Traditional Posters : Engineering
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Safety: Non-RF

Wednesday May 11th
Exhibition Hall  13:30 - 15:30

1785.   Cardiac Pacing in an MRI Environment  
Gene Hilton Payne1,2, Gaston Vergara2,3, Ravi Ranjan2,3, Kamal Vij4, Nelly Volland1,2, Eugene Kholmovski1,2, Sathya Vijayakumar1,2, Josh Blauer2,5, Kimberly Johnson2,3, Greg Gardner2,5, Glenn Meredith6, Tongbai Meng6, Rob MacLeod2,5, and Nassir F Marrouche2,3
1UCAIR, Department of Radiology, University of Utah, Salt Lake City, UT, United States, 2CARMA Center, University of Utah, Salt Lake City, UT, 3Department of Cardiology, University of Utah, Salt Lake City, UT, United States, 4SurgiVision, Inc., Irvine, CA, United States, 5SCI, University of Utah, Salt Lake City, UT, United States, 6Center for Applied Medical Imaging, Siemens Corporate Research, Princeton, NJ, United States

During an RF ablation procedure for treatment of atrial fibrillation, cardiac pacing is sometimes used to enforce a normal sinus rhythm at a specific rate. With the ultimate goal of performing this atrial fibrillation treatment inside an MR scanner, it will be necessary to perform pacing in this environment. Presented are the experimental setup and methods for safely pacing on a porcine subject inside a 3T MR scanner. Also presented are electrogram data that show effective pacing of the subject. The results indicated that pacing was safe and effective inside the MR scanner.

1786.   Increased PNS thresholds using a Novel Composite Gradient System 
Kenneth Craig Goodrich1, William Bradfield Handler2, Seong-Eun Kim1, John Rock Hadley1, Ulrich A Rassner3, Blaine A Chronik2, and Dennis L. Parker1
1UCAIR, University of Utah, Salt Lake City, Utah, United States, 2Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, 3Radiology, University of Utah, Salt Lake City, Utah, United States

The purpose of this study was to test PNS levels associated with a novel gradient system that allows an insert gradient to be used simultaneously with whole-body gradient system. 5 volunteers underwent PNS testing using whole body gradients and a head/neck insert. Three gradient configurations were measured; body gradients, insert gradients, both systems operating synchronously. The pulse sequence consisted of 64, 1 msec trapezoid pulses with 400 microsecond slew time. The PNS threshold for composite gradients was higher than for the body gradients only. Composite gradients may allow increased gradient performance while decreasing PNS relative to whole body gradients alone.

1787.   Threshold for Peripheral Nerve Stimulation with Ultra-Fast Gradients 
Irving N Weinberg1, Pavel Stepanov2, Steven C Glidden3, Howard D Sanders4, Daniel Warnow4, Alan B McMillan5, Rao P Gullapalli6, Piotr M Starewicz7, Kai-Ming Lo8, Amnon Fisher9, J Patrick Reilly10, Michael S Niziol11, and Stanley T Fricke12
1Weinberg Medical Physics LLC, Bethesda, Maryland, United States, 2Weinberg Medical Physics LLC, 3Applied Pulsed Power Inc., Freeville, New York, United States, 4Applied Pulsed Power Inc.,5Radiology, University of Maryland, Baltimore, Maryland, 6Radiology, University of Maryland, Baltimore, 7Resonance Research, Inc, Billerica, Massachusetts, 8University of Maryland, 9Physics, Technion-Israel Institute of Technology, Haifa, Israel, 10Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, 11Family Practice Associates, Dryden, New York, 12Radiology, Children's National Medical Center, Washington, DC

Prior clinical trials have examined peripheral nerve stimulation (PNS) for magnetic gradients with ramp times of 50 µs and higher. We conducted a prospective IRB-approved controlled clinical trial in which 26 volunteers were exposed to magnetic gradient pulses with ramp times as short as 3.5 microseconds. The data suggests that at 3.5 µs, the threshold of gradient dB/dt (unipolar pulses) for 50% PNS in the general population would be 128,000 T/s (with substantially lower thresholds for younger subjects), representing dB/dt and slew rate thresholds more than 1,000 times higher than in typical MRI scanners.

1788.   Maximum dB/dt and Switching Noise in 1.5T MRI Scanners for Safety Evaluation of Active Implantable Medical Device 
Neha Bharat Butala1, Ramez Emile Necola Shehada1, Peter Nabil Costandi1, Ali Dianaty1, and Kevin Jurkowski1
1Cardiac Rhythm Management Division, St. Jude Medical, Sylmar, CA, United States

Active implantable medical devices (AIMD) in patients undergoing MRI, present a risk of tissue stimulation at gradient dB/dt rates lower than the imposed limits for direct stimulation. Additionally, the gradient amplifier noise, “ripple” could interfere with AIMD, compromising safety. The dB/dt and associated ripple were investigated in 1.5T MRI scanners. A total of 126 measurements were performed using Faraday coils in various scanners and bore locations, while running different clinical sequences. The magnitude and location of maximum dB/dt and ripple was identified. This information may be valuable for assessment of unintended gradient stimulation hazard to demonstrate MR compatibility of AIMD.

1789.   Magnetic field monitoring using a novel wireless sensor system in an Intra-Operative MRI Workflow 
Kirk Champagne1,2, Tim Hoeppner2, David Weber2, Ta-yung Liu1, Mehran Fallah-Rad1, and Mark Alexiuk1,3
1IMRIS, Winnipeg, Manitoba, Canada, 2Electrical and Computer Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, 3Institute of Industrial Mathematical Sciences, University of Manitoba, Canada

Intra-operative OR suite designs that employ a high field movable MRI scanner require that safety checks be integrated into the surgical workflow. Existing safety checks may be complemented by a wireless sensor network that monitors the OR for potential safety hazards. We demonstrate the feasibility of such a system using Hall effect sensors. Testing with a movable 1.5T Siemens Espree scanner shows good agreement to magnetometer readings. A standard RF noise test (with the system in operation) showed an elevated baseline signal intensity but no image artifacts. Novelty of this system includes software-based thresholds and enables integrated room control.

1790.   In-Situ Study of Active Noise Control Applied to MRI Noise 
Mingfeng Li1, Brent Rudd1, Teik C Lim2, and Jing-Huei Lee3,4
1Mechanical Engineering, University of Cincinnati, Cincinnati, OH, United States, 2Mechanical Engineering, University of Cincinnati, Cincinnati, United States, 3School of Energy, Environment, Biological and Medical Engineering, University of Cincinnati, Cincinnati, OH, United States, 4Center For Imaging Reserch, University of Cincinnati, Cincinnati, OH, United States

Active noise control (ANC) for treating MRI noise effectively on a real life 4 T MRI scanner is presented in this study. Several MRI scanning sequences are used for demonstration. A dummy is equipped with an MRI compatible headset containing piezoceramic speakers with condenser microphones installed inside and outside the earpiece to measure the environmental sound in the immediate patient vicinity. During the in-situ test, the sound pressure level (SPL) was measured, both with and without the ANC. Results presented show the ANC system attained significant overall SPL reduction for all three scanning sequences tested.

