ISMRM 21st Annual Meeting & Exhibition 20-26 April 2013 Salt Lake City, Utah, USA

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
2351 -2395 Pulse Sequences & Applications
2396 -2400 RF Pulse Design
2401 -2420 Fat & Water: Methods & Evaluations
2421 -2447 MR Elastography
2448 -2479 Relaxometry
2480 -2504 Susceptibility
2505 -2525 Contrast Mechanism: From Exotic to Clinical Applications
2526 -2555 CEST, MT, APT
   

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
Pulse Sequences & Applications

2351.   Quantitative Comparison of Susceptibility-Weighted Methods in Deep Grey Matter in Multiple Sclerosis
Luca Y. Li1, Cheryl R. McCreary1,2, Fiona Costello3,4, and Richard Frayne3,4
1Seaman Family MR Research Centre, Foothills Medical Centre, Alberta Health Services, Calgary, Alberta, Canada, 2Departments of Radiology and Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada, 3University of Calgary, Calgary, Alberta, Canada, 4Hotchkiss Brain Institute, Calgary, Alberta, Canada

 
Accumulation of iron in deep grey matter structures has been shown to correlate with physical and cognitive and dysfunction in multiple sclerosis. MR susceptibility imaging could provide an objective surrogate marker for accumulation of iron. We compared normalized signal, SNR and CNR of the caudate nucleus, putamen, globus pallidus, and thalamus between T2* gradient echo and SWAN sequences on our 3T GE scanner. 13 subjects with multiple sclerosis and 5 healthy controls participated. Results suggest that changes in signal are more distinguishable on T2* GRE.

 
2352.   MR-Based Oxygen Extraction Fraction OEF Using Spatial ICA of Breath-Hold PARSE Acquisitions.
Charles G. Cantrell1, Rajiv G. Menon1, Parmede Vakil1, Sumeeth Vijay Jonathan1, and Timothy J. Carroll1
1Northwestern University, Chicago, IL, United States

 
We examined MR based OEF using spatial ICA of breath-hold PARSE acquisitions to determine the dynamic effects on brain oxygen absorbtion. Results clearly show a frontal shift in OEF during the period of induced stress followed by a return to the baseline after the stress is removed.

 
2353.   High Resolution Volumetric T1 Mapping Using a Novel MP3RAGE Method
Wei-Feng Hung1, Po-Tsun Chen1, Tzu-Chao Chuang1, Hing-Chiu Chang2, and Ming-Ting Wu3,4
1Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan, 2Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, United States, 3Department of Radiology, Kaohsiung Veteran General Hospital, Kaohsiung, Taiwan, 4School of Medicine, National Yang-Ming University, Taipei, Taiwan

 
MP2RAGE, which collects two volumes at different inversion times, can be applied for volumetric T1 mapping because the relationship between T1 and the ratio of two gradient echoes can be derived with a known inversion efficiency of adiabatic pulse. However, the over-estimation of inversion efficiency, which was simulated according to pulse profile, may lead to under-estimation of T1. An improved sequence, MP3RAGE, was developed to acquire data at three distinct inversion times, taking inversion efficiency as a free parameter to estimate T1 relaxation time more accurately.

 
2354.   Remember PSIF? a 2-Second Imaging Method for T2 Contrast at 7T
Yiu-Cho Chung1, Yanjie Zhu1, Xin Liu1, and Chao Zou1
1Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Key Laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China

 
T2 weighted imaging at 7T using TSE is challenged by B1 transmit field inhomogeneity and SAR limitation. We propose to use PSIF instead of TSE at 7T. PSIF uses low flip angle and is less sensitive to RF system imperfections. The high magnetic field offers the SNR needed in PSIF. Also, 2DPSIF is fast (2sec per image) due to short TR used. In 2DPSIF, the SNR of white matter is about 30, and the CNR between grey matter and white matter is about 18, sufficiently high for diagnostic purposes. 2DPSIF is a good alternative to T2 weighted TSE at 7T.

 
2355.   Rapid Whole-Brain Myelin Water Mapping Using Multi-Component Gradient Echo Sampling of Spin Echoes (McGESSE)
Yann Gagnon1,2, Neil Gelman1,2, Rob Nicolson3, and Jean Théberge1,2
1Medical Biophysics, University of Western Ontario, London, Ontario, Canada, 2Imaging, Lawson Health Research Institute, London, Ontario, Canada, 3Psychiatry, University of Western Ontario, London, Ontario, Canada

 
The myelin water fraction describes the proportion of the multi-exponential T2 decay in white matter originating from water trapped within the bi-layers of the myelin sheath. The most established method used to obtain the MWF involves the acquisition of 32 or more spin echoes but the inability to perform a multi-slice acquisition and the high specific absorption rate of this method are drawbacks that have motivated the development of alternative techniques. In this work, we described the in-vivo implementation of a novel strategy for rapid whole brain MWF mapping, based on the multi-component gradient echo sampling of spin echoes (mcGESSE).

 
2356.   Simultaneous Acquisition of Interslice Blood Flow, Magnetization Transfer Ratio Asymmetry, and MTR
Sung-Hong Park1,2, Jeffrey William Barker1,3, and Kyongtae Ty Bae1
1Radiology, University of Pittsburgh, Pittsburgh, PA, United States, 2Bio and Brain Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Daejeon, Korea, 3Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States

 
We investigated the feasibility of simultaneous mapping of interslice blood flow, MTR asymmetry, and MTR, using a recently developed method, alternate ascending/descending directional navigation (ALADDIN). The cumulative MT effects in edge slices from simulations based on a modified two-pool MT model were in agreement with empirical results . Simultaneous mapping of blood flow, MTR asymmetry, and MTR in the whole brain was feasible with ALADDIN within a clinically reasonable time of less than or equal to~7 min. Our proposed method provides readily a full spectrum of MR measurements useful to characterize a wide range of brain pathological conditions and functional evaluation.

