidos, Universidad Nacional de Educación a Distancia (UNED), Madrid, Spain; 3Cancer Genetics and Cancer Stem Cells Laboratory, Centre of Biological Research (CIB-CSIC), Madrid, Spain; 4Centro de investigación en red en salud mental (CIBERSAM), Madrid, Spain

Quantification in susceptibility imaging is becoming a request for many applications. Susceptibility effects have been studied mainly from two approaches, SWI and T2* relaxometry. However, most of the studies using these techniques were not particularly concerned with quantification issues. We have assessed the sensitivity and quantification ability of these techniques by comparing the measurements obtained using different types of images with the concentration of SPIO particles in the sample, using an agar phantom with different iron concentrations. Phase image contrast results in a linear relation with iron concentration similar to that obtained with T2* map, while requiring shorter acquisition time.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 88

13:30         4458.     A Three-Field Study of Cerebral Transverse Relaxation Rates in Vivo: Implications for Brain Iron Measurements

Ana Maria Oros-Peusquens1, Miriam Rabea Kubach1, Maija Laurila1, N. Jon Shah1,2

1Institute of Neurosciences and Biophysics, Research Centre Juelich, Juelich, Germany; 2Faculty of Medicine, Department of Neurology, RWTH Aachen University,  JARA, Aachen, Germany

Relaxation times in pure water and their field dependence is well predicted by the Blombergen-Purcell-Pound theory; this dependence for typical MRI fields is negligible. Proton relaxation times in tissue are different from those of pure water and have a pronounced field dependence possibly due to micro-structural ferritin content, for example. We report a 3-field study of T2/T2* in vivo performed with the aim of providing quantitative information about transverse relaxation in a field range of 1.5T-4T. Further, we discriminate between the linear and quadratic dependence of T2/T2* on field strength and investigate the correlation between the rate increase in regions with clear a linear dependence and their estimated iron content. The relevance of this methodology to brain iron content measurements in vivo is discussed.

14:00         4459.     Dependence of Blood R2 Relaxation Rate on Echo Spacing Using a CPMG Sequence at 7T

Alexander Graeme Gardener1, Susan Tracy Francis1, Penny Anne Gowland1

1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK

The dependence of measured in-vitro blood R2 relaxation rate on sequence parameters and sample oxygenation and haematocrit was investigated at 7T using a multi-echo CPMG sequence. Results show that as inter-echo spacing increases, measured R2 rates increase, with low oxygenation and high haematocrit blood samples showing the largest enhancement. Pure plasma showed little dependency on inter-echo spacing as expected. Results for fitting blood R2,0 components at 7T are presented, and compared to previous literature studies at lower field strengths.

14:30         4460.     Magnetic Field Correlation Contrast in the Human Brain at 7 Tesla

Maarten J. Versluis1,2, Andrew G. Webb1,2, Mark A. van Buchem1,2, Matthias J P van Osch1,2

1Radiology, Leiden University Medical Center, Leiden, Netherlands; 2C.J. Gorter Center for high field MRI, Leiden University Medical Center, Leiden, Netherlands

Magnetic field correlation (MFC) imaging was implemented to quantitatively measure magnetic field inhomogeneities at 7 T. The feasibility of the technique was shown by comparing 3 T and 7 T data of healthy volunteers for different brain regions. MFC measurements were performed at multiple echo times to differentiate between macroscopic and microscopic field inhomogeneities. In vivo MFC imaging at 7 T was found to be more sensitive than at 3 T and it was possible to differentiate between brain regions with different scales of inhomogeneities.

15:00         4461.     Quantitative Analysis of Transverse Relaxation Due to Strongly Magnetized Micron-Sized Spheres Subjected to Unrestricted Diffusion in Gradient Echo and Spin Echo Imaging: Validation of Theory with Experiments and Monte Carlo Simulation

Peter Roland Seevinck1, Koen Lucas Vincken1, Gerrit Hendrik van de Maat1, Chris J.G. Bakker1

1Image Sciences Institute, Department of Radiology , University Medical Center, Utrecht, Netherlands

The signal decay time course of FID and SE of an aqueous suspension of strongly magnetized micron-sized spheres was investigated in great detail to explore the influence of volume fraction, field strength and diffusion. Excellent agreement between MR experiments, Monte Carlo simulations and both the theory of the static dephasing regime and the strong field behavior was demonstrated based on R2, R2’ and R2* relaxation rates. This allows accurate prediction FID and SE signal behavior and quantification strongly magnetized spherical particles such as holmium- and iron-loaded microspheres and iron-labeled cells.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 88

13:30         4462.     SPIO: Positive Contrast by Adiabatic IRON Using Repetitve Inversion Pulses

Carsten Warmuth1,2, Arne Hengerer3, Robert Krieg3, Jörg Schnorr4, Michael Reinhardt5

1Visage Imaging GmbH, Berlin, Germany; 2Siemens AG, Erlangen, Germany; 3Healthcare sector, Siemens AG, Erlangen, Germany; 4Department of Radiology, Charité, Berlin, Germany; 5Bayer Schering Pharma AG, Berlin, Germany

We present a fast positive contrast iron oxide particle imaging technique based on IRON. By using repetitive inversion pulses, suppression of resonant fat and water protons is achieved independent of tissue T1 relaxation times.

14:00         4463.     Observation of Time Dependent Magnetic Field Correlation in the Human Brain

Kathleen A. Williams1, Kamila Szulc1, Caixia Hu1, Jens H. Jensen1, Joseph A. Helpern1,2

1Department of Radiology, CBI, NYU School of Medicine, New York, USA; 2Center for Advanced Brain Imaging, The Nathan Kline Institute, Orangeburg, NY, USA

The magnetic field correlation (MFC) is a quantitative MRI metric that characterizes magnetic field inhomogeneities generated in the brain by iron-rich tissue structures. The theoretically predicted time dependence of the MFC has been previously shown in phantoms. Here the time dependence of the MFC is demonstrated in vivo for human brain. By fitting to a model, the observed time dependence is found to be consistent with field inhomogeneities that vary on a length scale of 10 to 20 microns, which is comparable to the size of known iron-rich tissue structures within the brain.

14:30         4464.     Quantification of the Regional Non-Hemin Iron in Human Brain in Vivo Through the Apparent Transverse Relaxation Rate of the Tissue Water at 4.7T

Fumiyuki Mitsumori1, Hidehiro Watanabe1, Nobuhiro Takaya1

1National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan

Non-hemin iron (Fe) is known to cause neurodegeneration in several hereditary diseases. It has also been suspected to be closely related to the occurrence of Alzheimerfs and Parkinsonfs diseases. In the present study we propose a method to estimate the concentration of brain [Fe] in vivo through the high correlation between [Fe] and the apparent relaxation rate (R2õ) of the tissue water in human brain at 4.7T. The estimate was significantly improved when the contribution of macromolecular fraction to R2õ was taken into account. The result of estimation on 54 healthy subjects will be presented.

15:00         4465.     Estimation of T2* in Severe Iron Overload Patients with Weighed Least Squares T2*-IDEAL

Huanzhou Yu1, Ann Shimakawa1, Scott B. Reeder2, Jean H. Brittain3, Charles A. McKenzie4, Shreyas Vasanawala5

1Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA; 2Departments of Radiology, Medical Physics, Biomedical Engineering and Medicine, University of Wisconsin, Madison, WI, USA; 3Applied Science Laboratory, GE Healthcare, Madison, WI, USA; 4Department of Medical Biophysics, University of Western Ontario, London, ON, Canada; 5Department of Radiology, Stanford University, Stanford, CA, USA

Hepatic iron overload is a common chronic liver disease. Excess amounts of iron reduce T2* of liver from above 20ms to shorter than 1ms. We have previously demonstrated that T2* mapping can be achieved simultaneously with water-fat separation using a multi-echo T2*-IDEAL algorithm. However, in the presence of very short T2*, the images at late echoes have poor SNR, leading to substantial errors. In this work, we introduce a weighted least squares algorithm, which automatically decreases the impact of later, noisier echoes. We demonstrate in simulations and in-vivo studies that T2* values as short as 1ms can be effectively estimated.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 88

13:30         4466.     Assessment of Iron Concentration in a Two-Pool Model of Brain Tissue

Christian Langkammer1,2, Thomas Seifert-Held1, Michaela Soellinger1, Christian Enzinger1, Franz Fazekas1, Rudolf Stollberger2, Stefan Ropele1

1Department of Neurology, Medical University of Graz, Graz, Austria; 2Institute of Medical Engineering, Graz University of Technology, Graz, Austria

Using a ferritin phantom mimicking the composition of brain gray matter, we investigated the effect of iron load on the saturation line shape of water. Z-spectra were acquired under different saturation conditions by use of spoiled FLASH sequences with spectral presaturation. We observed a linear correlation between the maximum saturation effect (i.e., the direct saturation ratio) and iron concentration. Magnetization transfer and global susceptibility effects did not affect this relationship, favoring the use of this method for in vivo measurements of the iron content.

14:00         4467.     Towards Microcalcifcation Detection Using Susceptibility  Weighted Phase Imaging: Simulations and Phantom Experiments

Richard A. Baheza1, E. Brian Welch2, John C. Gore1, Thomas E. Yankeelov1

1VUIIS, Vanderbilt University, Nashville, TN, USA; 2Philips Healthcare, Philips, Cleveland, OH, USA

The presence of calcium deposits in the breast can be an indicator of malignancy, so the ability to detect such abnormalities by MRI would be significant. Calcium deposits have a different magnetic susceptibility from surrounding tissues that can in principle be observed using susceptibility weighted imaging (SWI). Here we introduce a technique to locate a susceptibility induced signature within a data set by computing the cross-correlation between a template and the target image.

14:30         4468.     Multi-Echo Spin-Echo (MESE) Signal Behavior of Paramagnetic Holmium-166 Loaded Microspheres for Radiotherapy: Experiment and Simulation

Gerrit Hendrik van de Maat1, Peter R. Seevinck1, Koen L. Vincken1, Hendrik de Leeuw1, Chris J. Bakker1,2

1Image Sciences Institute, University Medical Centre Utrecht, Utrecht, Netherlands; 2Department of Radiology, University Medical Centre Utrecht, Utrecht, Netherlands

The potential of multi-echo spin-echo (MESE) measurements for quantification of holmium-166 loaded microspheres (HoMS) was explored. This was done by investigating the signal decay due to HoMS by MR experiments on a gel series containing HoMS and by Monte Carlo simulations. Results were compared to the theoretical model of strong field behavior and appeared to be in good agreement for a wide range of HoMS concentrations. The study indicates the potential of MESE for the quantification of HoMS concentrations up to 20mg/ml.

15:00         4469.     Simultaneous Spin/Gradient Echo Acquisitions in Conjunction with Arterial Spin Labeling for Quantification of T2* by Single Shot 3D Spiral GRASE Imaging

Johannes Gregori1, Norbert Schuff1,2, Matthias Günther3

1Radiology & Biomedical Imaging, University of San Francisco, San Francisco, CA, USA; 2VA Medical Center , Center for Imaging of Neurodegenerate Diseases, CIND, San Francisco; 3Neurology, University Hospital Mannheim, University of Heidelberg, Heidelberg, Germany

Quantification of local T2*, which is used in fMRI as a surrogate for neuronal activity, can be difficult because static (R2’) and irreversible (R2) effects contribute to the decay. In this work, we developed a 3D mapping scheme based on GRASE, in which two spiral-out planar readouts per k-space partition are used to acquire a spin echo (governed by R2) and a time-shifted gradient echo (governed by R2’) on the ascending slope of the corresponding spin echo. From a combination of R2 and R2’, local T2* variations can be quantified. Measurements were also performed in conjunction with arterial spin labeling allowing to selectively measure T2* of labeled water.

 


 
Magnetization Transfer, Etc.
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 89

14:00         4470.     Efficient and Accurate Modeling of Pulsed Magnetization Transfer.

Dirk K. Müller1, André Pampel1, Toralf Mildner1, Torsten Schlumm1, Thies H. Jochimsen1, Harald E. Möller1

1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

Estimating quantitative magnetization transfer (MT) parameters using pulsed off-resonance saturation is a challenging task. We present a new fitting approach of estimating MT parameters for arbitrary pulse sequences using a fast and accurate description of the pulse sequence by solving the McConnell equations numerically using matrix algebra.

14:30         4471.     Reliability and Reproducibility of  High Resolution Magnetization Transfer Imaging on 3T

Ying Wu1,2, Hongyan Du3, Kelly H. Zou4, Shawn Sidharthan1, Eugene Dunkle, Robert Edelman1,2, Ann Ragin2

1Radiology, NorthShore University HealthSystem, Evanston, IL, USA; 2Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; 3Center on Outcomes, Research and Education, NorthShore University HealthSystem, Evanston, IL, USA; 4Global Medical R&D, Pfizer Inc, New York, NY, USA

The validity of quantitative MR methods for monitoring progression in Multiple Sclerosis, Alzheimer’s Disease and other chronic neurological diseases is limited by the reliability and reproducibility of the derived measurements. This investigation evaluated the reliability and reproducibility of a promising new high resolution strategy based on quantitative MT. The strategy was evaluated using conventional manually-defined region of interest measurements. In addition, the reliability and reproducibility of high resolution quantitative MT was also evaluated using automated methods aimed at eliminating operator bias further.

15:00         4472.     Quantitative Magnetization Transfer Imaging Using Non-Balanced SSFP

Monika Gloor1, Klaus Scheffler1, Oliver Bieri1

1Radiological Physics, University of Basel Hospital, Basel, Switzerland

Similar to balanced steady-state free precession (bSSFP), the signal of non-balanced SSFP (nb-SSFP, such as SSFP-FID or SSFP-echo) depends on magnetization transfer (MT) in tissues. Based on a binary spin-bath model, an extended SSFP signal equation is presented which takes MT effects into account. Using this new SSFP signal equation, quantitative MT imaging (qMTI) is demonstrated ex-vivo and in-vivo. High correlation with literature values is observed and furthermore, this method benefits from short acquisition times, high signal-to-noise ratios and off-resonance insensitivity.

15:30         4473.     Cardiac Magnetization Transfer Imaging Using SSFP at 3T

Oliver Michael Weber1,2, Peter Speier3, Klaus Scheffler1, Oliver Bieri1

1Radiological Physics, University of Basel, Basel, Switzerland; 2Siemens Healthcare, Zurich, Switzerland; 3Siemens Healthcare, Erlangen, Germany

An optimized bSSFP cine sequence was used to calculate magnetization transfer of the myocardium at 3T. MT values of 26% were found in normal myocardium, demonstrating the feasibility of cardiac MT imaging at 3T.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 89

13:30         4474.     Intra- And Inter-Scanner Variability of Magnetization Transfer Ratio Using Balanced SSFP

Monika Gloor1, Klaus Scheffler1, Oliver Bieri1

1Radiological Physics, University of Basel Hospital, Basel, Switzerland

Magnetization transfer ratio (MTR) has become an important tool to study various tissue abnormalities, such as demyelination in brain white matter. Recently, a new technique for measuring MTR has been proposed based on balanced steady-state free precession (bSSFP) with modified radiofrequency pulses. The reproducibility and variability of MTR-bSSFP was analyzed on six healthy volunteers using two different 1.5T clinical systems. Intra-scanner MTR measurements were well reproducible (< ±0.3 pu) and inter-scanner variation is below 0.5 pu for optimal flip angle settings ([pu]: percentage units). MTR-bSSFP benefits further from relatively low B1 sensitivity, high signal-to-noise ratios, and short overall acquisition times.

14:00         4475.     3D Amide Proton Transfer (APT) Imaging of the Whole Brain at 3T

He Zhu1,2, Joseph S. Gillen1,2, Peter B. Barker1,2, Peter C.M. van Zijl1,2, Jinyuan Zhou1,2

1Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Maryland, MD, USA; 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Maryland, MD, USA

Amide proton transfer (APT) imaging is a novel chemical exchange saturation transfer (CEST) based MRI modality that gives contrast due to endogenous cytosolic protein and peptide content, as well as tissue pH, in vivo. In this abstract, a fast 3D APT technique with whole-brain coverage that is suitable for clinical applications is presented. Preliminary results show that the APT signal in the brain is about 1-2.2% of the water intensity, and the highest APT signal is detected in the cerebellum.

14:30         4476.     Correlation of Potential Myelin Measures from Quantitative Magnetisation Transfer (QMT) and Multi-Component Driven Equilibrium Single Pulse Observation of T1 and T2 (McDESPOT)

Rebecca Sara Samson1, Sean C L Deoni2, Claudia A M Wheeler-Kingshott1

1Department of Neuroinflammation, UCL Institute of Neurology, London, UK; 2Centre for Neuroimaging Sciences, Institute of Psychiatry, London, UK

It has previously been suggested that both the restricted proton fraction (fb) measured from quantitative Magnetisation Transfer (qMT) and myelin water fraction (fm) from multi-component relaxometry are related to myelin content in the brain. Multi-Component Driven Equilibrium Single Pulse Observation of T1 and T2 (mcDESPOT) is a promising alternative to spin-echo multi-component T2 analysis. This pilot study investigates the correlation of fm measured via the mcDESPOT technique with fb at 1.5T in white and grey matter in three healthy volunteers.

15:00         4477.     An Improved Empirical Solution for Describing Chemical Exchange Saturation Transfer (CEST) MRI

Phillip Zhe Sun1

1Department of Radiology, Harvard Medical School, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA

An empirical solution based on a 2-pool exchange model has been proposed to describe CEST MRI, providing tremendous insights for quantitative CEST imaging. Nevertheless, the empirical solution is only a first order approximation, and susceptible to non-negligible errors when quantifying CEST imaging of fast exchange groups under practical conditions (i.e. intermediate RF powers). To properly guide future development of more sensitive exogenous PARACEST/LIPOCEST agents, we modified the simplistic empirical equation with a second order correction term, which showed good agreement with numerical simulation.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 89

13:30         4478.     Predicting Optimal Properties of CEST MRI Agents Under Practical Experimental Conditions

Phillip Zhe Sun1, Guanshu Liu2,3, Jinyuan Zhou2,4, Peter van Zijl2,4, Michael T. McMahon2,4

1Department of Radiology, Harvard Medical School, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; 2Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD; 3F. M. Kirby Center for functional Brain Imaging, Kennedy Krieger Institute , Baltimore, MD, USA; 4F. M. Kirby Center for functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA

Chemical exchange saturation transfer (CEST) imaging provides a sensitivity enhancement mechanism that allows measurement of microenvironment properties through dilute labile groups. Because in general CEST MRI contrast increases with the chemical exchange rate, there has been great interest in developing DIACEST/LIPOCEST/PARACEST agents with fast exchange rates. Here, we have examined CEST MRI contrast under practical experimental conditions, and derived the optimal properties of CEST agents at different exchangeable proton shifts from water using both analytical solutions and numerical simulations. In addition we have validated these experimentally for two different types of exchangeable protons.

14:00         4479.     Quantitative Pulsed CEST

Kimberly L. Desmond1, Greg J. Stanisz1,2

1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; 2Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

A clinically applicable, quantitative chemical exchange saturation transfer (CEST) technique was developed and demonstrated in a phantom containing 1M ammonium chloride. The fitting algorithm consisted of a two-pool compartmental model of the Bloch equations including exchange and pulsed off resonance excitation modeled by a piecewise constant approximation. The results of the fit provided estimates for T2a (T2 relaxation for the bulk water pool), M0c (size of the CEST pool relative to bulk water), T2c (T2 relaxation of CEST pool), and ω 0c (resonance frequency of the CEST pool).

14:30         4480.     Compensatory Amide Proton Transfer Ratio (CAPTOR) Imaging to Improve the Specificity of Tissue Acidosis MRI

Phillip Zhe Sun1, A Gregory Sorensen1

1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Charlestown, MA, USA

Amide proton transfer (APT) imaging has been shown sensitive to microenvironment pH and can detect ischemic tissue acidosis. However, the commonly used magnetization transfer (MT) asymmetry analysis is susceptible to concomitant RF irradiation effects (spillover, intrinsically asymmetric MT etc), and hence, may not be specific to pH-dependent APT mechanism. Here, we propose a compensatory APT ratio (CAPTOR) approach that subtracts the label scan (famide) from the mean of two compensatory images around the amide proton offset instead of a reference scan (-famide). Our data showed that CAPTOR had less heterogeneity among cerebral tissue types, and more specific to APT process.

15:00         4481.     In Vivo Myelin Water Imaging Using Z-Shimmed Multi-Gradient-Echo Pulse Sequences at 3T

Claudia Lenz1, Markus Klarhöfer1, Klaus Scheffler1

1Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland

Quantitative imaging of the myelin water fraction (MWF) is able to show demyelinating processes and therefore provides insight into the pathology of white matter (WM) diseases such as multiple sclerosis. So far, mapping of the MWF most often was performed using a multi-echo spin-echo sequence and fitting the biexponential T2 decay with a non-negative least-squares algorithm. In this work, a different approach is presented using multi-gradient-echo pulse sequences. This method has been introduced by one study measuring formalin-fixed brains. We present a solution for in vivo measurements using z-shimming as a correction for magnetic field inhomogeneities.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 89

13:30         4482.     Analytical Method for Correction of B1 Errors in High-Field Magnetization Transfer Ratio Mapping

Vasily L. Yarnykh1

1Radiology, University of Washington, Seattle, WA, USA

Magnetization Transfer Ratio (MTR) is known to strongly vary with B1. This circumstance restricts MTR applications in high magnetic fields. In this study, a simple analytical model of MTR dependence on B1 was derived. Based on this model, a correction algorithm employing a tissue-independent set of parameters was developed and tested for MTR mapping of the human brain at 3T. MTR correction was shown to be highly accurate across a wide range of B1 non-uniformities. Combination of this algorithm with fast B1 mapping enables whole-brain MTR mapping and histogram analysis on high-field scanners for a variety of neuroimaging applications.

14:00         4483.     Molecular Exchange in Breast Cells Studied with a New DW-MRI Method

Daniel Topgaard1, Ingrid Åslund, Carin Malmborg2, Anna Stenstam2, Karin Bryskhe2, Stina Oredsson

1Physical Chemistry, Lund University, Lund, --, Sweden; 2Colloidal Resource

An extension of diffusion weighted (DW) MRI, with two DW periods and an intermediate mixing time, is shown to be sensitive to molecular exchange between slow and fast components. The method is applied to healthy and cancerous breast cells yielding significant differences between the various cell types.

14:30         4484.     Incidental Magnetization Transfer Contrast by Fat Saturation Preparation Pulses in Multi-Slice MR Imaging: An Illustration of Look-Locker EPI Sequences

Wanyong Shin1, Hong Gu1, Yihong Yang1

1Neuroimaging Research Branch, National Institute on Drug Abuse, Baltimore, MD, USA

It is demonstrated that the frequency selective fat saturation preparation pulses generate incidental magnetization transfer contrast (MTC) effects in multi-slice imaging. Simulation reveals that the fractional signal loss by these MTC effects are severer when smaller flip angle, shorter TR, and larger slice number are applied. Incidental MTC effects induce a signal attenuation (up to 30%) and bias on T1 measurement (up to 20%) when inversion recovery Look-Locker EPI sequences are used. Furthermore, it is shown that water-only excitation pulses have the potential to minimize the signal attenuation and provide unbiased T1 measurement without fat artifacts in MR images.

15:00         4485.     In Vivo Tumor Detection and Characterization by Fixed-Point Imaging Using Active Feedback Fields

Jon Furuyama1, Dennis W. Hwang1, Yung-Ya Lin1

1Chemistry and Biochemistry, UCLA, Los Angeles, CA, USA

The use of a CW pulse in the presence of strong radiation damping can be seen to produce unique contrast enhancement, and can be a useful supplement to conventional methods in the detection of tissues with small

 


 
Magnetization Transfer, Etc. & Myelin Imaging
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 90

14:00         4486.     Multi-Parametric Approach to Automatic Regional Analysis of Quantitative Relaxation Times in the Brain

Benjamin Segun Aribisala1, Andrew M. Blamire1

1Newcastle Magnetic Resonance Centre, Newcastle University, Newcastle upon Tyne, Tyne and Wear, UK

A significant step in the analysis of imaging data is accurate definition of regions of interest (ROI) within a single tissue type. Analysis is often done by interactively defining ROI on each image under analysis (e.g. T1 or T2). This approach is sensitive to image resolution which introduces partial volume effects biasing the analysis. We propose a fully automatic multi-parametric approach whereby complementary information in multiple images is considered in order to classify each quantitative image into its tissue classes. We apply this method to brain data and demonstrate it is time efficient and largely free of partial volume effect.

14:30         4487.     Phase Contrast in the Post Mortem Rat Brain: Comparison with T2* and Histology

Ana Maria Oros-Peusquens1, Sebastian Hirsch1, Joerg Felder1, Avdo Celik1, M Cremer1, N. Jon Shah1

1Institute of Neurosciences and Biophysics, Research Centre Juelich, Juelich, Germany

The origins of phase contrast were investigated in a post mortem rat brain with high isotropic resolution (60&#61549;m) MRI. The phase contrast after formalin fixation was characterised in the whole brain and compared with T2* maps and cellular structure based on histology. Phase images acquired on a post mortem rat brain allow for a more complete visualisation of fine layers in the hippocampus and with higher contrast (factor 10-20) than with magnitude images alone. For hippocampal structures myelin and iron content are not the main contrast-generating factor. Instead, the phase contrast seems more correlated with the cell density as described by the intensity of Nissl staining in histology.

15:00         4488.     How Reliable Are Current Practices in Reconstructing Relaxation Spectra for Detecting the T2 Myelin Water Signal When Applied to Real in Vivo T2 Decays?

Keith S. Cover1

1Physics and Medical Technology, VU University Medical Center, Amsterdam, North Holland, Netherlands

The results of this study demonstrated that, for in vivo T2 decays of white matter measured using current practices, bias in both Whittall’s and Mackay’s nonnegative least squares and fitting a few monoexponentials reconstruction algorithms can yield highly reproducible but false positive detections of the T2 myelin water signal. In contrast, data conserving reconstruction matrices (DCRM) yielded highly reliable results but required several times the signal to noise ratio (SNR). More in vivo measurements of a variety of structures and pathologies at high SNR are required to determine the most useful trade off between reliability of the reconstruction algorithm and the SNR.

15:30         4489.     Inconsistency in Interpretation of T2 and Diffusion in White Matter

Sharon Peled1

1Radiology, Brigham and Women's Hospital, Boston, MA, USA

The short T2 component of the T2 curve measured in white matter is commonly assigned to myelin-associated water. A problem with this assignment is that water exchange times through the myelin sheath are not known – even minimal exchange would greatly reduce the size of this component to below the measured levels. Diffusion measurements indicate that such exchange exists. This incompatibility is described and solutions proposed.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 90

13:30         4490.     Variations in T2, T2* and T1 Between White Matter Tracts at 7.0 T

Eleanor F. Cox1, Pierre-Yves Herve2, Peter J. Wright1, Ashley Loftipur1, Olivier Mougin1, Susan E. Pritchard1, Tomas Paus2, Penny A. Gowland1

1SPMMRC, School of Physics & Astronomy, University of Nottingham, Nottingham, Nottinghamshire, UK; 2Brain & Body Centre, University of Nottingham, Nottingham, Nottinghamshire, UK

T2 and T2* have been shown to vary between white matter tracts. The aim of this study is to investigate the relationship between the relaxation times and known features of myelin density and axonal structure, by studying adjacent white matter tracts and comparing known differences in histology to the T2, T2* and T1 relaxation times of these tracts, measured at 7T.

14:00         4491.     Quantifying White Matter: Integrating Diffusion Tensor Imaging and Bound Pool Fractions

Nikola Stikov1, Lee Michael Perry2, John Mark Pauly1, Brian A. Wandell2, Robert F. Dougherty2

1Electrical Engineering, Stanford University, Stanford, CA, USA; 2Psychology, Stanford University, Stanford, CA, USA

We explore combining two quantitative MR contrast mechanisms in order to better understand the structure of white matter in the brain. Diffusion tensor imaging (DTI) can identify white matter fascicles and measure their diffusivity. The bound pool fraction (BPF) estimates the proportion of protons bound to macromolecules, such as myelin. We combine these two in order to obtain concurrent information about the direction, diffusivity, and myelin content of white matter tracts in the corpus callosum and the optic radiation. We conclude that DTI and BPF are complementary techniques that combine to provide a more complete insight into tissue microstructure.

14:30         4492.     High Resolution Myelin Water Imaging in Rat Spinal Cord in Vivo with Actively Decoupled Implanted RF Coil

Piotr Kozlowski1, Jie Liu2, Jenny Ch Tso1, Nathan Wolfe1, Andrew C. Yung1

1UBC MRI Research Centre, Vancouver, BC, Canada; 2ICORD, Vancouver, BC, Canada

Myelin water imaging has been used to characterize rat spinal cord pathology. However, this technique requires very high SNR and homogeneity of the B1 field, making it challenging to apply this technique in rat spinal cord in vivo. We have designed and built an RF implanted coil, which is actively decoupled from a volume coil. Here we present preliminary results of high spatial resolution myelin water imaging using this system.

15:00         4493.     Intrinsic Connectivity Contrast: A Novel Contrast Mechanism for Investigating a Wide Range of Brain Disorders

R. Todd Constable1, Yuko Hara2, Nallakkandi Rajeevan1, Fuyuze Tokoglu1, Xenios Papademetris1

1Diagnostic Radiology, Yale University, New Haven, CT, USA; 2Biomedical Engineering, Yale University, New Haven, CT, USA

A novel contrast mechanisms based on resting state connectivity BOLD fMRI data is presented which delineates areas in the gray matter that exhibit altered connectivity relative to control subjects. This approach is applicable to any neurodegenerative disorder and provides a new tool for localizing disrupted tissues.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 90

13:30         4494.     Pulsed Saturation Transfer for Quantifying CEST in the Presence of MT

Kimberly L. Desmond1, Greg J. Stanisz1,2

1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; 2Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada

The quantification of the CEST effect in-vivo is complicated by the presence of immobile macromolecules, which additionally results in a large MT effect. The MT component has a significant impact on the magnitude of the CEST effect, which reduces the validity of asymmetry-based techniques. We propose a method by which the parameters for both CEST and MT pool can be determined independently by fitting a three pool model to data from a pulsed saturation transfer experiment. This method is tested on a set of three phantoms, containing 1M ammonium chloride, 2% agar, and both compounds combined.

14:00         4495.     Multeslice Gradient Echo CEST Imaging

W Thomas Dixon1, Ileana Hancu1, A Dean Sherry2,3, James Ratnaker2, Donald E. Woessner2, Elena Vinogradov4, Robert E. Lenkinski4, David C. Alsop4

1GE Global Research, Niskayuna, NY, USA; 2UT Southwestern Medical Center, Dallas, TX, USA; 3Chemistry, U Texas Dallas, Richardson, TX, USA; 4Beth Israel Deaconess Medical Center, Brookline, MA

Contrast Enhanced Saturation Transfer imaging usually uses long CEST RF pulses to achieve the maximum, steady-state effect. Most transmitters do not provide long pulses. Long pulses slow imaging greatly or require rapid imaging methods that often limit image quality. A 2D gradient echo sequence with a short CEST pulse inserted before each observe pulse retains all the flexibility of the original gradient echo sequence. Keeping pulse and wait durations constant, increasing the number of slices increases TR and increases sensitivity just as in 3D imaging. The CEST effect was independent of slice position in a uniform CEST phantom.

14:30         4496.     Using the Linewidth of the Amide Proton CEST Effect of MRI-PARACEST Agents for PH Mapping

Alex Xuexin Li1,2, Craig K. Jones1, Mojmir Suchy1,3, Robert H.E. Hudson3, Ravi S. Menon1,2, Robert Bartha1,2

1Center for Functional and Metabolic Mapping, Robarts Research Institute, London, ON, Canada; 2Department of Medical Biophysics, The University of Western Ontario, London, ON, Canada; 3Department of Chemistry, The University of Western Ontario, London, ON, Canada

A technology to measure pH using the amide protons site of a thulium complex with a DOTAM-Glycine-Lysine ligand: Tm3+-DOTAM-Gly-Lys was developed. The pH can be determined uniquely from the linewidth of the asymmetry curve of the CEST spectrum in a manner independent of contrast agent concentration, intrinsic magnetization transfer effect, and temperature for a given saturation pulse. pH maps with standard deviation less than 0.1 pH units were obtained from 10 mM Tm3+-DOTAM-Gly-Lys solutions with different pH.

15:00         4497.     Application of Parallel Imaging to Reduce SAR in CEST Experiments

Elena Vinogradov1, Aaron K. Grant1, Phillip M. Robson1, Ilena Hancu2, W Thomas Dixon2, A Dean Sherry3,4, Robert E. Lenkinski1

1Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA; 2GE Global Research, Niskayuna, NY, USA; 3Department of Chemistry, University of Texas at Dallas, Dallas, TX; 4Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, USA

Chemical Exchange Saturation Transfer (CEST) contrast employs selective presaturation of the exchanging pool and subsequent observation of the reduction of the free water signal. Many potential applications of CEST agents, in particular Paramagentic CEST agents (PARACEST) are limited by the RF power required, that may exceed FDA approved SAR limits. Combination of Parallel Imaging (PI) with CEST should allow increased TR, and, hence, reduced SAR, without sacrificing image resolution or total scan time. Preliminary data shown here demonstrate combination of CEST with PI, and shows that the PI reconstruction does not alter the observable CEST effects.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 90

13:30         4498.     Amide Proton Transfer (APT) MRI: A 3T Vs. 7T Comparison

Guang Jia1, Jinyuan Zhou2, Seongjin Choi1, Wenbo Wei1, Steffen Sammet1, Daniel James Clark1, Stefan Fischer3, Michael V. Knopp1

1Department of Radiology, The Ohio State University, Columbus, OH, USA; 2Department of Radiology, Johns Hopkins University, Baltimore, MD, USA; 3Philips Medical Systems, Cleveland, OH, USA

The frequency difference between amide proton (3.5 ppm) and water resonance is 1043 Hz at 7T, much greater than 448 Hz at 3T, which may help reduce mixture of APT-MTR with the direct saturation effect to water signal. Our results shows better separation between the amide proton saturation and free water saturation profiles and a clearer dip that reflects the APT effect in the MT-spectrum of egg white at 7T than that at 3T. This study strongly suggests that the APT sequence should be extensively evaluated at ultra-high-field (7T) for tissue characterization.

14:00         4499.     Modeling the Influence of TR and Excitation Flip Angle on the MTR Obtained from 3D FLASH MRI

Gunther Helms1, Henning Dathe2, Peter Dechent1

1MR-Research in Neurology and Psychiatry, University of Göttingen, Göttingen, Germany; 2Biomechanics Group, Dept. of Orthodontics, Universityhospital, Göttingen, Germany

Modeling and optimization of the magnetization transfer ratios (MTR) obtained from FLASH MRI is often based on continuous-wave models that only implicitly account for excitation and relaxation during TR. These effects were explicitely modeled by an approximation of free relaxation between the RF pulses and verified on the human brain in vivo at 3T by variation of flip angle and TR. The influence of inhomogeneous RF fields could be readily incorporated. Choice of short TR and larger flip angles improved the MTR contrast and reduced the influence of RF inhomogeneity.

14:30         4500.     Optimization of Quantitative Magnetization Transfer Imaging Using a Selective Inversion Recovery Pulse

Ke Li1,2, Zhongliang Zu1,2, Junzhong Xu1,2, John C. Gore1,2, Heather M. Whitney1,3, Daniel F. Gochberg1,2

1Vanderbilt University Institute of Imaging Science, Nashville, TN, USA; 2Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA; 3Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA

Quantitative magnetization transfer (qMT) imaging maps properties of the tissues that are usually interpreted in terms of two pools of protons, corresponding to free and immobilized fractions. The selective-inversion-recovery fast-spin-echo (SIR-FSE) qMT technique developed recently includes an inversion time (ti) which is varied between 3.5 ms and 10 s, while the delay before the next sequence repetition (td) is held constant. qMT parameters are determined by fitting the resulting recovery to a bi-exponential function of ti using an approximate solution. In the current study, we employ a new protocol that varies both ti and td and fits the data with minimal approximations. Cramer-Rao lower bounds (CRLB) are calculated to select the variations in both ti and td that will maximize the precision-per-unit-time. Monte Carlo simulations support this approach by showing a large reduction in the resulting qMT parameter uncertainties. The optimization results are also confirmed by measurements on a series of BSA phantoms with different percent weight.