1791.   Methods for the Quantitative Assessment of Image Artifacts Caused by Implantable Devices 
Benjamin Anthony Coppola1, Ramez Emile Necola Shehada1, Peter Nabil Costandi1, Kevin Jurkowski1, and Ali Dianaty1
1Cardiac Rhythm Management Division, St Jude Medical, Sylmar, CA, United States

Susceptibility artifacts due to metallic implants may affect the interpretability of an anatomical image. Such artifacts may be quantified using ASTM standard F2119-07. A new method is proposed using image correlation that addresses voids in the image as well as geometric distortion. To test this method, a pacemaker was imaged with gradient echo and spin echo sequences in a variety of orientations. The results show that a threshold correlation coefficient of 0.7 conservatively outlines the region comprised of void/distortion. This definition of the image artifact area facilitates improved clinical interpretation with reduced risk of false diagnosis.

1792.   Evaluation of Magneto Alert Sensor (MALSE) to Improve MR Safety by Decreasing the Incidence of Ferromagnetic Projectile Accidents 
Conrad Steven Martin1, Tobias Frauenrath1, Celal Özerdem1, Wolfgang Renz1,2, and Thoralf Niendorf1,3
1Berlin Ultrahigh Field Facility, Max-Delbrueck Center for Molecular Medicine, Berlin, Germany, 2Siemens Medical Solutions, Siemens, Erlangen, Germany, 3Charité Campus Buch, Humboldt-University, Experimental and Clinical Research Center (ECRC), Berlin, Germany

The magnetic forces of fringe magnetic fields of MR systems on ferromagnetic components can impose a severe patient, occupational health and safety hazard. MRI accidents are listed as number 9 of the top 10 risks in modern medicine. With the advent of ultrahigh field MR systems including passively shielded magnet versions, this risk, commonly known as the missile or projectile effect is even more pronounced. A strategy employing magnetic field sensors which can be attached to ferromagnetic objects that are commonly used in a clinical environment is conceptually appealing for the pursuit of reducing the risk of ferromagnetic projectile accidents.

1793.   How safe are intrauterine devices at MRI procedures with field strength beyond 1.5T? 
Jaane Rauschenberg1, Jens Groebner1, Wolfhard Semmler1, and Michael Bock1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

The widely used intrauterine contraceptive devices (IUD) had been evaluated for MR-safety only up to field strengths of 1.5T. In this work we performed ASTM measurements of 5 different IUDs at 3T. Additionally, we estimate the potential risk at 7T examinations. The metal-free hormone-containing Mirena IUD has a magnetic retraction thread but it does not produce hazardous heating. For copper-alloy IUDs no magnetic force and no torque could be detected; however, the temperature rise due to RF was up to 3°C during 15 min at 3T. For 7T head examinations no potential risk could be detected with the hardware used.

1794.   Experimental design to measure neurocognitive effects due to static magnetic field and to movement within the stray field at 0T, 1.5T, 3T, and 7T 
Jaane Rauschenberg1, Jens Groebner1, Angela Heinrichs2, Anne Szostek2, Patric Meyer2, Frauke Nees2, Georgios Paslakis3, Maria Gilles3, Michael Bock1, Michael Deuschle3, Herta Flor2, and Wolfhard Semmler1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany, 2Department of Cognitive and Clinical Neuroscience, Central Institute of Mental Health, Mannheim, Germany, 3Department of Psychiatry and Psychotherapy, Central Institute of Mental Health, Mannheim, Germany

Up to now, no sufficient experimental data about the exposure especially to movements in the stray field of MR systems are available. In this study the neurobehavioral effects is measured during the exposure to static fields and during controlled movements in the stray fields of different field strength. For this purpose we designed a magnetic field dosimeter, a motion system, a 7T compatible presentation tool, and a 0T MR system for control measurements. It could be shown that the experimental design is suitable for this complex study. First results show no significant effects on the exposure to static magnetic fields.

1795.   Understanding of the existing and future medical procedures with MR scanners: a novel tool for estimation of occupational exposure 
Valentina Hartwig1, Rossana Tortorelli2, Nicola Vanello2, Giulio Giovannetti1, Vincenzo Positano3, Luigi Landini2, and Maria Filomena Santarelli1
1Institute of Clinical Physiology - CNR, Pisa, Italy, 2Department of Information Engineering, University of Pisa, Italy, 3Fondazione Toscana Gabriele Monasterio, Pisa, Italy

Occupational workers operating magnetic resonance imaging (MRI) and spectroscopy (MRS) are repetitively and lengthy exposed to large static magnetic fields and to low frequency time varying magnetic fields. In 2004, the European Union adopted the Physical Agents (Electromagnetic Fields) Directive 2004/40/EC on the health and safety requirements for exposure to electromagnetic fields in the workplaces, which introduces significant restrictive limits on the use of clinical MRI. In this work a novel tool to estimate the induced current density due to worker movements in static magnetic field is presented. This tool represents a valid instrument to find the worst-case exposures situations.

1796.   Subject tolerance for a whole body 7T scanner 
Maarten J. Versluis1,2, Wouter M. Teeuwisse1,2, Hermien E. Kan1,2, Andrew G. Webb1,2, and 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

Patient tolerance for high field MRI examinations (7 Tesla) is important for the successful clinical introduction of these systems. The first 102 subjects that participated as volunteers in MRI examinations were asked to fill out a questionnaire to assess comfort and side effects, such as dizziness, metallic taste and overall comfort. Our results show that neuro MRI examinations at 7 Tesla are well tolerated, with only 3% of subjects rating the examination as unpleasant. Most mentioned complaints are dizziness moving in and out of the scanner and scanner noise.

1797.   Development of a template driven, adaptive, active noise cancellation (ANC) system for reduction of MR acoustic noise – initial results 
Daniel Güllmar1, Lucas A Bitzer1,2, and Jürgen R Reichenbach1
1Medical Physics Group, Jena University Hospital, Jena, Thuringia, Germany, 2School of Physics and Astronomy, Friedrich-Schiller-University, Jena, Thuringia, Germany

In this work we have evaluated the application of a template driven, adaptive, active noise cancellation system in order to reduce the acoustic noise, which accompanies each MR image acquisition. The system was tested offline using self-written Matlab software code and consists of a modified feed-forward ANC-System. The overall acoustic noise level reduction (frequency range 0-3000 Hz) was between 10 to 15 dB without and more than 25 dB with continuous adaptation. These achievements were obtained using parameter optimization of the LLMS algorithm and will be implemented in the future on DSP hardware for online acoustic noise cancellation.