 
2357.   Magnetization Transfer Prepared Gradient Echo CEST MRI at 7 Tesla
Zhuozhi Dai1, Jim Ji2, Gang Xiao3, Gen Yan1, Zhiwei Shen4, Guishan Zhang1, Lvhao Wang1, Phillip Zhe Sun5, and Renhua Wu1
1Medical Imaging, Medical College of Shantou University, shantou, guangdong, China, 2Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, 3Hanshan Normal University, Chaozhou, Guangdong, China, 4the provincial key laboratory of medical molecular imaging, Shantou, Guangdong, China, 5Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH and Harvard Medical School, Charlestown, Massachusetts, United States

 
CEST MRI is a relatively new contrast mechanism that is promising for clinical translation in a host of diseases including stroke, tumor and multiple sclerosis. However, the conventional CEST MRI requires significant sequence development and is susceptible to field inhomogeneity-induced distortion at high field. To address these limitations, we evaluated the magnetization transfer prepared gradient echo (MTPGE) MRI for CEST imaging. We validated and optimized the proposed MTPGE in creatine-gel phantom, and demonstrated the endogenous amide proton transfer (APT) MRI in vivo.

 
2358.   A Novel Method for Magnetization Transfer Ratio Imaging Without Requiring Separate Saturation Pulse
Jeffrey William Barker1,2, Kyongtae Ty Bae1, and Sung-Hong Park1,3
1Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3Bio and Brain Engineering, Korean Advanced Institute of Science and Technology, Daejeon, Yuseong-gu, Korea

 
We present a new technique for magnetization transfer (MT) ratio imaging that utilizes interslice MT effects inherent to multislice bSSFP imaging to generate MT contrast, which was controlled via an interslice delay (0-8s). We validated the source of contrast on a 4% agar phantom and saline phantom control. We also demonstrated the feasibility of in vivo MTR imaging by acquiring images in the brain of healthy normal volunteers (N = 5, age 24-49). Agar phantom images were homogeneous, and control images were free of contamination. Mean MTR values from all subjects for white and gray matter regions were (31.7±1.0)% and (21.7±1.2)%, respectively.

 
2359.   Prospective Acquisition: A Novel Application for Superluminal Photons in MRI
H. Morgan1, T. Traveler1, D. R. Who1, and E. Brown1
1Radiology, General Hospital, Memphis, TN, United States

 
Superluminal MRI has great potential for clinical imaging. Implementation of the method is straight forward on a clinical scanner with minimal changes. Here we report on a study with 89 patients where the technique was successfully applied with no adverse effects. All patients had their complete report available by the time they prepared for their scan. In few cases potential disruptions of the space-time continuum could be observed. Great efficiencies can be achieved reducing cost, staff idle time and patient waiting time.

 
2360.   Centric Reordered 2D BSSFP Imaging Using Variable Flip Angles for Fourier Decomposed MRI in the Lung
Dominique M.R. Corteville1, Åsmund Kjørstad1, Frank G. Zöllner1, and Lothar R. Schad1
1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Baden Württemberg, Germany

 
The variable flip angle approach for balanced steady-state free precession (bSSFP) imaging makes it possible to increase the signal-to-noise ratio (SNR) while keeping the specific absorption rate (SAR) constant. In this contribution the application of this technique to fourier decomposed (FD) proton pulmonary MRI is systematically investigated. For this purpose several flip angle schemes were combined with centric k-space reordering in such a way that the center of k-space was acquired with a higher flip angle than the periphery.

 
2361.   High Speed 3D B-SSFP at 6.5 mT
Mathieu Sarracanie1,2, Brandon Dean Armstrong1,2, and Matthew S. Rosen1,2
1Department of Physics, Harvard University, Cambridge, MA, United States, 2MGH/Martinos Center for Biomedical Imaging, Boston, MA, United States

 
The present work reports on the development of fast 3D imaging at very-low magnetic field (6.5 mT) based on the intrinsic 1H NMR signal using balanced steady state free precession (b-SSFP). This result is the first implementation of b-SSFP at very low magnetic field. The presented optimized bi-planar electromagnet combined with fast 3D imaging strategies and sparse sampling has potential to reach clinical standards for patient imaging and open new perspectives for new generation of lower-cost high-performance purpose-built imagers practical for operation in hospitals, battlefield medical facilities, or forward triage.

 
2362.   
Strategies for Improved 3D Small-Tip Fast Recovery (STFR) Imaging
Hao Sun1, Jeffrey A. Fessler2, Douglas C. Noll3, and Jon-Fredrik Nielsen3
1Electrical Engineering and Computer Science, The University of Michigan-Ann Arbor, Ann Arbor, Michigan, United States, 2Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States, 3Biomedical Engineering, The University of Michigan-Ann Arbor, Ann Arbor, Michigan, United States

 
Small tip fast recovery (STFR) imaging has been proposed recently as a potential alternative to balanced steady state free precession (bSSFP). STFR relies on a tailored “tip-up” RF pulse to achieve comparable signal level and image contrast as bSSFP, but with reduced banding artifacts. 2D STFR imaging can use fast 2D tailored pulses (e.g., spiral) in combination with RF-spoiling, but in many applications such as fMRI it is necessary to do 3D imaging. Designing a 3D RF pulse that accurately tailors the excitation pattern to the local B0 inhomogeneity over the entire imaging volume is a challenging and unsolved problem. Here we propose two complementary strategies for improved 3D STFR imaging: First we show that unbalanced non-RF-spoiled STFR imaging (“G-STFR”) is less sensitive to tip-up pulse error than the corresponding RF-spoiled sequence (“RF-STFR”). Second, we propose to use non-slice-selective tailored pulses for both tip-down and tip-up, and present two alternative RF pulse design algorithms.

 
2363.   
Rapid High Resolution 3D Volume Imaging of the Human Brain Using Spin Echo EPI, Parallel Imaging, Reduced-FOV Methods, and Oversampling Reduction at 7T
Christopher Joseph Wargo1 and John C. Gore1
1Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States

 
The aims of this research were to develop and evaluate an inner volume imaging approach to achieve high resolution with dramatically reduced scan times at the ultra-high field strength of 7T. This was accomplished using a combination of 3D multi-shot and single-shot EPI, parallel imaging using SENSE, reduced-FOV methods, and volume oversampling reduction by applying outer-volume suppression (OVS) bands at the ends of the 3D volume. Both 500 and 300 micron resolutions were achieved in the human midbrain without artifacts, within 3 to 7 minutes.