15:00         4501.     Impact of Magnetization Transfer on Relaxometry Using Transient Steady-State Free Precession Imaging

Jan Ole Blumhagen1, Francesco Santini1, Oliver Weber1, Klaus Scheffler1, Oliver Bieri1

1Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland

Several methods proposed the use of the transient response of balanced steady-state free precession (bSSFP) for quantification of relaxation times and spin densities. However, it has been shown that magnetization transfer (MT) affects the steady state of bSSFP and is dependent on pulse duration and repetition time. During transition to steady state also MT effects built up, thus it is likely that MT affects the estimation of relaxation parameters using transient SSFP methods. In this work, we will show exemplarily for inversion recovery bSSFP that significant deviations arise from MT.

 


 
RF Pulse Design
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 91

14:00         4502.     The Use of Binomial Pulses for Suppression of Long T2 Signals

Atsushi Mark Takahashi1

1Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA

Ultra short TE (UTE) imaging has the promise of visualizing tissues not previously visible with MRI. However, contrast in UTE is typically fairly flat because little T2* decay occurs prior to data acquisition. In this work, we propose the use of binomial excitation pulses as a way to selectively excite spins based on their intrinsic T2.

14:30         4503.     A Flexible Design Algorithm for Single-Shot 2D Circular/Elliptical OVS RF Pulses

Xiaoping Wu1, Nate Powell1, Malgorzata Marjanska1, Michael Garwood1, Kâmil Ugurbil1, Pierre-François Van de Moortele1

1Center for Magnetic Resonance Research and Radiology Department, University of Minnesota, Minneapolis, MN, USA

Outer Volume Suppression (OVS) is used to saturate unwanted MR signals in spectroscopy. Typically, OVS is performed with multiple conventional (e.g., sinc) pulses, suffering from low efficiency and high SAR. We have previously

15:00         4504.     High Resolution Reduced-FOV Single-Shot FSE Imaging Using 2DRF Pulses with Less Blurring and Low SAR

Jing Yuan1, Tzu-Cheng Chao2, Yi Tang1, Lawrence P. Panych3

1Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; 2National Taiwan University, Taipei; 3Department of Radiology, Brigham and Women's Hospital, Harvard Medical School,, Boston, MA, USA

RFOV imaging was developed for SS-FSE sequence using 2DRF pulses to reduce echo train length (ETL) and scan time. High resolution, low SAR and less blurring can be achieved in RFOV images due to the shorter ETL. In this study, scan time and blurring reductions were demonstrated in phantom images with reduction factors from two to five. 2.5X higher resolution (320*320) RFOV brain images were achieved within an even shorter time compared to that required for low-resolution (128*128) full FOV images. Significant blurring reduction results were also compared to full FOV images with the same nominal resolution.

15:30         4505.     Selective Composite Adiabatic Refocusing Pulses for 3D RARE Imaging

Ziqi Sun1

1Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA

A compact selective composite adiabatic refocusing pulse with nonlinear phase dispersion compensation capability was developed for 3D RARE imaging. The composite adiabatic pulse consisted of two adiabatic half passage (AHP) pulses with phase reversal in the second AFP pulse. A full echo train and significantly improved signal sensitivity and uniformity were observed using the selective composite adiabatic refocusing pulse in comparison to that of an amplitude-modulated selective refocusing pulse in 3D RARE imaging.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 91

13:30         4506.     An On-The-Fly Radiofrequency Pulse for Bilateral Excitation with Independently Modulated Phase

Ernesto Staroswiecki1,2, John M. Pauly2, Bruce Lewis Daniel1, Brian Andrew Hargreaves1

1Radiology, Stanford University, Stanford, CA, USA; 2Electrical Engineering, Stanford University, Stanford, CA, USA

In this abstract we present a method to excite multiple slabs with arbitrary radiofrequency pulses while modulating the phase of each slab independently, allowing the simultaneous acquisition of multiple volumes without imaging the non-excited volume between the slabs. We show an example of a bilateral acquisition where the peak B1 amplitude is only marginally higher than that of a single slab with the same RF pulse, and that results in negligible signal loss.

14:00         4507.     Multi-Frequency Parallel Transmit Fopr Multi-Slice Scan Acceleration

Laura Sacolick1, Florian Wiesinger1, Schulte F. Rolf1, Dong Chen1, Guido Kudielka1, Wolfgang Loew1, Mika W. Vogel1

1Imaging Technologies, GE Global Research, Munich, Bavaria, Germany

The majority of applications thus far for parallel RF transmission in MRI have focused on addressing problems of B1 homogeneity. Here an eight-channel parallel transmit system is demonstrated for a novel application in reducing scan time as well as SAR. The multiple transmit channels are used to produce RF pulses simultaneously at multiple carrier frequencies. These are used to excite and simultaneously acquire four slices, which are then reconstructed by SENSE. The rungs of a body TEM coil assigned to excite each slice are chosen to minimize SAR, and are phase shimmed to maximize B1 field homogeneity. Multi-frequency parallel transmit is used here to give significant scan acceleration that can be combined with multiple receive coil acceleration, and applied in a wide variety of applications.

14:30         4508.     Counteracting RF Inhomogeneity on the Upper Legs at 3T Using Strongly Modulating Pulses

Nicolas Boulant1, Alexandre Vignaud2, Pierre G. Carlier3

1CEA, NeuroSpin, Gif sur Yvette, France; 2Siemens Healthcare, St Denis, France; 3Pitié Salpêtrière University Hospital, Institute of Myology , Paris, France

Strongly modulating pulses have been used to homogenize the flip angle on upper legs at 3 T. The muscle and fat tissues were discriminated in the pulse design algorithm via their resonance frequencies to achieve different flip angles. By implementing a “double Ernst angle”, we demonstrate a higher signal to noise ratio for both tissues (on average) in addition to a better signal uniformity in spoiled gradient echo experiments. Measurements of the flip angle using the AFI sequence are also reported.

15:00         4509.     RF Pulses for in Vivo Spectroscopy at High Field Designed Using Optimal Control

Gerald B. Matson1,2, Karl Young1,3, Lana G. Kaiser1,3

1CIND, Veterans Affairs Medical Center, San Francisco, CA 94121, USA; 2Pharmaceutical Chemistry, University of California, San Francisco, CA, USA; 3Radiology, University of California, San Francisco, San Francisco, CA, USA

Localized in vivo spectroscopy at high magnetic field strength (> 3 T) is susceptible to localization artifacts such as the chemical shift artifact and the spatial interference artifact for J-coupled spins. This latter artifact results in regions of anomalous phase for J-coupled spins. The use of selective RF pulses with increased bandwidth can minimize the signals with anomalous phase, while further suppression of anomalous phase signals can be accomplished with selective saturation pulses. Here we demonstrate through examples that optimal control methods can provide new, improved bandwidth localization and saturation pulses for improved localized spectroscopy at high field.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 91

13:30         4510.     Electrodynamic Analysis of SAR and Transmit Homogeneity for RF Shimming on a Dielectric Cylinder

Riccardo Lattanzi1,2, Yudong Zhu1, Daniel K. Sodickson1

1Center for Biomedical Imaging, NYU School of Medicine, New York, NY, USA; 2Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, USA

This work explores the electrodynamic behavior of transmit homogeneity and SAR for RF shimming. Ultimate SAR was calculated for uniform target excitation profiles both in a transverse and in a coronal plane through the center of a homogeneous cylinder. The trade-off between profile fidelity and SAR minimization was investigated in the ultimate case, as well as in the case of transmit arrays with increasing numbers of elements. Our simulations enforced homogeneity not only in the amplitude but also in the phase of the excitation profile, and the results suggest that this becomes a particularly stringent constraint at high field strengths.

14:00         4511.     Slice-Selective Array-Optimized Composite Pulse for Simultaneous Improvement in Excitation Uniformity and Reduction of SAR

Bu Sik Park1,2, Kyunghyun Sung3, John McGarrity2, Zhipeng Cao2,4, Sukhoon Oh2, Mark Watson5, Scott Schilliak5, Labros Petropolous5, Christopher M. Collins2,4

1Bioengineering , The Pennsylvania State University, Hershey, PA, USA; 2Radiology, The Pennsylvania State University, Hershey, PA, USA; 3Radiology, Standford University, Stanford, CA, USA; 4Bioengineering, The Pennsylvania State University, Hershey, PA, USA; 5MR Instruments Inc., Minneapolis, MN, USA

To overcome challenges of inhomogeneous transmit B1 distribution and high specific absorption rate (SAR) at high field, we present a slice-selective array-optimized composite pulse designed to both improve B1 uniformity and reduce SAR using an 8-channel transmit head array loaded with a head model, and compare our result with the conventional quadrature driving method at 3T. The sequence was implemented on a 3D MRI simulator currently under development, and showed improvement in excitation uniformity and SAR compared to a conventional birdcage coil.

14:30         4512.     Experimental Estimation of Local SAR in a Multi-Transmit System

Ulrich Katscher1, Christian Findeklee1, Tobias Voigt2

1Philips Research Europe - Hamburg, Hamburg, Germany; 2Technical University Karlsruhe, Karlruhe, Germany

SAR management is a widely discussed topic at high main fields, particularly in the framework of multi-transmit systems. Typically, local SAR is estimated via patient model simulations, which, however, are too extensive for clinical routine. This study investigates a possible alternative local SAR estimation by post-processing the RF transmit element's sensitivities. To this goal, the recently published approach "Electric Properties Tomography" was adapted for non-quadrature RF excitation, typically applied in multi-transmit systems, e.g., for RF shimming. Local SAR distributions obtained in phantom experiments with an 8-channel transmit system at 3T show a high correlation with corresponding local SAR simulations.

15:00         4513.     Imaging Conductivity and Local SAR of the Human Brain

Tobias Voigt1, Olaf Doessel1, Ulrich Katscher2

1Institute of Biomedical Engineering, University of Karlsruhe, Karlsruhe, Germany; 2Philips Research Europe, Hamburg, Germany

The approach "Electric Properties Tomography" is applied to estimate electric conductivity and local SAR distributions in vivo. Mean conductivity values for different brain areas agree quantitatively with literature values. Corresponding local SAR generated by a Tx/Rx body coil at 1.5T is shown.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 91

13:30         4514.     A Novel Three Dimensional Radiofrequency Pulse for Small Voxel Excitation

Natee Ina1, Suwit Saekho1,2

1Radiological Technology, Chiang Mai University, Muang, Chiang Mai, Thailand; 2Biomedical Engineering Center, Chiang Mai University, Muang, Chiang Mai, Thailand

The three dimensional Radio Frequency pulse (3D RF) has benefit to many applications. The major limitation of this pulse is long pulse length. A novel 3D RF pulse design was based on the small tip angle approximation combining the multi-shot and the half-pulse scheme for a small volume excitation. Numerical integration of the Bloch equation demonstrated that the two shot pulses along the x-y direction weighted with two half pulses along z- direction for cylindrical excitation at the diameter and thickness of 12 mm and 10 mm respectively, provides 34% shorter pulse width compared to that of conventional two-shot pulse.

14:00         4515.     A Dual-Band Three-Dimensional Tailored RF Pulse for Simultaneous Susceptibility Artifact and B1+ Inhomogeneity Reduction

Cungeng Yang1, Weiran Deng1, V. Andrew Stenger1

1Department of Medicine, University of Hawaii, Honolulu, HI, USA

Susceptibility artifacts and B1+ inhomogeneity are major limitations in high field MRI. Three-dimensional (3D) RF pulses are useful for reducing B1+ inhomogeneity and spectral spatial pulses have been shown to reduce the through-plane signal loss susceptibility artifact. We present a dual-band 3D RF pulse design for simultaneously reducing susceptibility induced signal loss and B1+ inhomogeneity. The method is demonstrated in T2* weighted brain images at 3T using an RF body coil. The pulses were observed to work well for multiple slices and several volunteers. The method can easily be extended to parallel transmission applications or more complex B1+ profiles.

14:30         4516.     Correction of Parallel Transmit RF Pulses at 9.4 T Using Measured Gradient Waveforms

Xiaoping Wu1, J. Thomas Vaughan1, Kâmil Ugurbil1, Pierre-François Van de Moortele1

1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA

Parallel Transmission (PT) allows for applying accelerated multidimensional spatially selective RF pulses through independent Transmit (Tx) RF channels, a feature especially promising at very high magnetic fields to compensate for B1 field inhomogeneity. However, gradient waveform distortions due to gradient system imperfections and/or eddy current can result in very poor excitation profiles. It has been shown that such degradation of excitation patterns can be effectively reduced by using measured k-space trajectories for RF pulse design. In the present work, we conducted PT experiments on a 9.4 T human scanner and measured k-space trajectories to calculate corrected RF pulses, resulting in dramatic excitation accuracy improvement.

15:00         4517.     An Efficiency Metric for K-Space Trajectories

Christopher J. Hardy1, Luca Marinelli1

1GE Global Research, Niskayuna, NY, USA

To maximize speed, k-space trajectories should be designed to allow efficient traversal under conditions of constrained gradient amplitude and slew rate. We employ a rate remapping algorithm to always push gradient amplitude or slew rate to the limit over the whole course of the trajectory, creating time-optimal gradient waveforms. Given constant extent of 2D k-space coverage, the average density of coverage is assumed to be proportional to the total length of the trajectory. Trajectory length divided by the time of traversal can then be taken as an efficiency metric. Various trajectories are compared using this metric.

 


 
Pulse Sequences
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 92

14:00         4518.     Microstructural Assessment of Dental Tissues by Quantitative MRI Using Ultra-Short Echo Times (UTE): Initial In-Vivo Evaluation

Saïd Boujraf1,2, Christian Hofmann1,3, Johannes Ulrici4, Erich Hell4, Bernd Haller3, Volker Rasche1

1Department of Internal Medicine II, University Hospital of Ulm, Ulm, Germany; 2Department of Biophysics and Clinical MRI Methods, Faculty of Medicine and Pharmacy of Fez, Fez, Morocco; 3Department of paraodontology, Dental University Clinic of Ulm, Ulm, Germany; 4Sirona Dental Systems GmbH, Bensheim, Germany

This work demonstrates the application of in-vivo UTE-MRI for assessing hard-tissue features of teeth with sufficient spatial-resolution and tissue-contrast within reasonable scan time.

14:30         4519.     In-Vitro Quantification of Dental Filling Induced Artifacts in Dental Magnetic Resonance Imaging Using Ultrashort Echo Time (UTE) at 3 Tesla

Saïd Boujraf1,2, Christian Hofmann1,3, Regina Maschka3, Johannes Ulrici4, Erich Hell4, Bernd Haller3, Volker Rasche1

1Department of Internal Medicine II, University Hospital of Ulm, Ulm, Germany; 2Department of Biophysics and Clinical MRI Methods, Faculty of Medicine and Pharmacy of Fez, Fez, Morocco; 3Department of paraodontology, Dental University Clinic of Ulm, Ulm, Germany; 4Sirona Dental Systems GmbH, Bensheim, Germany

The aim of this study is assessing the sensitivity of UTE-MRI to artifacts induced by dental filling-materials, and to compare the resulting artifact levels in UTE Images to conventional 3D-spin-echo and 3D-gradient-echo techniques

15:00         4520.     Microstructural Assessment of Dental Tissues by Quantitative MRI Using Ultra-Short Echo Times (UTE): In-Vitro Evaluation

Saïd Boujraf1,2, Christian Hofmann1,3, Johannes Ulrici4, Erich Hell4, Bernd Haller3, Volker Rasche1

1Department of Internal Medicine II, University Hospital of Ulm, Ulm, Germany; 2Department of Biophysics and Clinical MRI Methods, Faculty of Medicine and Pharmacy of Fez, Fez, Morocco; 3Department of paraodontology, Dental University Clinic of Ulm, Ulm, Germany; 4Sirona Dental Systems GmbH, Bensheim, Germany

The aim of this study is to proof the feasibility of UTE-MRI for assessing teeth morphology, including enamel, dentin, pulpa and root-material.

15:30         4521.     Imaging of Short T2 Species Using a Dual Adiabatic Inversion Recovery Ultrashort TE (DIR UTE) Sequence

Jiang Du1, Christine B. Chung1, Mark Bydder1, Won Bae1, Atsushi M. Takahashi2, Graeme M. Bydder1

1Radiology, University of California-San Diego, San Diego, CA, USA; 2Global Applied Science Laboratory, GE Healthcare Technologies, Menlo Park, CA, USA

Imaging of short T2 tissues requires not only a short echo time (TE) but also efficient suppression of long T2 tissues in order to maximize the short T2 contrast and dynamic range. This paper introduces a novel method of long T2 suppression using two long adiabatic inversion pulses, with the first pulse inverting the longitudinal magnetization of long T2 water protons and the second one inverting the longitudinal magnetization of fat protons. Ultrashort TE (UTE) acquisition starts when both inverted magnetization reach the nulling point. The feasibility of this technique was demonstrated on phantom, cadaveric samples and healthy volunteers.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 92

13:30         4522.     Improved Cardiac Shim Using Field Map Estimate from Multi-Echo Dixon Method

Peter Kellman1, Diego Hernando2, Saurabh Shah3, Sven Zuehlsdorff3, Andreas Greiser4, Renate Jerecic3

1National Institutes of Health, Bethesda, MD, USA; 2University of Illinois, Urbana, IL, USA; 3Siemens Medical Solutions, Chicago, IL, USA; 4Siemens Medical Solutions, Erlangen, Germany

Rapid field variation across the heart cause by tissue-air interface presents a challenge to cardiac imaging. An improved method for shimming is presented which estimates the fieldmap in the presence of rapid field variation and in regions containing both fat and water. The fieldmap is estimated using a multi-echo GRE acquisition and VARPRO solution for fat and water components. The multi-echo GRE sequence was implemented with parallel imaging reconstruction as a real-time, free-breathing, non-ECG gated 2D multi-slice acquisition, acquiring the volume in <7s. With the proposed shim method, the field variation in the user defined heart region was reduced significantly.

14:00         4523.     Fat Suppressed FSE Pelvic MR Imaging with Two New FSE Based Dixon Pulse Sequences: A Comparison of IDEAL FSE and FSE Triple Echo Dixon

Russell Norman Low1,2, Neeraj Panchal1,2

1Sharp and Children's MRI Center, San Diego, CA, USA; 2San Diego Imaging Medical Group, San Diego, CA, USA

We review our initial clinical experience with two new Dixon-based FSE sequences for fat suppressed pelvic MRI. Traditional fat-suppressed FSE imaging is often degraded by artifacts caused by magnetic field inhomogeneities. The large FOV required for pelvic imaging can exacerbate these artifacts. IDEAL FSE and Fast Spin Echo Triple Dixon (FTED) are two new sequences which generate fat-only and water-only images insensitive to magnetic field inhomogeneities. We explore the use of IDEAL FSE and FTED for pelvic MRI and compare them to conventional fat suppressed FRFSE T2-weighted imaging for image quality, homogeneity of fat suppression, artifacts, and lesion detection.

14:30         4524.     Comparison of Susceptibility-Weighted Imaging and Magnetic Field Correlation Imaging

Caixia Hu1, Jens H. Jensen1, Kathleen Williams1, Maria Fatima Falangola1, Joseph A. Helpern1

1Radiology, New York University, New York, NY, USA

Susceptibility-weighted imaging and magnetic field correlation imaging are two recently introduced techniques that yield image contrast sensitive to magnetic field inhomogeneities generated by iron rich regions within the brain. Here these two techniques are directly compared, and it is shown that they quantify distinct aspects of the pattern of field inhomogeneities.

15:00         4525.     Fast, High Resolution T2* Mapping Using 3D MGE and 3D EPI, with 3D Correction for Macroscopic Dephasing Effects

Simon Robinson1, Markus Barth2, Jorge Jovicich1

1Centre for Mind/Brain Sciences, University of Trento, Trento, Trentino, Italy; 2Centre for Cognitive Neuroimaging, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, Netherlands

T2* maps reflect local iron concentration but are limited in usefullness by dephasing due to static magnetic field gradients. We explore the utility of high resolution 3D EPI and 3D MGE sequences in reducing dephasing, and the correction of residual effects using a 3D model based on fieldmaps, which are calculated from phase information. Results are presented for the basal ganglia, which are of clinical interest in a number of pathologies. 3D MGE with acceleration factor 2, the fastest sequence tested, emerges as a reliable means to perform whole-brain submillimetre T2* mapping at 4T in just over 5 minutes.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 92

13:30         4526.     Reference Phantom Validation of T2-Mapping: Maximum Likelihood Estimation of T2 from Magnitude Phased-Array Multi-Echo Data

Clemens Bos1, Adri Duijndam1, Julien Sénégas2

1Philips Healthcare, Best, Netherlands; 2Philips Research Europe, Hamburg, Germany

High-resolution T2 maps are often biased by noise signal that is rectified and mimics persistent long T2 signal. Maximum likelihood estimation with explicit inclusion of noise statistics in the signal model has the potential to mitigate this bias, and to minimize the variance of the resulting T2-map. Maximum likelihood estimation of T2 was validated on the eurospin reference phantom. T2 values were accurate well within 5%. Maximim likelihood estimation is compatible with phased-array coils and parallel imaging. In conclusion, maximum likelihood estimation has utility for accurate and precise pixel-wise calculation of T2.

14:00         4527.     T -Weighted MRI Senses Partial Pressure of Oxygen

Dharmesh R. Tailor1, James E. Baumgardner2, Walter R. T. Witschey3, Ravinder Reddy1

1Radiology, University of Pennsylvania, Philadelphia, PA, USA; 2Anesthesia, University of Pennsylvania, Philadelphia, PA, USA; 3Biochemistry & Molecular Biophysics, University of Pennsylvania, Philadelphia, PA, USA

T-Weighted MRI is demonstrated as a technique for monitoring partial pressure of oxygen, an important physiologic parameter with obvious functional and clinical implications, with a sensitivity that is higher than that of both T1 and T2 weighting. The possibility of T-weighted MRI for imaging localized PO2 changes is also demonstrated in the rat and human brain.

14:30         4528.     MR Contrast Generated by Altering Parameters of Adiabatic Pulses: Theoretical Simulations and in Vivo  MRS Results

Silvia Mangia1, Timo Liimatainen1, Michael Garwood1, Pierre-Gilles Henry1, Shalom Michaeli1

1CMRR, Dept. of Radiology, University of Minnesota, Minneapolis, MN, USA

Rotating frame relaxation rates are measured during radiofrequency (RF) irradiation, and therefore can be altered by choosing different RF settings. The present work focuses on rotating frame relaxation methods based on adiabatic pulses, exploring how MR contrast can be created by using different pulse modulation functions, maximum amplitude or bandwidth of the adiabatic pulse. Results from theoretical simulations and animal MRS experiments are presented.

15:00         4529.     Contrast Enhancement for Early Tumor Detection by Active Feedback Self-Nutation

Sophia Y. Yang1, Fang Liu1, Dennis W. Hwang1, Yung-Ya Lin1

1Chemistry and Biochemistry, UCLA, Los Angeles, CA, USA

Active feedback fields can selectively lock spin components with a small frequency shift and concentration difference within an inhomogeneous sample to generate contrast, which would otherwise be difficult to obtain in conventional imaging. From our experiment with early tumor mice, we show that this concept can be applied for early tumor detection.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 92

13:30         4530.     Intra and Inter-Site Reproducibility of Myelin Water Volume Fraction Values Derived Using McDESPOT

Sean CL Deoni1, Rebecca Samson2, Claudia A.M. Wheeler-Kingshot2

1Centre for Neuroimaging Sciences, London, UK; 2Department of Neuroinflammation, UCL Institute of Neurology, London, UK

Multi-component Driven Equilibrium Single Pulse Observation of T1 and T2 (mcDESPOT) is a promising alternative to conventional T2-based approaches to multi-component relaxometry. An important attribute of any quantitative imaging method is the technique’s reproducibility, both across multiple time-points and across different imaging centres. Here we quantify the intra and inter-site reproducibility of mcDESPOT-derived myelin water volume fraction estimates, demonstrating high repeatability with intra and inter-site coefficients of variations of 0.069 and 0.07, respectively. Further, voxel-wise paired t-tests revealed no time-point or imaging site-specific biases.

14:00         4531.     Evaluation of K-T SENSE for Cardiac Imaging of Rats at 9.4T

Anthony N. Price1, Kenneth K. Cheung1, Shaihan J. Malik2, Mark F. Lythgoe1

1Centre for Advanced Biomedical Imaging, UCL Institute of Child Health, University College London, London, UK; 2Imaging Sciences Department, Hammersmith Hospital Campus , Imperial College London, London, UK

In recent years parallel imaging and dynamic undersampling have become routinely available in clinical cardiac MRI. However, these techniques have been slow to translate to the pre-clinical setting. In this abstract we present a full implementation and quantitative evaluation of up to 5x dynamically undersampled data using a four-channel array coil on a 9.4T experimental system. k-t SENSE reconstruction can provide an accurate estimation of LV ejection fraction in rats, using complete short axis cine data of 0.2 x 0.2 x 1mm resolution taking only 2-3 minutes to acquire.

14:30         4532.     Preserving Signal Contrast in Multi-Slice Black Blood Fast Spin Echo

Ananth J. Madhuranthakam1, Jesse L. Wei2, Jean H. Brittain3, Neil M. Rofsky2, David C. Alsop2

1Applied Science Laboratory, GE Healthcare, Boston, MA, USA; 2Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA; 3Applied Science Laboratory, GE Healthcare, Madison, WI, USA

When double inversion recovery (DIR) is used with single shot fast spin echo (SSFSE) to achieve multi-slice black blood images, the signal contrast is preserved in the first slice but degrades in later acquired slices due to the absence of sufficient recovery time. This is especially problematic for long T1 species, for instance, lesions with moderately prolonged T1 causing difficulty in diagnosis due to alterations in normally seen contrast. In this work, we demonstrate a technique to achieve black blood by using a preparation sequence to suppress fast moving spins while preserving signal contrast in all single shot slices.

15:00         4533.     Comparison of Black Blood and Bright Blood Cardiac MR Imaging by Prospective- And Retrospective ‘wireless’ Gating Methods for Evaluation of Mouse Heart Function at 9.4T

Sandra Margaretha Bovens1,2, Bernard C. te Boekhorst1, Meike van den Berk1, Kees W. van de Kolk1, Arno Nauerth3, Niels Gadellaa1, Marcel G. Nederhoff1,2, Gerard Pasterkamp1, Michiel ten Hove1, Cees J. van Echteld4

1Cardiology, University Medical Center Utrecht, Utrecht, Netherlands; 2InterUniversity Cardiology Institute of the Netherlands, Utrecht, Netherlands; 3Bruker Biospin MRI GmbH, Germany; 4Novartis Institutes for BioMedical Research, Basel, Switzerland

CMR is often used in mice, for the determination of cardiac function. We introduced a fast, multislice black blood approach with a ‘wireless’ retrospective gating method. The CNR of retrospective gating methods are higher than the prospective methods. There are no significant differences between the bright- and black blood methods, or the prospective and retrospective methods. The introduced ‘wireless’ multislice black blood method is fast and the SNR is comparable to that of bright blood methods. The inter-observer variability decreases, thus showing a fast, reliable ‘wireless’ alternative for the determination of cardiac function with a black blood sequence.

 


 
Sequences & Techniques
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 93

14:00         4534.     Optimization of Variable-Density Cartesian Sampling for Time-Resolved Imaging

Reed F. Busse1, Kang Wang2, James H. Holmes1, Jean H. Brittain1, Frank R. Korosec3

1Applied Science Laboratory, GE Healthcare, Madison, WI, USA; 2Medical Physics, University of Wisconsin, Madison, WI, USA; 3Radiology, University of Wisconsin, Madison, WI, USA

A number of Cartesian sampling patterns were considered to optimize system performance for time-resolved imaging applications. Two k-t sampling density functions were compared, a two-value “top-hat” function and a continuous function proportional to 1/kr. The effect k-t sampling distribution, including bit-reversed time ordering and point-wise k-space interleaving was also assessed. Modeling studies simulating rapid contrast arrival in an angiography application were performed. Reconstruction errors due to temporal dynamics – temporal blur and coherent artifacts – were found to be lowest for the approach with 1/kr k-t sampling density and bit-reversed point-wise interleaving of k-t samples.

14:30         4535.     A Low Curvature Uniformly Sampled Trajectory for 3D Imaging: The Interlocking Loops Trajectory

Eric Wong1

1University of California, San Diego, La Jolla, CA, USA

K-space trajectories with uniform sampling and low curvature allow for fast sampling. We introduce here a novel 3D trajectory based on two interlocking loops that uniformly samples a sphere, with low curvature at all points.

15:00         4536.     Shells with Integrated RadiaL and Spiral (SWIRLS): An Improved Shells K-Space Trajectory

Yunhong Shu1, Matt A. Bernstein1

1Radiology, Mayo Clinic, Rochester, MN, USA

An improved method to sample k-space on a spherical surface is described. The novel trajectory, named shells with integrated radial and spiral (SWIRLS), eliminates the need for two helical spiral interleaves that cover the “polar icecap” region in the original shells trajectory. Phantom and volunteer experiments demonstrate the feasibility of the SWIRLS method. It has improved temporal efficiency compared to the shells trajectory, while overcoming the problems with phase discontinuity.

15:30         4537.     On Optimal Encoding of Flow in Three-Directional Phase-Contrast Sequences

Francesco Santini1, Michael Markl2, Klaus Scheffler1

1Radiological Physics, University of Basel Hospital, Basel, Switzerland; 2Medical Physics, University Hospital Freiburg, Freiburg, Germany

Three-directional flow encoding by means of phase-contrast sequence is becoming popular for clinical applications. In order to keep reasonable scan times, there is often the need to compromise on temporal resolution of the acquired dataset. In this work, an analysis of the behavior of the standard flow encoding method with respect to the dynamics of the velocity waveform is provided. An alternative reconstruction algorithm, implementing a “view sharing” principle along the velocity direction is presented, which improves the time resolution at no additional cost. The optimized reconstruction method is validated in vivo.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 93

13:30         4538.     Improved Radial Spoiled Gradient Echo Imaging with Randomized RF Phases and Gradient Moments

Wei Lin1, Hee Kwon Song1

1Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA

Conventional spoiled gradient echo imaging with quadratic RF spoiling generates non-ideal signal intensities, particularly at short repetition times and large flip angles. This translates to significant errors in various quantitative applications based on T1-weighted image contrast. This work proposes a novel spoiling scheme, based on random gradient moments and RF phases, in conjunction with the radial acquisition scheme to suppress artifacts caused by TR-to-TR signal variations. The proposed method achieves ideal spoiling within a wide range of flip angles (00-900) and repetition times (5-3000 ms). Simulations and phantom experiments demonstrate the superior performance over conventional RF spoiling.

14:00         4539.     Effects of Relaxation During RF Pulses on the Signal Intensity of Spoiled Gradient Echo Sequences

Nicolas Boulant1

1CEA, NeuroSpin, Gif sur Yvette, France

We present an analysis of the steady state signal in the presence of relaxation during RF pulses in spoiled gradient echo sequences. It is shown that a minor attenuation of the magnetization vector, of the order of one to some percent, can have dramatic consequences on the measured signal in the short TR/long T1 applications, yielding in some cases a substantial loss of signal at the Ernst angle. Measurements on a phantom at 3 teslas are performed to verify this analysis.

14:30         4540.     Simultaneous Acquisition of Gradient Echo / Spin Echo BOLD and Perfusion with a Separate Labeling Coil

Christopher Glielmi1, Qin Xu1, Richard Cameron Craddock2,3, Xiaoping Hu1

1Department of Biomedical Engineering, Georgia Institute of Technology / Emory University, Atlanta, GA, USA; 2School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, USA; 3Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA

We present a new sequence that complements arterial spin labeling with simultaneous acquisition of gradient echo and spin echo BOLD. These three contrasts have complementary characteristics and simultaneous acquisition facilitates comparison of each measure’s specificity and reproducibility.

15:00         4541.     Recovery of Signal Loss Due to In-Plane Susceptibility Gradients in Gradient Echo EPI by Acquiring Extended Phase-Encoding Lines

Kwan-Jin Jung1,2

1BIRC, University of Pittsburgh, Pittsburgh, PA, USA; 2Bioengineering Department, University of Pittsbrguh, Pittsburgh, PA, USA

The in-plane susceptibility gradient causes an echo shift which results in signal loss and ripple artifact in gradient echo imaging. This become more severe in the gradient echo EPI due to a low gradient strength applied in the phase-encoding direction during the long echo train. An approach of using the z-shim in the PE direction was developed. However, this method has the same disadvantage of increasing the scan time two or three times as in the through-plane z-shimming. A new approach is to acquire the echo signals that are shifted outside the regular data acquisition time by acquiring more echoes outside the regular TDAQ. This will recover the signal loss as well as remove the ripple artifact without increasing the scan time significantly.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 93

13:30         4542.     Field Map Measurements Using a TrueFISP Sequence

Sven Zuehlsdorff1, Peter J. Weale1, Saurabh Shah1, Andreas Greiser2, Renate Jerecic1

1Siemens Medical Solutions USA, Inc., Chicago, Il, USA; 2Siemens AG Healthcare Sector, Erlangen, Germany

A homogeneous static magnetic field (B0) is essential for many clinical applications requiring TrueFISP imaging. Typically, 3D gradient echo (GRE) sequences are used estimate the B0-field inhomogeneity. However, these approaches are typically susceptible to motion (such as cardiac or respiratory motion) and flow. In this study, the spectral response function of a 2D TrueFISP sequence was utilized to estimate deviations of the B0-field. Field maps of different body regions such as brain and heart have been obtained.

14:00         4543.     Simultaneous B1 and T1 Mapping Based on Modified "Actual Flip-Angle Imaging"

Tobias Voigt1, Ulrich Katscher2, Kay Nehrke2, Olaf Doessel1

1Institute of Biomedical Engineering, University of Karlsruhe, Karlsruhe, Germany; 2Philips Research Europe, Hamburg, Germany

We present a new, fast, and accurate simultaneous B1 and T1 mapping method based on the "Actual Flip angle Imaging" (AFI) sequence. In terms of accuracy and signal to noise ratio it seems to outperform standard AFI B1 mapping. The quantitative T1 estimation of the presented approach is in good agreement with reference T1 measurements. The approach has been successfully tested with healthy volunteers.

14:30         4544.     Modulated Repetition Time Look Locker (MORTLL):  a Method for Rapid High Resolution Three Dimensional T1 Mapping

Neville Dali Gai1, John Butman1

1Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, USA

A modification of the Look-Locker (LL) technique that enables high resolution T1 mapping over the physiologic range of intracranial T1 values is presented. The modifications include the use of a 3D balanced SSFP acquisition (for high SNR and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization. The technique makes it possible to image a volume of thin contiguous slice with high resolution and accuracy using a simple fitting procedure for three LL phases in a reasonable time and is particularly well suited for imaging long T1 species. The T1 values obtained in WM, GM and CSF are compared with those obtained using inversion recovery spin echo imaging (gold standard) as well as with a 8 phase LL with a three parameter model and correction described in literature. T1 values obtained in multiple phantoms and from six volunteers showed excellent agreement with IR-SE T1 values.

15:00         4545.     A Multi-Spectral Three-Dimensional Acquisition Technique for Imaging Near Metal Implants

Kevin M. Koch1, John E. Lorbiecki1, R Scott Hinks1, Kevin F. King1

1Applied Science Laboratory, GE Healthcare, Waukesha, WI, USA

Metallic implants used in bone and joint arthroplasty induce severe spatial perturbations to the B0 magnetic field used for high-field clinical magnetic resonance. These perturbations distort slice-selection and frequency encoding processes applied in conventional two-dimensional techniques and hinder the diagnosis of complications from arthroplasty. Here, a method is presented whereby multiple three-dimensional fast-spin-echo images are collected at offset RF transmission and reception frequencies. It is demonstrated that this technique can be used to generate a composite image that is devoid of slice-plane distortion and possesses greatly reduced distortions in the readout direction, even in the immediate vicinity of metallic implants.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 93

13:30         4546.     Phase Accrual During Excitation in Ultrashort TE (UTE) Imaging:  an Alternate Definition of TE for Phase Measurements

Jing-Tzyh Alan Chiang1, Michael Carl2, Mark Bydder1, Jiang Du1, Robert F. Mattrey1, Graeme Bydder1

1Radiology, University of California San Diego, San Diego, CA, USA; 2Applied Science Laboratory, GE Health Care

MR imaging of tissues with submillisecond T2’s is possible with UTE (ultrashort TE) sequences that utilize half RF excitation pulses and radial projection readouts. For UTE sequences, TE is customarily defined to be from the end of the half RF pulse to the beginning of radial projection readout. We present data here that show phase accrual in UTE imaging to be more than expected for this customary definition of TE. Numerical calculations show this is largely due to phase accrual before the end of the RF pulse, and we suggest an alternate definition of TE for phase calculations in UTE.