1798.   Daily Longitudinal Quality Assessment in MRI: From short-term fluctuations to long-term stability 
Peter Brunecker1, Claudia Kunze1, Anja Grebe1, Chao Xu1, Ivana Galinovic1, and Jochen B Fiebach1
1Center for Stroke Research Berlin (CSB), Charité, Berlin, Germany

Monitoring of long-term alterations in MRI scanner parameters is essential for observational studies extending over several years. However, during this time intentional adjustments of the scanner hardware can actively introduce changes on a mid-term scale. To investigate this, daily phantom measurements were performed over a time period of 20 months and mean signal magnitude, signal-to-noise ratio, and uniformity were estimated. We found that sudden alterations of the absolute signal magnitude in our data were triggered by technical maintenance. We suggest that using a correction based on the stepwise constant behavior of scanner hardware parameters in time could prevent such alterations.

1799.   Benchtop measurements of gradient induced heating 
William Bradfield Handler1, Chad Tyler Harris1, and Blaine Alexander Chronik1
1Physics & Astronomy, University of Western Ontario, London, Ontario, Canada

The heating of a metal due to an oscillating magnetic field has been characterized to better understand the effects of gradient heating of implants and devices used inside the scanner bore. The results can guide the engineering of implants and devices, and there safe use within the MR environment.

Traditional Posters : Engineering
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
MR Engineering: Other

Thursday May 12th
Exhibition Hall  13:30 - 15:30

1800.   MRI Magnet Coils Stray Capacitance Effects and the Circuit Analysis Method 
Yihe Hua1, Anbo Wu1, Chao Yang2, Yan Zhao1, Ye Bai2, Fengshun Tan2, and Shike Huang2
1Global Research Center, GE, Shanghai, China, People's Republic of, 2GE Healthcare, China, People's Republic of

The MRI magnet composed of a set of multi-layer solenoidal coils provides the main magnetic field for MRI imaging. Due to the large number of turns in each main coil, its overall parasitic capacitor is possibly at a few nF level. Together with their large inductance, the coils may have a resonance frequency in KHz range, which is within the gradient pulse signal bandwidth. Circuit analysis method considering parasitic capacitance effects has been developed for different types of superconducting magnets to examine the voltage induced at main coil terminals, dielectric loss in main coils and the impact to the input impedance of gradient coils.

1801.   Initial Performance of A Multiple-Magnet Helium Recovery System 
Albert R Cross1
1University of Lethbridge, Lethbridge, Alberta, Canada

This paper presents the performance to date of our helium recovery and liquefication system that supports a 3 magnet imaging centre.

1802.   Development of a temperature variable MRI system using a 1.0 Tesla yokeless permanent magnet 
Yasuhiko Terada1, Katsumi Kose1, and Tomoyuki Haishi2
1Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan, 2MRTechnology, Tsukuba, Ibaraki, Japan

A temperature variable MRI system was developed using a 1.0 Tesla yokeless permanent magnet. The magnetic field inhomogeneity was evaluated to achieve MR imaging over a wide temperature range (-5 to +45 °C). The RMS inhomogeneity in the central 15 mm square cubic area increased from 5 to 18 ppm from 35 to -5 °C with decreasing temperature. This inhomogeneity variation was mainly caused by z2 and x2 terms except the first order inhomogeneity. A plant specimen was imaged at -5 and 5 °C to demonstrate the usefulness of the system. The free water signal visualized at 5 °C disappeared at -5 °C while the structured water signal was still visible at -5 °C.

1803.   Performance of SQUID sensor arrays for MRI of the brain 
Koos Zevenhoven1, and Risto J Ilmoniemi1
1Department of Biomedical Engineering and Computational Science (BECS), Aalto University, Helsinki, Finland

While the state of the art in MRI has moved into multiple-tesla magnetic fields, another approach, ultra-low-field (ULF) MRI, has emerged, where the precession field is in the microtesla range. This is made possibly by pulsed pre-polarization fields and highly sensitive superconducting quantum interference device (SQUID) sensors. While ULF MRI has advantages in improved T1 contrast and compatibility with other techniques such as biomagnetic measurements, the SNR of the images is still low for applications. In the absence of applicable studies, we describe and demonstrate approaches to analyzing and optimizing SQUID sensor arrays for ULF MRI.

1804.   Non-contact cardiac gating with ultra-wideband radar sensors for high field MRI 
Olaf Kosch1, Florian Thiel1, Bernd Ittermann1, and Frank Seifert1
1Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany

We have developed a contact less approach for the detection of cardiac mechanics by means of ultra-wideband (UWB) radar. and applied it for cardiac gating in high field MR. To extract beneficial information from UWB radar for cardiac MRI the decomposition of respiratory and cardiac displacements is mandatory, since the MRI data have to be unambiguously assigned to the state of the individual respiratory and cardiac cycle. We applied blind-source separation (BSS) based on several time-delayed second order correlation matrices to decompose the UWB signals and extract a pure cardiac component. In this work we present the application of cardio gating based on UWB radar signals simultaneously acquired during a clinical 3T cardio sequence utilizing retrospective image reconstruction.

1805.   Metamaterial Media for MRI Applications 
Marcos Alonso Lopez Terrones1, Jose Miguel Algarín1, Manuel J. Freire1, Peter M. Jakob2,3, Volker C. Behr2, and Ricardo Marques1
1Electronics and Electromagnetism, University of Seville, Seville, Andalucia, Spain, 2Experimental Physics 5, University of Würzburg, Würzburg, Bavaria, Germany, 3Research Center Magnetice Resonance Bavaria, Würzburg, Bavaria, Germany

Metamaterials are artificial composites whose electromagnetic properties can achieve phenomena not observed in natural materials. The application of the metamaterials in MRI has been previously explored in several works. In this work, we explore the application of split-ring metamaterial slabs with zero and high permeability, which will reject and confine, respectively, the RF magnetic field at 1.5 Tesla. The experiments were performed in combination with a receive-only loop coil. SNR maps were calculated from a series of identical phantom measurements for both the µ=0 and the µ infinite slabs and compared with the situation where the slabs were removed.

1806.   Fast EPR Acquisition with Adaptive Heterogeneous Clocking (AHC) 
Zhiyu Chen1, David Johnson1, George Caia1, Ziqi Sun1, Sergey Petryakov1, Alexandre Samouilov1, and Jay Zweier1
1Davis Heart and Lung Research Institute, Ohio State University, Columbus, Ohio, United States

Electron Paramagnetic Resonance Imaging (EPRI) can provide insight into in vivo anatomic and functional imaging of free radicals and paramagnetic molecules and their role in disease in small animal models. However, there is a need to expedite the data acquisition and post-processing to enable new EPRI applications. While previous work has used a fixed-rate master clock to pace all A/D and D/A conversion activities of the data acquisition electronics, Adaptive Heterogeneous Clocking (AHC) significantly reduces communication between the host computer and gradient hardware by using different clocks to pace the A/D and D/A functions of our acquisition cards. Projections containing up to 4096 points can be acquired in as little as 10 – 20 ms using AHC. Nearly real-time acquisition can be performed for complex computer-generated gradient waveforms, which will enable a variety of new sampling patterns.