 
2364.   Diagonal Multi-Slab Inner Volume 3D GRASE Imaging for High Resolution T2 Weighted fMRI
An T. Vu1, David A. Feinberg2,3, Noam Harel1, Kamil Ugurbil1, and Essa S. Yacoub1
1Radiology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 2Advanced MRI Technologies, Sebastopol, CA, United States, 3Helen Willis Neuroscience, University of California, Berkeley, Berkeley, CA, United States

 
Single shot 3D GRASE provides T2 weighted images with high isotropic resolutions in a single shot. However it has yet to see wide usage in fMRI in part due to its limitation of imaging only a small field of view. Multi-slab 3D approaches could extend the FOV. However, with inner volume imaging, orthogonally oriented refocussing RF pulses saturate potential neighboring slabs. Here we present a method for multi-slab 3D GRASE inner volume imaging for fMRI which avoids the problem of saturated neighboring slabs and allows imaging of multiple regions of interest without extending TR and without any significant SNR penalties.

 
2365.   Simultaneous Multi-Volume GRASE Imaging
Liyong Chen1,2 and David A. Feinberg2,3
1Advanced MRI Technologies, LLC, Sebastopol, CA, United States, 2Helen Wills Neuroscience Institute, University of California, Berkeley, CA, United States, 3Advanced MRI Technologies, Sebastopol, CA, United States

 
A new approach for encoding multiple slabs and multiple 3D volumes simultaneously was proposed by applying orthogonal multibanded excitation and refocusing rf pulse slabs in zoomed 3D GRASE. This approach greatly increase spatial resolution (zoomed) and spatial coverage.

 
2366.   3D Adiabatic FSE with GRASE Acquisition at 4T
Naoharu Kobayashi1 and Michael Garwood2
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 2University of Minnesota, Minneapolis, Minnesota, United States

 
We introduce a novel adiabatic 3D FSE sequence that overcomes the high SAR and long scan time in 3D adiabatic FSE by using the following 4 techniques: (1) Variable-rate selective excitation (VERSE), (2) gradient- and spin-echo (GRASE) acquisition, (3) k-space undersampling, and (4) image space phase correction. The image space phase correction played a critical role to reconstruct odd and even echo data as a single image. The proposed sequence allowed 3D in vivo human brain FSE imaging with acceptable SAR and scan time at 4T.

 
2367.   3D Center-Out EPI with Cylindrical Encoding
Manoj Shrestha1, Toralf Mildner1, Christian Labadie1, and Harald E. Möller1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany

 
3D center-out EPI with cylindrical encoding is proposed as a rapid sampling method of 3D k-space enabling ultra-short echo time. Acquisition of multiple center-out EPI half-planes is performed while the (EPI) phase-blip gradient is rotated. 3D k-space is thus usually encoded along the read direction, and radially encoded in the planes perpendicular to it. The feasibility of the approach is demonstrated by preliminary images which are compared to imaging methods like 3D FLASH and 2D EPI. Due to the cylindrical sampling and an inherent manifold oversampling of the central k-space line, a lower susceptibility to subject motion can be expected.

 
2368.   Radial Single-Slab 3D Turbo Spin Echo (SPACE)
John P. Mugler, III1, Simon Bauer2, Dominik Paul2, Alto Stemmer2, and Berthold Kiefer2
1Radiology & Medical Imaging, University of Virginia, Charlottesville, VA, United States, 2Siemens Healthcare, Erlangen, Germany

 
Optimized, single-slab, 3D fast/turbo spin-echo (FSE/TSE) imaging (e.g., CUBE, SPACE, VISTA) has recently gained popularity for various clinical applications. While commercial implementations use conventional Cartesian sampling of k space, certain applications may benefit from the favorable properties of non-Cartesian k-space trajectories. The purpose of this work was to incorporate radial k-space sampling into optimized, single-slab, 3D FSE/TSE imaging, and to perform a preliminary evaluation of imaging performance. We found that good image quality can be obtained when radial k-space sampling is combined with the very long spin-echo trains and variable-flip-angle refocusing RF pulses used in state-of-the-art single-slab 3D FSE/TSE techniques.

 
2369.   in-vivo Brain 3D RSI (Rosette Spectroscopic Imaging) with Spherical/ellipsoidal Encoding. Comparison to 3D RSI with Cylindrical Encoding and to Ellipsoidal CSI.
Claudiu Schirda1, Tiejun Zhao2, Ovidiu C. Andronesi3, and Fernando Emilio Boada1
1Radiology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States, 2Siemens Medical Solutions, Pittsburgh, PA, United States, 3Radiology, Massachusetts General Hospital, Boston, MA, United States

 
Rosette Spectroscopic Imaging (RSI) with spherical encoding is demonstrated in-vivo brain and using the braino MRS phantom. The PSF function is compared to the PSF for RSI with cylindrical encoding and to CSI with ellipsoidal/spherical encoding.

 
2370.   High Resolution Radial 3D Ultra-Short Echo Time Imaging in vivo
Karl-Heinz Herrmann1, Martin Krämer1, Martin Stenzel2, Hans-Joachim Mentzel2, and Jürgen R. Reichenbach1
1Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 2Pediatric Radiology, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany

 
Ultra-short echo time imaging (UTE) allows visualization of structures with very short T2 relaxation times. Commonly, slice selective 2D double-half RF-pulse UTE with radial readouts is used. However, 3D radial center-out trajectories (“spiky ball”) have several advantages: Short, hard excitation pulses lead to extremely short echo times, oversampling is possible in all directions avoiding foldover artifacts, and extreme over-sampling of k-space renders the acquisition very robust against motion with excellent SNR. We present 3D UTE in vivo images with excellent resolution and display of anatomical details.