14:00         4547.     Assessment of Motion Sensitized Driven Equilibrium (MSDE) Improvement for Whole Brain Application

Makoto Obara1,2, Masatoshi Honda3, Yutaka Imai3, Marc Van Cauteren1, Kagayaki Kuroda2

1Philips Electronics Japan, Minato-ku, Tokyo, Japan; 2Graduate School of Information Science and Engineering, Tokai University, Hiratsuka, Kanagawa, Japan; 3Department of Radiology, Tokai University, Isehara, Kanagawa, Japan

Improvement of MSDE for whole brain application was assessed in human volunteers study. The signal obtained by the improved MSDE sequence was compared with a conventional MSDE sequence at cerebrum area. The improved MSDE sequence achieved both better image homogeneity than when acquired with the conventional MSDE and the signal drop typical in conventional MSDE is absent. It is indicating that improved MSDE sequence is less sensitive to B0 and B1 inhomogeneity and EC effects. Therefore, it may be appropriate for whole brain application.

14:30         4548.     Non-Contact Tracking of Involuntary Head Motions by Ultra-Wideband Radar for Improved High- And Ultra-High Field Magnetic Resonance Brain Imaging

Florian Thiel1, Mathias Hein2, Jürgen Sachs2, Ulrich Schwarz2, Tomasz Lindel1, Frank Seifert1

1Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany; 2Ilmenau University of Technology

Subject motion appears to be a limiting factor in numerous MR imaging applications, especially at high and ultrahigh fields. For head imaging the subject’s ability to maintain the same head position for a considerable period of time places restrictions on the total acquisition time. In particular, head tremor, may render certain high-resolution techniques inapplicable. Furthermore, if the very high spatial resolution offered by ultrahigh-field MR scanners shall be exploited, the displacements caused by respiration and cardiac activity have to be considered. Thus, we propose applying a novel method, based on an ultra-wideband radar technique to monitor involuntary head displacements.

15:00         4549.     Non-Linear Effects at High-Speed Moving Table Imaging

Ulrich Katscher1, Oliver Lips1

1Philips Research Europe - Hamburg, Hamburg, Germany

Continuously moving table imaging is an alternative to multi-station techniques for, e.g., MR angiography. In the past years, the provided table speed increased from typically ~1 cm/s up to ~5 cm/s. Assuming a long-term continuation of this trend of increasing table speed, one has to keep in mind that at table speeds approaching ~3&[middot]109 cm/s, non-linear, relativistic effects has to be taken into account. This study investigates possible consequences, particularly on scan time and RF field distortions due to the Lorentz transformation. The study is based on simulations due to the current lack of suitable MR systems.

 


 
Parallel Imaging
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 94

14:00         4550.     SVD Eigenimage Based SENSE

Yu Li1, Feng Huang1, Wei Lin1, Charlie Saylor1, Arne Reykowski1

1Advanced Concept Development, Invivo Diagnostic Imaging, Gainesville, FL, USA

In this study, an eigenimage theory was developed for SENSE. Using singular value decomposition (SVD), the full FOV image can be reconstructed by summing several eigenimages weighted by some coefficients calculated from the eigenvalues of a sensitivity matrix. Based on this theory, a data-driven regularization technique was proposed to overcome the challenges of inaccurate sensitivity maps and noise amplification in SENSE reconstruction. This is a new technique that can offer simplicity and efficiency in SENSE g-factor control and artifact suppression.

14:30         4551.     High Pass SENSE

Feng Huang1, Yu Li1, Wei Lin1, Charlie Saylor1, Arne Reykowski1

1Invivo Corporation, Gainesville, FL, USA

A method to reduce noise/artifact level in images reconstructed by SENSE through artificial image sparsity is presented. The sparsity of an image can be artificially increased through a high pass filter in k-space. With constraint of sparsity, the image reconstructed by regularized SENSE with high pass filtered data can be efficiently denoised. G-factor map is used to produce the sparsity-regularization map. Experiments show that the proposed method reconstructs images with reduced noise level than conventional SENSE, and 1D net acceleration factor 4 can be achieved with an 8-channel coil.

15:00         4552.     An Unsupervised Method to Enhance Both SNR and Edges for PPI

Weihong Guo1, Feng Huang2

1Department of Mathematics, University of Alabama, Tuscaloosa, AL, USA; 2Advanced Concept Development, Invivo Corporation, Gainesville, FL, USA

Partially parallel imaging (PPI) techniques reduce acquisition time at the cost of signal to noise ratio (SNR). In this work, an unsupervised adaptive method is proposed to reduce noise/artifact level, as well as to sharpen edges. This method is based on Non-local Means (NL-Means). Results of the application to GRAPPA, with both phantom and in vivo data, demonstrate that the proposed method is able to increase SNR, to preserve the fine structures, and to sharpen the edges at the same time.

15:30         4553.     GRAPPA Operator for Wider RadiaL Band (GROWL)

Wei Lin1, Feng Huang1, Yu Li1, Charles Saylor1, Arne Reykowski1

1Invivo Corp., Philips Healthcare, Gainesville, FL, USA

A self-calibrated parallel imaging reconstruction method is proposed for azimuthally undersampled radial dataset. GRAPPA extrapolation operators were used to widen each radial view into a band consisting of several parallel lines, followed by a standard regridding procedure. Self-calibration is achieved by regridding central k-space region, where Nyquist criterion is satisfied, to a rotated Cartesian grid. Applying the proposed reconstruction method to in vivo radial gradient echo images demonstrated a removal of most streaking artifacts at data reduction factors R = 4 and 8, using an eight-element coil array.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 94

13:30         4554.     Atlas Based Sparsification of Image and Theoretical Estimation (ABSINTHE)

Eric Pierre1, Nicole Seiberlich2, Stephen Yutzy1, Jean Tkach2,3, Mark Griswold2,3

1Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA; 2Radiology, Case Western Reserve University; 3University Hospitals of Cleveland

In GRAPPA, higher acceleration factors can be achieved with less noise enhancement when reconstructing sparse images. In this study, the ABSINTHE technique has been developed to render undersampled in vivo brain images sparser by removing the “normal” brain information using Principal Component Analysis with a training set of similar brain images. The resulting undersampled sparse images are then reconstructed using GRAPPA. The effectiveness of ABSINTHE for reconstructing undersampled simulated and in-vivo data is demonstrated, and an improved image quality in terms of lower artifact powers is shown for ABSINTHE in comparison to the standard GRAPPA technique.

14:00         4555.     Reconstruction Efficiency and Accuracy Improvement in Real Time Dynamic Parallel Imaging Through Explicit Tracking of Calibration Information

Roger Nana1, Xiaoping Hu1

1Biomedical Engineering, Emory University / Georgia Institute of Technology, Atlanta, GA, USA

This paper presents an approach for improving image reconstruction in dynamic parallel imaging in cases with cyclic changes in coil calibration information. The variation of the calibration information is ascertained by a consistency measure, and the cyclic nature of the variation is used to improve the reconstruction efficiency and accuracy by allowing time frames to share calibration information and avoid using inconsistent calibrating frames. The method is demonstrated using TGRAPPA with free-breathing cardiac imaging data. The method is simple and robust and can be applied to other real-time parallel dynamic image reconstructions

14:30         4556.     O-Space Imaging: Tailoring Encoding Gradients to Coil Profiles for Highly Accelerated Imaging

Pelin Aksit Ciris1, Jason Peter Stockmann1, Lick-Kong Tam1, Robert Todd Constable1,2

1Biomedical Engineering, Yale University, New Haven, CT, USA; 2Diagnostic Radiology & Neurosurgery, Yale University, New Haven, CT, USA

O-space imaging is a novel MRI method which achieves very short imaging times by collecting highly independent information at each acquisition, through selecting encoding gradients that complement spatial localization provided by coils. Instead of conventional phase encoding, alternative encoding schemes with projection directions orthogonal to coil sensitivity profiles and each other, are employed. O-space imaging was evaluated using a radially varying gradient field and a circumferentially distributed coil array, with various noise levels, number of coils, and encoding schemes. Results identified superior encoding schemes, and indicate feasibility of high acceleration factors with accurate knowledge of the field.

15:00         4557.     Parallel Imaging Technique Using Localized Gradients (PatLoc) Reconstruction Using Orthogonal Mode Decomposition

Fa-Hsuan Lin1, Thomas Witzel1, Jonanthan Polimeni1, Juergen Hennig2, Gerrit Schultz2, John W. Belliveau1, Lawrence L. Wald1

1A. A. Martinos Center, Massachusetts General Hospital, Charlestown, MA, USA; 2Department of Diagnostic Radiology, medical Physics, University Hospital Freiburg, Freiburg, Germany

Using conventional imaging sequence, the parallel imaging technique using localized gradients (PatLoc) system requires combining different gradient coils to generate two sets of gradient fields in order to complete “frequency” and “phase” encodings. Previously it was suggested using two orthogonal circular symmetric (OCS) fields to accomplish this requirement. Here we propose to use singular value decomposition (SVD) to automatically decompose the gradient information and suggest the linear combinations for two orthogonal gradients for the pulse sequence. Such orthogonal mode (OM) PatLoc fields were demonstrated with improved image reconstruction in up to 4-fold accelerated acquisitions.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 94

13:30         4558.     Comparison of TSENSE, K-T SENSE and PINOT Fast Imaging Methods on Cine MRI

Lei Hou Hamilton1, Javier Acebrón Fabregat2, David Moratal2, Senthil Ramamurthy3, Sebastian Kozerke4, Marijn E. Brummer5

1School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, USA; 2Universidad Politécnica de Valencia, Valencia, Spain; 3Children’s Healthcare of Atlanta, Atlanta, GA, USA; 4University and ETH Zurich, Zurich, Switzerland; 5School of Medicine, Emory University, Atlanta, GA, USA

In this study we compare the performance of three MRI fast imaging methods, TSENSE, k-t SENSE and PINOT on real cardiac cine images. These methods combine parallel imaging with UNFOLD, k-t BLAST and Noquist, respectively. These methods have been implemented under similar net reduction factors. A direct comparison of reconstructed images and an analysis of noise levels show that TSENSE and k-t SENSE have better SNR but tend to blur edges, while PINOT, with no filtering or interpolation, favorably preserves edge detail at a cost of decreased SNR.

14:00         4559.     Comparison of Kt-SENSE and Kt-GRAPPA Applied to Cardiac Cine and Phase Contrast Imaging

Bernd André Jung1, Sebastian Kozerke2

1Dept. of Diagnostic Radiology, Medical Physics, University Hospital, Freiburg, Germany; 2Institute for Biomedical Engineering, ETH Zürich, Switzerland

To reduce scan time in time-resolved imaging, advanced parallel imaging techniques have been introduced such as kt-SENSE, kt-GRAPPA, and PEAK-GRAPPA as an extension of kt-GRAPPA. In this work, kt-SENSE was compared to PEAK-GRAPPA in terms of error, noise behavior and temporal fidelity for cardiac Cine and phase contrast data.

14:30         4560.     Optimized Parallel Imaging for Dynamic PC-MRI with Multi-Directional Velocity Encoding

Hsu-Hsia Peng1, Simon Bauer2, Hsiao-Wen Chung1, Juergen Hennig2, Bernd Jung2, Michael Markl2

1Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; 2Department of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany

In dynamic phase contrast (PC) MRI using standard GRAPPA several central k-space (ACS) lines are acquired separately for each velocity direction and each cardiac phase for calculating the reconstruction weights (WS). We developed two methods, which calculated WS with reduced ACS. The effects on image quality and flow quantification were compared to fully-sampled data, standard GRAPPA, and TGRAPPA. The results show that the two proposed methods can improve scan efficiency while maintaining image quality and accuracy of measured flow or tissue velocities. Compared to TGRAPPA, the proposed methods were more accurate in evaluating flow velocity. In conclusion, the proposed reconstruction strategies are promising for dynamic multi-directionally encoded acquisitions.

15:00         4561.     Extending GRAPPA Kernels to 4D: Application on Time-Resolved 3D Phase Contrast Imaging

Bernd André Jung1, Simon Bauer1, Michael Markl1

1Dept. of Diagnostic Radiology, Medical Physics, University Hospital, Freiburg, Germany

Improved scanner performance and recent methodological development enable multi-dimensional data acquisition such as time-resolved 3D phase contrast imaging with three-directional velocity encoding. To speed up acquisition times for 3D data acquisition, parallel imaging techniques have been introduced. For time-resolved imaging, parallel imaging techniques have been developed such as kt-SENSE and kt-BLAST, kt-GRAPPA, and PEAK-GRAPPA as an extension of kt-GRAPPA. Previous applications of these methods focused on time-resolved 2D imaging. The aim of this work was to extend spatio-temporal PEAK-GRAPPA acceleration to reconstruction for time-resolved 3D phase contrast data acquisition to fully exploit data redundancy along all spatial and temporal directions.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 94

13:30         4562.     TV Regularization for High-Pass GRAPPA with Higher Net Acceleration Factor

Xiaojing Ye1, Yunmei Chen1, Feng Huang2

1Department of Mathematics, University of Florida, Gainesville, FL, USA; 2Invivo Corporation, Gainesville, FL, USA

High-pass GRAPPA (hp-GRAPPA) suppresses the central calibration signal to reduce image support. When the number of ACS lines is limited, this suppression results in insufficient calibration signal which causes residual aliasing artifacts. We propose a total variation regularized GRAPPA technique to calculate supplemental calibration signal for hp-GRAPPA. The experimental results, with comparisons with conventional GRAPPA and hp-GRAPPA, show that the proposed method can generate images with lower noise/artifact level when only 32 ACS lines are used with reduction factor 4. This work enables hp-GRAPPA with limited ACS lines, and hence increases the net acceleration factor while preserving the image quality.

14:00         4563.     In-Vivo-Sensitivity-Based Regularization of Parallel MR Image Reconstruction

Qi Duan1, Ricardo Otazo1, Jian Xu2, Daniel K. Sodickson1

1Radiology, Center for Biomedical Imaging, NYU School of Medicine, New York, NY, USA; 2Siemens Medical Solutions USA Inc., New York, NY, USA

This abstract demonstrates the technical feasibility of regularization of parallel MR image reconstruction using in vivo coil sensitivities. This new approach not only combines coil sensitivity calibration and regularization of the inverse problem, but also provides better signal-to-noise ratio performance than a corresponding two-step scenario without substantially increasing residual aliasing artifacts. Ultimately, this approach could be applied to any SENSE-based parallel MRI technique, especially at high acceleration factor and when pure coil sensitivity profiles are difficult to estimate.

14:30         4564.     In Vivo Receive Sensitivity Measurement

Jinghua Wang1, Maolin Qiu1, June Watzl1, Robin de Graff1, Robert Todd Constable1

1Diagnostic Radiology, Yale School of Medicine, New Haven, CT, USA

Inhomogeneous receive sensitivity, which is object-dependent, strongly affects the uniformity of MRI signal intensity acquired with parallel imaging techniques at high field. Various methods have been proposed to estimate the receive sensitivity in order to reduce spatial variations in signal intensity caused by the receive sensitivity nonuniformities. A primary challenge is to separate the contribution of tissue contrast, inhomogeneous transmit field and receive sensitivity to signal intensity. Here, we propose a novel rotating object method to estimate the receive sensitivity of a transmit/receive coil. The proposed method is validated using phantom experiments at 4.0 and 7.0 T.

15:00         4565.     Updating Pre-Scan Sensitivity Maps with the Minimum Number of ACS Lines

Feng Huang1, Yu Li1, Wei Lin1, Charlie Saylor1, Arne Reykowski1

1Invivo Corporation, Gainesville, FL, USA

There are advantages to use pre-scann sensitivity maps, such as intensity correction, higher net acceleration factor, etc. However, if there is motion between pre-scan and the target acquisition, then serious aliasing artifacts may occur because of the misregistered sensitivity maps. It is shown in this work that the misregistration can be corrected with as few as 3 extra auto-calibration signal (ACS) lines. The quality of the reconstructed image can be significantly improved with the updated sensitivity maps.

 


 
Image Reconstruction
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 95

14:00         4566.     Reconstruction of Retrospectively-Gated Cardiac Data Using a Combination of GRAPPA, SPACE-RIP, UNFOLD and an Adaptive Regularization Scheme

Tzu-Cheng Chao1,2, William Scott Hoge3, Jing Yuan4, Hsiao-Wen Chung2, Bruno Madore4

1Department of Radiology, Brigham and Women's Hospital, Harvard Medical School,, Boston, MA, USA; 2Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; 3Department of Radiology,, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; 4Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA

A novel retrospectively-gated reconstruction approach is proposed for accelerated cardiac cine imaging. The approach combines advantageous features from fast-imaging methods such as GRAPPA, SPACE-RIP, UNFOLD, kt-SENSE, SHRUG and GEYSER. The result is a reliable algorithm, tested up to acceleration factors of 6.3 (subsampling factor of 8), and featuring fast reconstruction processing.

14:30         4567.     High Spatial Frequencies Are More Dynamic Than Low Spatial Frequencies in Cardiac Motion

Mireia Sanz Blasco1, Sumati Krishnan2, David Moratal1, Senthil Ramamurthy3, Marijn E. Brummer2

1Universitat Politècnica de València, València, Spain; 2Pediatrics/CRC, Emory University, Atlanta, GA, USA; 3Children's Healthcare of Atlanta, Atlanta, GA, USA

A spatiotemporal spectral analysis is presented of kt-space in cine images in the presence of several types of cardiac motion. The temporal spectral content of each k-space view is quantified by a single spectral coefficient. Paradoxically, comparison of these coefficients between k-space views for phantom simulation data and in short-axis cardiac MRI data reveals greater relative changes in high spatial frequencies than in low spatial frequencies.

15:00         4568.     Real-Time Shallow-Breathing Cardiac MRI Using Patient-Adaptive Parallel Imaging

Behzad Sharif1, John Andrew Derbyshire2, Anthony Z. Farnesh2, Robert J. Lederman2, Yoram Bresler1

1Coordinated Science Lab, Department of Electrical & Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA; 2Cardiovascular Branch, NHLBI, National Institutes of Health, DHHS, Bethesda, MD, USA

The goal of real-time cardiac MRI is to reconstruct high quality images from data acquired with no cardiac synchronization. The previously proposed PARADISE imaging technique achieves high resolutions for non-gated breath-hold imaging by optimally adapting data acquisition and image reconstruction to the signal support information and coil sensitivities. We propose a modified PARADISE scheme that allows for shallow breathing and can capture the breathing-induced beat-to-beat cardiac motion variability. By comparing the results to breath-hold gated cine, it is demonstrated that the proposed technique achieves high quality artifact-free images with desirable spatiotemporal resolution.

15:30         4569.     An Auto-Calibrated K-T Approach for Fast 3D Dynamic Contrast-Enhanced Abdominal Imaging

Peng Lai1, Anja C. Brau1, Philip J. Beatty1, Shreyas Vasanawala2, Manojkumar Saranathan3

1Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA; 2Department of Radiology, Stanford University, Stanford, CA, USA; 3Applied Science Laboratory, GE Healthcare, Rochester, MN, USA

This study proposed a new fast imaging approach, kats ARC (Autocalibrating Reconstruction for Cartesian Sampling with k- & adaptive-t-space data synthesis) for accelerating 3D dynamic contrast-enhanced MRI. The proposed method utilizes a new undersampling pattern compatible with 2D acceleration and exploits contrast kinetics information in autocalibration signals to adaptively determine the temporal interpolation window. Its effectiveness was investigated in comparison with conventional fast imaging methods based on simulation and validated in a patient study. Both simulation and in-vivo studies showed that kats ARC could improve overall image quality and temporal fidelity than conventional methods. This work demonstrates that kats ARC is a promising technique for highly-accelerated 3D DCE abdominal imaging.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 95

13:30         4570.     Accelerated Acquisition and Reconstruction of Non-CPMG Fast Spin Echo Sequences

Ken-Pin Hwang1,2, Patrick Le Roux1, Xiaoli Zhao3, Zhiqiang Li3

1Applied Science Laboratory, GE Healthcare, Waukesha, WI, USA; 2Department of Imaging Physics, University of Texas MD Anderson Cancer Center, Houston, TX, USA; 3MR Engineering, GE Healthcare, Waukesha, WI, USA

Non-CPMG FSE produces a stable echo train in the presence of phase variations at the beginning of the train, but creates two signal families that must both be fully acquired for recombination. A close examination of the signals suggest that they are related by a slowly varying function that can be estimated with just the low order portion of k-space. This forms the basis for a new method for accelerating non-CPMG acquisitions by eliminating artifacts that occur with single encoding of non-CPMG data. The technique is demonstrated for both Cartesian single shot FSE and multishot PROPELLER applications.

14:00         4571.     Spline-Based Variational Reconstruction of Variable Density Spiral K-Space Data with Automatic Parameter Adjustment

Benedicte Delattre1, Jean-Noël Hyacinthe1, Jean-Paul Vallée1, Dimitri Van De Ville2,3

1Faculty of Medicine, University of Geneva, Geneva, Switzerland; 2Biomedical Imaging Group (BIG), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; 3Work supported in part by the Center for Biomedical Imaging (CIBM), Geneva and Lausanne, Switzerland

Small-animal cardiac imaging is very challenging because we face with several problems like resolution or flux artifacts. One possible way to assess them is the use of non-Cartesian acquisition scheme like variable density spiral. Regridding reconstruction, which is the most popular alternative, however introduces noticeable artifacts due to k-space interpolation, especially when dealing with undersampled trajectories. We propose a variational approach where the image is described by a spline model and where an automatic adjustment of the regularizing weight is implemented. We evaluate our framework for various degrees of the spline model and different orders of derivation of the regularizer.

14:30         4572.     Spiral MR Reconstruction Using FOCUSS

Hisamoto Moriguchi1, Yutaka Imai1

1Radiology, Tokai University, Isehara, Kanagawa, Japan

It has recently demonstrated that the focal underdetermined system solver (FOCUSS) can successfully be adapted to angularly undersampled projection reconstruction (PR). Images reconstructed using PR-FOCUSS are of high quality. In this study, FOCUSS can be extended to spiral trajectories with reduced spiral interleaves. The newly proposed method is referred to as eSpiral FOCUSSf. Images reconstructed using Spiral FOCUSS substantially reduce aliasing artifacts from those reconstructed using conventional reconstruction methods, e.g. gridding. The algorithm can also be applied to general non-uniform sampling methods. Spiral FOCUSS is a quite useful reconstruction technique that permits faster spiral acquisition while maintaining image quality.

15:00         4573.     Automatic Regularization for Magnetic Resonance Inverse Imaging

Aapo Nummenmaa1, Matti S. Hamalainen1, Fa-Hsuan Lin1,2

1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; 2Institute for Biomedical Engineering, National Taiwan University, Taipei, 106, Taiwan

We propose a simple method for automatic regularization of dynamic magnetic resonance Inverse Imaging (InI). Regularization is interpreted in a Bayesian way, as a variance parameter of a Gaussian prior, and marginal likelihood is used to estimate these parameters. The proposed method is compared to the presently used ad hoc regularization of InI by using empirical data from a visual stimulation experiment. Possible extension of the method for dynamic modeling of the regularization parameters is discussed.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 95

13:30         4574.     Optimal Combination and Filtering for 7 T – Phase Images

Shan Yang1, Kai Zhong1, John Grinstead2, Oliver Speck1

1Biomedical Magnetic Resonance, Otto-von-Guericke-University, Magdeburg, Germany; 2Siemens Medical Solutions USA Inc., Portland, USA

Images based on signal phase showed superior and complementary contrast at 7 Tesla compared to magnitude images. However, due to the strong RF inhomogeneity at 7 T and a lack of a body coil, it is difficult to obtain sensitivity map for each individual array element. In this study, we systematically compared the effects of different filter kernel sizes (&#61555;) on the resulting phase images using 4 different combination and filtering methods.These parameters result in optimized phase image quality at 7 T even for other resolution settings.

14:00         4575.     Improved Coil Combination for Homodyne-Corrected Phased Array Images

Ryan Fobel1, Greg J. Stanisz1

1Sunnybrook Research Institute, Toronto, ON, Canada

Homodyne detection is a reconstruction method commonly used to reduce the number of high-frequency phase encodes for faster imaging or to correct for off-centered, partial echoes for shorter effective TEs. It also has useful properties for low-SNR imaging and negative polarity signals (e.g. Inversion recovery). When multichannel data sets are combined with the root-sum-of-squares technique, many of its benefits are negated because all of the phase information is lost. This study derives a simple modification to the root-sum-of-squares method that preserves phase information. A significant reduction to the noise floor and magnitude bias is demonstrated.

14:30         4576.     A Selective Acceleration and Multi-Resolution Approach to Multi-Echo Imaging

Suchandrima Banerjee1, Cornelius Von Morze2, Douglas AC Kelley1, Philip J. Beatty1, Daniel B. Vigneron2, Eric T. Han1

1Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA; 2Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA

Multi-echo sequences provide a time-efficient means to acquire – in a single scan - multiple images, each at a different clinically relevant contrast weighting. Parallel imaging has the potential to further increase the time efficiency of such sequences, but its application can be limited by the signal-to-noise ratio (SNR) available at the longest acquired echo time. To overcome this limitation, this work proposes a scheme that selectively applies parallel imaging to the higher SNR echoes, while reducing the spatial resolution and maintaining Nyquist sampling of the lower SNR echoes. We demonstrate the efficacy of this method for two dual echo applications.

15:00         4577.     Improved Visualization of the Subthalamic Nuclei by Reducing Susceptibility Induced Signal Losses in T2* Weighted Multi-Gradient-Echo Images

Steffen Volz1, Elke Hattingen2, Christine Preibisch1,3, Thomas Gasser4, Ralf Deichmann1

1Brain Imaging Center, University Frankfurt, Frankfurt, Hessen, Germany; 2Department of Neuroradiology, University Hospital, Frankfurt, Hessen, Germany; 3Abteilung für Neuroradiologie, Klinkum rechts der Isar der TU München, München, Germany; 4Department of Neurosurgery, University Hospital, Frankfurt, Hessen, Germany

T2*-weighted gradient echo images yield good contrast of iron-rich brain structures. However, they are also sensitive to macroscopic field inhomogeneities, limiting anatomical information from affected areas. An image postprocessing method based on the evaluation of phase information is presented. A pixelwise image intensity correction of the original images acquired at different TE is performed in a first step and a combination of these images using optimized weighting factors is performed in a second step. The resulting images feature reduced signal losses in areas with major field gradients, while a contrast-to-noise (CNR) analysis in deep brain structures demonstrates good contrast.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 95

13:30         4578.     Effect of Reordering on Dynamic Contrast Enhancement

Vibhas Deshpande1, Gabriel Acevedo-Bolton2, Helmuth Schultze-Haakh3, David Saloner2, Gerhard Laub3

1Siemens Medical Solutions USA Inc., San Francisco, CA, USA; 2VA, San Francisco, CA, USA; 3Siemens Medical Solutions USA Inc., CA, USA

Various reordering schemes with different benefits can be used for dynamic contrast-enhanced imaging. The effect of the reordering schemes on the contrast dynamics is however unclear. The purpose of this study was to evaluate contrast dynamics with linear, centric and radial centric-out k-space trajectory. Data were acquired in a flow phantom with a gradient-echo sequence and short and long injections. For short injections, radial centric-out trajectory shows artifacts because of varying T1’s during the scan. Artifacts are reduced with a longer injection. Contrast-enhancement is less with radial centric-out as compared to linear or centric if T1’s vary during the scan.

14:00         4579.     Improved Image Quality by Noquist Acceleration of Cardiac MRI

Senthil Ramamurthy1, David Moratal2, James W. Parks3, Stamatios Lerakis4, Marijn E. Brummer4

1Children Research, Children's Healthcare of Atlanta, Atlanta, GA, USA; 2Universitat Politècnica de València, Valencia, Spain; 3Cardiology, Sibley Heart Center, Atlanta, GA, USA; 4Emory University, Atlanta, GA, USA

The Noquist method for accelerated cardiac imaging takes advantage of the spatiotemporal redundancy whenever the field of view contains static regions. Notable characteristics of Noquist compared to alternative methods include full preservation of spatiotemporal resolution. This study reports first results of a implementation of Noquist for a prospectively gated dynamic cardiac imaging method (GE FastCARD). A conventional image and a Noquist-accelerated image with the same acquisition parameters are compared. For the same acquisition time, Noquist-accelerated image shows clear improvement in image clarity. The improvement in image resolution clearly outweighs the SNR penalty associated with Noquist.

14:30         4580.     Comparison of Prospective ECG-Gated MRI with Wireless, Retrospective Gated MRI for Evaluation of Heart Function in Healthy and Infarcted Mouse Heart

Sandra Margaretha Bovens1,2, Bernard C. te Boekhorst1, Krista den Ouden1, Kees W. van de Kolk1, Arno Nauerth3, Marcel G. Nederhoff1,2, Gerard Pasterkamp1, Michiel ten Hove1, Cees J. van Echteld4

1Cardiology, University Medical Center Utrecht, Utrecht, Netherlands; 2InterUniversity Cardiology Institute of the Netherlands, Utrecht, Netherlands; 3Bruker Biospin MRI GmbH, Germany; 4Novartis Institutes for BioMedical Research, Basel, Switzerland

To assess (murine) left- and right ventricular heart function, ECG-triggered CMRI is often used. In mice with a myocardial infarction or cardiac hypertrophy it is sometimes challenging to get a good ECG signal. Therefore we compared a ‘wireless’ retrospective gating method with a prospective gating method in mice with and without infarcted hearts. The SNR and CNR of the retrospectively gated data are higher than that of the prospectively gated data. The ‘wireless’ retrospective gating method gives comparable results with regard to the cardiac function parameters, in the control mice as well as the mice with myocardial infarction.

15:00         4581.     A Navigator Gated Free-Breathing FSE for Black Blood Cardiac Imaging

Liuquan Cheng1, Yi Wang2, Pascal Spincemaille2, Thanh D. Nguyen2, Qian Zhao1, Na Yang1

1Radiology, Chinese PLA General Hospital, Beijing, China; 2Radiology, Weill Medical College of Cornell University, NY, NY, USA

Breath-holding acquisition is one of the obstacle for cardiac MRI especially on the patient with heart insufficiency. A navigator echo gated, double/triple IR FSE was developed to acquire the black blood T2WI images in free-breathing mode.

 


 
Reconstruction:  Sparsity & Dynamics
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 96

14:00         4582.     Recoverability Bounds for Parallel Compressive Sensing MRI

Joshua D. Trzasko1, Armando Manduca1

1Center for Advanced Imaging Research, Mayo Clinic, Rochester, MN, USA

Compressive Sensing (CS) and parallel imaging are two distinct techniques in MR imaging that allow for accelerated acquisition while retaining image quality. Recent advances have shown that these two methods may be naturally combined to provide even taster exams. In this work, we investigate the theoretical signal recovery properties of the hybrid model and derive a relationship between recoverability, the sampling model, and coil sensitivity profiles.

14:30         4583.     Investigation of Sparsifying Transforms for Compressed Sensing in MRI Reconstruction

Christopher Baker1, Kevin King2, Dong Liang1, Leslie Ying1

1Eletrical Engineering, University of Wisconsin at Milwaukee, Milwaukee, WI, USA; 2Global Applied Science Lab, GE Healthcare, Waukesha, WI, USA

In compressed sensing (CS) MRI reconstruction, the level of sparsity and incoherence achieved by the transform affects the under-sampling that can be performed. This work investigates contourlets and the discrete cosine transform (DCT) as sparsifying transforms for CS reconstruction and compares them with the widely used wavelet transform. Results show that the contourlet transform performs about the same as the wavelet, while the DCT on small image patches outperforms the wavelet in CS reconstruction of MR images. The observation suggests that use of a DCT on small image patches may improve the CS reconstruction quality.

15:00         4584.     Sparse Image Reconstruction Using the Generalized Sampling Theorem for MR Angiography

Nicole Seiberlich1, Hyun Jeong2, Timothy J. Carroll2,3, Mark A. Griswold1

1Radiology, Case Western Reserve University, Cleveland Heights, OH, USA; 2Biomedical Engineering, Northwestern University, Chicago, IL, USA; 3Radiology, Northwestern University, Chicago, IL, USA

GST-MRA, a novel method to reconstruct highly undersampled sparse images using ideas from the Generalized Sampling Theorem, is introduced here. In order to reduce the number of image pixels to be reconstructed, a soft mask is created using the composite image, and only those pixels which contain signal in this mask are reconstructed. This method is demonstrated for the reconstruction of high frame rate images of an AVM patient with a 2D acceleration factor of >20. In addition, parallel imaging in the form of coil sensitivity maps can also be incorporated into the method, further increasing the reconstruction fidelity.

15:30         4585.     Evaluation of Continuous Approximation Functions for the L0-Norm for Compressed Sensing

Carlos A. Sing-Long1,2, Cristian A. Tejos1,2, Pablo Irarrazaval1,2

1Departamento de Ingenieria Electrica, Pontificia Universidad Catolica de Chile, Santiago, R.M., Chile; 2Biomedical Imaging Center, Pontificia Universidad Catolica de Chile, Santiago, R.M., Chile

Compressed Sensing allows reconstructing signals from some of its Fourier coefficients, if they are sparse in some representation. It is usually implemented as an l1-minimization, although it was recently shown that the reconstruction process can be accelerated and the undersampling rate increased by using continuous approximations of the l0-norm. We evaluated the performance of four different approximation functions in terms of reconstruction error, number of iterations to convergence and size of the reconstructed signal’s support. We observed that their convergence properties differed significantly, and we recommend a rational function with discontinuous derivative at the origin.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 96

13:30         4586.     Comparative Evaluation of  L1  Vs Lp Minimization Techniques for Compressed Sensing MRI

Juan Carlos Ramirez Giraldo1, Joshua D. Trzasko1, Armando Manduca1

1Center for Advanced Imaging Research, Mayo Clinic, Rochester, MN, USA

Compressed sensing(CS) can provide accurate reconstructions from highly undersampled data for certain types of MR scans, allowing faster acquisition times. Standard CS is based on l1-norm minimization, which offers mathematical guarantees of global convergence. It is known that fewer samples are required for CS based on minimization of an l0-norm, but this is mathematically more difficult and no convergence guarantees exist. We compare standard l1-norm CS with two algorithms that approximate the l0-norm with the lp-norm (p between 0 and 1), with different sampling pattern densities and parameterizations. Despite the lack of theoretical guarantees, both lp-norm algorithms always outperformed standard l1-norm CS.

14:00         4587.     Compressed Sensing Reconstruction Based on Maximum Intensity Projection Images

Dong-Hyun Kim1,2, Sung-Min Gho1

1Electrical and Electronic Engineering, Yonsei University, Shinchon-Dong, Seoul, Korea; 2Radiology, Yonsei University, Shinchon-Dong, Seoul, Korea

Compressed sensing algorithm is best fit for images that can have sparse representations in image domain. The 3D volumetric information is best viewed using a maximum intensity projection (MIP) image format. Here, work on combining MIP image with the compressed sensing algorithm is presented, and investigate the usefulness of this approach.

14:30         4588.     Compressed Sensing in Dynamic Enhanced Lung Imaging: A Comparison with K-T BLAST

Jia-Shuo Hsu1, Su-Chin Chiu1, Tzu-Cheng Chao2, Yi-Ru Lin3, Hsiao-Wen Chung1

1National Taiwan University, Taipei, Taiwan; 2Brigham and Women's Hospital, Harvard Medical School,; 3Naitonal Taiwan University of Science and Technology

Dynamic contrast-enhanced lung imaging, with high resemblance with dynamic cardiac imaging for having high intensity variation constrained in relatively limited image space together with corresponding sparsity in the corresponding x-f space, may serve as a potential candidate for the CS techniques. This work shows while k-t BLAST was shown to be a well-performing alternative for dynamic CE lung imaging [4], CS may also be an encouraging candidate as it slightly outperforms k-t BLAST while remaining relatively stable in different phases

15:00         4589.     Incorporating Self-Referenced Information Into Compressed Sensing in Dynamic Imaging

Tzu-Cheng Chao1,2, Bruno Madore2, Ming-Long Wu3, Jing Yuan2, Hsiao-Wen Chung1

1Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; 2Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; 3Brain Imaging and Analysis Center, Duke University, Durham, NC, USA

Compressed Sensing is a newly developed fast imaging method aimed at robustly recovering the signal from undersampled datasets. In this work, we propose a modified sampling scheme to facilitate the reconstruction algorithm, based on an Orthogonal Matching Pursuit, for dynamic imaging purposes. Cardiac cine and fMRI data were used to test the approach and evaluate performance. The proposed modifications enabled significant reductions in computation time (about a 1.4 to 2 fold reduction).