1807.   A Mechanism to Produce Translational and Rotational Motion of a Phantom Inside an MR Scanner 
Thomas Prieto1, Brian Armstrong2, Michael Brzeski2, Robert Barrows2, Todd Kusik2, Maxim Zaitsev3, Oliver Speck4, and Thomas Ernst5
1Neurology, Medical College of Wisconsin, Milwaukee, WI, United States, 2Electrical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI, United States, 3Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 4Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany, 5Medicine, University of Hawaii, Honolulu, HI, United States

We present a novel drive mechanism for a computer controlled motion simulator to manipulate the position of a spherical phantom in an MR scanner. The drive mechanism uses 2 custom non-ferrous air motors to drive gears and timing pulleys to produce 2 cm of displacement along the Z axis and 20 degrees of rotation about the X axis at frequencies up to several Hz. The motion simulator will be useful in developing prospective motion correction methods as well as in other situations where a motion reference is needed.

1808.   Feasibility Study of MREIT in Clinical Applications 
Volkan Emre Arpinar1, Mark J Hamamura1, and Lutfu Tugan Muftuler1
1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, Irvine, CA, United States

Several in vitro studies have shown that the electrical impedance of malignant tissues is significantly higher than those of normal and benign tissues. Therefore, impedance imaging has the potential as a diagnostic tool in cancer. Magnetic Resonance Electrical Impedance Tomography (MREIT) is a technique that is used for imaging impedance distribution inside an object noninvasively. In MREIT, an external current is injected into the object and magnetic field perturbations due to this current are measured. Impedance images can be formed from these measurements.

1809.   Bimodal MRI-optics endoluminal probe for early stage colorectal cancer diagnosis: Design and Preliminary in-vivo results. 
Anoop Ramgolam1, Raphaël Sablong1, Sandrine Bouvard2, Hervé Saint-Jalmes3, and Olivier Beuf1
1CREATIS-LRMN, CNRS UMR 5220; Inserm U1044; INSA-Lyon; Université Lyon 1, Lyon, Rhone-Alpes, France, 2TIGER/IDEE, Neuroscience Research Center, Lyon, Rhone-Alpes, France, 3LTSI, Inserm U642, University Rennes1; Département d’Imagerie, centre Eugène Marquis, Rennes, Ille et Vilaine, France

Currently only 40% of colorectal cancers are detected during early stages. Flat adenomas (colorectal cancer precursors) which develop just underneath the colonic mucosa, inducing subtle morphological alteration partly explain the low sensitivity of White Light Endoscopy at early stages. We have designed a prototype of a bimodal endoluminal probe capable of simultaneously extracting morphological and biochemical data through high spatial resolution MRI and optical spectroscopy (autofluorescence; diffuse reflectance) respectively. We hereby present the designing process along with the promising preliminary in vivo results allowing mucosa-submucosa complex differentiation correlated to optical data obtained on a rabbit via this novel MRI-optics technique.

1810.   MR-based Attenuation Correction in an Animal for Radiotracer Quantification 
Mark Jason Hamamura1, Hon J Yu1, Seunghoon Ha1, Werner W Roeck1, James W Hugg2, Douglas J Wagenaar2, Dirk Meier3, Bradley E Patt2, and Orhan Nalcioglu1,4
1Tu & Yuen Center for Functional Onco-Imaging, University of California, Irvine, CA, United States, 2Gamma Medica, Inc. (Clinical Division), Northridge, CA, United States, 3Gamma Medica, Inc. (Industrial Division), Fornebu, Norway, 4Department of Cogno-Mechatronics Engineering, Pusan National University, Pusan, Republic of Korea

Accurate radiotracer quantification in SPECT and scintigraphy requires attenuation correction (AC) of the nuclear projection data. In this study, we acquired MR and scintigraphic images of two vials containing 99mTc sestimibi implanted in a rat using a novel MR-SPECT system. The MRI data was then used to perform AC of the scintigraphic data. The results demonstrate improved accuracy for radiotracer quantification when performing AC using data acquired from simultaneous MR and SPECT imaging.

1811.   Investigation of a Dual-Function Applicator for RF Hyperthermia and MRI 
Desmond Teck Beng Yeo1, Xing Yang2, Jing Wu3, Lorne Wyatt Hofstetter1, Joseph E Piel1, Eric W Fiveland1, Keith J Park1, and Thomas K Foo1
1Imaging Technologies, GE Global Research, Niskayuna, NY, United States, 2Power Conversion Circuits Lab, GE Global Research, Shanghai, China, People's Republic of, 3Electrical and Computer Engineering, Northeastern University, Boston, MA, United States

Adjuvant mild RF hyperthermia of tumors significantly increases the effectiveness of radio- and chemo-therapy. However, the conventional two-system approach may suffer from SNR and cross-talk issues. We propose a dual-function applicator design based on modified MR loop coils and demonstrate with simulated and experimental data that the modified radiating elements may perform specific absorption rate (SAR) steering for regional RF hyperthermia. The proposed array can enable contemporaneous heating and imaging without using the scanner’s birdcage body coil, thus enabling parallel imaging and placement of imaging coils closer to the body during RF hyperthermia.

1812.   An adaptive MR-compatible lens 
Julian Maclaren1, Florian Schneider2, Michael Herbst1, Murat Aksoy3, Daniel Kopeinigg3, Juergen Hennig1, Roland Bammer3, Maxim Zaitsev1, and Ulrike Wallrabe2
1Medical Physics, Dept. of Radiology, University Medical Center Freiburg, Freiburg, Germany, 2Dept. of Microsystems Engineering - IMTEK, University of Freiburg, Freiburg, Germany, 3Dept. of Radiology, Stanford University, Stanford, United States

MR-compatible camera systems are used for head tracking, eye tracking, and in interventional MRI. However, a limited depth of focus and small field of view provide a challenge for in-bore cameras, particular if the goal is to monitor a moving subject. In this work we present an MR-compatible adaptive lens and objective. Focusing on a checkerboard tracking target is demonstrated during simultaneous MR imaging. RF interference tests and field distortion measurements indicate excellent compatibility with the MR system.