 
2371.   Evidence of Tissue Conductivity as a Source of Signal Inhomogeneities in Ultrashort Echo Time (UTE) Imaging
Ferdinand Schweser1,2, Li Huang1,3, Karl-Heinz Herrmann1, Martin Krämer1, Andreas Deistung1, and Jürgen R. Reichenbach1
1Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 2School of Medicine, Friedrich Schiller University Jena, Jena, Germany, 3Abbe School of Photonics, Faculty for Physics and Astronomy, Friedrich Schiller University Jena, Jena, Germany

 
In this contribution we investigated with a dedicated phantom experiment B1+ contributions to UTE signal inhomogeneities and showed that B1-related effects substantially affect the UTE signal. By applying Electric Property Tomography (EPT) to the complex-valued UTE signal we demonstrate that B1-effects due to the underlying tissue electrical conductivity are a major source of both magnitude and phase UTE signal inhomogeneity.

 
2372.   High-Resolution 3D-FMRI at 9.4 Tesla with Intrinsically Minimised Geometric Distortions
Rüdiger Stirnberg1, Daniel Pflugfelder1, Tony Stöcker1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine - 4, Research Centre Juelich GmbH, Jülich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

 
The application of a 3D-EPI sequence with intrinsically minimised geometric distortions for high-resolution functional imaging (fMRI) is demonstrated in vivo at 9.4 Tesla. In addition to acceleration by means of ramp sampling and parallel imaging, a further increase of the effective imaging bandwidth is achieved by segmentation in the blipped phase encode dimension. The presented results indicate the potential but also the practical limitations (e.g. acceptable temporal resolution) of minimising geometric distortions without employing further post-processing. However, resulting activation patterns, which precisely match the expected locations, prove the feasibility of segmented 3D-EPI for high-resolution fMRI at 9.4 Tesla.

 
2373.   MRiLab: Performing Fast 3D Parallel MRI Numerical Simulation on a Simple PC
Fang Liu1, Richard Kijowski2, and Walter F. Block1,3
1Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States

 
A simulation package named MRiLab is introduced here for performing efficient and flexible 3D numerical MRI simulation on simple PC. MRiLab features user-friendly interface and optimized programming-free modules that well suits for MR pulse sequence design and image reconstruction technique development. Associated tools are also provided for analyzing multiple spin evolution, MR signal and k-space formation, local SAR distribution, etc. With the simulation acceleration accompanied by GPU and multi-threaded CPU, MRiLab has proven to be a fast and effective parallel simulation framework with minimum computation hardware requirements.

 
2374.   Combination of Multiplexed EPI with EPIK (EPI with Keyhole) for Reduced Image Distortions at 3T
Seong Dae Yun1 and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Jülich, Germany, 2JARA - Faculty of Medicine, RWTH Aachen University, Aachen, Germany

 
The relatively high imaging speed of EPI has led to its widespread use in dynamic MRI studies. For even faster acquisition of multiple slices using EPI, the M-EPI (Multiplexed EPI) method has been recently presented (Feinberg et al.). However, the use of multiple RF pulses for multiple-slice excitation causes an increase of readout duration, which in turn increases image distortions. To overcome this problem, in this work M-EPI has been combined with EPIK (EPI with Keyhole) which has been proven to be effective in reducing the EPI image distortions. Experiments were performed at 3T and the method was validated with a phantom as well as on human brain data.

 
2375.   A New K-Space Trajectory for Compressed Sensing MRI
Ya Li1 and Ran Yang1
1School of Information Science and Technology, Sun Yat-Sen University, Guang Zhou, Guang Dong, China

 
we propose a new k-space trajectory named as four leaved rose curve (FLRC),which is a short, smooth, variable density and random-like. Simulations show that FLRC trajectory has better fidelity than spiral. It is well-suited for CS-MRI, because of: 1) The locations of FLRC sampling points are more irregular than spiral. And these artifacts are different. For spiral, the artifact looks like more regular, however, it is noise-like for FLRC. 2).The FLRC trajectory has more smaller side-lobe of PSF than spiral . That means incoherence what is the very important requirements should be satisfied for application of CS.

 
2376.   
An Efficient Scheme of Trajectory Optimization for Both Parallel Imaging and Compressed Sensing
Enhao Gong1, Feng Huang2, Kui Ying3, Xuening Liu4, and George Randy Duensing5
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Philips Healthcare, Shanghai, China, 3Department of Engineering Physics, Tsinghua University, Beijing, China, 4Department of Automation, Tsinghua University, Beijing, China, 5Philips Healthcare, Gainesville, FL, United States

 
Undersampling of k-space is a widely adopted approach for fast imaging. Instead of using a fixed sampling trajectory, trajectory optimization has been proposed for both Parallel Imaging and Compressed Sensing to achieve significantly improved reconstruction. Here we present an efficient scheme for clinically applicable trajectory optimization by using one scan in the exam as references and fast pseudo-reconstruction. Experiments on in-vivo datasets illustrated the proposed scheme can results in great improvement of reconstruction using Parallel Imaging and Compressed Sensing.

 
2377.   Simultaneous T2 Prep and Motion Tracking Using Volume Projections
Liheng Guo1, Di Xu1, and Daniel A. Herzka1
1Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States

 
We test the feasibility of performing motion tracking during T2 preparation (“T2 prep”) for the purpose of scan time reduction. For demonstration purposes, a single fully balanced readout is inserted in the midpoint between the innermost pair of T2 prep refocusing RFs to acquire a projection of the imaging volume. Preliminary motion phantom study has shown that this technique does indicate motion without visibly disturbing T2 contrast image quality. More elaborate motion readouts that can be inserted into T2 prep and their performance in human warrant further study.

 
2378.   Can Flow Be Measured with a Flow-Compensated Sequence?
Bo Xu1, Pascal Spincemaille2, Tian Liu2, and Yi Wang1
1Biomedical Engineering, Cornell University, Ithaca, New York, United States, 2Weill Cornell Medical College, New York, New York, United States

 
A new flow quantification measured is proposed. Multi-echo gradient echo sequence is used for data acquisition. Polynomial fit of multi-echo phase data is used to extract field inhomogeneity information. Coefficient of the fit is directly related to flow velocity. Thus by changing the background field inhomogeneity, flow could be quantified. This method is validated in phantom and in vivo experiments.