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 96

13:30         4590.     Compressed Sensing for Active Feedback Contrast-Enhanced in Vivo Tumor Imaging

Luan Vu1, Jon Furuyama1, Thomas Goldstein2, Stanley Osher2, Yung-Ya Lin1

1Chemistry and Biochemistry, UCLA, Los Angeles, CA, USA; 2Applied Mathematics, UCLA, Los Angeles, CA, USA

The ability to successfully reconstruct images without having to collect the entire k-space is valuable for parameter optimization and can lead to a higher success rate for the detection of early tumors. Other k-space trajectories can be used to further improve the performance of the algorithm, such as concentrating the kept data points towards the center of k-space, while deleting more points around the edges (results not shown). As a result, strategic k-space sampling (beyond purely random) can be employed to further accelerate data acquisition.

14:00         4591.     Blade by Blade Compressed Sensing for PROPELLER

Eric Aboussouan1, Jim Pipe1

1Barrow Neurological Institute, Phoenix, AZ, USA

This work proposes to use compressed sensing to fill missing lines of individual PROPELLER blades which are then gridded together. By making use of the inherent data redundancy of PROPELLER, such a scheme is thought to greatly reduce the risk of losing image features, which can be a concern with iterative reconstruction methods. This method could be used in applications where parallel imaging is not suitable (e.g. for PROPELLER spine imaging).

14:30         4592.     Self-Adjusted Regularization Ratio for Robust Compressed Sensing

Feng Huang1, Yunmei Chen2

1Advanced Concept Development, Invivo Corporation, Gainesville, FL, USA; 2Department of Mathematics, University of Florida, Gainesville, FL, USA

A self-adjustment technique is proposed in this work to automatically optimize the ratio between regularization term and data fidelity term in regularized reconstruction framework. Using compressed sensing (CS) as an example, experiments with both phantom and in vivo data sets demonstrated that the proposed method made the regularized reconstruction framework less sensitive to the choice of regularization parameter. This work dramatically reduces the difficulty of parameter decision and increases the practicability of regularized reconstruction techniques.

15:00         4593.     Compressed Sensing for Motion Artifact Reduction

Joelle Karine Barral1, Dwight George Nishimura1

1Electrical Engineering, Stanford University, Stanford, CA, USA

Navigators can effectively track rigid-body motion of limited amplitude. However, data associated with significant motion need to be discarded, which often results in unacceptable artifacts. We propose to use a pseudo-random trajectory and compressed sensing theory to reconstruct datasets where data corrupted by motion and detected by navigators have been rejected. When data are acquired with a pseudo-random trajectory, motion occurring over several TRs results in a randomly undersampled dataset that can be accurately reconstructed. Simulation and experimental results are presented.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 96

13:30         4594.     Reconstruction of Magnetic Resonance Inverse Imaging Using the Minimum L-1 Norm Constraint

Fa-Hsuan Lin1,2, Thomas Witzel1, Jonanthan Polimeni1, John W. Belliveau1

1A. A. Martinos Center, Massachusetts General Hospital, Charlestown, MA, USA; 2Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan

Magnetic resonance inverse imaging (InI) can obtain an unprecedented temporal resolution by using a minimal gradient encoding and solving inverse problems from multiple channels of the coil array measurements. To reconstruct InI data, additional constraint must be supplied to obtain a unique solution. Here we used the minimum L-1 norm constraint to reconstruction InI fMRI data. Compared to the minimum L-2 norm results, the minimum L-1 norm reconstructions are more spatially focal and have higher sensitivity in detecting the activity of human visual system.

14:00         4595.     An Improved Approach in Applying Compressed Sensing in Parallel MR Imaging

Bing Wu1, Richard Watts2, Rick Millane1, Philip Bones1

1Depeartment of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand; 2Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand

A new approach that improves the effectiveness of compressed sensing (CS) in parallel MR imaging (pMRI) is proposed. Instead of directly combining the CS recovery process with parallel imaging operators as has been previously reported, a two step reconstruction is used. A conventional SENSE-like reconstruction which gives a high fidelity reconstruction with high noise level is first made, then a CS reconstruction based on the prior knowledge of the SENSE reconstruction is performed to reduce the noise level, hence achieving a high fidelity reconstruction with low noise level. It is demonstrated using in-vivo data set that this new approach outperforms SENSE reconstruction or CS reconstruction alone.

14:30         4596.     A Novel Fast Dynamic Cardiac Data Reconstruction Method Using Prior Knowledge and Adaptive Matching Pursuits

Muhammad Usman1, Philip G. Batchelor1

1Division of Imaging Sciences, Kings College London, London, UK

Recently, variants of matching pursuit methods such as Regularized Orthogonal Matching Pursuit (ROMP), Compressive Sampling Matching Pursuit (CoSAMP)and Sparsity Adaptive Matching Pursuit (SAMP) have been proposed and shown to give exact reconstruction for sufficiently sparse signals. Compared to the conventional OMP, these variants offer faster reconstructions. The SAMP has an additional advantage that it does not require any prior knowledge about the signal sparsity which is the case when recovering the practical compressible signals. Based on SAMP algorithm and the prior knowledge obtained from the sliding window reconstruction from the under-sampled data, we propose a scheme that can provide faster dynamic cardiac MR reconstructions compared to exisiting iterative schemes such as OMP.

15:00         4597.     HTGRAPPA: TGRAPPA Based B1-Weighted Image Domain Reconstruction for Real-Time MRI

Haris Saybasili1,2, Peter Kellman1, Mark A. Griswold3, J. Andrew Derbyshire1, Michael A. Guttman1

1NIH/NHLBI, Bethesda, MD, USA; 2Biomedical Engineering Institute, Bogazici University, Istanbul, Turkey; 3Case Western Reserve University, USA

We present a new parallel imaging algorithm based on TGRAPPA for real-time MRI, called HTGRAPPA and its real-time, low-latency implementation suitable for interventional MR applications. Our method calculates GRAPPA coefficients in the k-space, and transfers them in the image domain. These image domain GRAPPA weights were combined into composite unmixing coefficients using adaptive B1-weight estimates and optimal noise weighting. That way, convolution operations in the k-space are avoided during the reconstruction, thus blazingly fast reconstruction speeds are achieved. More than 70 frames per second reconstruction performance is achieved on 30 coil, rate 4 dataset (up to 265x faster than TGRAPPA).

 


 
Artifacts I
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 97

14:00         4598.     A Real-Time Motion Compensation Package and Active Marker Headband for Brain MRI

Melvyn Boon King Ooi1, Sascha Krueger2, William J. Thomas3, Srirama V. Swaminathan4, Truman R. Brown1,3

1Biomedical Engineering, Columbia University, New York, USA; 2Philips Research Europe, Hamburg, Germany; 3Radiology, Columbia University, New York, USA; 4Philips Medical Systems, Cleveland, OH, USA

A prospective, intra-image compensation strategy for rigid-body motion is presented. A short tracking-sequence, interleaved into the imaging-sequence, measures the positions of three active-markers integrated into a headband worn by the subject. During head motion, the rigid-body transformation that realigns these markers is fed back to update the image-plane – maintaining it at a fixed orientation relative to the head – before the next segment of k-space is acquired. The complete package requires minimal additional hardware and can be flexibly incorporated into multiple imaging-sequences, promoting transferability to clinical practice. Improvements in image quality are evaluated in 3D-MPRAGE brain MRI during volunteer motion.

14:30         4599.     In-Vivo Applications of Optical Real-Time Motion Correction Using a Monovision System

Murat Aksoy1, Matus Straka1, Stefan Skare1, Rexford Newbould2, Samantha Holdsworth1, Juan Santos3, Roland Bammer1

1Department of Radiology, Stanford University, Stanford, CA, USA; 2GlaxoSmithKline, London, UK; 3Department of Electrical Engineering, Stanford University, Stanford, CA, USA

Real time motion correction using an external optical tracking system has been suggested as a way to perform rigid head motion correction for MRI. In this study, we demonstrated the motion correction efficacy of our real-time monovision system that uses a single camera mounted inside the magnet bore on the head coil. Experiments were carried out using a gradient echo and a spin echo sequence with the subject performing varying degrees of in-plane and through plane motion. The results show that the current system is effective in removing both in plane and through plane motion.

15:00         4600.     Image Instability Evaluation and Motion Correction for High-Resolution MRI of the Rat Retina

Xiaodong Zhang1, yingxia Li1, Timothy Q. Duong2

1Yerkes National Primate Research Center, Emory University, Atlanta, GA, USA; 2Research Imaging Center, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
This study systemically examined these potential animal and hardware issues, and implemented solutions to maximize stability for high-resolution structural, physiological and functional MRI of the rat retina. Studies were performed on phantoms and the in vivo retinas to distinguish between potential animal and hardware issues. Solutions to maximize retinal MRI stability and protocols to evaluate and verify temporal stability are detailed.

15:30         4601.     Rotation Correction with Self-Navigated MRI

Jason Mendes1, Dennis L. Parker1

1UCAIR, University of Utah, Salt Lake City, UT, USA

This work provides a demonstration that in-plane rotational motion that occurs during the acquisition of MRI data can be quantified using a self-navigation technique. The proposed technique compares adjacent sets of measurement lines in k-space to detect and quantify object rotation. This method can be applied to any segmented sequence that samples k-space in sets of equally spaced lines. It does not require any patient preparation or the acquisition of separate navigator data. The method only requires a slight increase in the field of view along the phase encoding direction, but the increase required is small enough that resolution or total scan time are not significantly affected.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 97

13:30         4602.     A Kalman Filtering Framework for Prospective Motion Correction

Julian Maclaren1, Oliver Speck2, Jürgen Hennig1, Maxim Zaitsev1

1Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany; 2Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany

Tracking head position and prospectively adjusting the imaging volume is becoming an increasingly popular means of preventing motion artefacts in MRI. However, the technique imposes stringent requirements on the accuracy of the tracking system used. For high-resolution imaging, these requirements are difficult to achieve in practice. We present a Kalman-filtering based approach that improves pose estimation and prediction and enables estimation of residual errors. This makes retrospective correction of residual motion artefacts possible. The result is a reduction in the required accuracy of the tracking system itself.

14:00         4603.     Reducing Artifacts in Dynamic MRI Movies Using a Spline Interpolated Sliding Window Technique

Eric Frederick1,2, Iga Muradyan1, Mirko Hrovat3, Hiroto Hatabu1, Samuel Patz1

1Radiology, Brigham and Women's Hospital, Boston, MA, USA; 2Physics, University of Massachusetts at Lowell, Lowell, MA, USA; 3Mirtech, Brockton, MA, USA

A spline interpolated sliding window technique is proposed to reduce intensity pulsation artifacts in rectilinearly sampled dynamic MRI movies. The technique is tested on both simulated MRI data and experimentally with a dynamic phantom.

14:30         4604.     Pitfalls of Complex Summation and Its Variant Method in Synthesizing the Phase-Cycled SSFP Images to Suppress the Band Artifact

Kwan-Jin Jung1,2

1BIRC, University of Pittsburgh, Pittsburgh, PA, USA; 2Bioengineering Dept, University of Pittsburgh, Pittsburgh, PA, USA

The SSFP image suffers from the band artifact. The complex summation (CS) method has been reported to be better than the maximum intensity projection (MIP) in suppressing the band artifact. However, it was noted recently that CS has an inherent deficiency in suppressing the band artifact due to phase incoherence across the phase-cycled images. It was described that a magnitude-weighted CS method (MWCS) was more reliable than CS and SoS (square-of-sum) in suppressing the band artifact. In this abstract, the pitfalls of CS and its variant MWCS are studied further with an experimental demonstration and simulation. It is found that the band suppression of synthesis methods depends on the flip angle and relaxation times. The CS and MWCS were demonstrated to perform worse than MIP in the phantom experiment. Besides, CS had an abnormal image intensity due to the chemical shift.

15:00         4605.     Azimuthal Sorting in Tandem with Elliptical Reordering (ASTER): A New K-Space Reordering Scheme for Reduced Motion Sensitivity

Manojkumar Saranathan1, Ersin Bayram2, Ananth Madhuranthakam3

1Applied Science Laboratory, GE Healthcare, Rochester, MN, USA; 2MR Engineering, GE Healthcare, Waukesha, WI, USA; 3Applied Science Laboratory, GE Healthcare, Boston, MA, USA

MRI is very sensitive to motion, particularly in 3D acquisitions where temporally localized motion can propagate across the whole reconstructed volume. In cardiac and abdominal imaging applications, subjects are required to suspend their respiration for a period of 15-25s to minimize ghosting and blurring artifacts. Breath-holding poses difficulties in pediatric and elderly subjects. We propose ASTER (Azimuthal Sorting in Tandem with Elliptical Reordering), a novel k-space reordering scheme that minimizes sensitivity to motion whilst permitting flexible combination with magnetization preparation schemes. We demonstrate the validity of our scheme using PSF simulations and volunteer data from abdominal imaging.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 97

13:30         4606.     In-Vivo Flow-Artifact Suppression Using Parallel Spatially Selective Excitation

Johannes Thomas Schneider1,2, Martin Haas2, Jürgen Hennig2, Sven Junge1, Wolfgang Ruhm1, Peter Ullmann1

1Bruker BioSpin MRI GmbH, Ettlingen, Germany; 2Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany

Parallel spatially-selective excitation / TransmitSENSE allows specific excitation of defined regions. In the present study this technique was successfully applied to the removal of motion artifacts in rat imaging: Signal from vessels in the rat head which showed up as ghost artifacts superimposed on the rat’s brain could be efficiently suppressed by selective excitation of the rat brain only. These in-vivo results underline the potential of TransmitSENSE for the prevention of artifacts originating from flow or motion.

14:00         4607.     Prospective Motion Correction with Stereoscopic Optical Tracking at 7T

Daniel Stucht1,2, Peter Schulze1, Maxim Zaitsev3, K. A. Danishad1, Ilja Y. Kadashevich1, Oliver Speck1

1Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany; 2IBMI, Otto-von-Guericke University, Magdeburg, Germany; 3Dept. of Radiology, Medical Physics, Universital Hospital Freiburg, Freiburg, Germany

In this study an implementation of prospective motion correction on a 7T MR scanner is presented. The potentially higher resolution in 7T requires longer acquisition times without patient motion. The reduction of motion artefacts is shown for motion between different scans and motion during the aquisition of image data in different resolutions up to 1024x1024. The results of in vivo and phantom measurements are shown. The achievable artifact-free image resolution is limited by the accuracy of the tracking data.

14:30         4608.     The Effect of Magnetization Transfer on Rapid T2 Estimation with Phase-Cycled Variable Nutation SSFP

Hendrikus Joseph Alphons Crooijmans1, Klaus Scheffler1, Oliver Bieri1

1Radiological Physics, University of Basel Hospital, Basel, BS, Switzerland

The transversal relaxation time (T2) found by means of two phase-cycled variable nutation steady-state free precession measurements analysis (DESPOT2) is subject to magnetization transfer (MT) effects when imaging tissues. To explore this possible effect, human brain is measured with a balanced SSFP sequence using several RF pulse durations and compared the results with a multi-contrast spin echo reference T2 measurement. It is found that MT can have a severe influence on the found T2 value.

15:00         4609.     Correction of Off-Resonance Effects in Multi-Component Driven Equilibrium Single Pulse Observation of T1 and T2 (McDESPOT)

Sean CL Deoni1

1Centre for Neuroimaging Sciences, London, UK

mcDESPOT is a promising new approach to whole-brain multi-component relaxometry. However, as the method utilizes data acquired using the rapid steady-state free-precession imaging sequence, it is sensitive to off-resonance effects leading to substantive errors in the derived myelin water fraction and relaxation time estimates. Here we suggest a simple approach allowing the near complete removal of these artifacts and demonstrate the efficiency of the technique in vivo.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 97

13:30         4610.     A New Synthesis Method of Phase-Cycled SSFP Images to Remove the Band Artifact by Combining Complex Summation and Maximum Intensity Projection Techniques

Kwan-Jin Jung1,2

1BIRC, University of Pittsburgh, Pittsburgh, PA, USA; 2Bioengineering Dept, University of Pittsburgh, Pittsburgh, PA, USA

The complex summation technique (CS) is known to be effective in reducing the band artifact as a synthesis method of multiple phase-cycled images. However, it was noted that CS is not reliable due to phase incoherence in the multiple phase-cycled images. On the other hand, the maximum intensity projection (MIP) and spectral decomposition synthesis (SDS) techniques do not have the phase-related problem even though they might be less effective in reducing the band artifact. Here, the advantages of CS and MIP are combined as a more effective synthesis method to take advantage of both techniques in reducing the band artifact without the detrimental effect of the phase incoherence. This new technique was confirmed by a phantom experiment at 3T to perform much better than other existing methods in reducing both the band artifact and image noise.

14:00         4611.     19F/1H Simultaneous 3D Radial Imaging of Atherosclerotic Rabbits Using Self-Navigated Respiratory Motion Compensation

Jürgen Rahmer1, Jochen Keupp1, Shelton D. Caruthers2,3, Oliver Lips1, Todd A. Williams3, Samuel A. Wickline3, Gregory M. Lanza3

1Philips Research Europe, Hamburg, Germany; 2Philips Healthcare, Andover, MA, USA; 3Washington University, St. Louis, MO, USA

MR molecular imaging of low doses of tracer material often requires long scan times and makes motion compensation strategies desirable. 3D radial imaging with golden section profile interleaving allows auto-navigated motion compensation. Here, it is applied to simultaneous 19F/1H imaging of the aorta of atherosclerotic rabbits after systemic administration of 19F-based angiogenesis-targeted nanoparticles. Tracking of respiratory motion is

14:30         4612.     High Frame Rate Cardio-Respiratory Imaging Using Model-Based Reconstruction

Pierre-André Vuissoz1,2, Freddy Odille1,3, Brice Fernandez1,4, Maelene Lohezic1,4, Adnane Benhadid1,2, Damien Mandry1,5, Jacques Felblinger2,6

1IADI, Nancy-Université, Nancy, France; 2U947, INSERM, Nancy, France; 3Centre for Medical Image Computing, University College London, London, UK; 4Global Applied Science Lab., GE healthcare, Nancy, France; 5CHU de Nancy, Nancy, France; 6CIC-IT 801, INSERM, Nancy, France

The recently described Generalised Reconstruction by Inversion of Coupled Systems (GRICS) algorithm enables to build a model of image deformation correlated to physiological sensors such as ECG or respiratory belt. Since these physiological signals are recorded at high sampling rate, this enables to reconstitute a real time high resolution (256x256) movie of thoracic motion with quality comparable to breath-hold acquisitions. 18 reconstitutions of thoracic motion of 16s long at 25fps. have been computed. Both breathing and cardiac beating of the healthy subject can be observed in different orientations, in particular cardiac short axis and both vertical and horizontal long axes.

15:00         4613.     On the Feasibility of Accelerating Self-Gated Cine Cardiac Imaging in Rodents Using SENSE

Christof Baltes*1, David Ratering*1, Markus Rudin1,2

1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 2Institute of Pharmacology and Toxicology, University Zurich, Zurich, Switzerland

Self-gated MR imaging has been demonstrated to be a useful tool for cardiac MRI in small rodents. However, the method suffers from long acquisition times. For this reason, the feasibility of accelerating self-gated cardiac imaging in rodents using SENSE was investigated in this work. Fully sampled cine cardiac images of the rat were acquired using the IntraGate technique. Computer simulations exploring the effect of residual respiratory motion artifacts on the SENSE reconstruction revealed that higher demands on the respiratory compensation are required for the accelerated compared to the fully sampled acquisition.

 


 
Artifacts II
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 98

14:00         4614.     Removal of Residual Motion Artifacts in FMRI Using Constrained Independent Component Analysis

Kiran Kumar Pandey1, Douglas C. Noll1

1Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA

Image-registration in fMRI only corrects for bulk movements, leaving secondary artifacts - spin history, motion induced field inhomogeneity changes, interpolation errors - untouched. Secondary artifacts increase variance and reduce sensitivity of fMRI. Methods using motion parameters as “Nuisance Explanatory Variables” or ICA are used to isolate/remove residual motion artifacts. Use of ICA requires isolation and then identification of motion components before removal. We used constrained ICA to isolate/identify these components in one step using motion parameters as references. Use of cICA efficiently and effectively removed residual motion artifacts without “manual” identification step and, increased the sensitivity of BOLD fMRI studies.

14:30         4615.     Wii – Highly Sensitive Tracking of Patient Motion

Olga Tymofiyeva1, Michael Ledwig1, Kurt Rottner2, Ernst-Juergen Richter2, Peter Michael Jakob1

1Dept. of Experimental Physics 5, University of Würzburg, Würzburg, Bavaria, Germany; 2Dept. of Prosthodontics, Dental School, University of Würzburg, Würzburg, Bavaria, Germany

Numerous medical MRI applications suffer from patient motion and require motion control. A simple and low-cost motion tracking system is proposed which is based on the infrared light detection camera built-in in a Wii Remote (Nintendo), connected via Bluetooth to a computer for analysis. The proposed system allows for detecting patient motion with sensitivity below 40µm and can become a solution for a wide range of MRI applications, in which real-time patient motion control is required.

15:00         4616.     Prospective Head Movement Correction for High-Resolution MRI Using a Single Camera

Lei Qin1,2, Fenghua Jin2, Yang Tao2, Jeff H. Duyn1

1NINDS, National Institutes of Health, Bethesda, MD, USA; 2Univ of Maryland, College Park, MD, USA

We propose a novel prospective motion correction method for MRI based on positional tracking with a single video camera. A short training scan, using whole-brain EPI during intentional head motion, serves to relate camera images of the human face to head position. With this information, motion during a real-time MRI scan is estimated by correlating each newly captured camera image with the one from the training data. The corresponding motion parameters are fed back to the MRI scan computer to adjust scan parameters. Results show the system is able to correct motion for high-resolution anatomical MRI.

15:30         4617.     On the Application of Phase Correction and Use of K-Space Entropy in Partial Fourier Diffusion-Weighted EPI

Samantha J. Holdsworth1, Stefan Skare1, Roland Bammer1

1Lucas MRS/I Center, Stanford University, Stanford, CA, USA

It is well-known that diffusion-weighted (DW) imaging is very sensitive to the effects of brain motion, even in single-shot (ss)-EPI. Pulsatile brain motion that occurs during the application of the DW gradients can result in the non-linear dispersion of k-space, corresponding to signal dropout and shading in the image domain. Here we explore the use of k-space entropy as a metric to identify k-space corrupted by non-linear brain motion; the use of peripheral cardiac gating and non-gating; phase correction applied before both homodyne and POCS reconstruction; as well as the number of overscans that should be used to avoid significant artifacts due to pulsatile brain motion.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 98

13:30         4618.     Comparison of Physiological Trigger Modes for DWI in the Abdomen

Tobias Binser1, Harriet C. Thoeny2, Chris Boesch1, Peter Vermathen1

1Dept. of Clinical Research, University of Bern, Bern, Switzerland; 2Dept. of Radiology, Inselspital Bern, Bern, Switzerland

A major problem in abdominal diffusion-weighted imaging (DWI) is related to physiological motion artifacts caused by respiration and cardiac pulsation. In the present study we compared different physiological triggering methods, namely respiratory versus combined respiratory-cardiac gating techniques in DWI of the kidney. The main objective was to evaluate if respiratory-cardiac double triggering is advantageous for the determination of diffusion parameters, especially for the stability of microperfusion components in addition to apparent diffusion coefficients (ADC). The results from repeated measurements show a significant improvement of data stability for respiratory-cardiac double triggering over respiratory triggering alone.

14:00         4619.     Comparison of Quantitative Artifact Level in TGRAPPA and TSENSE Reconstruction During Deep Breathing

Mihaela Jekic1, Yu Ding2, Yiu-Cho Chung3, Subha V. Raman4, Jennifer Dickerson4, Sven Zuehlsdorff3, Sonia Nielles-Vallespin3, Orlando P. Simonetti

1Biomedical Engineering, The Ohio State University, Columbus, OH, USA; 2Davis Heart and Lung Research Institute, The Ohio State University; 3Siemens Healthcare; 4The Ohio State University Medical Center

We quantitatively compared the artifact performance of TGRAPPA and TSENSE real-time cine imaging under the condition of deep breathing, which can cause the chest wall to move in and out of the FOV and also can create a mismatch between the coil sensitivity map and the actual coil position. We applied an autocorrelation-based approach to quantify the artifacts in 30 myocardial slices, exploiting their spatially fixed nature at 1/3 and 2/3 FOV for rate 3 acceleration. We found that TGRAPPA performed better than TSENSE in terms of quantitative artifact level, which was in agreement with qualitative physician-assigned artifact scores.

14:30         4620.     Respiratory Navigation Scheme for Free-Breathing 3D SPGR Liver Imaging: Technical Feasibility

Anja C.S. Brau1, Yuji Iwadate2, Ersin Bayram3, Phillip M. Young4, Shreyas Vasanawala4, Robert J. Herfkens4

1Applied Science Lab, GE Heathcare, Menlo Park, CA, USA; 2Applied Science Lab, GE Healthcare, Hino, Japan; 3GE Healthcare, Waukesha, WI, USA; 4Department of Radiology, Stanford University Medical Center, Palo Alto, CA, USA

Breath-held 3D dynamic contrast-enhanced gradient echo imaging is an important component of abdominal MR exams. However, for patients who cannot breath-hold, motion artifacts can compromise diagnostic utility. Thus a respiratory-navigated acquisition is desirable; however, a navigated acquisition should remain sufficiently fast to capture contrast dynamics and minimize the impact on image contrast. In this work, we present the preliminary technical feasibility of a respiratory navigation scheme applied to a conventional fat-suppressed 3D SPGR sequence as well as to a 3D chemical species-based water-fat separation sequence.

15:00         4621.     Simple Method for Free-Breathing Multi-Slice T2w-TSE Liver Imaging Without PACE

Sang-Young Zho1, Jaeseok Park2, Dong-Hyun Kim1,2

1Electrical and Electronic Engineering, Yonsei University, Shinchon-Dong, Seoul, Korea; 2Radiology, Yonsei University, Shinchon-Dong, Seoul, Korea

PACE technique enables liver imaging with T2w-TSE sequence for patients who have difficulty holding their breath. One of limitation of PACE is relatively long scan time. If we do imaging liver without it, scan time will be reduced. For this, one projection line is added to conventional 2DFT TSE sequence and shows reduced respiratory motion artifact.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 98

13:30         4622.     3-D Prospective Motion Correction for MR Spectroscopy

Brian Keating1, J C. Roddey2, Weiran Deng1, Anders Dale2, Nathan White3, V Andrew Stenger1, Thomas Ernst1

1Dept. of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA; 2Dept. of Neurosciences, University of California at San Diego, La Jolla, CA, USA; 3Cognitive Science, University of California at San Diego, La Jolla, CA, USA

Patient motion during MR spectroscopy (MRS) acquisitions compromises the spectral quality. Therefore, we adapted a 3D image-based prospective motion correction module for use with a 1H PRESS sequence. A spiral navigator is acquired immediately prior to the MRS water suppression module, to obtain three orthogonal images from which head motion is estimated. By applying the appropriate rotations and translations, the voxel can be made to remain stationary with respect to the brain. Spectra acquired during head motion demonstrate improved spectral quality, including a reduction in lipid contamination, lower line width, and spectral reproducibility, when motion correction is applied.

14:00         4623.     Real-Time Prospective Rigid-Body Motion Correction with the EndoScout Gradient-Based Tracking System

Andre Jan Willem van der Kouwe1,2, Barry Fetics3, Dmitry Polenur3, Abraham Roth3, Erez Nevo3

1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; 2Department of Radiology, Harvard Medical School, Brookline, MA, USA; 3Robin Medical Inc., Baltimore, MD, USA

Motion during MR acquisitions causes considerable wasted scan time and confounds clinical diagnosis. We present an integrated solution for tracking and correcting rigid body head motion in real-time using the EndoScout gradient-based tracking system and the Siemens 3T TIM Trio MR scanner. The EndoScout probe consists of six small coils, and its location and orientation in the switching fields can be determined by the voltages induced in the coils. By rigidly affixing the probe to an object, the location of the object can be tracked in real-time. We demonstrate that the system provides real-time prospective motion correction during MR imaging.

14:30         4624.     Real-Time Optical Motion Correction for Diffusion Tensor Imaging

Murat Aksoy1, Matus Straka1, Stefan Skare1, Rexford Newbould2, Samantha Holdsworth1, Juan Santos3, Roland Bammer1

1Department of Radiology, Stanford University, Stanford, CA, USA; 2GlaxoSmithKline, London, UK; 3Department of Electrical Engineering, Stanford University, Stanford, CA, USA

Due to its prolonged acquisition time and inherent motion sensitivity, motion correction for DTI is a must for clinically acceptable image quality. In this study, we used a real-time optical motion correction system that relies on monovison to correct for rigid head motion artifacts in DTI. The proposed system employs a single camera mounted on the head coil and a planar marker with a checkerboard pattern on it. Relative changes in marker pose are used to update the gradient and RF waveforms in real-time. Results show that the proposed system is effective in correcting for pixel misregistration and signal dropouts caused by patient motion in DTI.

15:00         4625.     Variable Sampling Density Spherical Navigator Echoes (VSD SNAV) for Prospective 3D Alignment

Junmin Liu1,2, Maria Drangova1,2

1Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada; 2Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada

An improved spherical navigator-based technique for prospective inter-scan realignment is presented. Instead of acquiring a set of orbital trajectories to cover the entire surface of a k-space sphere to determine rotation, combined with a linear navigator to determine translation, a two-shot variable density helical spiral spherical navigator (VSD SNAV) was adapted. Using the VSD-SNAV resulted in reduction of the navigator acquisition time from 19 s to 50 ms, while maintaining accuracy for translations up to 20 mm and rotations as large as 20 degrees. In vitro and in vivo results are presented.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 98

13:30         4626.     Self-Navigator for Free-Breathing 3D SSFP Cardiac Imaging: Center of Mass Along the Slice Direction Versus the Image Signal Sum Using the Center of K-Space.

Pascal Spincemaille1, Jing Liu1, Thanh Dang Nguyen1, Martin Prince1, Yi Wang1

1Radiology, Weill Medical College of Cornell University, New York, NY, USA

The k-space center signal has been used for self-navigating of respiratory motion that is very useful for SSFP imaging. However, this signal is slice location and geometry dependent and is affected by blood flow and heart motion, which may lead to ineffective motion sensitization. In this study, the kz axis is repeatedly sampled and Fourier transformed to generate a projection of the image volume onto the slice axis. The center-of-mass of this projection is proposed as a respiratory gating signal and is shown to provide superior respiratory motion artifact suppression when compared to the use of the center-of-k-space signal only.

14:00         4627.     Practicality Makes a Comeback: Dynamic MRI Without the Overhead

Uygar Sümbül1, John Mark Pauly1

1Electrical Engineering, Stanford University, Stanford, CA, USA

A causal, continuously auto-calibrating acceleration algorithm is presented for dynamic MRI. The algorithm does not need any extra data acquisition to calibrate itself and works with arbitrary readout trajectories. The reconstruction is fast and it adapts almost instantaneously to changing imaging parameters. Therefore the algorithm is suitable for applications such as catheter tracking and image guided therapy. In-vivo cardiac MRI results demonstrate that the algorithm decreases the temporal blur when compared to the sliding window reconstruction.

14:30         4628.     Computational Model of the Left Ventricle Motion Using Tagged Magnetic Resonance Imaging (TMRI)

Mohammed Dahawy Alenezy1, Tareq M. Alrefae2, Jack Shi1, Mehmet Bigen3

1Physics and Astronomy, University of Kansas, Lawrence, KS, USA; 2Kuwait University, Khaldiya, Kuwait, Kuwait; 3Radiology, Medical School of South Carolina, USA

A computational model is proposed to study the motion of left ventricle (LV) using tMRI data. The LV wall motion is decomposed into the deformation component ,along the short axis and the rotation component, along the long axis of LV. rotational motion is represented by 2-D non-linear rotational transformation and the deformation is described by a 1/r function. The tMRI data of Eight different subjects were studied . It was found that there is a significant difference in the deformation parameter between the diabetic and the healthy rats and human. There is no significant difference in the average twist between human and rat heart.The torsion of rat heart is, however, found to be substantially larger than that of human.

15:00         4629.     Free Breathing Black-Blood Systolic Imaging Using Heart Rate Prediction and Motion Compensated Reconstruction

Maelene Lohezic1,2, Brice Fernandez1,2, Julien Oster2,3, Damien Mandry2,4, Olivier Pietquin3,5, Pierre-Andre Vuissoz2,3, Jacques Felblinger2,3

1Global Applied Science Lab., GE Healthcare, Nancy, France; 2IADI, Nancy-Université, Nancy, France; 3U947, INSERM, Nancy, France; 4CHU de Nancy, Nancy, France; 5IMS Research Group, SUPELEC-Metz Campus, Metz, France

High resolution black-blood systolic imaging is difficult to obtain due to long acquisition time incompatible with breath hold and to preparation time needed. A new method allowing free breathing black-blood systolic imaging is presented and validated on five healthy volunteers. It combines RR interval prediction, respiratory motion estimation and motion compensated reconstruction. The proposed method showed improvements when compared to the average of 3 free breathing acquisitions and to breath-hold images. Results have been obtained on 256x256 acquisitions. They can be extended to higher resolutions, allowing accurate examination of heart structures, even right ventricle wall or papillary muscles.

 


 
Artifacts III
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 99

14:00         4630.     3-D Multi-Coil Motion Correction for Spiral Projection Imaging

Kenneth O. Johnson1, Eric Aboussouan1, James G. Pipe1

1Keller Center for Imaging Innovation, Barrow Neurological Institute, Phoenix, AZ, USA

Motion correction has been successfully demonstrated for single coil data using Spiral Projection Imaging. Extending motion correction to multi-coil data poses additional challenges. This work investigates an approximation method applied to multi-coil data, that proves successful on synthesized data.

14:30         4631.     Quantitative Evaluation and Optimization of 3D PROspective MOtion (PROMO) Through Offline Simulation

Jian Zhang1,2, Daniel Rettmann3, Eric Han4, Cooper Roddey5, Nate White5, Joshua Kuperman5, Juan Santos1, Anders Dale5,6, Ajit Shankaranarayanan4

1Department of Electrical Engineering, Stanford University, Stanford, CA, USA; 2Department of Radiology, Stanford University, Stanford, CA, USA; 3Global Applied Science Lab, GE Healthcare, Rochester, MN, USA; 4Global Applied Science Lab, GE Healthcare, Menlo Park, CA, USA; 5Department of Neuroscience, University of California, San Diego, La Jolla, CA, USA; 6Department of Radiology, University of California, San Diego, La Jolla, CA, USA

In this work, quantitative off-line evaluations have been performed to study the accuracy and stability of PROMO. With the aid of our off-line PROMO simulation package, various impacting factors, including navigator prescription parameters, navigator reconstruction filters, image noises, and motion patterns, have been studied. An optimal PROMO parameter configuration has been proposed. And both simulation and in vivo results show that this optimization improves the algorithm performance significantly. Furthermore, since our offline system contains independent coordinate translation and gradient adjustment simulation module, it can be easily applied to evaluate other motion correction algorithms as well.

15:00         4632.     Geometric Distortion Correction in Echo Volumar Imaging

Wenlong Qian1, Paul M. Glover1, Richard W. Bowtell1

1SPMMRC, University of Nottingham, Nottingham, UK

Echo volumar imaging (EVI) is highly sensitive distortion due to magnetic field inhomogeneities because of its long echo train length. This sensitivity can be reduced by using parallel imaging to shorten the echo train length, but significant distortion can still remain in images acquired in vivo. Here we have therefore extended two distortion correction methods that have previously been used with EPI to EVI. The first is based on using a field map and the second involves point spread function (PSF) mapping. Images obtained from phantom and human brain show that correction using a PSF-based deconvolution is robust and effective.