1813.   1D RF Phase Gradient Coil for TRASE RF Imaging 
QunLi Deng1, Jonathan Sharp1, Vyacheslav Volotovskyy2, Boguslaw Tomanek1, and Scott King2
1Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, AB, Canada, 2Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, MB, Canada

A RF phase gradient transmit coil array, (capable of producing a gradient of either sign) has been designed for the TRASE RF imaging method. The array consists of a Double Maxwell coil and a curved Helmholtz coil to create respectively a sine field and a cosine field. 3D simulations showed large usable volumes for both coil components. Experiments were performed on a vertical field 0.2T MRI system. Field mapping confirmed good homogeneity and phase linearity and a correct RF power drive ratio between the two coil components. 1D TRASE data of four small doped water bottles were acquired successfully.

1814.   Efficient Data Compression for Distributed Detection in Wireless High-Density Arrays: a Simulated Study 
Jean-David Jutras1, B. Gino Fallone1,2, and Nicola De Zanche1,2
1Dept. of Oncology, University of Alberta, Edmonton, Alberta, Canada, 2Dept. of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada

Wireless links have been proposed to connect MR array receiver coils to the rest of the system to eliminate the safety and crosstalk issues of current coaxial cables. However, the limited data rates supported by wireless links restrict the number of coil channels that can be transmitted to well below those of the state-of-the-art high-density arrays that would benefit the most from wireless technology. In this work, two independent methods of compressing MR data prior to transmission are simulated that when combined can readily reduce it to 1/3 or less of the original amount with negligible impact on image quality.

1815.   Quantum Perspectives in Radiation Damping: Rabi Nutation and the Onset of Free Induction Decay 
James Tropp1
1Global Applied Science Lab, GE Healthcare Technologies, Fremont, CA, United States

The rate of radiation damping in magnetic resonance is investigated by solving the Bloch Kirchoff equations, and also by calculating the Rabi nutation rate via the Jaynes-Cummings formalism of quantum optics. It is found that Rabi nutation accounts for the weak early damping only; and it is noted that stimulated emission may contribute to the stronger damping which develops later.

1816.   Evaluation of the Effect of Phase Errors on the Performance of a Butler Matrix 
Enrico Pannicke1, Wolfgang Driesel2, Andre Pampel3, Toralf Mildner4, and Harald E. Möller1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2Max Planck Institute for Human Cognitive and Brain Sciences, 3Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany, 4Max Planck Institute for Human Cognitive and Brain Sciences, Germany

The Butler matrix transforms the N channels of a phased array into a new set of so-called eigenmodes with useful properties for both reception and transmission. In the current work, we performed simulations of an eight-channel phased array based on microstrip transmission line (MTL) elements and driven in an eigenmode configuration to investigate the effects of errors of individual components of the Butler matrix on the obtained electromagnetic fields. Results of the calculations were compared to experimental data recorded at 3 T.

Traditional Posters : Engineering
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Hardware for Animal MRI

Monday May 9th
Exhibition Hall  14:00 - 16:00

1817.   An 8-channel metamaterial T-R coil at 9.4T 
Andreas Senn1, Andreas Peter1, and Jan G. Korvink1,2
1Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, Baden-Württemberg, Germany, 2Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Baden-Württemberg, Germany

Application of CRLH metamaterial transmission lines in MR coil design.

1818.   Novel Orthogonal Double Solenoid (ODS) Volume RF Coil for Small Animal Imaging 
Krishna N Kurpad1
1Radiology, University of Wisconsin, Madison, WI, United States

Solenoids are known to be inherently high SNR coils that also generate highly homogeneous radio frequency magnetic (B1) fields. Traditional solenoidal coils generate B1 field that is parallel to the static magnetic (B0) field. Here, we present a novel variant of the solenoid coil, the Orthogonal Double Solenoid (ODS) coil that generates transverse B1¬ field when placed with its axis parallel to the B0 field in dedicated high field small animal horizontal bore systems. We conclude that the performance of a linear ODS coil is comparable to commercial quadrature birdcage coils with sufficient head room for further improvement.

1819.   Transceiver double crossed saddle for rodents at 2T 
Daniel Papoti1, Edson Luis Gea Vidoto1, Mateus José Martins1, Alfredo O Rodríguez2, and Alberto Tannús1
1Instituto de Física de São Carlos, São Carlos, São Paulo, Brazil, 2UAM Iztapalapa, DF, Mexico, Mexico

Small animal MR imaging and spectroscopy, where spatial resolution is a limiting factor, requires the use of distinct transmit and receive coils. This approach makes easier the optimization of the RF field homogeneity for transmit-only coils and signal-to-noise ratio for receive-only coils. It also requires that RF coils should be electrically decoupled, commonly using PIN diodes. This work describes the development and double crossed coil operating in the transceiver mode for magnetic resonance imaging of rodents at 2T. Experimental and theoretical comparisons of coil performance were carried out using a standard birdcage coil.

1820.   A 20 Coil Array System for Parallel Imaging-Accelerated Multiple Mouse MRI 
Marc Stephen Ramirez1, Yunyun Chen2, Stephen Y Lai2, and James Andrew Bankson1
1The Department of Imaging Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States, 2The Department of Head and Neck Surgery, The University of Texas M. D. Anderson Cancer Center, Houston, TX, United States

The traditional multimouse MRI methodology in which volume coils are dedicated to many mice must be reconsidered for short routine imaging protocols due to unnecessary complication of preparing and scanning many animals simultaneously. Instead we propose imaging a more manageable number of mice faster by dedicating phased arrays to each mouse and employing parallel imaging (PI) techniques. An array consisting of five transmit and 15 receive coils was selected as a throughput-optimized configuration for the next generation of 16-channel small-animal MRI systems. Details of the fabrication, testing, and in vivo use of the system for PI-accelerated multiple-mouse MRI are described.

1821.   High Throughput Microimaging of Mouse Brain and Embryo 
Jun Dazai1, Michael Wong1, Christine Laliberté1, and R Mark Henkelman1
1Mouse Imaging Centre, The Hospital for Sick Children, Toronto, Ontario, Canada

Anatomical abnormalities, especially in neuroanatomy, are important indicators of human disease and their respective mouse models. Using magnetic resonance imaging (MRI) and subsequent image analysis, minute abnormalities in the mouse brain and embryos can be detected. Using a custom-built 16-coil solenoid array, 16 mouse brains were imaged concurrently to produce high-resolution, ex vivo 3D datasets with an effective throughput of less than 45 minutes per sample.

1822.   Improving whole brain coverage and Signal-to-Noise ratio using novel intra-oral and over head surface coil array in rat under 9.4T 
Rupeng Li1, Phillip Bishop2, Andrzej Jesmanowicz2, Andrew Nencka2, J,B, Stephenson IV3, Christopher Pawela2, Ji-Geng Yan3, Anthony G Hudetz4, Hani Matloub3, and James S Hyde1
1Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, 2Biophysics, Medical College of Wisconsin, 3Plastic Surgery, Medical College of Wisconsin, 4Anesthesiology, Medical College of Wisconsin

A more-sensitive approach to whole-brain acquisition of the rat is showed here. It consists of an array of coils on the upper surface in combination with intra-oral coils supported on a bite bar. The intra-oral coil is customized with the coil surface directly contacted to the upper palate. This novel coil array design voids the tissue interference from the side and the bottom of the rat brain, and minimizes the signal drop off. This two coil array also causes apparent improvement in the SNR. This design could also be used for other small animal studies.