 
2379.   PatLoc Single Shot Imaging
Sebastian Littin1, Jakob Assländer1, Andrew Dewdney2, Anna M. Welz1, Hans Weber1, Gerrit Schultz1, Jürgen Hennig1, and Maxim Zaitsev1
1Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Healthcare Sector, Siemens AG, Erlangen, Germany

 
It has recently been proposed to use non-linear gradient encoding fields in order to reduce peripheral nerve stimulation and to allow for spatially varying resolution in different areas of the FOV. An industrially built PatLoc gradient insert coil brings us in the range of single shot imaging. The aim of this study is to show the feasibility of spiral and EPI imaging.

 
2380.   MR Pulse Sequence Design with Artificial Neural Networks
Nahal Geshnizjani1, Kenneth A. Loparo1, Dan Ma2, and Mark A. Griswold2,3
1Dept. of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, Ohio, United States, 2Dept. of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 3Dept. of Radiology, University Hospitals of Cleveland and Case Western Reserve University, Cleveland, Ohio, United States

 
This work presents a framework for automatic Pulse sequence design. We used Artificial Neural Networks (ANN) with a novel sequential block structure to design a system to automatically construct MR pulse sequences. We are able to predict a pure but extended T2-weighted signal from a TrueFisp sequence. This method can be utilized in MR Fingerprinting by designing non-traditional randomized pulse sequences for quantitative imaging

 
2381.   Real-Time, Self-Gated Spiral Flow Imaging Using Sliding-Window Phase Matching Reconstruction
Wei Feng1, Yang Xuan1, Jiani Hu1, and Ewart Mark Haacke1,2
1Radiology, Wayne State University, Detroit, Michigan, United States, 2Biomedical Engineering, Wayne State University, Detroit, Michigan, United States

 
A real-time, self-gated spiral flow imaging sequence using a sliding window phase matching reconstruction is proposed. The acquisition for reversed flow encodings was separated into a negative reference block and a positive acquisition block. View-shared reconstruction in each block was performed before phase contrast images were generated using a novel sliding window phase matching algorithm for self-gating. Experiments on normal volunteers and under different breathing conditions show that the proposed method can accurately quantify blood flow in real time.

 
2382.   Gradient-Modulated SWIFT
Jinjin Zhang1,2, Djaudat Idiyatullin1, Curtis Andrew Corum1, Naoharu Kobayashi1, and Michael Garwood1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 2Department of Physics, University of Minnesota, Minneapolis, Minnesota, United States

 
We report Sweep Imaging with Fourier Transformation (SWIFT) using time varying gradients during excitation. Gradient-modulated offset independent adiabaticity (GOIA) approach was used to modify the pattern of the RF pulse. Linear response theory was used to derive the signal evolution. A specific correlation method to retrieve the spin density for this case was developed. This method greatly increases the versatility of the SWIFT method and allows, for example, RF power reduction and increasing of the effective acquisition bandwidth. These conclusions are supported by simulations, resolution phantom experiments, and imaging of human brain in vivo using different types of gradient modulation.

 
2383.   Dual-Echo Magnetic Resonance Spectroscopy Imaging: Application to Traumatic Brain Injury
Elijah George1,2, Steven Roys1,3, Jiachen Zhuo1, Chandler Sours4, and Rao P. Gullapalli1
1Magnetic Resonance Research Center, University of Maryland School of Medicine, Baltimore, MD, United States, 2Bioengineering, University of Maryland, College Park, MD, United States, 3Diagnostic Radiology & Nuclear Medicne, University of Maryland, Baltimore, MD, United States, 4Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, United States

 
In Magnetic Resonance Spectroscopy studies of the human brain, the echo time (TE) of acquisition plays a huge role in determining which metabolite signals are present in the spectrum in addition to how well the baseline for signal quantification can be defined. Given that the scan times are long for MRSI, seldom both the long and short TE data is obtained on the same subject within the same session. Herein we describe a dual-echo (DE) MRSI acquisition that is capable of simultaneously acquiring both long and short TE data sets with the same scan time as a standard MRSI method and apply it on traumatic brain injury patients where the short and long T2 metabolites provide invaluable information.

 
2384.   3D Curved Slice Imaging
Hans Weber1, Sebastian Littin1, Gigi Galiana2, Feng Jia1, Anna M. Welz1, Robert Todd Constable2,3, Jürgen Hennig1, and Maxim Zaitsev1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Diagnostic Radiology, Yale University, New Haven, CT, United States,3Biomedical Engineering, Yale University, New Haven, CT, United States

 
ExLoc allows excitation and geometrically matched spatial encoding of curved slices by the application of a set of nonlinear, but locally orthogonal, encoding fields. So far the concept could be demonstrated for slices with one curved dimension. In this study, we apply ExLoc to a planar gradient system, generating field components with nonlinear variation along all three dimensions. For the first time, this allows selection and encoding of slices with two curved dimensions.

 
2385.   Potential Impact of Time-Varying Gradient Delays in the EPI Train on Nyquist Ghost Correction
Silke Hey1, Jos Koonen1, Zhaolin Chen1, and Johan van den Brink1
1Philips Healthcare, Best, Netherlands

 
Reliable phase correction for long fMRI scans is crucial to ensure low ghost levels. Phase correction strategies are based on the measurement of gradient delays, usually using a phase navigator. In this work, we show that gradient delays vary across the echo train depending on the used echo-spacing frequency. This variation may change in the course of long fMRI acquisitions (several minutes). That is why, accurate and robust correction of the Nyquist ghost in EPI requires determination of the gradient delays at the echo time of the EPI sequence.

 
2386.   Flip Angle ModulatioN Scheme (FANS) to Achieve an Arbitrary Signal Modulation in SPGR
Yongchuan Lai1
1GE Healthcare, Beijing, China

 
Spoiled gradient-recalled echo (SPGR) is widely used for T1 contrast applications. A variable flip angle (FA) scheme may be used to mitigate the signal modulation caused by Mz preparation. However, the challenge remains to find an appropriate variable flip angle scheme given a desired signal modulation. Here we propose a novel algorithm, Flip Angle modulatioN Scheme (FANS), to find such an optimal FA scheme to achieve an arbitrary signal modulation. FANS is implemented with the BRAVO of GE 1.5T scanner and better CNR is achieved in both simulation and in vivo scan.