15:30         4633.     Evaluation of EPI Geometric Distortion Correction Using Phase Labeling for Additional Coordinate Encoding (PLACE)

Sheeba Arnold1, Markus Vogler2,3, Oliver Hinds1, Susan Whitfield-Gabrieli4, Michael Hamm5, Josef Pfeuffer5, Christina Triantafyllou1,6

1Athinoula A. Martinos Imaging Center, McGovern Institute for Brain Research, MIT, Cambridge, MA, USA; 2Siemens HealthCare, Erlangen, Germany; 3University of Applied Sciences Hof, Germany; 4Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA; 5Siemens Medical Solutions USA Inc., Charlestown, MA, USA; 6Athinoula A. Martinos Center for Biomedical Imaging, Radiology, MGH, Harvard Medical School, Charlestown, MA, USA

Among the methods proposed for EPI geometric distortion correction Phase Labeling for Additional Coordinate Encoding (PLACE) has the advantage that it does not require post-processing steps because the correction happens real-time during acquisition. In this study we evaluate the PLACE method quantitatively, first with a finger-tapping task by inducing artificial distortions, and then compared it

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 99

13:30         4634.     Compensation of Respiration-Induced Off-Resonance in Real-Time Spiral k-t BLAST Imaging

Holger Eggers1

1Philips Research Europe, Hamburg, Germany

Free breathing leads not only to direct motion artifacts in abdominal real-time imaging, but also to respiration-induced field inhomogeneity artifacts. Their compensation would normally require a dynamic field mapping and a complex off-resonance correction. In this work, a simple, approximate approach is proposed for this purpose instead and is demonstrated in real-time spiral k-t BLAST imaging. It essentially involves a derivation of resonance frequency offsets from phase variations in the low frequency k-space samples of the imaging data and a subsequent, corresponding demodulation of the imaging data before their reconstruction for each receive coil element.

14:00         4635.     Free-Breathing Dynamic Magnetic Resonance Imaging of the Abdomen

Frederik J. de Bruijn1, Yan Zhang1,2, André M. Sprengers3, Aart J. Nederveen3, Jaap Stoker3, Rolf M. Lamerichs1

1Philips Research, Eindhoven, Netherlands; 2Leiden Institute of Advanced Computer Science, Leiden University, Leiden, Netherlands; 3Department of Radiology, Academic Medical Center, Amsterdam, Netherlands

Abdominal magnetic resonance imaging (MRI) is complicated by tissue motion as well as by weak tissue contrast. The major source of motion is respiration, which can be dealt with by breath-hold imaging or by respiratory triggering. Nevertheless, these commonly used methods are known to have their limitations in terms of patient burden as well as in image quality. We propose a method that allows 3-dimensional (3D) motion-compensated imaging of the bowel in the presence of continued respiratory motion and normal bowel peristalsis. The method is based on a computationally efficient spatiotemporal recursive search cube matching algorithm which allows accurate real-time volumetric motion estimation and compensation for the respiratory motion. We are currently evaluating the application to motion-compensated reconstruction of dynamic contrast-enhanced data of the colon.

14:30         4636.     Improved R2* Measurement  Accuracy with Absolute SNR Truncation and Optimal Coil Combination

Xiaoming Yin1,2, Saurabh Shah3, Peter Kellman4, Andrew C. Larson1,5

1Department of Radiology, Northwestern University, Chicago, IL, USA; 2Department of Electrical Engineering and Computer Science, Northwestern University, Evanston , IL, USA; 3Siemens Medical Solutions,, Chicago, IL, USA; 4Laboratory of Cardiac Energetics, NIH, Bethesda, MD, USA; 5Department of Electrical Engineering and Computer Science, Northwestern University, Evanston, IL, USA

R2* is typically estimated via mono-exponential fitting of signal decay within a series of GRE images combined by root sum-of-square (RSS) approach. However, RSS approaches rectify and bias noise in later TEs, resulting in systematic fitting errors. Our work investigated the accuracy of low SNR R2* measurements. By combining a truncation model with array coil combination methods, we found that SNR-based truncation can be an effective method to reduce measurement error. Given that the SNR threshold providing minimum error in the truncation process may be unknown to us, the optimal B1-weighted combined method is the optimal choice for R2* measurement.

15:00         4637.     A General Method for Correction of Intensity Inhomogeniety in Two Point Dixon Imaging

Ola Friman1, Olof Dahlqvst Leinhard2,3, Peter Lundberg2,3, Magnus Borga3,4

1MeVis Research, Bremen, Germany; 2Department of Medicine and Health, Linköping University, Linköping, Sweden; 3Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden; 4Department of Biomedical Engineering, Linköping University, Linköping, Sweden

Two point Dixon imaging can be used for quantitative fat estimation. However, field inhomogeneities pose a problem that needs to be corrected for before quantitative measurements can be obtained. We present a general framework for field inhomogeneitiy correction by fitting a set of smooth 3D spatial basis functions to voxels with high fat content. By choosing the number of basis functions, the smoothness constraint of the field can be controlled. The method is evaluated by measuring the FWHM of the fat peak in histograms for different number of basis functions. It is also compared to a previous method with good results.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 99

13:30         4638.     Scanner Calibration for Multisite Geometric Accuracy: How to Do It

Berkay Kanberoglu1, Ted Trouard2, Lina Karam1, Josef P. Debbins3

1Electrical Engineering, Arizona State University, Tempe, AZ, USA; 2Biomedical Engineering, University of Arizona, Tucson, AZ, USA; 3Keller Center for Imaging Innovation, Barrow Neurological Institute, Phoenix, AZ, USA

This study uses available processing methods to build a "pipeline" which can geometrically calibrate multiple MRI systems and then independently verify the calibration for use in longitudinal volumetric brain studies.

14:00         4639.     PET Effects on MR Data Quality in an Integrated MR-PET Human Brain Scanner

Thomas Benner1, Andre J. W. van der Kouwe1, Ciprian Catana1, Michael Hamm2, A. Gregory Sorensen1, Bruce R. Rosen1

1Radiology, Athinoula A. Martinos Center, Charlestown, MA, USA; 2Siemens Medical Solutions, Charlestown, MA, USA

New combined MR-PET systems allow simultaneous acquisition of MR and PET data. We sought to evaluate the effect of the PET insert of a BrainPET prototype on the quality of the MR data with regard to RF noise, shim, signal-to-noise ratio (SNR) and temporal SNR. Two sets of scans were performed: with the PET insert in operating mode in the scanner bore and with the PET insert switched off outside the bore. The result show that the PET insert does not appear to have any significant effect on the MR scanner data regarding RF noise, shim, SNR and temporal SNR.

14:30         4640.     Motion Induced Magnetic Susceptibility and Field Map Estimation in FMRI

Desmond Yeo1, Jeffery Fessler2, Boklye Kim3

1tbyeo@umich.edu; 2fessler@eecs.umich.edu; 3boklyek@umich.edu, Ann Arbor, MI, USA

Head rotation during fMRI time series acquisition may cause nonlinear field-inhomogeneity changes and lead to dynamic geometric distortion. The use of image registration to estimate dynamic field inhomogeneity maps from a static field map is not sufficient. This work retrospectively estimates magnetic susceptibility induced field maps of an object affected by out-of-plane rotation, given a static field map and the associated object motion parameters. It estimates a susceptibility map from a static field map using regularized image restoration techniques, and applies rigid body motion to the estimation. The dynamic field map is then computed using susceptibility voxel convolution.

15:00         4641.     Performance of Stereo Vision and Retro-Grate Reflector Motion Tracking Systems in the Space Constraints of an MR Scanner

Brian Armstrong1, Brian Andrews-Shigaki2, Robert T. Barrows1, Todd P. Kusik1, Thomas Ernst2, Oliver Speck3

1Electrical Engineering and Computer Science, UW-Milwaukee, Milwaukee, WI, USA; 2Medicine, University of Hawaii, Honolulu, HI, USA; 3Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany

Motion tracking and prospective compensation is one approach to reducing motion artifact in MR scans. Optical motion tracking is a leading candidate method to obtain the needed real-time motion data. The repeatability and accuracy of two optical motion tracking systems, stereo vision (SV) and retro-grate reflector (RGR), are investigated under the space constraints of an MR scanner. An optical bench and precision tilting rotary table provide geometric stability and highly accurate presentation of poses. Results indicate that achieving sufficiently accurate motion tracking in an MR bore remains a challenge for prospective motion compensation.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 99

13:30         4642.     Combine Reconstructions Using Non-Local Operator and Its Application in PPI

Weihong Guo1, Hu Cheng2, Feng Huang3

1Department of Mathematics, University of Alabama, Tuscaloosa, AL, USA; 2Department of Psychological and Brain Sciences, Indiana University, IN, USA; 3Advanced Concept Development, Invivo Corporation, Gainesville, FL, USA

Given a set of reconstructions with different noise/artifact distribution, it is possible to generate an image with higher signal to noise ratio (SNR) than each single reconstruction through weighted summation. An efficient weight calculation method is proposed in this work to automatically and adaptively integrate advantages of GRAPPA and SENSE reconstructions.Quantitative and qualitative results have shown advantages of the proposed model.

14:00         4643.     Retrospective Self-Navigated Cine Imaging Using the Unused Echo in Alternating TR SSFP

Hsu-Lei Lee1, Ajit Shankaranarayanan2, Krishna S. Nayak1,3

1Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA; 2Global Applied Science Lab, GE Healthcare, Menlo Park, CA, USA; 3Keck School of Medicine, University of Southern California, Los Angeles, CA, USA

In alternating TR SSFP, a low-resolution readout of the target scan plane can be acquired during the often-unused short TR. We collect data from free-breathing continuous wideband SSFP sequence and demonstrate successful retrospective self-navigation using this signal. This method can avoid temporal blurring caused by respiration in a cardiac scan without using a separate navigator sequence, removes the dependence on patients’ ability to perform breath-holds, and allows for longer scan time to acquire higher spatial and temporal resolution images.

14:30         4644.     Cardiac and Respiratory Motion Compensated Reconstruction Driven Only by 1D Navigators

Freddy Odille1, Sergio Uribe2, Tobias Schaeffter2, David Atkinson1

1Centre for Medical Image Computing, University College London, London, UK; 2Division of Imaging Sciences, King's College London, London, UK

Motion compensated reconstruction for arbitrary motion is a difficult task requiring prior knowledge about motion. One way to deal with this is to constrain the time component of motion to be correlated with certain motion sensors, such as bellows, ECG, or navigators. Here we propose an extended analysis of MR-navigators, based on 1D nonrigid registration on a per-coil basis, and principal component analysis of the resulting 1D motion fields. The method allows detection of motion eigenmodes from the imaging data themselves, which are then used to constrain a motion-compensated reconstruction for free-breathing cardiac imaging, without the need for external ECG.

15:00         4645.     Real-Time Adaptive Motion Correction for Coronary MR Angiography

Markus Henningsson1,2, Sergio A. Uribe Arancibia1, Andrea J. Wiethoff1,3, Philip G. Batchelor1, Rene M. Botnar1

1Division of Imaging Sciences, King's College London, London, UK; 2NIHR Biomedical Research Centre at Guy’s & St Thomas’ Hospital and King’s College London , London, UK; 3Philips Healthcare, Reigate, UK

Artifacts due to residual coronary motion remain an impediment to diagnostic coronary MRA in a small but substantial amount of patients. The purpose of this study was to investigate a method (AF) that determines a patient specific correction factor which continuously updates throughout the course of the scan. 7 healthy volunteers were scanned and the LCA visibility was analyzed, and the result showed that the AF performs better than a constant 0.6 factor with a navigator on the diaphragm, as well as a 1.0 factor with a navigator on the heart.

 


 
Artifacts IV
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 100

14:00         4646.     Real-Time Motion Corrected MRS Using EPI Navigators

Aaron T. Hess1, Matthew Dylan Tisdall2,3, Ernesta M. Meintjes1, Andre J. W. van der Kouwe2,3

1Human Biology, University of Cape Town, Cape Town, South Africa; 2Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; 3Department of Radiology, Harvard Medical School, Brookline, MA, USA

In this abstract we present a real-time motion navigation technique for MRS. The technique uses a low resolution echo planar imaged (EPI) volume acquisition (duration < 500ms), inserted in the relaxation time of each TR before the spectroscopy excitation. The EPI images are processed online and co-registered using PACE in order to provide real-time feedback to adjust the imaging coordinate system for rigid body translation and rotation. Our results demonstrate this technique can be incorporated into single voxel spectroscopy without increasing acquisition duration or impacting on the spectral quality.

14:30         4647.     Phase Based Navigator Echo Analysis with a Virtual Large Loop RF Coil

Yuji Iwadate1, Kenichi Kanda2, Akira Nabetani1, Tetsuji Tsukamoto1

1Japan Applied Science Laboratory, GE Yokogawa Medical Systems, Hino, Tokyo, Japan; 2MR Engineering, GE Yokogawa Medical Systems, Hino, Tokyo, Japan

Phase based navigator echo analysis is useful in navigator gated imaging but sometimes affected by an inhomogeneous sensitivity of a receiver RF coil. We propose a method that uses virtual large loop coil to obtain a homogeneous phase background. By adding two navigator data sets vectorially, sensitivity of the virtual large loop coil had a homogeneous phase, which resulted in accurate motion detection with phase based navigator echo analysis. Future work will involve the phase compensation to apply to a larger number of coil elements of phased arrays.

15:00         4648.     The Effects of Induced B0 and B1 Magnetic Field Perturbations on Efforts to Image Near Embedded Metal Hardware

Kevin M. Koch1, Kevin F. King1, Graeme C. McKinnon1

1Applied Science Laboratory, GE Healthcare, Waukesha, WI, USA

Recent developments have demonstrated an improved capability of MR imaging near metal implants. These new methods are capable of removing bulk image distortions near commonly utilized metal implants. Here, we explore the more nuanced image intensity effects due to B1 perturbations and severe B0 gradients on these recently demonstrated imaging approaches. Computational field estimates are utilized to simulate MR images near simple metal implant geometries. These simulations generally agree with empirically measured images, and therefore help explain the remaining limitations to imaging near metal implants.

15:30         4649.     Quantitative Evaluation of Metal Artifact with New Turbo Spin Echo Imaging Techniques

Chen Lin1, Brian Dale2, Larry Friggle3, Leverett Neville1, Annette Douglas-Akinwande1, Kenneth Buckwalter1

1Radiology, Indiana University School of Medicine, Indianapolis, IN, USA; 2Siemens Healthcare; 3Radiloogy, Clarian Health Partners, Indianapolis, IN, USA

The artifact from metal hardware was evaluated and quantified for 2D TSE with Cartesian and BLADE (radial) k-space samplings as well as for 3D TSE with constant and variable refocusing flip angle schedules. These results can be used to optimize imaging of patients with orthopedic hardware.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 100

13:30         4650.     Rigid Body Motion Detection with Lissajous Navigator Echoes

Marcus G. Ullisch1,2, Tony Stöcker1, Mark A. Elliott3, Kaveh Vahedipour1, N. Jon Shah1,4

1Institute for Neurosciences and Biophysics, Research Centre Juelich, Juelich, Germany; 2Department of Psychiatry and Psychotherapy, University Hospital Aachen, Aachen, Germany; 3Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA; 4Faculty of Medicine, Department of Neurology, RWTH Aachen University, JARA, Aachen, Germany

Spherical Navigator Echoes have been used successfully as a means of estimating rotation in MRI but suffer from one shortcoming. Near the pole the slewrate of the gradient waveform increases so rapidly, that the pole caps have to be left unsampled. Thus, rotation estimation errors occur when features rotate out of the sampled area. For rotations perpendicular to the windings of the spiral a reduced accuracy compared to rotations along the windings has been reported. Here we present an alternative sampling scheme for the spherical surface which is able to sample the complete surface while staying within the slewrate limits of the hardware.

14:00         4651.     Noise Bias Correction for Signal Averaged Images

Elena Olariu1, Arturo Cardenas-Blanco2, Ian Cameron1,3

1Physics, Carleton University, Ottawa, Ontario, Canada; 2Ottawa Health Research Institute; 3Diagnostic Imaging, Ottawa General Hospital

Clinical MR images are corrupted by noise which may reduce the reliability of quantitative analyses. The extraction of the true MR signal intensity from noisy MR magnitude images is confounded by a bias, which will be referred to here as Rician Bias (RB), caused by noise rectification in the magnitude calculation for low intensity pixels. Averaging in the image domain reduces the effective noise but not the noise bias. For low SNR a post-processing scheme to correct the noise bias combined with a limited amount of signal averaging is preferable. The RB correction method discussed here, which is an implementation of the theory developed by Koay and Basser, has been previously described2. The results are extended here to consider the effect of signal averaging and inaccuracies in the value of óg used.

14:30         4652.     PARAMAP: An Automated Imaging Analysis Tool for Quantitative CEST Molecular Imaging: Validation in Vitro

Julien Flament1, Benjamin Marty1, Sébastien Mériaux1, Julien Valette1, Christelle Medina2, Caroline Robic2, Marc Port2, Franck Lethimonnier1, Fawzi Boumezbeur1

1NeuroSpin, I2BM, Commissariat à l'Energie Atomique, Gif-sur-Yvette, France; 2Research Division, Guerbet, Roissy-Charles de Gaulle, France

CEST agents are promising new contrast agents for MR molecular imaging. Yet, their susceptibility to parameters such as B0 or B1 is a real issue to achieve truly quantitative CEST imaging. In this study, we acquired B0 and B1 maps along with the CEST on and off-resonance images to generate quantitative CEST maps using a home-made imaging analysis software called PARAMAP. PARAMAP is based on the numerical simulation of the Bloch equations modified for chemical exchange incorporating B0 and B1 dependencies. The efficiency of our analysis tool was verified in vitro.

15:00         4653.     Rapid Motion Detection Using Pre-Rotated Baseline Spherical Navigator Echoes

Junmin Liu1,2, Maria Drangova1,2

1Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada; 2Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada

A new spherical navigator echo (SNAV) registration method is presented. Our algorithm starts from collecting a set of pre-rotated baseline SNAVs, which randomly and uniformly cover a predetermined rotation range. The rotation angles between a transformed and baseline position are determined by identifying the minimum of a cost function calculated by subtracting the transformed SNAV from the set of pre-rotated baseline SNAVs. Preliminary results demonstrate that accurate translation and rotation parameters can be extracted in less than 50 ms, compared to the 5 seconds required for the previously used iterative registration approaches.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 100

13:30         4654.     Increasing the Effectiveness of the UNFOLD Technique by Removing Phase Trends

Yanle Hu1

1Imaging Research Center, University of Texas at Austin, Austin, TX, USA

To increase temporal resolution in dynamic MRI studies, under-sampling techniques are typically used. One way to remove aliasing artifacts associated with under-sampling is to use the UNFOLD technique, which purposely interleaves under-sampled k-space trajectories across time frames to move aliasing peaks away from true signal peaks in the spectrum, and then filter out aliasing peaks to get alias-free images. The phase drift in signal may shift and broaden aliasing peaks. Removing linear and quadratic phase trends before the implementation of UNFOLD can ensure that aliasing artifacts are removed effectively without increasing the number of frequency components to be filtered out.

14:00         4655.     TV Regularization for Segmented GRAPPA with Higher Net Acceleration Factor

Yunmei Chen1, Xiaojing Ye1, Haili Zhang1, Jiangli Shi1, Feng Huang2

1Department of Mathematics, University of Florida, Gainesville, FL, USA; 2Invivo Corporation, Gainesville, FL, USA

Segmented GRAPPA is superior to GRAPPA but requires significant amount of ACS lines. We propose a total variation regularized GRAPPA technique to produce a full calibration k-space with limited ACS lines. In the next step, the full calibration k-space data is used as calibration signal for segmented GRAPPA. The experimental results, with comparisons with GRAPPA and high-pass GRAPPA, show that the proposed method can generate images with lower artifacts/noises level when only 32 ACS lines are used with reduction factor 4. This work enables segmented GRAPPA with limited ACS lines, and hence increases the net acceleration factor while preserving the image quality.

14:30         4656.     MPRAGE Using EPI Navigators for Prospective Motion Correction

Matthew Dylan Tisdall1,2, Aaron Hess3, Andre van der Kouwe1,2

1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; 2Radiology, Harvard Medical School, Brookline, MA, USA; 3Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa

We present initial results from a novel method for real-time motion correction in MPRAGE imaging. We use high-speed, 32^3 EPI volumes as navigators, interspersed in the dead time of the MPRAGE sequence. We estimate rigid body motion from the EPI volumes and correct the MPRAGE's acquisition location before each readout block.

15:00         4657.     Iterative Image Reconstruction for PROPELLER-MRI: Through-Plane Motion Considerations

Ashish A. Tamhane1, Mark Anastasio1, Konstantinos Arfanakis1

1Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, IL, USA

In PROPELLER image reconstruction using gridding, through-plane motion artifacts are minimized by assigning low “quality” weights to affected blades. Iterative image reconstruction can reduce artifacts that arise from data inconsistencies and minimize image noise by use of regularization strategies. “Quality” weights similar to those used in gridding can also be incorporated in iterative image reconstruction in order to reduce the effects of through-plane motion. The goal of this study was to assess the performance of iterative PROPELLER image reconstruction with un-weighted and weighted least squares cost functions in the presence of through-plane motion, and compare it to that of gridding.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 100

13:30         4658.     Correction for Chemical Shift Artifacts in Magnetic Resonance Electrical Impedance Tomography

Mark Jason Hamamura1, Orhan Nalcioglu1, Lufti Tugan Muftuler1

1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, CA, USA
Chemical shift artifacts in magnetic resonance electrical impedance tomography (MREIT) degrade the accuracy of the reconstructed conductivity. In this study, we investigated the use of a modified 3-point Dixon technique to remove these artifacts in a simple fat/water phantom. The results demonstrate that this technique can be used to correct for chemical shift artifacts in MREIT.

14:00         4659.     DCE-MRI Tumor Registration by Using TV-L1 Optical Flow

Michael Hofer1, Thomas Pock2, Karin Kapp3, Thomas Bauernhofer4, Franz Ebner5, Rudolf Stollberger1

1Institute of Medical Engineering, Graz University of Technology, Graz, Austria; 2Institute for Computer Graphics and Vision, Graz University of Technology, Graz, Austria; 3Department of Radiotherapy-Radiooncology, Medical University Graz, Graz, Austria; 4Department of Oncology, Medical University Graz, Medical University Graz, Austria; 5Department of Radiology, Medical University Graz, Graz, Austria

Non-rigid image registration, independent from contrast changes in dynamic time series, is implemented using a TV-L1 optical flow algorithm to compensate physiological and unintentional motion to get a better quantification of DCE-MRI data. Contrast invariant structure images of the whole sequence are created and registered to a template image which is defined by the structure image of the first component of the principal component analyses. The performance of the algorithm was evaluated using real patient DCD-MRI tumor sequences where movement artifacts of tumor and surrounding tissue could be markedly reduced which subsequently improved the quantification of DCE-MRI data.

14:30         4660.     Self-Navigated IDEAL Water-Fat Separation

Yun Jiang1, Jeffrey Tsao1

1Global Imaging Group, Novartis Institutes For BioMedical Research, Cambridge, MA, USA

IDEAL water-fat separation is being adopted in quantitative analysis of adiposity. The presence of motion during acquisition causes motion artifacts, which can result in quantification inaccuracies. To overcome this challenge, a double-echo navigator technique was incorporated in the IDEAL sequence to monitor the signal fluctuation caused by motion. Retrospective motion correction led to a substantial reduction of motion artifacts, thereby improving the accuracy and robustness of the quantification.

15:00         4661.     Impact of B1 Inhomogeneities on AIF Selection in DCE-MRI at 3 Tesla

Robert Merwa1, Gernot Reishofer2, Thorsten Feiweier3, Karin Kapp4, Franz Ebner2, Rudolf Stollberger1

1Institute of Medical Engineering, Graz University of Technology, Graz, Austria; 2Department of Radiology, Medical University of Graz, Graz, Austria; 3MED MR PLM AW Neurology, Siemens AG Healthcare Sector, Erlangen, Germany; 4Department of Radiation Therapy, Medical University of Graz, Graz, Austria

Dynamic contrast-enhanced MRI was performed in combination with a special sequence in order to determine B1 inhomogenities. AIF and tissue concentrations were calculated and the kinetic parameters Ktrans and Ve were determined with a generalized kinetic model. The absolute deviation of the maximum values of two comparable AIFs can be improved by a factor greater than 10 and the root mean square deviation concerning the two AIFs can be decreased by a factor greater than 5 if B1 inhomogeneities are corrected. Also the deviations of Ktrans and Ve in respect of the two AIFs are significantly lower.

 


 
Image Analysis I
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 101

14:00         4662.     Morphometry of Intratumoral Enhancement Patterns on 4D Spectral Images for Differential Diagnosis of Breast Tumors in Dynamic Contrast-Enhanced MRI

Sang Ho Lee1,2, Jong Hyo Kim2,3, In Chan Song2,3, Yun Sub Jung1,2, Jeong Seon Park4, Woo Kyung Moon3

1Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Korea; 2Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea; 3Department of Radiology, Seoul National University College of Medicine, Seoul, Korea; 4Department of Radiology, Hanyang University College of Medicine, Seoul, Korea

This study demonstrates the importance of quantitatively capturing spatio-temporal properties of intratumoral enhancement patterns for MR-based breast tumor diagnosis. MR-time-series images were registered for motion compensation and tumor regions were segmented semi-automatically from our proposed perfusion index map enhancing tumor contrast. Eigenvalues were obtained for voxel-wise temporal enhancement curves within tumor by using singular value decomposition (SVD), generating eigenvalue maps. The spatial variations of eigenvalues within tumor were captured by 3D geometric moment invariants (GMIs). The potential of our SVD-based GMI features in differentiation of benign and malignant tumors is validated by classification performance using least square support vector machine.

14:30         4663.     Application of Vessel Exclusion for Development of Computer-Aided Diagnosis for Breast MRI

Muqing Lin1, Ke Nie1, Jeon-Hor Chen1,2, Orhan Nalcioglu1, Min-Ying Lydia Su1

1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, CA, USA; 2Department of Radiology, China Medical University, Taichung, Taiwan

The purpose is to evaluate the reduction of vessel contamination in the hot-spot search of breast lesions on DCE-MRI. This is particularly important for development of automated CAD that identified lesions and characterizes the suspicious impression. The blood vessels show strong contrast enhancements and the wash-out pattern, which is a strong malignancy feature. The initial hot spot search was performed using a kernel of 3x3 pixels throughout the entire breast. The vessels were identified using a computer algorithm-based method based on 2D and 3D. We have shown that our algorithm can successfully exclude vessels and reduce false positive detection.

15:00         4664.     Association of Carotid Atherosclerosis Eccentricity with High Risk Plaque Features: An MRI Study

Huijun Chen1, Li Dong1, William S. Kerwin1, Wei Yu2, Hideki Ota1, Hunter Underhill1, Xihai Zhao1, Zhaoqi Zhang2, Zach Miller1, Thomas S. Hatsukami3, Chun Yuan1

1Department of Radiology, University of Washington, Seattle, WA, USA; 2Department of Radiology, Beijing Anzhen Hospital, Beijing, China; 3Department of Surgery, University of Washington, Seattle, WA, USA

Multi-contrast weighted MRI identified plaque features in carotid artery, such as intraplaque hemorrhage (IPH) and thin or ruptured fibrous cap, have been reported to be predictors of subsequent stroke. On the other hand, plaque eccentricity of carotid artery has been found to be associated with ipsilateral cerebrovascular events in an ultrasonography study. In this study, we sought to assess the association between plaque shape and high risk plaque features in carotid artery, and a novel eccentricity index (EI) of plaque using MR imaging was established. The result shows that the plaques with high risk features (presence of IPH and thin or ruptured fibrous cap) have relatively high EI, which suggests the proposed EI from carotid MRI could be a potential predictor of high risk plaque.

15:30         4665.     Depiction of SPIO in Atherosclerotic Plaque Using True Resolution SGM

Gopal Varma1, Marcus Richard Makowski1, Hannes Dahnke2, Stephen Keevil3, Rene M. Botnar1, Tobias Schaeffter1

1Division of Imaging Sciences, King's College London, London, UK; 2Philips Healthcare, Hamburg, Germany; 3Medical Physics, Guy's & St Thomas' NHS Foundation Trust, London, UK

Detection of atherosclerotic plaque with iron oxide contrast agents that induce a susceptibility effect in MRI is sometimes hindered by competing sources of negative contrast. Although positive contrast techniques aid in detection, hyper-intensities are often over-emphasised and may thus fail to accurately depict the plaque. We present a “true resolution” positive contrast method post-processing that provides a more accurate depiction of e.g. SPIO induced susceptibility effect with relation to its source.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 101

13:30         4666.     A MRI-Based Virtual Cystoscopy System for Evaluation of the Entire Bladder

Jerome Zhengrong Liang1, Lihong Li2, Chaijie Duan1, Su Wang1, Mark Wagshul1, Hongbing Lu3

1Radiology, Stony Brook University, Stony Brook, NY, USA; 2Dept. of Engineering Science and Physics, The City University of New York, Staten Island, NY, USA; 3Biomedical Engineering, Fourth Military Medical University, Xi¡¯an, Shannxi, China

Bladder cancer is the fifth leading cause of cancer-related deaths in the US and is difficult to manage because of the high recurrence rate after resection of the tumors (as high as 80%). It is essential to detect bladder abnormalities in a non-invasive and convenience manner, especially for follow-ups on resection. This paper presents a MRI-virtual cystoscopy system, which extracts the bladder wall from T1 images where the wall is enhanced while the urine and surrounding fat are suppressed. It analyzes the extracted wall and detects abnormal features automatically. Test results are encouraging by FROC merit.

14:00         4667.     Deconvolution and QSI of Simulated Phase Images of the Human Brain: Applications to Assess Susceptibility

Guenther Grabner1,2, Siegfried Trattnig1, Markus Barth2

1Department of Radiology, Medical University of Vienna, Vienna, Austria; 2Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands

MR phase images reflect the magnetic susceptibility of tissues but the phase image is a convolution of the susceptibility map with the typical pattern of magnetic dipole. This leads to very complex phase patterns in areas of differing susceptibility. The challenge is to estimate the underlying tissue susceptibilities. We wanted to assess how accurate the underlying properties can be determined by performing filtered deconvolution and QSI on a simulated phase model.

14:30         4668.     Simulation of Nasal Air Flow from MRI Data – a Feasibility Study

Arthur Peter Wunderlich1, Barbara Doll2, Marc Scheithauer3, Wolfgang Freund1, Karsten Urban4, Ulrich Simon2

1Diagnostic and Interventional Radiology, Univ.-Clinic Ulm, Ulm, Baden-Württemberg, Germany; 2Scientific Computing Centre, University Ulm, Ulm, Baden-Württemberg, Germany; 3Otolaryngology, Univ.-Clinic Ulm, Ulm, Baden-Württemberg, Germany; 4Institue for Numerical Mathematics, University Ulm, Ulm, Baden-Württemberg, Germany

To study the feasibility of simulating the nasal air flow in inspiration and expiration with finite volume methods, we investigated one healthy subject with high-resolution MRI during breathing of a) room air and b) menthol. In a third experiment, the same sequence was used c) after inhalation of xylometazoline, a widely used decongestant drug. Nasal airways were segmented from MRI data and inspiratory as well as expiratory flow in all three conditions was simulated with mathematical methods. Simulations reveal pressure-flow-curves separately for both conchae as well as flow distribution in nasal airways and their dependence on medication.

15:00         4669.     MR Elastography Inversions Without Phase Unwrapping

Kevin John Glaser1, Richard Lorne Ehman1

1Radiology, Mayo Clinic, Rochester, MN, USA

MR elastography (MRE) is a phase-based technique for noninvasively measuring the mechanical properties of tissue in vivo. MRE data can be adversely affected by unmanageable phase aliasing due to motion, SNR, and various magnetic field effects, which can degrade estimates of material properties like the shear stiffness. This work derives and demonstrates a method for processing MRE data without having to unwrap the phase data which yields elastograms comparable to those from conventional algorithms. It is expected that this will increase the flexibility and utility of MRE for applications including brain and abdominal imaging.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 101

13:30         4670.     A Model-Based Fully Automatic Algorithm for Brain Extraction on 3D MRI Scans

Babak A. Ardekani1, Alvin H. Bachman1

1Center for Advanced Brain Imaging, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, USA

A model-based automatic algorithm is presented for brain extraction on 3D MRI scans. Given a structural MRI of the head, the objective is to classify each voxel within the image volume as either brain or non-brain. Brain extraction, as a preliminary step, often improves the results of inter-subject non-linear image registrations. It is also a very useful first step in automatic brain tissue classification algorithms. We have compared the algorithm presented in this paper with several previously published programs and have found it to be superior to those techniques. An implementation of this algorithm is freely available online at: www.nitrc.org/projects/art.

14:00         4671.     A Robust Parametric Method for Bias Field Estimation and Segmentation of MR Images

Chunming Li1, Li Wang2, J. Chris Gatenby1, Adam Anderson1, John C. Gore1

1Vanderbilt University, Nashville, TN, USA; 2School of Computer Science & Technology, Nanjing University of Science and Technology, China

In this work, we propose a novel parametric method for joint image segmentation and bias field estimation for MR images. The bias field is parameterized as a linear combination of smooth basis functions. Image segmentation and bias field estimation are performed by minimizing a cost function. A desirable advantage of the proposed method is its robustness to initialization, which thereby allows fully automatic applications. Comparisons with other methods show the advantage of our method in terms of accuracy and robustness.

14:30         4672.     Template-Based Bias Correction: Application to Paediatric Brain MRI

Maria Murgasova1, Joseph V. Hajnal2, Serena J. Counsell2, A David Edwards2, Daniel Rueckert1

1Department of Computing, Imperial College London, London, UK; 2Robert Steiner Magnetic Resonance Unit, Imaging Sciences Department, MRC Clinical Services Centre, Imperial College London, London, UK

We propose a novel template-based bias correction method highly effective for removal of stronger bias fields usually present in MR images acquired by modern high magnetic field MR scanners. The bias field is estimated by weighted least square B-spline fitting to a difference of log-transformed image and an aligned and intensity-adjusted template image. The method is applied 35 pediatric brain MR images acquired using a MP RAGE sequence on a 3T MR scanner. The bias correction with B-spline control point spacing between 50 and 75 mm substantially improves EM-based classification of brain tissues in these images.

15:00         4673.     Artificial Neural Network Analysis of Differences in Fiber Tracks Between Term and Preterm Children

Lutfi Tugan Muftuler1, Ke Nie1, Orhan Nalcioglu1, Christine E. McLaren2, Min Ying Su1

1Center for Functional Onco-Imaging, University of California, Irvine, CA, USA; 2Department of Epidemiology, University of California, Irvine, CA, USA

VBM techniques can be applied to DTI parameter maps to investigate local differences in white matter structures between patient and control groups. However, tractography is essential to investigate tract morphology and brain connectivity. Here, we developed an Artificial Neural Network based analysis to select a set of features that can achieve the highest differentiation power between the two groups. Once these features are found, inferences about the morphological differences in fiber tracts can be made. Compared to traditional statistical analysis methods, ANN was found to have higher prediction rates in complex and non-linear relationships among a large number of variables.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 101

13:30         4674.     High Resolution Positive Contrast Imaging: Application to the Visualization of Localized Vascular Abnormalities

Thomas G. Perkins1, Julien Sénégas2, Hannes Dahnke2, Elliot Sandberg3,4, William W. Orrison5,6

1Philips Healthcare, Cleveland, OH, USA; 2Philips Research Europe, Hamburg, Germany; 3Department of Radiology, VAMC, Denver, CO, USA; 4Departments of Radiology and Neurology, University of Colorado Health Science Center, Aurora, CO, USA; 5Nevada Imaging Centers, Las Vegas, NV, USA; 6Touro University Nevada College of Osteopathic Medicine, Henderson, NV, USA

Positive contrast imaging based on susceptibility gradient mapping (SGM) is a relatively new technique that produces maps with high contrast-to-noise ratio for areas of local magnetic susceptibility variation. Applying high resolution SGM to assess localized abnormalities associated with hemosiderin deposition in conditions such as traumatic brain injury or cavernous angiomas could provide additional clinical information for detection and diagnosis. The purpose of this study was to explore the potential clinical utility of SGM to provide better characterization of cavernous angiomas, and shows the potential utility of positive contrast imaging for the visualization of localized vascular abnormalities.