1823.   Eight-channel array coil optimized for functional imaging of awake monkeys at 7T 
Azma Mareyam1, James Blau1, Jonathan Polimeni1,2, Boris Keil1,2, Reza Farivar1,2, Thomas Benner1,2, Wim Vanduffel1,2, and Lawrence L Wald1,3
1A.A Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachussetts General Hospital, Charlestown, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Division of Health Sciences and Technology, Harvard-MIT, Cambridge, MA, United States

High-field functional MRI of non-human primates provides elevated BOLD contrast but requires an optimized coil design to boost the SNR, facilitate image acceleration, and maintain mechanical and electrical stability during the awake primate experiment. We present an 8-channel receive-only coil array optimized for high-resolution whole-brain imaging of the awake primate. Imaging performance is compared with other available 3T and 7T arrays.

1824.   A customized coil arrangement for PatLoc imaging inside a 9.4 T MRI spectrometer 
Elmar Fischer1, Raghad Aal-Braij2, Andreas Peter2, Jürgen Hennig1, Jan Gerrit Korvink2,3, and Maxim Zaitsev1
1Radiology, University Medical Center Freiburg, Freiburg, Germany, 2Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany, 3Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany

This work is on the implementation and successful test of a self-built RF coil arrangement inside a PatLoc gradient coil for experiments inside a 9.4 T Bruker small-animal scanner. An eight-leg high-pass birdcage resonator with a very thin wall of only 0.5 mm wall thickness around the sensitive volume has been constructed and was successfully tested in transceive mode on a silicon oil phantom. Using the resonator in combination with an in-house built eight-channel receive array coil, experiments inside a PatLoc gradient coil in the bore of the 9.4 T Bruker small animal scanner could be performed. In-vivo experiments on mice are planned.

1825.   Quadrature RF Coil and Phased Array Operation at 21.1 T 
Jose Antonio Muniz1,2, Malathy Elumalai1,3, Ihssan S Masad1,2, William W Brey1, Petr L. Gor'kov1, and Samuel Colles Grant1,2
1National High Magnetic Field Laboratory, The Florida State University, Tallahassee, FL, United States, 2Chemical & Biomedical Engineering, The Florida State University, Tallahassee, FL, United States, 3Electrical & Computer Engineering, The Florida State University, Tallahassee, FL, United States

The use of ultra-high magnetic fields for magnetic resonance imaging has the ability to produce data with increased SNR, higher spatial resolution and/or reduced imaging times. In order to take advantage of these benefits, the efficient design of RF coils is crucial, especially at higher frequencies. The goal of this work is to construct a transmit-receive quadrature driven saddle pair array that will provide improved SNR over similarly sized single loop surface coils and volume coils at 21.1 T. Further, the implementation of multi-channel configurations may extend these benefits to include improved homogeneity and reduced imaging times.

1826.   Comparison of Transmit Coil Configurations for Multiple-Mouse MRI with Receive-Only Coils 
Marc Filipe Carias1, John G Sled1, Mark R Henkelman1, and Brian J Nieman1
1Mouse Imaging Centre, Hospital for Sick Children, Toronto, Onratio, Canada

Multiple-mouse MRI (MMMRI) accelerates preclinical studies by imaging multiple mice simultaneously. We explored two possible transmit coil configurations for a MMMRI set up with separate transmit and receive coils: one with individual transmit coils for each mouse and one with a single large transmit coil for all mice. We observed that a single large transmit coil offered excellent image quality and some SNR benefit over the multiple transmit coil case. The large transmit coil is also appropriate for most imaging applications where high B1 field strength is not a requirement.

1827.   Mobile Coil Array for Interventional MRI 
Meng-Chi Hsieh1,2, San-Chao Hwang3, Hsu Chang3, and Jyh-Horng Chen1,2
1Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, 2Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, 3Division of Medical Engineering Research, National Health Research Institutes, Zhunan, Taiwan

In this work, a high resolution whole mice body image using mechanically sliding coil array was demonstrated for interventional MR. Three fixed coil arrays were situated on the bottom of mice body while the mechanically mobile small coil loop with high S/N, was put on the top of mice head to perceive higher S/N on the volume of interest (VOI). One high SNR quality image of mice head captured by mobile loop and three homogenous quality images of mice body acquired by associated fixed rectangular coils were acquired and used for image reconstruction using parallel imaging to speed up imaging time. Compared with conventional array coils, this design offers more freedom for target detection and offers higher SNR on the target area.

1828.   Dynamic imaging of a minipig's knee using a multichannel array and a movement device 
Sairamesh Raghuraman1,2, Joachim Schrauth1, Daniel Weber1, Frank Resmer2, Peter Michael Jakob1, Titus Lanz2, and Daniel Haddad3
1University of Wuerzburg, Wuerzburg, Germany, 2RAPID Biomedical GmbH, Rimpar, Germany, 3MRB Research Centre, Wuerzburg, Germany

Dynamic imaging of the cruciate ligaments in the complex curvature of minipig's knee is achieved using a multi-channel receive array and a movement device synchronised with sequence. Characterization of the coil along with static images and snapshots from dynamic images are presented.

1829.   Complementary-Output PIN Diode Driver for Animal Imaging 
Barbara L Beck1,2, Joshua E Slade1, and Huadong Zeng1,2
1McKnight Brain Institute, University of Florida, Gainesville, FL, United States, 2National High Magnetic Field Laboratory, Tallahassee, FL, United States

PIN diodes are a basic component used in MRI coils to control decoupling circuits, allowing operation of either transmit-only or receive-only coils. A PIN diode driver is necessary to send out the appropriate forward bias current and reverse bias voltage for the diode to function properly. However, small animal MRI systems may not be configured with PIN diode drivers and commercial PIN drivers are very expensive. As an alternative, we have developed a low cost driver that can output the required forward bias current and reverse bias voltage to successfully drive multiple PIN diodes.

Traditional Posters : Engineering
Click on to view the abstract pdf and click on to view the pdf of the poster viewable in the poster hall.
Gradients, Shims & Magnets: Design, Construction & Characterization

Tuesday May 10th
Exhibition Hall  13:30 - 15:30

1830.   Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI 
Dimitrios Sakellariou1, Cedric Hugon1, Angelo Guiga1, Aubert Guy1, Sandrine Cazaux1, and Philippe Hardy1
1CEA Saclay, Gif sur Yvette, Essonne, France

We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals.