 
2387.   High-Order B0 Shimming with Compensating RF Pulses Enables Efficient and Uniform Flip Angles
Vincent Oltman Boer1, Irene M.L. van Kalleveen2, Peter R. Luijten2, Robin A. de Graaf3, and Dennis W.J. Klomp2
1Radiology, University Medical Center Utrecht, Utrecht, NL, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, NL, Utrecht, Netherlands, 3Department of Diagnostic Radiology, Yale University, New Haven, CT, United States

 
Here we show how the additional degrees of freedom of a higher order B0 shim system can be utilized to compensate the flip angle variations generated by RF coils. The principle of compensation relies on linking spatially similar B0 and B1 distributions with an RF pulse with an appropriate frequency response. Experimental results in the human brain at 7T show that a compensating RF pulse in combination with a third order B0 offset field can mitigate the flip angle variations associated with a surface coil.

 
2388.   Turbo Spin Echo O-Space: Avoiding Artifacts and Enhancing Contrast
Gigi Galiana1, Dana Peters1, Leo K. Tam1, and Robert Todd Constable1
1Diagnostic Radiology, Yale University, New Haven, Connecticut, United States

 
O-Space imaging has been shown to provide good reconstructions from a minimal number of echoes, suggesting it could be a useful strategy for accelerated imaging. To further reduce scan time, we are developing strategies that will allow O-space acquisitions to play out in a turbo spin echo train. By carefully ordering the center place acquisitions, using offsets to control the TE of low frequency data, and applying spatially and temporally varying filters in reconstruction, we can dramatically reduce artifacts and improve contrast in TSE O-Space images.

 
2389.   
Ultra-High-Resolution Imaging of the Human Brain at 9.4 T Using K-Space Weighted Acquisition
Juliane Budde1, Gunamony Shajan1, Klaus Scheffler1,2, and Rolf Pohmann1
1Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, 2Department for Biomedical Magnetic Resonance, University of Tübingen, Tuebingen, Germany

 
Imaging with high spatial resolutions suffers from low SNR, long durations and high sensitivity to artifacts. K-space weighted imaging by acquiring a varying number of averages depending on the position in k-space constitutes a means to reduce signal contamination from adjacent voxels as well as to increase the apparent SNR. The resulting advantages are evaluated for high resolution human brain imaging at 9.4 T, yielding a gain in SNR of between 15 % and 28 % compared to conventional 3D GRE. With this technique, it was possible to acquire images from the human brain with voxel volumes of 14 nl.

 
2390.   Real-Time SPatiotemporal ENcoding Imaging of Renal Kinetics in Perfused Mice
Eddy Solomon1, Avigdor Leftin1, Peter Bendel2, and Lucio Frydman1
1Chemical Physics, Weizmann Institute of Science, Rehovot, Israel, 2Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel

 
One of real-time MRI’s aims is to monitor fast dynamic processes. Here we explore the use of “ultrafast” SPEN MRI, as a candidate for monitoring in real time the injection of contrast material into a mouse at high fields. Thanks to SPEN's ability to yield quality images even in challenging environments and in zoomed regions, fast perfusion phenomena could be viewed in both or in a single mouse kidney.

 
2391.   
Black Blood MRI of the Carotid Arteries with Local Excitation Coils at 7 Tesla
Tijl A. van der Velden1, Wouter Koning1, Maarten J. Versluis2, Dennis W.J. Klomp1, Peter R. Luijten1, and Jaco J.M. Zwanenburg1
1Radiology, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, 2Radiology, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands

 
When imaging plaque formation in the carotid artery black blood methods like DIR are used to increase the contrast between the vessel wall and the lumen. Due to the absence of a built-in volume coil the traditional black blood methods cannot be used at 7 tesla. This work evaluated the performance of 6 different black blood methods using local excitation coils. Evaluation was performed based on the suppression of the blood as well as the effects on the static tissue in a phantom setup. In-vivo experiments with healthy volunteers were performed to validate the performance when imaging the carotid artery.

 
2392.   Enhancement of the Myelin Rich Regions in MR Images in the Mouse Brain in vivo Using IR-UTE with a Cryo-Coil at 9.4 T.
Weronika Piedzia1, Krzysztof Jasinski1, Katarzyna Kalita1, Boguslaw Tomanek1,2, and Wladyslaw Piotr Weglarz1
1Department of MRI, Institute of Nuclear Physics PAN, Krakow, Malopolskie, Poland, 2Department of Clinical Neurosciences and Radiology, University of Calgary, Calgary, Alberta, Canada

 
Efficiency of the IR-UTE pulse sequence in improving contrast to noise ratio (CNR) of myelin and other structures in mouse brain in vivo at 9.4T using standard volume coil and CryoProbe was assessed. 2D UTE and IR-UTE with two inversion recovery times (TI): 500 ms and 1000 ms were used. Positive enhancement of CNR for white matter in relation to CSF and grey matter was observed in images obtained with IR-UTE (TI = 1000 ms), when compared to 2D UTE. An increase in CNR of approximately 2.5-fold was observed using CryoProbe as compared to birdcage coil for each structure.

 
2393.   In Vivo Optimisation of GABA Measurements in the Hippocampus Using MEGA-PRESS at 3T
Bhavana S. Solanky1, Niamh Cawley2, Anna Graca1, Richard Anthony Edward Edden3,4, Olga Ciccarelli2, and Claudia Angela M. Wheeler-Kingshott1
1NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom, 2Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, London, United Kingdom, 3Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States, 4F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

 
GABA is the main inhibitory neurotransmitter. Using MEGA-PRESS editing techniques GABA measurements in many areas of the brain but have been reported mainly limited to large voxels in areas of B0 homogeneity. 1H MRS measures in the hippocampus, which has an important role in memory and cognitive function, are limited due its small size, strong susceptibility changes and the pulsatile flow of cerebrospinal fluid. This study successfully measured GABA in vivo in the hippocampus at 3T using cardiac triggered MEGA-PRESS. A mean value of 1.7mM was found. This protocol allows reliable absolute measures of GABA in the hippocampus.