14:00         4675.     Rapid Quantification of Stroke Infarct from Diffusion Weighted Images

Sumit K. Nath1, Rakesh Mullick1, Dattesh Shanbhag1, Uday Patil2

1Imaging Technologies Lab, GE Global Research, Bangalore, Karnataka, India; 2Conulting Radiologist, GE Global Research, Bangalore, Karnataka, India

A vital step in the evaluation of acute and chronic stroke involves volume quantification of the infarct as determined from diffusion-weighted images (DWI). The routine assessment of infarct size is by visual review of the approximate size reported along with the location of the defect with reference to the brain anatomy. Assessment of the infarct volume is critical to management decisions in acute stroke, especially for thrombolytic therapy, and calls for quantitative methods. There are multiple efforts to develop post-processing methods to segment and automatically measure the infarct from DWI images. Given T2 shine-through artifacts from pre-existing old infarcts in the DWI images make this task very challenging. In order to offer a robust workflow for this evaluation we present a hybrid (visualization and segmentation) method to address this. The core concept is to integrate the presentation of maximum intensity projections (MIP) of the DWI data to the user to select suggestive infarct regions and use an underlying level-set based (top-down) image segmentation approach for rapid quantification of suspect regions

14:30         4676.     Noise Performance of IDEAL Considering Relaxation and Multiple Spectral Peaks of Fat

Stephan van Zyl1, Peter Börnert2, Holger Eggers2, Michael M. Morlock1

1Hamburg University of Technology, Hamburg, Germany; 2Philips Research Europe, Hamburg, Germany

In the past, water/fat separation algorithms like IDEAL have been further refined to account for finite signal lifetime (T2*) and the multi-peak nature of the fat spectrum. IDEAL is known to obtain good noise performance. Here, the noise performance of T2*-IDEAL and MP-IDEAL was evaluated using the Cramér-Rao bound (CRB). The results were independently verified with the effective number of signal averages (NSA) obtained by Monte Carlo simulations and phantom experiments. Investigations have shown that a reduction in NSA is to be expected when using T2*-IDEAL and MP-IDEAL. Short encoding times are therefore absolutely essential.

15:00         4677.     Efficient and Effective Anisotropic Smoothing of Diffusion Tensor Images in Log-Euclidean Framework

Qing Xu1, Adam W. Anderson1, John C. Gore1, Zhaohua Ding1

1Vanderbilt University Institute of Imaging Science (VUIIS), Vanderbilt University, Nashville, TN, USA

We present a technique to denoise diffusion tensor images by performing non-iterative anisotropic smoothing in the Log-Euclidean framework. The diffusion tensors are first transformed to tensor logarithm space to perform Euclidean computing for vectors. Then an anisotropic smoothing algorithm for multi-channel image is implemented with an unconditionally stable and second order accurate semi-implicit scheme, which allows us to choose large step size and thus use one iteration to achieve optimal effect. The tests with in vivo DTI data have demonstrated that there is up to 50% improvement on the principal diffusion directions with one iteration of anisotropic filtering.

 


 
Image Analysis II
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 102

14:00         4678.     Leveraging Open Source/Freeware Tools and Design Methodologies in Translational Research: A Siemens-Based Case Study -- From Raw Diffusion and Structural Data to PACS and the Web

Rudolph Pienaar1, Ruopeng Wang1, Bruce Fischl1, Van Wedeen1, Patricia Ellen Grant1

1Radiology, Massachusetts General Hospital, Boston, MA, USA

This paper demonstrates a simple and robust method of assembling powerful image processing pipelines based on collections of largely independent image processing tools. These pipelines are open source in nature, and underlying components either open source or freeware. In this study, the pipelines are deployed to a Linux workstation and images collected on Siemens scanners. This Linux workstation can process data directly on the scanner itself, or receive DICOM data from a conventional hospital PACS. Final outputs are automatically parsed for access via the web, or are re-transmitted back to a PACS.

14:30         4679.     NeuroGrid Portal: A Web Interface Providing Processing Tools for Neuro-Imaging Research

Ali A. Khanban1,2, Yu Chen3, Gianlorenzo Fagiolo2, Nick C. Fox4, Derek L. G Hill5, Daniel Rueckert1, Jo V. Hajnal2

1Imperial College London, UK; 2Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, UK; 3University College London, UK; 4Dementia Research Centre, Institute of Neurology, University College London, UK; 5IXICO Ltd, The London BioScience Innovation Centre, 2 Royal College Street, London, UK

NeuroGrid portal is a web portal designed to provide medical image processing applications in an easy to use web-based environment for the neuro-imaging community. Many applications which require high technical expertise to install and fine tune can be accessed with a few mouse clicks and will be run on remote servers. All the transactions use secure HTTPS protocols and users can share their data with other registered users if they want to. Some of the most frequent tasks faced in imaging research, such as image format conversion, correction of anatomical orientation, registration and segmentation are available on NeuroGrid Portal.

15:00         4680.     High Dynamic Range Processing Improves Global Contrast

Jerod Michael Rasmussen1, Vinod Kaimal2

1University of California, Irvine, Irvine, CA, USA; 2MIR Preclinical Services, Ann Arbor, MI, USA

High Dynamic Range (HDR) techniques are applied to images weighted by T1, T2 and proton density values to create a novel HDR image. ROIs were drawn around specific tissues including bone, muscle and ligament. Each ROI was evaluated to determine effects of the HDR technique on local contrast. The resulting image retained the best local contrast features from each respective weighting, resulting in an increase in global contrast.

15:30         4681.     Consistency in Automated Versus Manual Definition of MRI Scan Volume Orientations of the Human Heart

Harald Sepp Heese1, Sebastian P. M. Dries2, Daniel Bystrov2, Jochen Peters3, Olivier Ecabert3, Juergen Weese3, Chiel J. den Harder4, Wendy de Kok4, Arianne M. van Muiswinkel4

1Philips Research , Hamburg, Germany; 2Philips Research, Hamburg, Germany; 3Philips Research, Aachen, Germany; 4Philips Healthcare, Best, Netherlands

Definition of anatomically consistent and accurate scan volume orientations is a prerequisite for diagnostic reliability both for manual and automated MRI scan planning. The proposed method automatically recognizes major structures of the human heart from unseen breathing-gated, ECG-triggered, isotropic 3D MRI volumes, and calculates anatomical landmarks of these structures. Based on a set of training samples, for which automatically calculated landmarks and user-defined examples of scan volume orientations are available, the proposed method infers corresponding scan volume orientations for unseen images. Performance of the proposed recognition/planning method is compared to manually defined scan volume orientation for a four chamber view.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 102

13:30         4682.     Simultaneous Mapping of Functional Connectivity and Activation Using Real-Time FMRI

Dae-Jin Kim1, Bumhee Park1, Hae-Jeong Park1

1Department of Radiology and Nuclear Medicine and Research Institute of Radiological Science, Yonsei University College of Medicine, Seoul, Korea

The aim of this study is to develop real-time platform for functional connectivity and activation using real-time fMRI. We performed the motion fMRI experiments, and visualized the functional connectivity and activation for the ongoing paradigm. On 3.0T MRI scanner, fMRI scanning was performed using EPI sequences with TR=3sec. Online correlation coefficients as regional functional connectivity and task-related activations were calculated and simultaneously visualized for 116 brain regions. We demonstrated the feasibility of real-time fMRI monitoring for the functional connectivity. It was possible to monitor the functional activity in real time environments, and to localize the subject¡¯s task performance.

14:00         4683.     Simple Subject-Specific Spatial Smoothing for BOLD FMRI

Robert L. Barry1,2, John A. Sexton1,3, John C. Gore1,2

1Vanderbilt University Institute of Imaging Science, Nashville, TN, USA; 2Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA; 3Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA

Spatial smoothing (SS) is a crucial processing step preceding statistical analyses of blood-oxygenation-level-dependent (BOLD) fMRI data. Although previous works have shown that the optimal SS kernel size varies both between subjects and active regions of interest (ROIs) within subjects, the use of a single kernel size for one or many subjects is virtually ubiquitous. A simple and computationally efficient automated algorithm based on matched filter theory is presented that determines the SS kernel size to maximize t-statistics for a given ROI. The results also emphasize the benefits of locally adaptive SS techniques to optimize BOLD contrast-to-noise in single-subject analyses.

14:30         4684.     Evaluation of the Image Intensity Non-Uniformity Correction Power in Voxel-Based Morphometry

Masami Goto1,2, Osamu Abe3, Tosiaki Miyati4, Hiroyuki Kabasawa5, Takeshi Iwatsubo6, Hiroshi Matsuda7, Fumio Yamashita8, Shigeki Aoki9, Harushi Mori3, Naoto Hayashi10, Kenji Ino1, Keiichi Yano1, Kyouhito Iida1, Kazuo Mima1, Kuni Ohtomo3

1Radiological Technology, University of Tokyo Hospital, Bunkyo-ku, Tokyo, Japan; 2Graduate School of Medical Science, Kanazawa University, odateno, kanazawa, Japan; 3Radiology, University of Tokyo, Bunkyo-ku, Tokyo; 4Graduate School of Medical Science, Kanazawa University, odateno, Kanazawa, Japan; 5Japan Applied Science Laboratory, GE Yokogawa Medical Systems, Ltd, Hino-shi, Tokyo, Japan; 6Neuropathology, University of Tokyo, Bunkyo-ku, Tokyo, Japan; 7Nuclear Medicine, Saitama Medical University International Medical Center, Hidaka, Saitama, Japan; 8Radiology, National Center Hospital of Neurology and Psychiatry, Kodaira, Tokyo, Japan; 9Radiology, Juntendo University, Bunkyo-ku, Tokyo, Japan; 10Computational Diagnostic Radiology and Preventive Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan

Because we compared the same volunteer group, it was supposed to be no significant group difference. However, there are significant group differences. The cause will be due to intensity non-uniformity in the 3T image. If there is no significant group difference, such an intensity correction is believed to be efficient. In the present study, the intensity non-uniformity correction is more effective in SPM5 than N3. It is impossible to measure greal brain volumeh and there is no gold standard of brain volume measurement. However, this result suggests that intensity non-uniformity correction is necessary to reduce inhomogeneity between MR scanners.

15:00         4685.     Effects of the Modulation in the White Matter Voxel Based Morphometry

Ozlem Ozmen Okur1, Cengizhan Ozturk1, Kubilay Aydin2

1Bogazici University Biomedical Engineering Institute, Istanbul, Turkey; 2Istanbul Medical School, Istanbul University, Instanbul, Turkey

Voxel Based Morphometry (VBM) aims to reveal the differences between different populations&#8217; brains by making voxel based comparisons on MR brain images. SPM is quite a common tool utilized for VBM analyses. We computed the goodness of non-rigid registration metric (mutual information) in order to reveal the relationship between the registration quality and VBM results in SPM5 in case of with and without modulation. Additionally, we registered the images onto the groups&#8217; own template (group averages), too; and evaluated these templates&#8217; effects in the VBM analysis.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 102

13:30         4686.     A Robust Breast Segmentation Method to Support Computer Aided Evaluation and Breast Density Assessment

Gokhan Ertas1, Martin O. Leach1

1Cancer Research UK Clinical Magnetic Resonance Research Group, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK

Breast anatomy on MR images is affected by intensity inhomogeneity and partial volume effects. In images acquired from different centres and scanners, there is considerable variation in the extent of these effects.

14:00         4687.     Development of a Computer Algorithm-Based Method for Identification of Blood Vessels on Dynamic Contrast Enhanced Breast MRI

Muqing Lin1, Jeon-Hor Chen1,2, Ke Nie1, Orhan Nalcioglu1, Min-Ying Lydia Su1

1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, CA, USA; 2Department of Radiology, China Medical University, Taichung, Taiwan

We presented an algorithm based method for identification of blood vessels on dynamic contrast enhanced breast MRI. The algorithm is consisted of global histogram equalization, a filter bank based on Wavelet Transform and Hessian Matrix, and high-pass filtering to enhance vessels, then thresholding. The procedure was first performed on 2D MIP then extended to 3D. The detected vessels were converted to a vasculature skeleton by thinning, and compared to radiologist’s drawing. The mean correct detection rate was 85%, the incorrect detection rate (detected by algorithm not by radiologist) was 15%, and the missed-rate (identified by radiologist not by algorithm) was 21%.

14:30         4688.     Design of an MR Phantom for Comparison of Frequency Based Texture Analysis Techniques

Robert Allan Brown1,2, Richard Frayne2,3

1Biomedical Engineering, University of Calgary, Calgary, AB, Canada; 2Seaman Family MR Research Centre, University of Calgary, Calgary, AB, Canada; 3Radiology and Clinical Neurociences, University of Calgary, Calgary, AB, Canada

Texture analysis is an image analysis technique that complements standard pixel intensity methods. Textural features of MR images are associated with clinically important genetic differences in some brain tumors as well as being of interest in detection of other diseases. This abstract reports the design of an MR phantom to investigate and compare texture analysis techniques. Two techniques are compared and their repeatability measured using this phantom and imaging from a volunteer.

15:00         4689.     Demonstration of a Novel Edge Analysis Technique Using a Purpose Built MR Phantom

Robert Allan Brown1,2, Ashley D. Harris1,2, Richard Frayne2,3

1Biomedical Engineering, University of Calgary, Calgary, AB, Canada; 2Seaman Family MR Research Centre, University of Calgary, Calgary, AB, Canada; 3Radiology and Clinical Neurociences, University of Calgary, Calgary, AB, Canada

In many diseases, the interface between diseased and healthy tissue may contain a great deal of information. One example is the brain tumor oligodendroglioma, where characteristics of the tumor margin are significantly associated with 1p/19q co-deletion, which is a marker for good response to chemo- and radiation-therapy. In this abstract we report the design of a phantom to simulate “invasive” and “non-invasive” tissue border properties, and use a novel edge analysis technique to quantify these features.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30         Computer 102

13:30         4690.     Automatic Quality Assessment in Structural Brain Magnetic Resonance Imaging

Bénédicte Mortamet1, Matt A. Bernstein2, Clifford R. Jack Jr2, Jeffrey L. Gunter2, Chadwick Ward2, Paula J. Britson2, Reto Meuli3, Jean-Philippe Thiran4, Gunnar Krueger1

1Advanced Clinical Imaging Technology, Siemens Suisse SA, Healthcare Sector IM&WS - CIBM, Lausanne, Switzerland; 2Mayo Clinic, Rochester, MN, USA; 3Centre Hospitalier Universitaire Vaudois and University of Lausanne; 4Ecole Polytechnique Fédérale de Lausanne (EPFL), Signal Processing Laboratory (LTS5), Lausanne, Switzerland

Quality assessment of MRI is of great importance to derive reliable diagnostic information. As automated quantitative image analysis is being increasingly used in routine, automated measures of quality are needed. Based on a single magnitude image, we propose a procedure that automates the classification of data quality and allows detecting patient-/scanner-related artifacts. Validated on 750 datasets, the approach proofs to be a very promising candidate to perform quality assurance analysis for clinical practice and research. It could greatly improve clinical workflow through its ability to rule-out the need for a repeat-scan while the patient is still in the magnet bore.

14:00         4691.     Simultaneous Identification of Noise and Estimation of Noise Standard Deviation in MRI

Cheng Guan Koay1, Evren Özarslan1, Carlo Pierpaoli1

1National Institutes of Health, Bethesda, MD, USA

Analysis of MRI data usually entails a series of processing steps. One of these steps is noise assessment, which includes both the identification of noise and the estimation of noise variance (standard deviation). In MRI, the identification of noise has received less attention than has the estimation of noise variance. Here, we propose a novel approach to simultaneously identify noise and estimate the standard deviation of noise from a data structure commonly used in MRI. Experimental data acquired using an 8-channel phased array coil were used to investigate the feasibility and the stability of the proposed technique.

14:30         4692.     A Framework for Correcting the Noise-Induced Bias in Noisy Magnitude MR Signals

Cheng Guan Koay1, Evren Özarslan1, Peter J. Basser1

1National Institutes of Health, Bethesda, MD, USA

A long-standing problem in MRI is correcting noise-induced bias in magnitude signals. This problem is particularly pressing in diffusion MRI obtained at high diffusion-weighting. Here, we present a scheme to address this problem by transforming noisy Rician signals to noisy Gaussian signals. Real experimental data are used to illustrate the proposed framework and demonstrate its effectiveness in removing the noise-induced bias.

15:00         4693.     Characterization of Image Heterogeneity Using Minkowski Functionals

Holly C. Canuto1,2, Mikko I. Kettunen1,2, Charles I. McLachlan3, Anant S. Krishnan1, Andre' A. Neves1,2, De-en Hu1, Michael P. Hobson3,4, Kevin M. Brindle1,2

1Biochemistry, The University of Cambridge, Cambridge, Cambridgeshire, UK; 2Cancer Research UK, Cambridge, Cambridgeshire, UK; 3Metropolis Data Consultants, Cambridge, Cambridgeshire, UK; 4Astrophysics, Cavendish Laboratory, The University of Cambridge, Cambridge, Cambridgeshire, UK

Tumor cell death following treatment is a good prognostic indicator for treatment outcome. The spatially heterogeneous nature of cell death has recently been exploited, using the morphological descriptors Minkowski Functionals, to enhance the sensitivity of detection of a MR contrast agent targeted to bind to apoptotic cells. Since tissue morphology is a very sensitive indicator of underlying tissue biology we have used 2D Minkowski Functionals to parameterize the morphological heterogeneity present in T2-weighted MR images of tumors before and after drug-treatment. We have shown that we can detect a treatment response in the absence of a contrast agent.

 


 
Image Analysis III
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 103

14:00         4694.     Landmark-Based Prostate MR Image Matching Using Incompressible Large Deformation Diffeomorphism

Xiaofeng Liu1, Steven Roys2, Jerry L. Prince1,3, Rao Gullapalli2

1Computer Science, Johns Hopkins University, Baltimore, MD, USA; 2Radiology, University of Maryland Baltimore, Baltimore, MD, USA; 3Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA

Magnetic resonance (MR) imaging and spectroscopy with an endorectal coil is a standard clinical procedure for prostate cancer diagnosis. However images and spectra are obtained when the prostate is in a distorted state due to the use of the endorectal coil. For optimal delivery of radiation dose to the cancerous tissue during therapy, these deformed images need to be transformed back to their non-deformed state. We propose an incompressible large deformation diffeomorphism method for landmark-based prostate image matching, which preserves the incompressibility, an important physical property of the prostate. Preliminary results on 2D images demonstrate the effectiveness of this method.

14:30         4695.     Non-Rigid Registration of T1 MR Images Constrained with Fractional Anisotropic (FA) Maps

Xia Li1, Benoit Dawant2, Xin Hong1, Zhaohua Ding1, John Gore1, Adam Anderson1

1Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA; 2Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN, USA

Conventional T1 or T2 weighted MR images provide basic contrast information for brains. However, those images are limited because they provide little contrast between distinct white matter structures. Diffusion tensor imaging (DTI) is a complementary tool that provides information on the orientation and integrity of white matter fiber bundles. The co-registration of intra- or inter-subject DTI data in a standard coordinate space allows us to perform statistical analysis of DTI images, or compare data across subjects. In this study, a non-rigid registration algorithm, which combines both T1 weighted MR images and DTI information, is proposed, in order to retain both MR information and the significant micro-structural information about tissues.

15:00         4696.     Metrics for Quantifying the Quality of MR Images

Francisco Prieto1,2, Marcelo Guarini1,2, Cristian Tejos1,2, Pablo Irarrazaval1,2

1Departamento de Ingeniería Eléctrica, Pontificia Universidad Católica de Chile, Santiago, Chile; 2Biomedical Imaging Center, Pontificia Universidad Católica de Chile, Santiago, Chile

Evaluating the quality of reconstruction techniques in MRI is a difficult task. The Root Mean Square Error (RMSE) is commonly used to compare reconstructed images, although it does not correlate well with subjective perception of quality. We present two new metrics which incorporate human perception factors. One is based on the null space of the transformation from one image to the compared one, and the other on the variation of the Just Noticeable Differences map for different contrasts. Visual experiments show that both indexes provide more information than the RMSE and we propose them as metrics for comparing images.

15:30         4697.     Improved Visualization of Iron-Rich Structures in the Brain with 3D Multiecho GRE Imaging

Yunhong Shu1, Matt A. Bernstein1, Marsha Swatosh1, John Huston1, Kiaran P. McGee1, Kendall H. Lee2

1Radiology, Mayo Clinic, Rochester, MN, USA; 2Neurologic Surgery, Mayo Clinic, Rochester, MN, USA

Reliable localization of subthalamic nucleus (STN) and small veins is a critical step in the surgical planning of deep brain stimulation (DBS) for Parkinson’s disease. 3D MR imaging has been used to guide placement of the lead tips to the STN. A multiple-echo gradient-echo (GRE) pulse sequence can be used to acquire a set of T2*-weighted imaging volumes. There remain, however, multiple options to post-processing the 3D image sets to enhance the visualization of the STN and the small veins. The purpose of this study is to evaluate the performances of several of those post-processing methods to find an optimal technique.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 103

13:30         4698.     Use of Multi-Spectral MR Data to Generate an Attenuation Map for Application to PET/MR Hybrid Imaging

Harry Robert Marshall1,2, Robert Z. Stodilka1,2, Benoit Lewden1, Jean Theberge1,2, Eric Sabondjian1,2, Alexandre Legros1, Andrea Mitchell1, Lela Dorrington1, Jane Sykes1, Frank S. Prato1

1Imaging, Lawson Health Research Institute, London, ON, Canada; 2Medical Biophysics, The University of Western Ontario, London, ON, Canada

Attenuation correction is necessary to generate quantitatively accurate PET images but it is not straightforward in PET/MR hybrid imaging. One method to generate an attenuation map under such circumstances is to segment the MR images into tissue types and to assign said tissue types their known attenuation coefficients. The aim of our study was to determine whether using multispectral MR is beneficial to this end, and if so, which combination of pulse sequences is most effective. We confirmed that multispectral MR yields superior attenuation maps than single MR data sets, but the best combination of sequences depends upon anatomical position.

14:00         4699.     Navigator Filtering Using Principal Component Analysis.

Sergio Andres Uribe Arancibia1, Philipp Batchelor1, Claudia Prieto1, Reza Razavi1, Tobias Schaeffter1

1Division of Imaging Sciences, King's College London, London, UK

Cardiac MR usually requires either navigator echoes or k0 profiles to monitor diaphragm position. Unwanted signals that interfere navigator projections may lead to an incorrect respiratory motion. In this abstract we propose a novel method for filtering navigator projections using a singular value decomposition. The method cleans the projections rather than a derived respiratory signal. Results showed unwanted noise was removed from the projections leading to a robust respiratory motion detection.

14:30         4700.     Augmenting Surgery Planning for Neoadjuvant Chemotherapy Patients by 3D Transformation of Prone Breast MR Images to the Supine Images in the Operating Room Setting

Ruparani Chittineni1, Jeon-Hor Chen1,2, Orhan Nalcioglu1, Min-Ying Su1

1Tu & Yuen Center for Functional Onco-Imaging, Irvine, CA, USA; 2Department of Radiology, China Medical University, Taichung, Taiwan

 

15:00         4701.     Implicit Reference-Based Group Registration in Structural and Functional MRI Studies

Xiujuan Geng1, Hong Gu1, Thomas J. Ross1, Yihong Yang1

1Neuroimaging Research Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA

We propose an implicit reference-based group (IRG) registration method with a high-dimensional elastic deformation model to align structural or functional images within groups. The performance of the IRG method was evaluated using T1-weighted MR images with pre-defined ROIs and compared with reference-based registration methods. Results show that IRG registration produces better registration performance in terms of higher relative overlaps. IRG registration was also applied to an fMRI study with a motor and visual task. The statistical detection power is improved by the elastic registration compared to the affine approach and IRG registration further increases the power compared to reference-based methods.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 103

13:30         4702.     Effects of Patient Population Specific Atlases on Automatic Segmentation of Subcortical Structures in Freesurfer

Istvan Csapo1, Jared Price1, Troy Russell1, Jeff Dewey1, Ekta Sem1, Daniel McCaffrey1, Charles R. Guttmann1, Bradford Navia2, David F. Tate1

1Radiology, Brigham and Women's Hospital, Boston, MA, USA; 2Tufts New England Medical Center, Boston, MA, USA

We set out to investigate whether using manually labeled training data from a specific patient cohort to build probabilistic atlases for Freesurfer improves the automatic segmentation of novel images from the same cohort compared to the segmentations using the default atlas. 106 brain images were segmented and manually corrected. 64 of these images were used to build 6 different atlases. The other 42 images were segmented with Freesurfer using the new atlases. The results were compared to the manual segmentations. Out of the 8 subcortical structures investigated, the hippocampus segmentations were significantly improved with the new population specific atlases.

14:00         4703.     A Simple Semi-Automated Method for Caudate Volume and Shape Analysis

Karlene M. Fraser1, Mitul A. Mehta2, Ruth L. O'Gorman1,3

1Neuroimaging, Maudsley Hospital, London, UK; 2Centre for Neuroimaging Sciences, Institute of Psychiatry, London, UK; 3Neuroradiology, King's College Hospital, London, UK

Here we present a simple, semi-automated method for evaluating the volume and shape of the caudate nucleus. The shape is quantified by the surface area to volume (SA/V) ratio, calculated from contours defining the edge of the caudate on a segmented grey matter map. This method was applied to images from 17 healthy adults and the accuracy and inter-rater reproducibility was assessed. The volume measures showed good agreement with literature values. Significant laterality differences emerged, with the right caudate demonstrating higher volume and surface area and lower SA/V relative to the left (p<0.005). The method also showed good reproducibility, (ICC=0.83-0.9).

14:30         4704.     Automatic Segmentation of Deep Grey Matter Structures for the Assessment of DTI Images

Emil Malucelli1, David Neil Manners1, Claudia Testa1, Caterina Tonon1, Giovanni Rizzo1, Valerio Carelli2, Giuseppe Nicoletti3, Aldo Quattrone3, Bruno Barbiroli1, Raffaele Lodi1

1Dipartimento di Medicina Interna dell’Invecchiamento e delle Malattie Nefrologiche, University of Bologna, Bologna, Italy; 2Dipartimento di Scienze Neurologiche , University of Bologna, Bologna, Italy; 3Institute of Neurological Sciences, National Research Council, Cosenza, Italy

Time-consuming manual selection of regions of interest is currently one limiting factor in the clinical use of DTI. Methods exist to automatically identify deep brain structures using high resolution images. We evaluated the possibility of automatically segmenting structures of deep grey matter in diffusion tensor maps using high resolution T1-weighted images. We compared manual and automatic segmentation in ten controls. Results were indistinguishable for quantification of mean diffusivity in thalamus, pallidus and putamen, but not caudate. Using automatic segmentation, three patients with well-characterized neurological disorders showed differences compared to controls, in line with those expected from the known pathologies.

15:00         4705.     Reliability and Validity of MRI-Based Automated Volumetry Software Relative to Manual Measurement of Subcortical Structures in HIV-Infected Patients from a Multisite Prospective Study

Jeffrey Dewey1, George Han2, Troy Russell1, Jared Price1, Daniel McCaffrey1, Ekta Sem1, Joy Chinazom Anyanwu1, Charles Guttmann1, Bradford Navia3, Ronald Cohen2, David Tate1

1Center for Neurological Imaging, Brigham and Women's Hospital, Boston, MA, USA; 2Warren Alpert School of Medicine at Brown University, Providence, RI, USA; 3Tufts New England Medical Center, Boston, MA, USA

While software packages designed to automatically identify subcortical structures can greatly increase the efficiency of volumetric studies, notable differences in the performance of these tools have previously been reported. The purpose of this study was to compare the accuracy and consistency of volumetric data for several clinically relevant subcortical structures obtained using three methods: manual tracing, Freesurfer, and SPM. Freesurfer output was more accurate and consistent relative to manual tracings than that of SPM in the majority of structures. However, the inaccuracy and variability of both tools suggest that researchers supplement their use with visual inspection to ensure reliable data.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 103

13:30         4706.     Calculation of Optic Nerve Dimensions Using Gaussian Fitting of MR Images

Li Sze Chow1, Lauren Wallis1, Nigel Hoggard1, Simon J. Hickman2, Martyn N.J. Paley1

1Academic Unit of Radiology, University of Sheffield, Sheffield, UK; 2Department of Neurology, The Sheffield Royal Hallamshire Hospital, Sheffield, UK

The aim of this study was to develop a program to accurately calculate the optic nerve diameter, area and volume using Gaussian fitting of the acquired MR images. The program will be used in a new study of optic neuritis on 1.5T and 3.0T MR systems with both T1- and T2-weighted 3D Spectral Presaturation Inversion Recovery (SPIR) sequences and much shorter scan times. This study has also shown that T2W images are suitable for measuring the actual optic nerve’s dimension; whereas T1W images can be used to measure the optic nerve and the sheath and CSF surrounding the nerve.

14:00         4707.     Multilevel Segmentation and Classication of MS Lesions

Alvina Goh1, Christophe Lenglet2, Mariappan Nadar3

1Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA; 2Center for Magnetic Resonance Research & Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA; 3Siemens Corporate Research, Princeton, NJ, USA

This paper focuses on the segmentation and classification of multiple sclerosis lesions in magnetic resonance images. As MRI is the primary tool used in the diagnosis of multiple sclerosis, there is substantial interest in developing an algorithm that will detect lesions from such images. We present a flexible framework in which segmentation and classification are integrated. We assume that we are given a training set of MRI images which contains manually labeled regions of MS lesions. The algorithm we used combines two effective techniques from the computer vision literature: graph-based bottom-up methods and top-down generative models.

14:30         4708.     Computer-Aided GBM Tumor ROI Contouring and Mapping Framework for Structural and Physiological MR Images in a Multi-Center Clinical Trial

Jing Huo1, Matthew S. Brown1, Jeffry R. Alger2,3, Whitney B. Pope3, Hyun J. Kim3, Kazunori Okada4, Jonathan G. Goldin3

1Department of Radiological Sciences , UCLA, Los Angeles, CA, USA; 2Department of Neurology, UCLA, Los Angeles, CA, USA; 3Department of Radiological Sciences, UCLA, Los Angeles, CA, USA; 4Computer Science Department, San Francisco State University, San Francisco, CA, USA

The main contribution is to develop a computer-aided 3D multi-modal tool for clinical trials with GBM brain tumor. First we developed a 3D semi-automated segmentation tool to contour the tumor on T1-weighted contrast-enhanced volumetric images and then a 3D tumor ROI mapping tool to map the tumor contours from T1w images onto all the physiological images including dynamic contrast enhance (DCE) images, dynamic susceptibility contrast-enhanced (DSC) and diffusion-weighted (DW) images. We applied the tool to about 650 scans and did the quantitative evaluation with a sub-group of 31 patients. 20 out of 31(64.5%) have over 90% overlap ratio.

15:00         4709.     Model Error Maps as Robust Features for T1/T2-Weighted Data Segmentation

Umesh Suryanarayana Rudrapatna1, Annette van der Toorn1, Ivo A. Tiebosch1, Josien P.W Pluim1, Rick M. Dijkhuizen1

1University Medical Center Utrecht, Utrecht, Netherlands

T1- and T2-weighted data segmentation has hitherto relied upon parametric maps and intensities as primary features. The parametric maps contain the necessary information explicitly, but become unreliable at low SNR. To overcome this hurdle, building on estimation theory results, we propose using functions based on fitting-errors when specific relaxivities are assumed. This approach leads us to a simpler linear estimation problem and provides for incorporation of prior knowledge about relaxivities, the reliability of which does not critically affect the outcome. Feature selection filters, the results of which generalize to a broad class of supervised and unsupervised learning scenarios testify the merits of this strategy.

 


 
Analysis of Dynamic Processes
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 104

14:00         4710.     Motion Correction for Perfusion Weighted Images in Stroke: Approach and Impact on Quantification

Rakesh Mullick1, Dattesh Shanbhag1, Uday Patil1, Xiaodong Tao2

1Imaging Technologies Lab, GE Research, Bangalore, Karnataka, India; 2Imaging Technologies Lab, GE Research, Niskayuna, NY, USA

Head motion while imaging stroke, neoplasic and neuro-degenerative disease is often observed during routine clinical imaging. Even with head stabilization, involuntary head movement can cause image artifacts leading to incorrect diagnosis. These artifacts have acute effects in select (extended duration) image sequences targeted to acquire spatio-temporal data like perfusion-weighted imaging and functional imaging scans. It is therefore imperative to address motion artifacts either early in the imaging chain or through a post-processing step. In cases of acute stroke, where time to image is of utmost importance, the extended duration of scan due to use of navigators precludes their use and places more importance on retrospective motion correction through image segmentation/registration techniques. In this work we present an approach based on image registration to align the spatio-temporal data, evaluate the impact on quantification of stroke related perfusion maps. The underlying challenge to correct and evaluate motion artifacts is further discussed.

14:30         4711.     Model-Based Automatic Detection of the Anterior and Posterior Commissures on MRI Scans

Babak A. Ardekani1,2, Alvin H. Bachman1,3

1Center for Advanced Brain Imaging, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, USA; 2Department of Psychiatry, New York University School of Medicine, New York, USA; 3Emeritus Professor, City College of CUNY, New York, USA

A model-based fully automatic algorithm is presented for detection of the anterior and posterior commissures (AC/PC) on 3D MRI scans. The algorithm has several advantages over previously published methods for solving this problem. It is fast, accurate, and robust in the presence of image artifacts. It does not rely on any specific image contrast or location of the corpus callosum. It is flexible in its definition of these landmarks (e.g., center versus edge of the AC/PC cross-section with the mid-sagittal plane). It relies on a relatively small number of parameters whose default values rarely need to be changed.

15:00         4712.     MARM: Multiscale Adaptive Regression Models for Neuroimaging Data

Yimei Li1, Hongtu Zhu2, Dinggang Shen3, Songyuan Tang4, Weili Lin3

1Biostatistics, UNC-CH, USA; 2Biostatistics and Biomedical Research Imaging Center, UNC-CH, Chapel Hill, NC, USA; 3Radiology and BRIC, UNC-CH, USA; 4UNC-CH,, Radiology and BRIC, USA

We develop a multiscale adaptive regression model for spatial

15:30         4713.     Statistic Model of Respiratory Motion by Using Dynamic MRI

Gang Gao1, Jamie McClelland1, Dave Hawkes1

1Centre for Medical Image Computing, University College London, London, England, UK

The accurate delivery of medical treatments to internal organs (e.g. MR guided intervention) that are subject to considerable respiratory motion has proved to be difficult. A motion model that can predict the internal motion from respiratory surrogate signals (e.g. the displacement of points on the skin surface) can help improve this situation. we are presenting a method of building respiratory motion models using the statistical technique called CCA and dynamic MRI. In this abstract, we have demonstrated that the MR-based CCA models can accurately predict the internal organ motion from respiratory surrogates measured from the skin surface. Additionally, we have compared the CCA model with a previously-reported PCA-based modelling technique by using the same MR data. The experimental results show the CCA model is superior to the PCA model in 3 out of 4 cases and appears to be more stable than the PCA model.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 104

13:30         4714.     Automatic Macro-Vessel-Minimization Using Independent Component Analysis and Local Scaling Functions

Gernot Reishofer1, Stephen Keeling2, Robert Merwa3, Christian Enzinger4, Stefan Ropele4, Rudolf Stollberger3, Franz Ebner5

1Department of Radiology / MR-Physics, Medical University of Graz, Graz, Austria; 2Institute for Mathematics and Scientific Computing, University of Graz, Graz, Austria; 3Institute of Medical Engineering, Graz University of Technology , Graz, Austria; 4Department of Neurology, Medical University of Graz, Graz, Austria; 5Department of Radiology / Division of Neuroradiology, Medical University of Graz, Graz, Austria

Independent component analysis has the potential to separate the signal assigned to macro vessels from tissue signal in DCE-MRI data. This enables an algorithm for minimizing macro-vessel signal in perfusion imaging to avoid overestimation of hemodynamic parameters. We set out to eliminate user dependency by automating the selection of appropriate ICs using a local scaling function technique. Furthermore we preserve the static tissue signal of the macro vessel representing IC by editing the time dependent mixing matrix in the ICA model before the back transformation is performed. The implemented algorithm is fast and stable and therefore applicable for clinical use.

14:00         4715.     Hemodynamic Characterization of the Trans-Thoracic Circulation by Contrast-Enhanced Magnetic Resonance Imaging

Massimo Mischi1, Harrie CM van den Bosch2, Jacques A. den Boer, Jan Verwoerd3, Rene JE Grouls2, Hendrikus HM Korsten2

1Eindhoven University of Technology, Eindhoven, Netherlands; 2Catharina Hospital; 3Philips Healthcare

A minimally-invasive characterization of the trans-thoracic circulation (TTC) by contrast magnetic resonance imaging (MRI) is presented and validated in vitro. The clinical feasibility of the method is also tested with five healthy volunteers. A bolus of a paramagnetic agent is intravenously injected and detected by MRI in the right and left ventricles. A parametric deconvolution is designed for the estimation and hemodynamic interpretation of the TTC dilution impulse response. This permits in the assessment of the intra-thoracic blood volume as well as the ratio between contrast convection and dispersion in the TTC. The results are accurate and motivate further investigation.

14:30         4716.     Volume Tracking - A Novel Method for Visualization and Quantification of Cardiac Blood Flow

Johannes Töger1, Håkan Arheden1, Gustaf Söderlind2, Einar Heiberg1

1Clinical Physiology, Lund, Skåne, Sweden; 2Mathematics, Numerical Analysis, Lund, Skåne, Sweden

The detailed interactions between blood, myocardium, valves and vessels are still incompletely understood. Although three-dimensional, time-resolved Phase Contrast MRI promises greater insights into cardiac blood flow, no single solution to the visualization problem exists. In this study Volume Tracking, a novel method for visualization and quantification of cardiac blood flow is developed and validated.