1831.   Influence of Protection Circuit on Quench Characteristics for Clinical MRI Superconducting Magnets 
Ran Zhang1, Feng Liu2, Xiuhe Wang1, and Stuart Crozier2
1School of Electrical Engineering, Shandong University, Jinan, Shandong, China, People's Republic of, 2School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Queensland, Australia

The design and optimization of quench protection circuit for magnetic resonance imaging (MRI) superconducting magnets require extensive and accurate information about quench behaviors under the action of different quench protection systems. Conventional quench simulation with analytical approach has difficulty in dealing with nonlinear problems. In this study, a commercial three dimension FEM software OPERA-3D/QUENCH is employed to address the quench characteristics of actual 1T clinical MRI magnets with both symmetric and asymmetric configurations. Passive and active protection systems are involved to identify the influence of different protection circuit on the quench performances. The modeling process and setup for the solving are discussed in detail. Critical safety-related quantities such as maximum temperature, current and voltage of superconducting coils and the variation of fringe field during the transition are provided comparatively. By comparing the correspondent simulation results, it is concluded that the one type of quench protection system is not applicable for all the superconducting magnets and the selection of quench protection circuit demands considerable investigation.

1832.   A Single Magnet Fast Field-Cycling MRI System with Detection at 0.5T 
Gareth Reynold Davies1, Kerrin James Pine1, David John Lurie1, and Fred Goldie2
1Bio-medical Physics, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom, 2Tesla Engineering Ltd., Storrington, United Kingdom

We are studying the unique contrast that is available from the variation of proton relaxation in different magetic field strengths. This is accessable through the use of fast field cycling magnet systems which can switch form zero field to 0.5 T, and anywhere in between, in 15 ms.

1833.   A field offset coil for spatially localised in vivo field-cycling relaxometry 
Kerrin James Pine1, Fred Goldie2, and David John Lurie1
1Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, Scotland, United Kingdom, 2Tesla Engineering Ltd, Storrington, West Sussex, United Kingdom

Relaxometric properties of tissue vary greatly depending on the field strength at which they are measured. This is endogenous information not available from conventional imagers with fixed magnetic field strengths. One appealing approach is the "insert coil": a compact, portable addition to a conventional imager which can offset the main magnetic field B0 over a volume of interest. We describe the parameters of such a coil and its integration with a body-sized system. The coil is used in conjunction with a volume-localised inversion-recovery pulse sequence to plot T1dispersion in a human volunteer’s fingers over a range of field strengths.

1834.   Innovations in gradient coil construction 
William Bradfield Handler1, Brian Dalrymple1, Craig K Goodrich2, Dennis L Parker2, Timothy John Scholl3,4, Frank Van Sas1, and Blaine Alexander Chronik1
1Physics & Astronomy, University of Western Ontario, London, Ontario, Canada, 2University of Utah, U.C.A.I.R., Salt Lake City, Utah, United States, 3Robarts Research Institute, Imaging Research Laboratories, London, Ontario, Canada, 4Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada

Innovations in gradient coil construction techniques, both mechanical and computational will be presented with an example which is a head gradient coil built for UCAIR, Salt Lake City.

1835.   Insert Gradient Subsystem Tuning by Direct Impedance Measurements 
Wesley M Skeffington1, Franco M Martinez-Seantiesteban2, Bruce D Collick3, Andrew Alejski2, Brian K Rutt4, Luis J Garces1, and Paul M Szczesny1
1GE Global Research, Niskayuna, NY, United States, 2Robarts Research Institute, University of Western Ontario, London, Ontario, Canada, 3GE Healthcare, Waukesha, WI, United States,4Radiology Department, Stanford University, Stanford, CA, United States

Insert or specialty gradient coils enhance the capabilities of whole-body MRI systems. Use of the system’s gradient amplifiers without modification on insert coils can result in poor waveform fidelity, leading to reduced image quality. A method for using direct impedance measurements of a gradient coil to program a digitally controlled amplifier for operating on both whole-body and specialty gradient coils is presented. Use of the measured coil model resulted in a 93% reduction in coil current error and improved image quality.

1836.   Experimental validation of an improved analytical temperature distribution model for gradient coils 
Peter T. While1, Michael Poole2, Hector Sanchez Lopez2, Larry K. Forbes1, and Stuart Crozier2
1School of Mathematics and Physics, University of Tasmania, Hobart, TAS, Australia, 2ITEE, University of Queensland, Brisbane, QLD, Australia

Excessive heating is a considerable problem in gradient coil operation. An improved analytical model is presented for simulating the spatial steady-state temperature distribution for cylindrical gradient coils. The model includes resistive power deposition by current density, thermal conduction through a number of cylindrical layers and radial cooling via convection and radiation. Simulations are shown to compare well to experimentally measured temperature distributions for two coils of inherently different winding structure. Additionally, rise-times to reach thermal equilibrium are predicted. Many coil parameters and thermal material properties may be varied and the model provides a good utility prior to manufacture.

1837.   Planar gradient system for imaging with non-linear gradients 
Sebastian Littin1, Anna Masako Welz1, Daniel Gallichan1, Gerrit Schultz1, Christian Cocosco1, Jürgen Hennig1, Willem de Boer2, and Maxim Zaitsev1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Institute of Experimental nuclear Physics, KIT, Karlsruhe, Germany

We present a concept study of a planar gradient system for MR imaging with non-linear gradients, similar to the previously developed PatLoc system. This planar gradient system consists of 3 independent gradient channels with force and torque balance and will be integrated in our modified whole-body scanner equipped with 6 gradient channels. Simulations of the gradient system and image-reconstruction have been performed, showing that the coil achieves extended FOV for 2D imaging by combining three of its channels. Availability of such a gradient system will open new perspectives for flexible region-specific encoding in different body regions.

1838.   Novel Gradient Transparent RF Shielding Technologies for integrated PET/MR 
Daniel Truhn1, Fabian Kiessling1, and Volkmar Schulz1,2
1Institute of Experimental and Molecular Imaging, RWTH Aachen, Aachen, NRW, Germany, 2Philips Research Europe, Aachen, Germany

We demonstrate that a multiple shell setup exhibits favourable advantages over a single shell shielding enclosure in the context of simultaneous PET/MR imaging. It is shown that effects on the MR gradient fields can be reduced without compromising the shielding at high frequencies.

1839.   A practical insert design for dreMR imaging in the human head 
Chad Tyler Harris1, William B Handler1, Jamu K Alford2, and Blaine A Chronik1
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, 2Martinos Center for Biomedical Imaging, Massachusetts General Hospital/Harvard Radiology, Boston, MA, United States

Delta relaxation enhanced magnetic resonance (dreMR) is a new technology, which allows the specific detection of targeted agents only after they have chemically bound to their target molecule. This method utilizes an electromagnet insert coil in order to alter the main magnetic field as a function of time in an otherwise standard MR scanner. Previously, we have developed dreMR insert coils specifically for small animal imaging. In this study, we present a practical, actively shielded, dreMR coil insert design suitable for imaging of the human head.