 
2394.   Signal Behavior of FLASE and TSE for Measuring Trabecular Bone - Theory and Experiments
Jakob Kreutner1, Peter M. Jakob1,2, and Daniel Haddad3
1Research Center Magnetic-Resonance-Bavaria, Würzburg, Bavaria, Germany, 2Experimental Physics 5, University of Würzburg, Würzburg, Bavaria, Germany, 3MRB Research Center, Würzburg, Bavaria, Germany

 
The usage of spin echo sequences for imaging trabecular bone is limited by the low number of echoes that can be acquired per excitation due to the long echo spacing compared to T2-relaxation. Instead of using a 90° excitation pulse and wait for full T1-relaxation, we calculated the signal for different combinations of turbo factor, repetition time and excitation angle with constant scan time and compared these to a widely-used FLASE protocol. Calculations and experiments show in good agreement, that TSE can achieve a higher signal than FLASE at the cost of a slightly broadened point spread function.

 
2395.   Imaging the Mandibular Nerve at High Isotropic Resolution Using a Turbo Spin Echo with Local Look
Jakob Kreutner1, Andreas J. Hopfgartner2, Julian Boldt3, Kurt Rottner3, Ernst J. Richter3, Peter M. Jakob1, and Daniel Haddad4
1Research Center Magnetic-Resonance-Bavaria, Würzburg, Bavaria, Germany, 2Experimental Physics 5, University of Würzburg, Würzburg, Bavaria, Germany,3Prosthodontics, Dental School, University of Würzburg, Würzburg, Bavaria, Germany, 4MRB Research Center, Würzburg, Bavaria, Germany

 
Precise knowledge of the course of the mandibular nerve is necessary for choosing correct positioning and size of dental implants. Using a 3D Turbo Spin Echo with Local Look, allows 0.5mm isotropic resolution within 6.5 minutes scan time. The nerve canal can be easily traced due to the high contrast to the surrounding bone marrow. Distances can be easily quantified and a 3D reconstruction can be done.

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
RF Pulse Design

2396.   
A Simultaneous Multi-Slice Fast-Kz RF Pulse for Reduced B1+ Inhomogeneity
Robert James Anderson1, Benedikt A. Poser1, William A. Grissom2, and Victor Andrew Stenger1
1Dept. of Medicine, University of Hawaii, Honolulu, HI, United States, 2Dept. of Biomedical Engineering, Vanderbilt Universiy, Nashville, TN, United States

 
There is recent interest in Simultaneous Multi-Slice (SMS) imaging because of reduced imaging times. SMS excitation is typically achieved with a single-slice pulse modulated to excite N identical slices. However, there has been little work done on extending SMS excitations to multi-dimensional RF pulses. For example, the “Fast-kz” or “spokes” 3D RF pulse has been shown to excite thin slices with in-plane B1+ inhomogeneity reduction. We present a simple, analytical “proof-of-concept” SMS Fast-kz pulse for correcting the central brightening associated with B1+ inhomogeneity from a volume transmitter. We demonstrate the excitation of multiple B1+ inhomogeneity compensated brain slices at 3T.

 
2397.   Multidimensional Pulses Based on Spatiotemporal Encoding Concepts
Jean-Nicolas Dumez1 and Lucio Frydman1
1Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel

 
The concepts of spatiotemporal encoding are exploited to design a new class of multidimensional pulses. In particular, 2D pulses are implemented, which operate in a hybrid direct and reciprocal excitation space. These hybrid 2D pulses are shown to be compatible with SPEN as well as Fourier imaging. In the case of Fourier imaging, a self-unfolding mechanism can be used to retrieve the region of interest even when it overlaps with excitation sidebands, thus allowing for larger bandwidths. Phantom experiments at 7T are used to illustrate the properties of SPEN-based multidimensional pulses.

 
2398.   Complex Multiband Spectral-Spatial RF Pulse Design for Hyperpolarized C-13 Applications
Adam B. Kerr1, Peder E.Z. Larson2, Daniel B. Vigneron2, and John M. Pauly1
1Electrical Engineering, Stanford University, Stanford, CA, United States, 2Radiology, UCSF, San Francisco, CA, United States

 
A novel approach for designing multiband spectral-spatial RF pulses with complex spectral profile specifications is described. Example RF pulses for application to C-13 imaging are presented and experimentally validated. The complex profile capability is also exploited to achieve a 20% reduction in the peak B1 required by a complex-phase spectral-spatial pulse compared to its linear-phase analog by optimizing the phase for each spectral band.

 
2399.   B1+-Selective RF Pulses and Their Design Using a Rotated Shinnar-Le Roux Algorithm
William A. Grissom1 and Mark D. Does1
1Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, United States

 
A new class of B1+-selective RF pulses is presented that produce excitation only over a prescribed |B1+|, and are designed using the Shinnar-Le Roux algorithm. The pulses' amplitude waveforms resemble refocused gradient trapezoids, while their frequency waveforms resemble sine-modulated slice-selective pulses. Simulated and experimental validation results are presented, including a simulated comparison to an adiabatic (BIR-4) pulse. The pulses could be used for reduced-FOV imaging based on B1+, or in place of non-selective adiabatic pulses, where they would have the advantage of providing a uniform excitation over only a prescribed B1+ range, with a minimum pulse duration.

 
2400.   A Spectral Spatial Fat Suppressing Pulse for Simultaneous Multi-Slice Excitation
Robert James Anderson1, Benedikt A. Poser1, and Victor Andrew Stenger1
1Dept. of Medicine, University of Hawaii, Honolulu, HI, United States

 
Two methods for achieving simultaneous multi-slice (SMS) excitation, multi-band and PINS RF pulses, are combined with a fat-suppressing spectral-spatial pulse in order to minimize the time needed to acquire a single volume of the brain. Both pulses are shown to excite only the water signal across nine simultaneously excited slices of a water/oil phantom and a human brain. Without the need to run a fat-saturating pre-pulse and the almost nine-fold reduction in acquisition times due to SMS, it was possible to acquire a volume with voxel size 3.5x3.5x5mm3 within a TR of 275ms.