15:00         4717.     Estimation of Left Ventricle Parameters from Cine MR Data: Fully Automatic Versus Manual Analysis.

Thomas Ki-Yong Broussaud1, Alain Nchimi1

1Medical Imaging Dept., CHC Saint-Joseph, Liège, Belgium

We present a study consisting in comparing the performances of automatic versus manual segmentation for estimating functional parameters of the left ventricle. The automatic analysis tested here consists in global detection of the left ventricle followed by local deformation of an active contours. Our study shows limitations of automatic analysis and supports quantitative evaluation of automatic analysis approaches.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 104

13:30         4718.     In Vivo Cardiac NMR Diffusion Weighted Imaging(DWI) for the Human Heart: Tackling Motion Issue with Temporal Maximum Intensity Projection(TMIP)-DWI and First Results in Humans

Stanislas Rapacchi1, Pierre Croisille2, Magalie Viallon3, Denis Grenier1, Peter Kellman4, Han Wen4

1Creatis-LRMN, Université Lyon 1, INSA Lyon, Lyon, France; 2Hopital Cardiologique et Pneumologique L. Pradel, Lyon, France; 3Hopital Cantonal Universitaire de Genève, Genève, Switzerland; 4National Heart, Lung and Blood Institute, NIH, Bethesda, MD, USA

Diffusion weighted imaging in the heart is greatly affected by contractile motion and remains challenging to date. Stimulated-echo approaches have relatively low signal level and require complete beat-to-beat positional repeatability which may not be met in patients. With spin-echo techniques, Gamper et al. recently proposed a robust motion-compensated sequence. However, through-slice diffusion was still difficult to measure. From their work, we developed an alternative approach for DWI, where a number of single-shot images of the same diffusion weighting are acquired at a series of different time points in diastole, and these are projected along the temporal axis by maximum-intensity-projection (tMIP) to form a true DWI. Through quantifying the motion-induced signal loss in DWI of a single slice based on experimental myocardial strain, we show the validity of tMIP and preliminary results in free-breathing scans of volunteers.

14:00         4719.     Adaptive Trigger Delay Using a Predictive Model Applied to Black Blood Fast Spin Echo Cardiac Imaging in Systole

Brice Fernandez1,2, Julien Oster2,3, Maelene Lohezic1,2, Damien Mandry2,4, Olivier Pietquin2,5, Pierre-André Vuissoz2,3, Jacques Felblinger2,3

1Global Applied Science Lab., GE Healthcare, Nancy, France; 2IADI, Nancy-Université, Nancy, France; 3U947, INSERM, Nancy, France; 4CHU de Nancy, Nancy, France; 5IMS Research Group, Supelec Metz Campus, Metz, France

Cardiac-gated Fast Spin Echo (FSE) sequences with black blood preparation provide detailed anatomical information to clinical cardiac MR applications. However, the black blood preparation time is too long to allow this acquisition scheme to run in systole, hence black blood FSE are usually performed in diastole. Overcoming this limitation requires to predict the R-R interval to launch the preparation properly and to handle instantaneous heart rate variability. This approach has been implemented and tested on four healthy volunteers, and compared with fixed trigger delay (TD). Results demonstrate accurate depiction of the myocardium at end-systolic phase in black blood.

14:30         4720.     Doubled Scan Efficiency in Multi-Slice Real-Time Cine TrueFISP Cardiac Imaging by Pseudo-Continuous Sliding Slice Acquisition

Andreas Greiser1, Sven Zuehlsdorff2, Edgar Mueller1

1Siemens AG Healthcare Sector, Erlangen, Bavaria, Germany; 2Siemens Medical Solutions, Chicago, IL, USA

Real-time cine TrueFisp cardiac imaging offers multiple slice acquisitions within a single breathhold. Typically, the steady state preparation is established utilizing a full heartbeat per slice. Hence, only every other heartbeat is used to collect data. A simple elimination of the preparation heartbeats reduces the contrast of blood and myocardium in the first few phases. This work presents a novel method that shifts the slice position between consecutive phases by a distance small compared to slice thickness. High contrast is maintained throughout all cardiac phases providing whole heart coverage within a single breathhold.

15:00         4721.     3D Dynamic Contrast-Enhanced Using Undersampled Golden-Radial Phase Encoding

Claudia Prieto1, Sergio Uribe1, Reza Razavi1, David Atkinson2, Philipp Beerbaum1, Tobias Schaeffter1

1Division of Imaging Sciences, King's College London, London, UK; 2Centre for Medical Imaging Computing, University College of London, London, UK

A new acquisition and reconstruction strategy for 3D isotropic DCE-MRI has been proposed. The proposed method is based in a new undersampled dynamic acquisition which combines a 3D radial phase encoding trajectory with the golden angle profile order, providing explicit regularization for iterative reconstructions. The main advantages of this approach are: (i) it allows retrospective reconstructions with different temporal resolutions, (ii) it does not require bolus track previous scan and (iii) it reduces strike artefacts and noise in comparison with the non-explicit regularized reconstructions. The method was tested, using a 32-channel coil and iterative SENSE reconstructions, in phantoms and patients.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 104

13:30         4722.     Time-Resolved Contrast-Enhanced Radial Ghost MRA

Hyun Jong Jeong1, Ioannis Koktzoglou2, Christopher S. Eddleman3, John Sheehan4, James Carr4, Timothy John Carroll1,4, Robert Edelman5

1Biomedical Engineering, Northwestern University, Chicago, IL, USA; 2Radiology, Northshore University Hospital, Evanston, IL, USA; 3Neurological Surgery, Northwestern University, Chicago, IL, USA; 4Radiology, Northwestern University, Chicago, IL, USA; 5Radiology, North Shore University Hospital, Evanston, IL, USA

A novel time-resolved contrast-enhanced MR angiography technique is introduced. The technique does not require subtraction and uses ghost images to separate the vessels from background tissues. The SNR loss resulting from subtraction of pre-contrast images from the post-contrast frames is prevented. Based on inducing ghost artifacts arising from inconsistency in k-space data, this technique is combined with radial sliding window reconstruction for time-resolved imaging.

14:00         4723.     Time-Resolved MRA Using Radial Multi-Echo Sequence and Sliding Window Reconstruction

Hyun Jong Jeong1, Saurabh Shah2, Christopher S. Eddleman3, John Sheehan4, James Carr4, Timothy John Carroll1,4

1Biomedical Engineering, Northwestern University, Chicago, IL, USA; 2Siemens Medical Solutions, Chicago, IL; 3Neurological Surgery, Northwestern University, Chicago, IL, USA; 4Radiology, Northwestern University, Chicago, IL, USA

We introduce a technique to decrease the actual acquisition time to decrease the temporal footprint and achieve true acceleration for time-resolved MRA by taking multiple echoes per TR, acquiring a full 3D volume in 7 seconds without parallel imaging. Combined with radial sliding window reconstruction, we obtained time resolved MRA with frame rates comparable to clinical X-Ray DSA, resulting in complete separation of arterial and venous phases. The technique has been verified in flow phantoms as well as volunteers and patients in vivo.

14:30         4724.     Fast Imaging Sequence for Free-Breathing Planning in Cardiac Imaging

Tamer A. Basha1, Monda L. Shehata2, Nael F. Osman1,2

1ECE Dept, Johns Hopkins University, Baltimore, MD, USA; 2Dept of Radiology, Johns Hopkins University, Baltimore, MD, USA

In this work, we propose a fast black-blood pulse sequence which requires scan duration as short as one heartbeat. This can be used for free-breathing cardiac imaging planning, which helps to reduce the overall scan time and the number of breath-holds during the exam.

15:00         4725.     T2 Weighted Preparation with Selective Response: Contrast Mechanism for Dark Blood Imaging and Arterial-Venous Discrimination

Peter Kellman1, Anthony Z. Faranesh1, J. Andrew Derbyshire1, Logi Vidarsson2

1National Institutes of Health, Bethesda, MD, USA; 2The Hospital for Sick Children, Toronto, Canada

T2-selective imaging may be used to provide contrast between tissues with differing T2 values and to provide suppression of long T2 species. Conventional T2 mapping or linear combination filtering requires multiple T2 weighted acquisitions. It is possible to design a selective T2-weighted RF preparation which has the benefit of a single acquisition. Selective T2-preparations have been demonstrated for imaging the meniscus of the knee with short T2. Initial results for cardio-vascular application are presented for a new design approach based on adiabatic pulses and phase sensitive reconstruction. This method has potential applications to oximetry and other tissue classification.

 


 
Receive Arrays
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 105

14:00         4726.     Comparison of Large Phased Arrays Using Stacked Segments

Wolfgang Driesel1, André Pampel1, Toralf Mildner1, Stefan Hetzer1, Harald E. Möller1

1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

Medium-sized stacked combinations of loop coils with a microstrip transmission-line element (MTL) as basic elements for large coil arrays are compared in extensive computer simulations. The calculations indicate a good SNR performance and a potential for imaging with acceleration in all three directions.

14:30         4727.     Multi Arm Archimedean Coil for High Field MRI

Sofia Sanchez1, Silvia Sandra Hidalgo1, Sergio Enrique Solis1, Mario Rosas1, Alfredo Odon Rodriguez1

1CI3M, UAM Iztapalapa, Mexico, City, Mexico

Spiral coils have been used for various MRI applications as single-channel coils and array coils. Archimedes introduced a special type of spiral consisting of two arms or more. The Archimedean spiral geometry has not been studied for MRI applications according to the literature reported. Computer simulations of the magnetic field for different Archimedean spiral coil configurations were computed using a Finite Element Method. For comparison, the magnetic field of circular-shaped coil with similar dimensions was also performed. Archimedean coils showed higher magnetic field intensity than the popular circular coil at 300 MHz.

15:00         4728.     Noise Figure Limits for Circular Loop MR Coils

Ananda Kumar1,2, William Alan Edelstein1, Paul Arthur Bottomley1,2

1Radiology, Johns Hopkins University, Baltimore, MD, USA; 2Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, USA

Loop coils are fundamental building blocks of phased arrays. For phased arrays using large numbers of loops, loop size is critical in determining detection efficiency. As loop size decreases, coil noise becomes dominant and adversely affects realizable SNR by increasing system noise figure. There are consequent limits to SNR gains as array element number increases and element size shrinks. 1 dB noise figure contributions are reached for coils with radii 23 mm at 1.5T, 16 mm at 3T and 10 mm at 7T. Constructing arrays out of smaller coils than these at such fields is therefore of questionable value.

15:30         4729.     A High Temperature Superconducting (HTS) Coil for Imaging of Human Extremities

Hoon-Sin Cheong1, Ivo Volkov2, Neil Alford3, Chris Randell4, Jim Wild1, Martyn Paley1

1Academic Radiology, University of Sheffield, Sheffield, South Yorkshire, UK; 2Materials, London South Bank University, London, Middlesex, UK; 3Materials, Imperial College London, London, Middlesex, UK; 4MRI, Pulseteq Limited, Gloucester, Gloucestershire, UK

A 10-turn, 70mm YBCO spiral surface coil was designed for clinical imaging of human extremities at 0.2T. Liquid nitrogen was added to cool the coil to 81K during image acquisitions. The phantom imaging test results show the YBCO coil has SNR advantages of 270% and 80% when compared to an equivalent copper coil at room temperature and 81K respectively. The in-vivo human hand images show good details of the bones and tissue structures. This means the YBCO coil was capable of producing useful anatomical images of human extremity even in a low-field environment.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 105

13:30         4730.     Hybrid Decoupling for RF Coils

dashen chu1, ricardo matias, Scott Lindsay, robert stormont, eddy boskamk, saban kurucay

1MR, ge healthcare, waukesha, wi, USA

The work presented in this abstract is the study of a new decoupling circuit for RF surface coils for MR imaging. The new decoupling circuit is designed to operate in two modes, one is for normal mode in which the appropriate DC biasing is present and the other one is abnormal mode in which the DC biasing is absent. The study was focused on the comparison between the characteristics of traditional active decoupling circuit and the proposed hybrid circuit. We provided experimental testing results including impedance data and temperature rise measurement due to RF heating.

14:00         4731.     Model-Based MRI Coil Tuning Algorithm

Liang Liu1, Charles Bouman1, Thomas Talavage1, Victor Taracila2, YunJeong Stickle2, Limin Feng2, Pei H Chan2, Fraser Robb2

1Purdue University, West Lafayette, IN, USA; 2GE Healthcare, Aurora, OH, USA

Model-based tuning algorithm for MRI coil array

14:30         4732.     Frequency Division Multiplex for Phased Array Receive Coils

Joseph Iannotti1, Steven Go1, Kevin Dufel1, Bill Platt1, Eric Fiveland1

1General Electric Global Research Center, Niskayuna, NY, USA

A novel way of combining multiple receive channels into a single coax cable reducing bulk and simplifying cable routing constraints while allowing for parallel image acquisition

15:00         4733.     Coil Performance Vs. Preamplifier Location in the MR Phased Array

Randy O. Giaquinto1, Joseph E. Piel1

1GE Global Research Center, Niskayuna, NY, USA

A study is presented comparing the performance of two coil arrays, with preamplifiers located on the coil, and remotely. In our particular setup, it was found that remote preamps may result in a slight increased image SNR, at the expense of increased cable bulkiness and decreased patient ergonomics.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 105

13:30         4734.     A High Throughput 8 Channel Mouse Probehead for 9.4 T

Titus Lanz1, Matthias Müller1, Hannah Barnes2, Jürgen E. Schneider2

1RND, Rapid Biomedical, Rimpar, Germany; 2Cardiovascular Medicine, University of Oxford, Oxford, UK

Rodent MRI is well established but still puts substantial demands on combining highly sophisticated experimental setups with careful animal handling. Rodents, in particular disease models, may be very sensitive to the anaesthetic burden, and, therefore, minimal scan time is essential. In this work we present an 8 channel 9.4 T mouse probehead optimized for high throughput providing simple and speedy positioning and connecting up. The total setup time for the probehead including positioning and wiring is reduced to below 1 min. Probehead and animal can be handled completely independently.

14:00         4735.     A 16-Channel Rat-Body Array Coil with an Integrated Birdcage Transmitter at 7T

Martin Tabbert1, Marco Motz1, Marcos Lopez2, Erhard Pfrommer1, Sven Junge1

1Bruker BioSpin MRI GmbH, Ettlingen, Germany; 2Universität Würzburg, Germany

With this study we present a novel 16 channel array-coil with a transmitter coil for investigations on rats which is optimized for rat abdominal imaging. Decoupling electronics, phase shifters and preamplifiers are included in the coil. The receive-signals are amplified with 16 built-in low-impedance preamplifiers. An insulating network that reduces the coil-coupling by additional 6dB was designed. Compared to a quadrature resonator, the coil shows an SNR improvement of the 16-channel coil in the center of a transversal slice by a factor of 1.1 up to 2.5 regarding the periphery of the VOI. All advantages of parallel imaging techniques on small animals can be utilised, e.g. rats can be examined in shorter times by using accelerated 2D/3D imaging.

14:30         4736.     An Array RF Coil for Rabbit Thoracic Arteries Imaging at 200MHz

Raimo PJ Joensuu1

1AstraZeneca, Molndal, Sweden

A 4-channel array coil for rabbit’s thoracic arteries imaging at 4.7T has been constructed. The coil elements were made of a semi-rigid coaxial cable where the outer shield constitutes the receiver loop. In the Tx mode the center conductor is coupled to the circuit which changes the total inductance and detunes the coil. l/4 –cables are used to transmit the signal to the preamplifier and they also to transmit Tx/Rx control current to PIN-diodes. The l/4 –cables are covered with a resistive coating to curb sheet currents and Tx radiation scattering. Very good shielding from external disturbances has been demonstrated.

15:00         4737.     A Four Channel SENSE Microcoil Array with Integrated Physiology Support System for Imaging Four Mouse Brains

Marcelino Bernardo1, Peter Choyke2

1Molecular Imaging Program, NCI, SAIC-Frederick, Inc., Bethesda, MD, USA; 2Molecular Imaging Program, National Cancer Institute, Bethesda, MD, USA

A four channel SENSE mouse brain microcoil array with integrated physiology support and monitoring for imaging four mice simultaneously is presented. Phantom and in vivo images are have been acquired which illustrates the utility of the system for screening a large cohort of orthotopic and genetically engineered mouse brain tumor models.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 105

13:30         4738.     A Semi-Flexible 32-Ch RF Coil Array for Clinical 3T Brain Imaging

Yu Li1, Matthias Gyori1, KD McClellan1, Charlie Saylor1, Arne Reykowski1

1Advanced Concept Development, Invivo Diagnostic Imaging, Gainesville, FL, USA

In this study, a semi-flexible 32-channel RF coil array was developed for clinical brain imaging. In this coil, a semi-flexible mechanical structure was used to minimize the gap between the head and coil elements for different patients. The alignment of 32 coil elements was optimized to minimize the coil loss and overall coupling. It was demonstrated that this coil gives lower SENSE g-factor and higher SNR in depth compared with a standard eight-channel clinical RF coil in clinical brain imaging applications.

14:00         4739.     An Improved 28 Channel Coil Array for Optic Nerve Imaging

Robb Merrill1, J. Rock Hadley1, Emilee Minalga1, Dennis Parker1, Sathya Vijayakumar1, Seong-Eun Kim Choi1, Laura Bell1, John Rose2,3

1Dept. of Radiology (UCAIR), Salt Lake City, UT, USA; 2Neurovirology Laboratory VASLCHCS; 3Brain Institute

This work describes an RF coil optimized for imaging the Optic Nerve on a Siemens 3T MRI scanner. The coil was constructed using two fiberglass formers that fit together to maintain close coupling near the eyes for any arbitrary head size. The 28 coil elements were circular, constructed from 14-gauge wire, and arranged in a soccer ball layout to surround the entire head. Phantom studies showed that the coil provided ~35% greater rSNR at the optic chiasm and ~300% near the orbits compared to the 12-channel commercial coil. The improvement in rSNR allows performance of high resolution DTI.

14:30         4740.     Coil System for Optimal MR Mammography and MR-Guided Intervention

Bernadette Marie Kaufman1, Yoshinori Hamamura1, Ashok Menon1, Jovan Jevtic2

1MR, Invivo, Pewaukee, WI, USA; 2Milwaukee School of Engineering, Milwaukee, WI, USA

MR Mammography is a rapidly growing area of diagnostic imaging. It has been found useful for screening, diagnosis, staging, therapy-monitoring and pre-surgical planning. With the advent of high-channel count MR systems and parallel imaging techniques, RF technology must keep pace. Based on the different needs for excellent diagnostic MR imaging and interventional capability, a coil system was developed to meet both sets of requirements. A diagnostic coil was developed to exploit RF technology to achieve high signal and parallel imaging capability. An interventional coil was paired with it to achieve high SNR imaging and maximum interventional access.

15:00         4741.     Simplified RF Modeling of Coil Arrays Composed of Cylindrically Arranged Modules

Andre Pampel1, Wolfgang Driesel1, Harald E. Moeller1

1Nuclear Magnetic Resonance Unit, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

A simplified coil-modeling method for phased-array coils composed of cylindrically arranged elements was investigated. Provided a good decoupling between the coil elements is achieved, it is shown to be sufficient to calculate the electromagnetic fields of only one stacked element by full-wave electromagnetic simulation. Considering the boundary conditions describing the whole coil in these calculations, the transmit properties of the remaining elements can be obtained using matrix rotations thus considerably saving computation time and data storage space during the coil optimization process.

 


 
Receive Coil Development
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 106

14:00         4742.     SNR Benefits of Surface Coil Lift-Off at High Magnetic Field Strength

Qi Duan1, Graham Wiggins1, Bei Zhang1, Riccardo Lattanzi1, Bernd Stoeckel2, Daniel K. Sodickson1

1Radiology, Center for Biomedical Imaging, NYU School of Medicine, New York, NY, USA; 2Siemens Medical Solutions USA Inc., New York, NY, USA

This work demonstrates that SNR gains deep in an object can be achieved with a single loop coil by lifting the coil off the object surface. Experimental SNR measurements on a 3T Siemens Tim system were compared with full-wave electrodynamic simulations incorporating a realistic noise model. Close agreement between experiment and simulation was observed. Lift-off-related SNR benefits had a notably asymmetric distribution, with the greatest gains occurring on the far side of the object, opposite to the position of the coil.

14:30         4743.     A Novel Metamaterial Transmit/receive Coil Element for 7 T MRI – Design and Numerical Results

Jochen Mosig1, Achim Bahr1, Thomas Bolz1, Mark E. Ladd2

1RF&Dosimetry, IMST GmbH, Kamp-Lintfort, Nordrhein-Westfalen, Germany; 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Nordrhein-Westfalen, Germany

In this work numerical results for the novel usage of a metamaterial transmission line resonator as a transmit/receive coil are presented. On the basis of resonant antennas a coil element is designed for 7 Tesla. The metamaterial element consists of 4 unit cells, which are optimized for a series mode zeroth-order resonance. This resonance induces a constant current distribution along the element, resulting in a homogenous magnetic field in a larger volume compared to a conventional microstrip transmission line element. The metamaterial element can be easily extended by adding additional unit cells.

15:00         4744.     Improving SNR and RF by Adding a Stripline to Endorectal Coil for the 7T

Catalina S. Arteaga1, Bob van den Bergen1, Peter L. Luijten1, Uulke A. van der Heide1, Dennis W.J. Klomp1

1Radiology and radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands

Theorically adding tranceive/receive elements will increase the SNR and optimize the RF power deposition. We added a stripline into an endorectal loop coil system for the 7T MR. The obtained results proved that indeed the second element increased the SNR and homogeneity of the transmit field. Simulation results for the transmit field in quadrature and anti-quadrature and receive fields for the loop coil and the stripline were obtained showing similar results to the MR measurements. Simulations were also obtained for the calculation of the SAR for only the loop and the combined coils system obtaining a SAR max of 42% less for the combined system than for the loop only.

15:30         4745.     Trap Design Performance for RF Coils for Dual-Frequency MRI & MRS

Arash Dabirzadeh1, Mary Preston McDougall2

1Electrical Engineering, Texas A&M University, College Station, TX, USA; 2Biomedical Engineering, Texas A&M University, College Station, TX, USA

The performance of a trap design for multi-nuclear coils is studied, with particular emphasis on its potential application in designing second-nucleus coils that are “insertable” into existing proton coils without modification. Modeling, imaging, and spectroscopy at 4.7T demonstrate the insertability of a P-31 coil into surface, volume, and array proton coils. This work has particular applicability at high fields, where spectroscopy holds great promise and proton coil design becomes more complex.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 106

13:30         4746.     Design of a Patch Antenna for Creating Traveling Waves at 7 Tesla

Bei Zhang1, Graham Wiggins1, Qi Duan1, Daniel K. Sodickson1

1Radiology, Center for Biomedical Imaging, NYU School of Medicine, New York, NY, USA

Recently the use of traveling waves for high field MRI has been suggested as a promising method for large FOV imaging and comparatively uniform excitation. In the traveling wave system, conventional volume coils and surface coils used as the transmitter/receiver are replaced by a patch antenna, a kind of directional electromagnetic antenna, placed a considerable distance from the sample. Here, we provide details of our experience in the practical design of a patch antenna, and document its properties for traveling wave generation in a 7 Tesla scanner bore.

14:00         4747.     Low Eddy Current RF Body Coils

Ed Boskamp1, Bijay Shah1, Ken Rohling2, Anton Linz1

1GE Healthcare, Waukesha, WI, USA; 2GE corporate R&D, Schenectady, NY, USA

In birdcage RF Body coils the endrings are typically in a high dB/dt area of the gradient coil. Both rungs and endring segments can be slotted to prevent gradient eddy currents, but it is not clear how to cut the transfer area where the rungs meet the endring. This paper examines several shapes of this transfer area and their impact on SNR and heat generated by the eddy currents.

14:30         4748.     Litz Wire Radiofrequency Coils for Hyperpolarized Noble Gas Imaging of Rodent Lungs at 74 MT

William Dominguez Viqueira1,2, Warren Berger1, Juan Parra-Robles3, Giles E. Santyr1,2

1Imaging Laboratories, Robarts Research Institute, London, Ontario, Canada; 2Medical Biophysics, University of Western Ontario, London, Ontario, Canada; 3Academic Unit Of Radiology, University of Sheffield, Sheffield, UK

SNR at low magnetic field strength can be improved by reducing RF coil noise using Litz wire coils. In this work we compare coils built with four different wires types, conventional copper wire vs. three different Litz wire types for low field hyperpolarized noble gas imaging of rat lungs. The comparison was conducted at 866 kHz and 2.385 MHz corresponding to Larmor frequencies of 129Xe and 3He at 73.5 mT. The quality factors and the signal to noise ratio (SNR) for each coil at each frequency were measured. Results demonstrate the advantages of Litz wire over conventional copper wire at these frequencies.

15:00         4749.     A Numerical Comparison of Conservative E-Field Shield Designs in a Solenoidal Coil

Bu Sik Park1,2, Andrew G. Webb3,4, Christopher M. Collins2,5

1Bioengineering , The Pennsylvania State University, Hershey, PA, USA; 2Radiology, The Pennsylvania State University, Hershey, PA, USA; 3Bioengineering, The Pennsylvania State University, University Park, PA, USA; 4Radiology, Leiden University Medical Center, Leiden, Netherlands; 5Bioengineering, The Pennsylvania State University, Hershey, PA, USA

A method is presented to decrease power loss and heating in conductive samples using strategically shaped and positioned passive pieces of copper conductor, referred to here as “Ec shields,” within a solenoidal coil to decrease the conservative electric field (Ec) with little impact on the B1 field. Here we use numerical calculations to evaluate several versions of our design, as well as one previously-published design (the loop-gap cylinder) in their ability to decrease sample power loss with minimal impact on B1.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 106

13:30         4750.     Magnetron Volume Coil for Magnetic Resonance Imaging of Rodents

Jaime Fabian Vazquez1, Oscar Rene Marrufo1, Sergio Enrique Solis1, Silvia Sandra Hidalgo1, Alfredo Odon Rodriguez1

1CI3M, UAM Iztapalapa, Mexico, City, Mexico

A transceiver volume coil with slotted end-rings and similar to the standard birdcage is proposed in this work. Unlike the traditional birdcage coil, our coil design was formed with two slotted surface coils connected via rungs like the traditional birdcage coil. The coil end-rings were formed with circular slots evenly distributed. A coil prototype was developed to work at 7T and quadrature driven for rat body imaging. Phantom images showed an important improvement in performance compared to the birdcage coil. Rat body images were acquired to prove the viability of this coil design for high field MRI applications.

14:00         4751.     A Novel 4 T Double Tuned (1H-23Na) Surface Tem Resonator

Assunta Vitacolonna1, Sandro Romanzetti2, Nadim Jon Shah3,4, Marcello Alecci1

1Dipartimento di Scienze della Salute, University of L'Aquila, L'Aquila, Italy; 2Institute of Medicine,, Research Centre Jülich, Jülich, Germany; 3Institute of Medicine, Research Centre Jülich, Jülich, Germany; 4Faculty of Medicine, Department of Neurology, RWTH Aachen University, JARA, Aachen, Germany

A novel double-tuned TEM resonator suitable for the imaging of protons and sodium is presented. The coil was constructed based on a micro-strip design and was bench-tested and demonstrated 3 modes of resonance; the first was tuned for sodium and the third for protons. Images are presented from tests at 4 T.

14:30         4752.     A Simplified Procedure for Remote Tuning Local MRI Coils for Maximum Signal-To-Noise Ratio

William J. O'Reilly1, Paul K. Jackson2, Andrzej Jesmanowicz3

1Mercury Computer Systems, Inc, Chelmsford, MA, USA; 2Mercury Computer Systems, Inc, Reston, VA, USA; 3Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA

A procedure is described to develop a simple method of achieving the best signal-to-noise ratio for a coil-amplifier system. The method uses a remote adjustment of coil impedance under load inside the magnet without the need of using a network analyzer. The specialized graphical display was created to simplify the procedure and minimize the time to measure results. Four different preamplifiers were tested on a 3T scanner with a single surface coil.

15:00         4753.     Counter Rotating Current Coil for 3-D Eye Growth Study of Infant Rhesus Monkeys

Flora S. Ip1, Jenny Huang2, Kurt H. Bockhorst3, Kishore Mogatadakala3, Terry L. Blasdel4, Ponnada A. Narayana3, Earl L. Smith III2, Jarek Wosik1

1Texas Center for Superconductivity and Electrical Engineering Department, University of Houston, Houston, TX, 77204-5002, USA; 2College of Optometry, University of Houston, Houston, TX 77204-2020, USA; 3Diagnostic and Interventional Imaging, Houston Medical School, University of Texas Health Science Center, Houston, TX 77204-2020, USA; 4Animal Care Operations, University of Houston, Houston, TX 77204-2020

We report on the development of a clinically practical surface coil with sufficiently high SNR and large FOV suitable to perform MRI study and quantification of the effects of monocular form-deprivation on the pattern of peripheral refractive errors and eye shape in developing rhesus monkeys using a 7 T Bruker MRI scanner. The coil was designed to fit an infant head size and its design is based on counter rotating currents resonator concept. It consists of two 180 deg. rotated split copper squares separated by 15-mil dielectric substrate. Performance of the coil was tested and also compared with a single loop surface and volume coils. As expected from simulations, the coil exhibits high SNR combined with relatively large FOV.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 106

13:30         4754.     Low E-Field and Low Acoustic Birdcage Coil Design

Saikat Saha1

1GE Healthcare, Florence, SC, USA

This abstract presents a novel design of a low E-field and low acoustic Birdcage type of coil. In this coil, wider rungs with cutouts and or slits have been implemented at the highest eddy current (from the gradient coil interaction) locations to minimize the acoustic vibrations. The wide nature of the rungs reduces the patient loss and hence the SAR and the strategic placement of the cutouts control the bore noise to a great extent.

14:00         4755.     Reduced Sample Heating in High Field Micro-MRI Using a Copper Wire  Shield: Experimental and Numerical Results

Bu Sik Park1,2, Thomas Neuberger3, Andrew G. Webb3,4, Don C. Bigler5, Christopher M. Collins2,5

1Bioengineering , The Pennsylvania State University, Hershey, PA, USA; 2Radiology, The Pennsylvania State University, Hershey, PA, USA; 3Bioengineering, The Pennsylvania State University, University Park, PA, USA; 4Radiology, Leiden University Medical Center, Leiden, Netherlands; 5Bioengineering, The Pennsylvania State University, Hershey, PA, USA

In high field microimaging, sample power loss can cause significant temperature increases (ÄT), and the conservative electric field (Ec) can be a significant factor in the total sample electric field (Et). Based on previous research, we introduce a simple method to decrease sample power loss and related ÄT with minimal impact on the RF magnetic field (B1) distribution by using passive copper wires to shield the sample from the Ec of the coil. Numerical calculations show greatly-reduced Et in the sample with little effect on B1. Experimental measurement of ÄT showed it to be about 60% lower with the Ec shield for several different input powers.

14:30         4756.     Validation of Electromagnetic Field Simulation for MR Coil Design at 3 Tesla

Wolfgang Loew1, Georg Strauss2, Mika W. Vogel3

1Advanced Medical Applications Laboratory, GE Global Research , Garching n. Munich, Bavaria, Germany; 2Electrical Engineering, Information Technology, University of Applied Sciences Munich, Munich, Bavaria, Germany; 3Advanced Medical Applications Laboratory, GE Global Research, Garching n. Munich, Bavaria, Germany

To reduce labor costs new methods in MR coil development need to be introduced in the design phase. Electromagnetic field simulation software is a promising tool to accomplish the task. In this work, an EM-software was evaluated and compared with measurement results. For implementation as a new design tool, the software is optimized to match network measurements. In order to achieve reproducible results an experiment is designed to incorporate the settings match simulation and measurement.

15:00         4757.     Slotted End-Ring Volume Coil for Small Animal Magnetic Resonance Imaging at 7T

Oscar Rene Marrufo1, Sergio Enrique Solis1, Silvia Sandra Hidalgo1, Alfredo O. Rodriguez1

1CI3M, UAM Iztapalapa, Mexico, City, Mexico

A volume coil based on the high frequency cavity resonator is presented in this paper for whole-body MRI of rodents at 7 Tesla. This coil design has been previously tested on phantoms at 170 MHz (4T for protons) with standard spin echo sequences. The encouraging results obtained motivated us to develop a whole-body coil for rodents for higher field Magnetic Resonance Imaging. This coil design operates in the transceiver mode and was designed for small biological samples. Phantom data showed a performance improvement over the birdcage coil. Body rat images were acquired proving its viability for high field MRI applications.

 


 
Transmit Array Technology
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 107

14:00         4758.     Comparison of Coil Realisations for Applications Employing Parallel Excitation

Jörg Felder1, Sandro Romanzetti1, Marcello Alecci2, N. Jon Shah1,3

1Research Centre Jülich, Jülich, Germany; 2Scienze e Tecnologie Biomediche, Università di L'Aquila,, L'Aquila, Italy; 3Faculty of Medicine, Department of Neurology, RWTH Aachen University,  JARA, Aachen, Germany

Parallel excitation frequently employs volume coils consisting of single TEM resonator elements. However, this structure excites a transmit field which is closely confined around the conductors. A geometry known from antenna engineering, the bow-tie, can be employed to spatially expand the transmit field while maintaining the desired properties such as low inductive inter-element coupling and low geometry factor. Arrays consisting of bow-tie elements thus represent a veritable alternative for high field <B>B</B>1 shimming and transmit SENSE applications.

14:30         4759.     Alternating Impedance Element for 7T Multi-Channel Transceive Coil

Can Akgun1, Lance DelaBarre1, Carl J. Snyder1, Jinfeng Tian1, Anand Gopinath2, Kamil Ugurbil1, John Thomas Vaughan1

1University of Minnesota-Center for Magnetic Resonance Research, Minneapolis, MN, USA; 2Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities, Minneapolis, MN

The development and advancement of multi-channel transceiver coils has provided a means for signal transmission and reception at high magnetic fields. In these arrays, microstrip lines have been successfully implemented as magnetic field propagating elements. However, in-homogeneities at high fields demand the further development of these coils. To flatten the B1+ field along z-direction, a multi-section alternating impedance microstrip circuit is investigated. Imaging and simulation results obtained with these coils at 7T for phantoms and in the head are presented.

15:00         4760.     Shielded Microstrip Head Array at 7T

Bing Wu1, Chunsheng Wang1, Douglas Kelley2, Duan Xu1, Daniel Vigneron1,3, Sarah Nelson1,3, Xiaoliang Zhang1,3

1Radiology&Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA; 2GE Healthcare, San Francisco, CA, USA; 3UCSF/UC Berkeley Joint Group Program in Bioengineering, SanFrancisco&Berkeley, CA, USA

In most of ultra-high field microstrip array designs, the ground planes of microstrip elements are separated to minimize their mutual coupling. Practically, due to the space limitation, the size of ground planes of the microstrip elements is usually not large enough to become a “true” ground, the array may suffer from cable resonance, lower Q factors and imaging quality degradations. In this work we present an approach to improve the performance of such transceiver arrays by introducing RF shields outside the microstrip array and the feeding coaxial cables. With this improvement, reduced interaction among cables, better resonance stability, better Q-factors and thus improved imaging quality are achieved

15:30         4761.     Using Separated Volume Transmit and Local Receiver Arrays for Body Imaging at 7T

Carl Jason Snyder1, Lance DelaBarre1, Jinfeng Tian1, Can Akgun1, Greg Metzger1, Steen Moeller1, Kamil Ugurbil1, J. Thomas Vaughan1

1University of Minnesota, Minneapolis, MN, USA

To minimize known coil losses at higher field strengths, we developed a conservatively-sized volume stripline/TEM array for body imaging at 7T. Active PIN diode detuning allows it to be used in conjunction with local receive-only arrays. This TEM array is also a clamshell design, allowing it be either used as a whole- or half-volume array.