1840.   Reducing image artefacts in concurrent TMS/fMRI by passive shimming 
Andreas Bungert1,2, Christopher Chambers1, and John Evans1
1Cubric, School of Psychology, Cardiff University, Cardiff, Cardiff, United Kingdom, 2Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

In concurrent TMS/fMRI, susceptiblity effects of the mostly diamagnetic TMS-coil cause field inhomogneities and image artefacts. We demonstrate that these artefacts can be reduced using stainless steel attached to the TMS coil for passive shimming. An MR-compatible figure-of-8 TMS coil was used and the steel was distributed on the back of the coil, approximately along the wire. Field maps of the effects of the coil with and without the shim on B0 were acquired. Also the artefacts in EP-images were studied in a phantom and a human. The shim reduced field inhomogeneities by 50-70% and improved the EP-images significantly.

1841.   Autocalibration of Field Monitoring Arrays by Reference Tones 
David Otto Brunner1, Christoph Barmet1, Maximilian Haeberlin1, Bertram Jacob Wilm1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Monitoring of gradient waveforms significantly enhances the quality of reconstructed MR images especially in case of fast read-out schemes. For this the geometrical positions of the sensors have to be calibrated, which is typically done in a dedicated preparation. This becomes unmanageable if the probe positions are changing during scanning. Here we propose a novel approach that uses small signal tones on the gradients occupying portions of the FM spectrum that are otherwise unused in order to autocalibrate the monitoring setup during acquisition. These tones have marginal influence on the trajectory and no impact on the sequence.

1842.   An Autonomous System for Continuous Field Monitoring with Interleaved Probe Sets 
Benjamin Emanuel Dietrich1, Christoph Barmet1, David Brunner1, and Klaas Paul Pruessmann1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Zurich, Switzerland

In current magnetic field monitoring systems acquisition duration is limited by the dephasing of the NMR field probes either by T2 decay, internal field variation or externally induced fields. Thus prohibiting field monitoring of scans with strong dephasing gradients (as applied in diffusion MRI) or long coherence trains (such as balanced SSFP). To alleviate these problems very short coherence times (T2,T1~ms) can be chosen. A new method based on short lived T/R-NMR probes enables real-time, continuous field monitoring. This is achieved by an interleaved excitation of sets of probes and rapid T/R switching.

1843.   Using Spatio-Temporal Field Monitoring for Iterative Higher Order DSU Pre-Emphasis Calibration 
Ariane Fillmer1, Johanna Vannesjö1, Christoph Barmet1, Peter Boesiger1, Klaas P. Pruessmann1, and Anke Henning1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

We present a fast iterative pre-emphasis calibration approach applied to a 3rd order DSU system, using spatio-temporal field monitoring to determine the ideal pre-emphasis settings. The major advantage of this technique compared to FASTERMAP based approaches is the higher time resolution and the significantly decreased expenditure of time.

1844.   Eddy current compensation for a PatLoc gradient coil 
Anna Masako Welz1, Daniel Gallichan1, Andrew J Dewdney2, Walter R Witschey1, Christian A Cocosco1, Hans Weber1, Jürgen Hennig1, Jan G Korvink3,4, and Maxim Zaitsev1
1University Medical Center Freiburg, Department of Radiology, Medical Physics, Freiburg, Baden-Württemberg, Germany, 2Siemens Medical Solutions, Erlangen, Germany, 3Dept. of Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany, 4Freiburg Institute of Advanced Studies (FRIAS), University Freiburg, Freiburg, Germany

PatLoc imaging with non-linear quadrupolar gradients has been developed and realised for rapid MR imaging. This gradient coil is driven within a clinical 3T scanner with 6 gradient channels for simultaneous use of the linear and PatLoc gradients. For rapid imaging the gradient coil performance and accuracy is especially important. This abstract describes the measurement procedure and the compensation of eddy currents from around 300Hz to 30Hz, which improves image quality significantly.

1845.   A Novel Method of Insert Gradient Field Mapping on a Composite Gradient System 
Glen Morrell1, Joshua Kaggie2, K. C. Goodrich2, Seong-Eun Kim2, Sung Man Moon2, and Dennis Parker2
1Radiology, University of Utah, Salt Lake City, Utah, United States, 2Utah Center for Advanced Imaging Research, Salt Lake City, Utah, United States

We demonstrate a method of mapping the field patterns of insert gradient coils in a composite gradient system. Composite gradient systems allow the simultaneous use of whole body gradient coils and localized insert gradient coils within the same pulse sequence. These systems combine the speed of nonlinear local insert gradient coils for readout with the desirable linearity of slower whole body gradients for slice selection. Correction of image distortion requires accurate maps of the nonlinear insert gradient fields used for readout. Our method provides distortion-free maps of the gradient insert fields over the entire imaging volume in reasonable imaging time

1846.   Oscillating Magnetic Field Mapping using MRI 
Vivek R Bhatia1, and Luis Hernandez-Garcia1
1Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

We present a new measurement for oscillating magnetic fields in the KHz frequency range using magnetic resonance imaging. The method uses non-linear iterative minimization techniques to estimate the field map. We deomnstrate our technique by simulations and in vitro experiments.

1847.   Transmit k-space Calibration using Magnetic Field Probes 
Frederik Testud1, Christoph Barmet2, Martin Haas1, Denis Kokorin1, Juergen Hennig1, Klaas P. Pruessmann2, and Maxim Zaitsev1
1Medical Physics, Dept. of Radiology, University Medical Center Freiburg, Freiburg, Germany, 2ETH and University, Zurich, Institute for Biomedical Engineering, Zurich, Switzerland

Field probes have been used in the last years for dynamic magnetic field monitoring in order to reduce image artifacts by using the measured field dynamics in the reconstruction. Parallel spatially selective Excitation allows inner volume imaging where only specifically regions of interest are excited. This relies on exact matching of multidimensional RF pulses and the simultaneously traversed k-space trajectory. Four 1H field probes were used for calibrating k-space trajectories used during transmit. The measured trajectories were then used to calculate RF pulses which were then applied to excite target patterns.

1848.   SAR Reduction using Non-Linear Gradients 
Emre Kopanoglu1,2, Burak Akin1, Vakur B. Erturk2, and Ergin Atalar1,2
1National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey, 2Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey

Slice-profile is related to the frequency-spectrum of an RF envelope through the gradient field, which is conventionally linear. Although a rectangular pulse is more efficient as far as SAR is concerned, apodized sinc envelopes are widely used for excitation because the slice-profile of a rectangular pulse is not desirable. In this study, a method that employs non-linear gradients to modify the slice-profile of a rectangular pulse into a feasible one is proposed. As a sample study, the method is compared to an apodized sinc envelope, and showed 41% reduction in SAR as well as an increase in correct excitation in the region of interest from 71% to 94%.