13:30         4762.     An 8-Channel Rat-Body Array Coil for Transceive at 9.4T

Martin Tabbert1, Daniela Schinko1, Johannes Schneider1, Peter Ullmann1, Hans Post1, Sven Junge1

1Bruker BioSpin MRI GmbH, Ettlingen, Germany

This work discusses the development of a novel 8 channel array-coil for Transmit-SENSE applications at 9.4 T, which is optimized for investigations on rats. Every coil is decoupled from four neighbour coils by using geometrical or transformer decoupling. The remaining three coils are decoupled from their geometrical arrangement. For the measurements, an 8-channel TX/RX-switch was used. The results of accelerated imaging techniques show images without limitations of artefacts up to an acceleration factor of 3. Together with a multi-channel MRI-system, parallel transmission including PEX is possible. This allows undersampling and shortening of the k-space trajectory. Individual pulse shapes for each TX coil element are selectable.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 107

14:00         4763.     Calibration of Transceive-Array RF Power Using Lanthanide Shift Agents

Andrew T. Curtis1,2, Ravi S. Menon1

1Center for Functional and Metabolic Mapping, Robarts Research Institute, London, Ontario, Canada; 2Medical Biophysics, University of Western Ontario, London, Ontario, Canada

Parallel transmit arrays for high field MRI require extensive calibration to mitigate standing wave phase interaction effects. A power calibration method using NMR-active samples integrated into the coils is described and prototyped. It is simple, fast, robust, and solves an important first step in the transmitter array calibration (and B1+ mapping) process.

14:30         4764.     Boosting B1+ Efficiency for RF Transmit Surface Elements by a Radiative Antenna Design

Alexander J. Raaijmakers1, Jan J. W. Lagendijk1, Dennis W. Klomp2, Bob van den Bergen1, Cecilia Possanzini3, Paul R. Harvey3, Cornelis A. van den Berg1

1Department of Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands; 2Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands; 3MR systems, Philips Healthcare, Best, Netherlands

Conventional RF transmit coils store their energy in the near-field region. This region extends for approximately a quarter of a wavelength, which corresponds to 4 cm at 7T. Many regions of interest for MR imaging are likely to be located outside this 'near-field' region. As an alternative we present a radiative antenna, which radiates its energy away from the source, resulting in more efficient B1+ penetration. At a depth of 10 cm the radiative antenna shows 20% more B1+ in comparison to a stripline antenna for equal power and 60% more B1+ for equal SARmax.

15:00         4765.     Performance Optimization of a Multi-Channel Transmit Coil with Significant Coupling Between Elements

Mikhail Kozlov1, Robert Turner1

1Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Sachsen, Germany

We present an analysis of a commercial available 7T 8-ch coil. Despite significant coupling (Sxy&#8776;7 dB) between neighboring elements, the coil can be tuned either to prevent power splitting, or to achieve minimum reflected power. The latter tuning condition corresponds to the best coil performance regarding achievable B1+ magnitude for a given coil input power.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 107

13:30         4766.     Current Controlled Transmit/Receive Elements in Parallel Excitation and Parallel Imaging

Evgeniya Kirilina1, André Kuehne1, Tomasz Lindel1, Werner Hoffmann1, Thomas Riemer2, Frank Seifert1

1Medical Metrology, Physikalisch-Technische Bundesanstalt, Berlin, Germany; 2IZKF, Leipzig, Germany

Parallel excitation (PEX) techniques are cutting edge MRI applications complementing Parallel Imaging (PI) in its use of RF coil arrays. In conventional, power driven transmit arrays, electromagnetic coupling between the coil elements poses a major challenge since it distorts the excitation profiles of the individual elements and aggravates SAR control during parallel transmission. In this work we demonstrate that coupling issues may be circumvented by applying simple MOSFET based current sources to drive the transmit/receive array. The feasibility of combining PEX and PI for in-vivo experiments is demonstrated using a current controlled transmit and receive (2CONTAR) array is demonstrated.

14:00         4767.     An 8-Channel Add-On RF Shimming System for Whole-Body 7 Tesla MRI Including Real-Time SAR Monitoring

Andreas Klaus Bitz1,2, Irina Brote1,2, Stephan Orzada1,2, Oliver Kraff1,2, Stefan Maderwald1,2, Harald H. Quick1,2, Pedram Yazdanbakhsh3, Klaus Solbach3, Achim Bahr4, Thomas Bolz4, Karsten Wicklow5, Franz Schmitt5, Mark E. Ladd1,2

1Erwin L. Hahn Institute for MRI, Essen, Germany; 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany; 3University Duisburg-Essen, Duisburg, Germany; 4IMST GmbH, Kamp-Lintfort, Germany; 5Siemens Healthcare, Erlangen, Germany

An 8-channel add-on system for RF shimming was integrated into a 7 T whole-body MR scanner to enable research on the limits and benefits of RF shimming in various body regions. The system allows computer-controlled setting of amplitude and phase of each transmit channel by use of inexpensive vector modulators on the small-signal side of the system. Real-time supervision of the transmitted RF power was implemented to guarantee operation within the limits given in the IEC safety guidelines. The shimming system has already been successfully utilized for MRI of the human head, the abdomen, and thorax.

14:30         4768.     16-Bit Vector Modulator for B1 Shimming in 7T MRI

Pedram Yazdanbakhsh1, Sebastian Held1, Irina Brote2, Andreas Bitz2, Stephan Orzada2, Mark E. Ladd2, Klaus Solbach1

1High Frequency Technique, University Duisburg-Essen, Duisburg, NRW, Germany; 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany

The concept of B1-shimming is important for improving SNR and uniformity in MRI at high field. B1-shimming can be performed using multiple transmitters connected to a coil array. A homogeneous slice can be achieved by adjusting the magnitude and phase on each transmitter channel until a uniform composite excitation is obtained. In this paper a high resolution I-Q vector modulator has been designed to control the phase and amplitude of eight channels for B1 shimming in MRI at 7T. The IQ modulator replaces more expensive components like digitally controlled phase shifters and attenuators.

15:00         4769.     High-Bandwidth, High-Efficiency RF Amplitude Modulation for On-Board Transmit Amplifiers

Natalia Gudino1, Jeremiah A. Heilman2, Mark A. Griswold3

1Biomedical Engineering, Case Center for Imaging Research, Cleveland, OH, USA; 2Physics, Case Center for Imaging Research, Cleveland, OH, USA; 3Radiology, Case Center for Imaging Research, Cleveland, OH, USA

We present a novel, high efficiency system to modulate the amplitude of the RF output signal of a current mode class-D on-board amplifier (CMCD). The amplitude-modulating wave is used as the reference signal of a Pulse Width Modulated (PWM) controller that switches the gate of high frequency MOSFETs in a buck converter configuration. Current feedback is used to directly control the current in the transmit coil. We successfully showed the system can handle up to 20kHz AM signal and higher, and load insensitivity was significantly improved comparing with that of a tuned voltage-mode device.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 107

13:30         4770.     Reconfigurable Electronic Tune-Detune Circuit for RF Coil Systems

Peter Serano1, Mathew Brevard1, William Nastri1, Reinhold Ludwig2

1InsightMRI, Worcester, MA, USA; 2ECE, Worcester Polytechnic Institute, Worcester, MA, USA

This paper proposes an electronic circuit that enables the rapid tuning and detuning of RF coil configurations. A reconfigurable circuit capable of providing either a -30V or -250V reverse bias voltage for PIN diode controlled coil systems was designed, constructed, and tested. The switching time between tune and detune states is typically within 1μs.

14:00         4771.     A 32 Channel RF Array and Integrated Gradient Insert

Martyn NJ Paley1, James Paley2, Ian Young3

1Academic Radiology, University of Sheffield, Sheffield, Yorkshire, UK; 2Engineering, Imaging Systems Design, Skipton, Yorkshire, UK; 3Mechatronics, Imperial College, London, UK

Neonatal imaging requires low acoustic noise and SAR. A 32 channel transmit-receive array with an integrated gradient coil set has been developed for use in a neonatal incubator. The coil set was simulated using the Biot-Savart law in 3D using Matlab. The coil was manufactured using PCB technique with wire interconnects. The coil has been interfaced to a 32 channel spectrometer and performance tested in a 1.5T magnet.

14:30         4772.     Bo Anchored Spatial Excitation (BASE) for Effective Fat Suppression Under Bo Inhomogeneity: Implication for Parallel Transmission

Allen W. Song1, Nan-Kuei Chen1, Brian Soher2

1Brain Imaging and Analysis Center, Duke University, Durham, NC, USA; 2Radiology, Duke University, Durham, NC, USA

In this report we aim to achieve a uniform and targeted spatial excitation under Bo inhomogeneity. Specifically, we use fat suppression as an example to demonstrate a new strategy termed Bo anchored spatial excitation (BASE), where the transmit frequencies of individual channels are matched to those of the local regions under an inhomogeneous magnetic field. We show that this approach can effectively overcome the field inhomogeneities, and greatly reduce the off-resonance effects during excitation. It is hoped that this new BASE technique can find wide applications in imaging and spectroscopy in vivo in the presence of large field inhomogeneities.

15:00         4773.     Transmit SENSE with Measured and Simulated B1+ Fields

Yik-Kiong Hue1, Tiejun Zhao2, Hai Zheng1, Yongxian Qian1, Fernando E. Boada1, Tamer S. Ibrahim3

1University of Pittsburgh; 2Siemens Medical Solutions; 3Bioengineering and Radiology, University of Pittsburgh, Pittsburgh, PA, USA

Transmit sense method is explored using the measured B1+ and simulated B1+ on 7T. An unconventional highly coupled coil with slotted shield is used. The experiment is done with a water phantom that has brain-like properties. The simulated B1+ is calculated from the finite-difference time-domain algorithm and the measured B1+ is measured using flash sequence with multiple flip angles. The transmit sense pulse is designed with spiral trajectory with the acceleration factor of 1, 2, 3 and 4.

 
Safety, Monitoring, Predicition
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 108

14:00         4774.     SAR and Temperature Evaluations for B1 Shimming at 7 Tesla

Lin Tang1, Tamer S. Ibrahim2

1University of Oklahoma; 2Bioengineering and Radiology, University of Pittsburgh, Pittsburgh, PA, USA

In this work we provide complete 3D predictions of the B1+ fields, MRI images, energy absorption by the head and corresponding specific absorption rate (SAR) distributions, temperature rise distributions over the whole head for MRI experiments associated with quadrature and multi-transmit (B1 shimming) operations at 7 tesla.. Analysis on the relation between B1+ field distributions, MR images, SAR and ÄT (temperature change due to the RF excitation) distributions is conducted.

14:30         4775.     Comparing SAR Calculated in Multiple Human Body Models at 1.5T

Zhangwei Wang1, Christopher M. Collins2, Jason Jin1, Victor Taracila1, Qing X. Yang2, Fraser J. Robb1

1GE Healthcare Coils, Aurora, OH, USA; 2Department of Radiology, College of Medicine, The Pennsylvania State University, Hershey, PA, USA

Numerical models are used increasingly in field calculations for MRI engineering and safety assurance. We modified six currently available male and female models and for use with commercially available finite-difference time-domain software . Calculations show that the geometry of the model has a significant effect on SAR distribution and maximum local SAR value.

15:00         4776.     Fast E1, B1 and SAR Simulation with the Use of Graphics Processors

Lohith Kini1, Larry L. Wald2,3, Elfar Adalsteinsson1,4

1Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, USA; 2MGH, Harvard Medical School, A. A. Martinos Center for Biomedical Imagin, Charlestown, MA, USA; 3Harvard-MIT Division of Helath Sciences and Technology, MIT, Cambridge, MA, USA; 4Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, USA

Advances in graphics card processors have allowed for faster computation time for solving numerical equations that are highly parallelizable. In this study, we present the use of CUDA enabled graphics cards in FDTD simulations for SAR, E1 and B1 computation. The speed benefit is useful if, for e.g., SAR estimation for pTX is necessary for scanning individual subjects. A fast FDTD computation would also significantly speed up iterative optimizations of a coil design over a geometric parameter space. We show that steady state solutions are achieved quickly and that the running time is at least an order of magnitude greater than regular CPU computation.

15:30         4777.     Minimum SAR for RF Shimming by Allowing Spatial Phase Variation

Yigitcan Eryaman1, Celal Alp Tunc1, Ergin Atalar1

1Electrical Engineering, Bilkent University, Ankara, Turkey

The ultimate value of SAR for MRI coils is calculated for a uniform target transmit profile. By keeping the magnitude of the field within given bounds, the target profile with the optimum phase distribution is calculated. The phase and magnitude of the resulting field distribution is presented. Reduction in whole body SAR in comparison to zero phase target sensitivity is calculated for different magnetic field strengths.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 108

13:30         4778.     MRI-Compatible 12-Lead ECG: Improved MHD Suppression, Ischemia Monitoring, and Non-Invasive Cardiac Output

Ehud Jeruham Schmidt1, Gari Clifford2, Michael Jerosch-Herald1, Raymond Y. Kwong3, Laurence Epstein3, Daniel Kacher1, Charles L. Dumoulin4, Ferenc Jolesz1

1Radiology, Brigham and Womens Hospital, Boston, MA, USA; 2Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA; 3Cardiology, Brigham and Womens Hospital, Boston, MA, USA; 4Radiology, Cincinnati Children’s Hospital, Cincinnati, OH, USA

A 12-lead high-fidelity MRI-compatible ECG system is used to acquire ECG data outside the magnet, and at iso-center both head-first and feet-first. The three positions are compared to produce an ECG signal with substantial reduction of the Magneto-Hydrodynamic effect in one implementation, and to provide the net MHD effect in another implementation. Since the MHD effect is associated with flow in the aortic arch, it provides a non-invasive estimate of cardiac output, and can also be used to separate between premature and sinus rhythm beats.

14:00         4779.     Optimization of SAR Calculation for 3-D EM Time and Frequency Domain Data

Mikhail Kozlov1, Thomas Rothe1, Robert Turner1

1Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Sachsen, Germany

We present a fast and reliable SAR calculation procedure, versatile with regard to any 3-D EM solver strategies, and adapted to multi-core processing. When power loss and mass density data are provided on an equidistant temporary mesh, with well defined mesh refinement steps, a simple but robust iterative algorithm, involving prediction over cubic volumes of a specified mass, can significantly accelerate SAR calculation. Our in-house SAR calculation algorithm uses the Matlab parallel computing toolkit. Increasing the number of cores gave a nearly linear reduction of computation time. In addition to the 10-gram average SAR data relevant to IEC guidelines, values of the average SAR for any head or body part within a coil can be provided.

14:30         4780.     Acoustic Noise Reduction Through Pulse Sequence Design: Timings, Eddy-Currents, FMRI

Xingxian Shou1, Xin Chen1, Jamal J. Derakhshan2, Jeffrey L. Duerk2,3, Robert W. Brown1

1Department of Physics, Case Western Reserve University, Cleveland, OH, USA; 2Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA; 3Department of Radiology, University Hospitals, Cleveland, OH, USA

We have carried out further investigations of the mechanism of suppression of dominant frequencies in the acoustic noise spectra through “impulsive - anti-impulsive” Lorentz force cancellations. Pulse sequence timing recipes are given for killing multiple frequencies. The distinction between the Fourier transform envelope and its zeros for frequency suppression is emphasized. We establish that frequency clusters due to vibrations generated by eddy-currents are suppressed in exactly the same way as those due to gradient vibrations. Finally, it is pointed out that dominant noise peaks, which have a major influence on auditory fMRI studies, may be suppressed with this mechanism.

15:00         4781.     Experimental Study of Active Acoustic Noise Control in a 4T MRI Scanner In-Situ

Brent Rudd1, Mingfeng Lee1, Teik C. Lim1, Jing-Huei Lee2,3

1Mechanical Engineering, University of Cincinnati, Cincinnati, OH, USA; 2Biomedical Engineering, University of Cincinnati, Cincinnati, OH, USA; 3Center for Imaging Research, University of Cincinnati, Cincinnati, OH, USA

In this study, we outfitted a dummy with a pair of headphones containing piezoceramic speakers with optical microphones installed inside the earpieces, near the “patient” ear locations. The dummy was placed in the MRI scanner and the sound pressure level was measured during EPI scanning, both with and without the active noise control (ANC) system operating. Results presented show the ANC system operating in-situ attained significant SPL reduction at the first dominant frequency. To the best of our knowledge, this is the first demonstration that ANC can effectively reduce acoustic noise generated by an MRI scanner during a live scan.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 108

13:30         4782.     Numerical Determination of SNR Using an Anatomic Pixel Rat Brain Model

Rafael Rojas1, Sergio Enrique Solis1, Oscar Rene Marrufo1, Alfredo Odon Rodriguez1

1CI3M, UAM Iztapalapa, Mexico, City, Mexico

The signal-to-noise ratio is an accepted standard for measurement of quality in MRI. However, it is very difficult to derive analytical expressions from the Maxwell equations due to the complicated mathematical frame involved in it. The numerical study of the electromagnetic behavior for MRI coils and biological tissues is a good alternative. A numerical method based on Finite Element Method (FEM) to compute the SNR in a circular-shaped coil is presented here, and that was compared with the SNR calculated by a Varian algorithm from a real rat brain phantom image obtained with a 7T MRI system in our laboratory.

14:00         4783.     Modeling of RF Induced Implant Lead Current for MRI

Volkan Acikel1, Ergin Atalar1

1Bikent University Department of Electrical and Electronics Engineering, Ankara, Turkey

Induced current, due to RF field, on implant leads may cause serious heating problems. In this study, theoretical analysis of this problem is made by modeling lead in a similar manner with transmission-line lumped element circuit model. Induced currents are solved for different cases using this model and solutions are compared with method-of-moments solutions. It is found that this model is as accurate as MoM. Moreover, it gives more understanding on behavior of induced current and as heating problem is directly related to induced current. It enables us to develop new solutions and understand the current solutions for heating problem.

14:30         4784.     Fluoroptic Measurements of MRI-Related Heating at Cardiac Pacemaker Leads in Vivo: Initial Results

Peter Nordbeck1, Oliver Ritter1, Michael Friedrich2, Michelle Maxfield2, Marcus Warmuth3, Philipp Ehses3, Ingo Weiss2, Karl-Heinz Hiller4, Peter M. Jakob3, Mark E. Ladd5, Harald H. Quick5, Wolfgang R. Bauer1

1Medizinische Klinik I, Universität Würzburg, Würzburg, Germany; 2Biotronik GmbH & Co. KG, Berlin, Germany; 3Experimentelle Physik V, Universität Würzburg, Würzburg, Germany; 4Forschungszentrum MRB, Würzburg, Germany; 5Diagnostische und Interventionelle Radiologie, Universität Duisburg-Essen, Essen, Germany

Radio frequency-related heating of cardiac pacemaker leads in MRI is a serious concern preventing pacemaker patients to undergo routine MRI. Extensive in vitro investigations focused on this issue over the last years, but until then, in vivo investigations on the topic are very rare. In this study, a reliable method for in vivo temperature measurements at a pacemaker lead tip was developed, utilizing a fluoroptic temperature measurement system to avoid interferences of the measurement system with the MR scanner’s electromagnetic fields. Initial experiments show that this measurement technique allows for reproducible, precise temperature measurements at the lead tip in vivo.

15:00         4785.     The Safety of MRI in Patients with Implanted Sacral Neuromodulation Systems: RF-Induced Heating

John S. Thornton1, David W. Carmichael2, Shahid Khan3, Clare J. Fowler4, Thomas M. Kessler4

1Lysholm Department of Neuroradiology, National Hosiptal for Neurology and Neurosurgery, UCLH NHS Foundation Trust, London, UK; 2Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, UK; 3Department of Uro-Neurology, The National Hospital for Neurology and Neurosurgery, UCLH NHS Foundation Trust, London, UK; 4Department of Uro-Neurology, National Hospital for Neurology and Neurosurgery, UCLH NHS Foundation Trust, London, UK

A sacral neuromodulation system was located in an anthropomorphic tissue-equivalent gel phantom and electrode temperatures monitored with a fibre-optic thermometer. A 6.5 min FSE acquisition was performed in a 3Tesla Siemens system at a number of landmark positions and sequence SARS up to 2W/kg whole-body. When landmarked on the phantom head, electrode-associated temperature rises were 0.10oC or less. At other landmark positions, sequence SAR and temperature rises varied widely with position, but electrode-associated temperature increases were always < 2oC. MRI in patients with sacral neuromodulation implants may be safe but landmark, scanner and software-level specific SAR limits must be applied.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 108

13:30         4786.     SAR Behavior During Whole-Body MultiTransmit RF Shimming at 3.0T

Paul R. Harvey1, Zhiyong Zhai2, Michael Morich2, Giel Mens1, Gert van Yperen1, Gordon DeMeester2, Ingmar Graesslin3, Romhild Hoogeveen1

1Philips Healthcare, Best, Netherlands; 2Philips Healthcare, Cleveland, USA; 3Philips Research Europe, Hamburg, Germany

The dielectric properties of human tissue influence the RF uniformity that is achievable in MRI. Clinical 3.0T MRI systems capable of MultiTransmit RF technology have recently been introduced. Electromagnetic (EM) simulations have been used to evaluate the relationship between whole-body SAR, local SAR and head SAR as a function of patient and anatomy specific uniformity optimized RF shim settings. Results indicate that improved RF uniformity is consistent with reduced SAR thereby enabling shorter scan times in cases where SAR is limiting.

14:00         4787.     SAR Reduction in Parallel Transmission by Allowing Spatial Phase Variation

Haldun Ozgur Bayindir1, Yigitcan Eryaman1, Celal Alp Tunc1, Ergin Atalar1

1Electrical-Electronics Engineering, Bilkent University, Ankara, Turkey

In this work, a new SAR reduction method for parallel transmission is presented. Spatial phase variations in the excitation samples do not cause significant image degradation when phase variations are forced to be in an interval small enough (0-60 degrees interval is chosen in this work). The new method reduces SAR by releasing the phase constraints of the excitation samples. Method is tested for different time reduction factors. Results show that SAR reduction increases as time reduction factor gets higher. Optimal excitation profiles are tested with Bloch simulations and excitation errors caused by spatial phase variations are evaluated.

14:30         4788.     A Multi-Channel SAR Prediction and Online Monitoring System at 7T

Irina Brote1,2, Stephan Orzada1,2, Oliver Kraff1,2, Stefan Maderwald1,2, Harald H. Quick1,2, Pedram Yazdanbakhsh3, Klaus Solbach3, Karsten Wicklow4, Achim Bahr5, Thomas Bolz5, Mark E. Ladd1,2, Andreas K. Bitz1,2

1Erwin L. Hahn Institute for MRI, Essen, Germany; 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany; 3University Duisburg-Essen, Duisburg, Germany; 4Siemens Healthcare, Erlangen, Germany; 5IMST GmbH, Kamp-Lintfort, Germany

SAR prediction and monitoring are major concerns for MR systems, especially at ultra-high field where multi-transmit systems have recently been introduced to overcome problems concerning B1 inhomogeneity. The aim of this work was to design and implement a SAR prediction and monitoring system for a self-built RF shimming system on a 7T whole-body scanner for use in humans. All channels have to be supervised, and an individual SAR prediction has to be performed for each exposure scenario. Before scanning, the maximum permissible power for each channel is computed using numerical field distributions. During scanning, real-time monitoring has been implemented using a FPGA card which samples each channel and calculates time-averaged power.

15:00         4789.     Realisation of a Flexible Power Measurement Application for Parallel Transmit

Guido Kudielka1, Mika Vogel1, Wolfgang Loew1

1Imaging Technologies Europe, GE Global Research, Garching, Germany

Standard SAR measurement methods can no longer be used in Parallel Transmission (PTx) technique. An unstable RF excitation of one RF amplifier has significant effects on SAR. A flexible power monitor setup was developed to control the output of any PTx transmit system during scans and to detect any malfunctions in this system. With a programmable switch the RF signal of each amplifier was connected to a power sensor. A software application visualized these measurements and monitored to the signal stability. An excitation stop was implemented if the stability exceeds a defined threshold.

 


 
SAR in Implants & TX Arrays
Exhibit Hall 2-3                    Monday 14:00-16:00          Computer 109

14:00         4790.     Feasibility of Active Cable Trap to Attenuate MRI-Induced RF Currents

Marta Gaia Zanchi1, John Mark Pauly1, Greig Cameron Scott1

1Electrical Engineering, Stanford University, Stanford, CA, USA

We present a feasibility of active cancellation of unsafe RF guidewire currents induced during an MRI scan. Toward this goal, we have designed and built a prototype "active cable trap" based on Cartesian feedback and used it to demonstrate over 30 dB attenuation of RF wire currents on the bench. If the wire tip were in contact with tissue, this is equivalent to a 1000x reduction of heating by currents induced by RF fields. In comparison to passive cable traps and Q-spoiling loads, our newly developed active cable trap should not suffer from component loss and tuning interactions with wires.

14:30         4791.     Improved RF Safety of Interventional Devices Using Cable Traps

Krishna N. Kurpad1, Erik T. Bieging2, Mahdi S. Rahimi3, Orhan Unal1,4

1Radiology, University of Wisconsin - Madison, Madison, WI, USA; 2Biomedical Engineering, University of Wisconsin - Madison, Madison, WI, USA; 3Electrical and Computer Engineering, University of Wisconsin - Madison, Madison, WI, USA; 4Medical Physics, University of Wisconsin - Madison, Madison, WI, USA

 

15:00         4792.     New Method to Quantify RF Induced Currents Inside Conductive Wires

Michiel R. van den Bosch1, Marinus A. Moerland1, Astrid L. van Lier1, Lambertus W. Bartels1, Jan J. Lagendijk1, Cornelis A. van den Berg1

1Department of Radiotherapy and Radiology, University Medical Center Utrecht, Utrecht, Netherlands

Resonant waves can occur along metallic wires used in MRI guided interventions. Since it is hard to state the exact resonant wire length, there is a need for a tool to monitor the tissue heating at the tip of a wire. In this study we have developed a new methodology to estimate the induced current from the B1+ distortion around the wire. With this method we are able to quantify the current profile on wires for resonant and non-resonant conditions. This creates a powerful instrument to investigate the resonance of RF waves along metallic wires used for MRI guided interventions.

15:30         4793.     Continuous Monitoring of RF-Safety for Implantable MR-Conditional Devices

Ingmar Graesslin1, Julia Weller1, Peter Koken1, Jouke Smink2, Bjoern Annighoefer3, Sascha Krueger1

1Philips Research Europe, Hamburg, Germany; 2Philips Healthcare, Best, Netherlands; 3TU Hamburg-Harburg, Hamburg, Germany

The presence of an implantable active device (e.g. pacemaker or deep brain stimulator) usually represents a contraindication for an MR examination. A new non-invasive detection method of RF coupling with conductive parts of stationary devices, i.e. e.g. implanted devices, is proposed. The presence of such devices was detected reliably by the MR-system in real-time for a group of volunteers some holding a device near their body during scanning. The system even allowed detection of MR-conditional devices in the non-resonant, safe case, indicating an extremely high sensitivity.

 
Exhibit Hall 2-3                    Tuesday 13:30-15:30          Computer 109

13:30         4794.     Safety of Simultaneous Intra-Cranial EEG-FMRI: Magnetic Field Gradient Induced Voltages

David W. Carmichael1, Louis Lemieux1

1Dept. Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, UK

MR imaging of patients with implanted intracranial electrodes poses potential health risks, one of which is imaging gradient induced currents that could result in undesired stimulation. Voltages were recorded during an EPI sequence from intracranial electrodes implanted in a realistic test object filled with conductive gel. The main finding was that the measured switching magnetic field gradient induced voltages were small (0.04±0.01V), in the brain this will correspond to a current well below the medical devices limit for a single fault condition (0.5mA). Hence radiofrequency induced heating is likely to be the primary safety concern.

14:00         4795.     3D MRI Thermometry of MR-Induced Heating of a Wire and Determination of Total Generated Heat

Philipp Ehses1, Marcos A. Lopez1,2, Michael Friedrich3, Florian Fidler2, Peter Nordbeck4, Marcus Warmuth4, Peter M. Jakob1,2, Wolfgang R. Bauer4

1Dept. of Experimental Physics 5, Universität Würzburg, Würzburg, Germany; 2Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany; 3Biotronik GmbH & Co. KG, Berlin, Germany; 4Dept. of Internal Medicine I, Universität Würzburg, Würzburg, Germany

Possible tissue damage due to RF-induced heating is one of the main reasons for the contraindication of MRI examinations on patients with metallic implants. These heating effects are often examined in phantom studies with fiberoptic probes. Possible positioning errors and the lack of spatial coverage are two disadvantages of this approach. In this work, the temperature increase of a wire was monitored in a phantom with a recently proposed combination of an MRI thermometry method and simultaneous MRI heating. This method was adapted for three dimensions and the heat generated at the wire tip was calculated from a region of interest.

14:30         4796.     RF HEATING DUE to a DEEP BRAIN STIMULATION ELECTRODE at 9.4 T (400.2 MHz) in PORCINE HEADS

Devashish Shrivastava1, Timothy Hanson, Aviva Abosch, J. Thomas Vaughan

1CMRR, Radiology, University of Minnesota, Minneapolis, MN, USA

Deep brain stimulation electrode (3389, Medtronic Inc., Minneapolis, MN) did not cause any statistically significant heating at 9.4 T (400.2 MHz) in ex vivo, non-perfused porcine heads. RF heating was measured in the head-skin, brain, and air next to the head using fluoroptic probes with and without the electrode. A continuous wave RF power was delivered to the head using a tuned and matched, four loop, transmit and receive volume head coil for 1.5 hours. The whole head average SAR was close to 3 W/kg.

15:00         4797.     The Effect of Human Model Resolution on Numerical Calculation of SAR and Temperature in MRI

Zhangwei Wang1, Christopher M. Collins2, Shuren Zhao1, Fraser J. Robb1

1GE Healthcare Coils, Aurora, OH, USA; 2Department of Radiology, College of Medicine, The Pennsylvania State University, Hershey, PA, USA

Numerical calculation accuracy is related to model resolution. In this study, we adopted 2mm, 3mm, and 5mm human head models in a birdcage coil to investigate the SAR distribution and temperature rise. The results show that maximum SAR in any one cell, one gram, or 10 grams can increase significantly with model resolution. Conversely, the maximum temperature elevation shows more stability with model resolution, and even shows a moderate decrease as resolution increases.

14:30         4798.     Occupational Exposure to Electro-Magnetic Fields in MRI: A Survey of Working Practices from 1 T-7 T

Donald W. McRobbie1, Michael Oberle2, Annie Papadaki1, Rebecca Quest1, Kjell Hansson Mild3, Myles Capstick2, Jeff Hand1, Niels Kuster2

1Radiological Sciences Unit, Imperial College Healthcare, London, UK; 2IT'IS Foundation, Zurich, Switzerland; 3Radiation Physics, University of Umea, Umea, Sweden

A study of clinical practice in four European MR centres from 1T-7T revealed significant working practices which exceed ICNIRP Reference Values and proposed legislative Action Values for static and gradient field exposures. In particular, monitoring of patients undergoing general anaesthesia, interventional MRI and fMRI with a tactile stimulus exceeded dB/dt action values. Movement in the static field at 7T also exceeded the relevant action value. These practices are threatened by proposed legislation.

 
Exhibit Hall 2-3                    Wednesday 13:30-15:30          Computer 109

13:30         4799.     A Comparison of Local SAR Using Individual Patient Data and a Patient Template

Stefanie Buchenau1, Martin Haas1, Juergen Hennig1, Maxim Zaitsev1

1Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany

The aim of this work was to investigate the error that is introduced to SAR by erroneous information on the electric properties distribution of the individual patient. The standard FDTD method and a second method that uses measured B1 data to calculate electric fields were compared. It could be shown that the SAR distribution calculated for a patient template by FDTD method can fail due to slight differences in anatomy. In comparison the second method preserves the basic characteristics of this distribution if a homogeneous tissue is assumed. An appropriate choice of its electrical properties simulates a worst case scenario.

14:00         4800.     A Standard Implant for Determination of Local SAR in Testing of RF-Induced Heating of an Implant

John A. Jallal1, John A. Nyenhuis2, Sung Min Park1

1Purdue University, West Lafayette, IN, USA; 2Purdue University , West Lafayette, IN, USA

RF-induced heating of tissue surrounding implanted medical devices can occur during MRI scans due to device interactions with the B1 magnetic field. The present method for determining local SAR in RF-induced heating tests is calorimetry, in which temperature rise is measured in the phantom with no implant. A standard implant consisting of a 1/8” x 10 cm titanium rod has been developed to measure local SAR, for which the temperature rise at the ends is measured and compared with calculation to determine the local SAR. This new method provides improved accuracy and is faster than calorimetry.

15:00         4801.     Transmit Array Concepts for Improved MRI Safety in the Presence of Long Conductors

Maryam Etezadi-Amoli1, Marta Gaia Zanchi1, Pascal Stang1, William R. Overall1, Adam B. Kerr1, John M. Pauly1, Greig C. Scott1

1Electrical Engineering, Stanford University, Stanford, CA, USA

In this work, we investigate the potential of using transmit arrays to improve the safety of MRI in the presence of conductive guidewires and implant leads. We also demonstrate the feasibility of generalizing the concept of a transmit array to treat the guidewire as an additional array element that can be actively driven with a source of chosen magnitude and phase to cancel out undesired current induced by the imaging protocol.

 
Exhibit Hall 2-3                    Thursday 13:30-15:30          Computer 109

13:30         4802.     RF Energy Deposition and RF Power Requirements in Parallel Transmission with Increasing Distance from the Coil to the Sample

Cem Murat Deniz1,2, Riccardo Lattanzi1, Yudong Zhu1, Graham Wiggins1, Daniel K. Sodickson1

1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, USA; 2 Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, USA

Minimizing SAR while maintaining a homogenous excitation is one of the principal challenges associated with the use of ultra high magnetic field strengths. We investigated the SAR behavior and the power requirements for parallel transmission as the gap between transmit elements and the surface of the object is increased. Two simulated geometrical arrangements of coil elements around a sphere were explored: one in which an increasing number of coils of fixed size were placed in a belt of increasing radius around the object, and another in which a fixed number of coils with increasing radius was arranged at increasing distance from the object. We found that global SAR and peak SAR during parallel excitation decreases with liftoff, approaching the lowest SAR allowed by electrodynamics (i.e. the ultimate intrinsic SAR). However, input power requirements to achieve the desired excitation increases rapidly with lift-off. Thus, for parallel transmission there are SAR benefits in moving coils away from the object, but RF power requirements may represent a practical limiting factor.

14:00         4803.     SAR Assessment of Transmit Arrays: Deterministic Calculation of Worst- And Best-Case Performance

David Otto Brunner1, Jan Paska2, Juerg Froehlich2, Klaas Paul Pruessmann1

1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; 2Laboratory for Electromagnetic Fields and Microwave Electronics, ETH Zurich, Zurich, Switzerland

The SAR assessment from electromagnetic field simulation is a crucial step in safety validation of RF transmission systems. In the case of parallel excitation using transmit arrays this task is more intriguing since the distribution of the SAR deposition can vary significantly with changing field superposition of the elements in the array. In this work we present a method leading to a rigorous closed form calculation of worst case SAR deposition and optimum array performance with respect to local SAR deposition in the entire body. These evaluations can be used to set system power limitations and transmit array benchmarking respectively.

14:30         4804.     The Effect of Solution Electrical Conductivity in Pacemaker Lead Tip Heating at 1.5 Tesla

Deborah Anne Langman1, Ira B. Goldberg2, Paul J. Finn1, Jack W. Judy3, Daniel B. Ennis1

1Radiological Sciences, UCLA, Los Angeles, CA, USA; 2Electrical Engineering , UCLA, Los Angeles, CA, USA; 3Electrical Engineering, UCLA, Los Angeles, CA, USA

MR imaging of pacemakers poses the risk of thermal damage due to RF-induced heating at the pacemaker lead tip. The objective of this study was to investigate the effect of solution conductivity on RF induced heating of pacing leads using HEC, PAA, and saline solutions. Both the HEC and saline achieve peak heating near 0.5 S/m while heating in PAA solutions continues to decline with increasing conductivity. A conservative estimate of the energy deposited measured by RF-induced lead tip heating can be achieved using 0.5 S/m HEC, which exhibits little thermal convection and a peak in conductivity dependant heating.

15:00         4805.     Resistance and Inductance Based MRI-Safe Implantable Lead Strategies

Paul A. Bottomley1, William A. Edelstein1, Ananda Kumar1, Justin M. Allen1, Parag Karmarkar1

1Suite B307, 1101 E 33rd Street, SurgiVision, Inc, Baltimore, MD, USA

Concerns about RF heating of implanted devices routinely denies many patients the benefits of MRI. Here, RF resistive and inductance-based strategies for MRI-safe implanted lead design at 1.5T and 4 W/kg exposure are investigated both experimentally and theoretically using numerical electromagnetic analysis. Phantom studies show that, while unprotected leads heat >45°C in seconds, leads fabricated with distributed resistance or coiled, can limit heating as impedance is increased, but lead testing in multiple orientations is important. Such approaches may offer a viable path to MRI-safe implanted lead design, in applications where lead impedance and size do not impair lead utility.