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
Fat & Water: Methods & Evaluations

2401.   Fat Suppression Using the Gradient Reversal Technique for Continuously-Moving-Table Whole-Body MRI: A Comparative Study
Yeji Han1, Yoojin Lee1, Dong Chan Kim1, Joonsoo Kim1, and HyunWook Park1
1Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Daejeon, Korea

 
Continuously moving table (CMT) MRI is an efficient whole-body (wb) imaging technique for screening-type applications, which provides spatially and temporally continuous images. However, CMT-MRI has to pay careful attention to fat suppression because the rationale behind the conventional fat suppression approaches, including short tau inversion recovery (STIR) and fat saturation, is not applicable to the CMT cases. In this abstract, we propose an expansion of the GR technique for CMT sequences and compare it with other fat suppression techniques to demonstrate the efficiency of the GR algorithm for fat suppression.

 
2402.   
Utilization of a BSSFP Signal Model for Improved Fat/Water Decomposition in BSSFP Breast Imaging
Leah C. Henze Bancroft1, Diego Hernando2, Kevin M. Johnson3, Frederick Kelcz4, Roberta Strigel4, and Walter F. Block3,5
1Biomedical Engineering, University of Wisconsin - Madison, Madison, WI, United States, 2Radiology, University of Wisconsin-Madison, Madison, WI, United States, 3Medical Physics, University of Wisconsin - Madison, Madison, WI, United States, 4Radiology, University of Wisconsin - Madison, Madison, WI, United States, 5Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, United States

 
The IDEAL fat/water decomposition algorithm makes use of multipeak fat model that improves decomposition process with Gradient Echo and Spin Echo sequences. However, when a bSSFP sequence is used the resulting signal magnitude and phase responses can differ significantly from the standard multipeak fat signal model. Presented here are previously uncharacterized changes to this model due to bulk phase changes and amplitude modulations that occur with the use of a bSSFP sequence as well as a method for incorporating this model into a fat/water decomposition algorithm.

 
2403.   
Balanced SSFP-Like Imaging with Simultaneous Water-Fat Separation and Band Reduction Using Small-Tip Fast Recovery
Feng Zhao1, Hao Sun2, Jon-Fredrik Nielsen1, Jeffrey A. Fessler3, and Douglas C. Noll1
1Biomedical Engineering, The University of Michigan, Ann Arbor, MI, United States, 2EECS, The University of Michigan, Ann Arbor, MI, United States, 3EECS, University of Michigan, Ann Arbor, MI, United States

 
We propose to use a bSSFP-like imaging sequence, referred to as Small-tip Fast Recovery imaging (STFR), to simultaneously suppress banding artifacts and separate water/fat. This method works for both small and large tip angles, which is advantageous over a recently proposed bSSFP-based fat suppression method called LAMA.

 
2404.   Better Fat Saturation Employing DRFS
Xiaocheng Wei1, Yongchuan Lai1, and Weiwei Zhang1
1GE Healthcare, Beijing, Beijing, China

 
The traditional chemical shift selective (CHESS) radiofrequency pulse is often ineffective in suppressing lipid within a large field of view (FOV) due to the presence of B0 inhomogeneity. In this abstract, we propose a new method to suppress lipid signal, Dual-Region Fat Saturation (DRFS). DRFS divides a scan region into multiple sub-regions, in which the shimming could then be applied independently. Volunteer results show that compared with CHESS, DRFS could achieve better and uniform fat suppression across entire FOV, which enable DRFS a much broader application.

 
2405.   Respiratory Self-Gating for Free-Breathing Quantitative Fat/Water Imaging in the Abdomen
Tianjing Zhang1,2, Ning Jin1,3, Weiguo Li1,4, Xiaoming Yin1, and Andrew C. Larson1,2
1Radiology Department, Northwestern University, Chicago, Illinois, United States, 2Biomedical Engineering Department, Northwestern University, Evanston, Illinois, United States, 3Siemens Healthcare, Columbus, Ohio, United States, 4University of Illinois at Chicago, Chicago, Illinois, United States

 
This work introduces the combination of free-breathing technology with a fat/water separation method. A revised MGRE sequence was implemented to acquire imaging data during each volunteer’s free-breathing process, followed by an off-line image reconstruction. After that a global optimization algorithm was performed for fat/water separation. The results demonstrated that respiratory self-gated multiple gradient recalled echo sequence with the variable projection fat/water separation method is efficient in reducing the motion artifacts in abdominal imaging. In that way there are no restrictions for slice coverage, spatial resolution as well as scan time in the abdominal fat/water separation applications.

 
2406.   Improved Single-Pass Dual Echo Dixon Imaging with Ramp Sampling and Flexible Echo Times
Ken-Pin Hwang1,2, Olen Rambow2, Ersin Bayram3, John D. Hazle2, John E. Madewell4, Zachary W. Slavens5, Anthony T. Vu5, and Jingfei Ma2
1Global Applied Science Laboratory, General Electric Healthcare, Houston, TX, United States, 2Department of Imaging Physics, University of Texas MD Anderson Cancer Center, Houston, TX, United States, 3Global Applied Science Laboratory, GE Healthcare, Houston, TX, United States, 4Department of Radiology, University of Texas MD Anderson Cancer Center, Houston, TX, United States, 5MR Engineering, General Electric Healthcare, Waukesha, WI, United States

 
Errors in conventional two-point fat-water separation methods may occur when acquired echo times deviate far from those expected by the separation algorithm. Single-pass, dual-echo sequences are particularly vulnerable when pursuing high resolution at higher field strengths, where the increased frequency shift of lipid demands shorter echo times and echo spacings. This study alleviates this resolution limitation by extending the sampling window to the ramps of the readout pulses and freeing the echo time constraints with a flexible TE algorithm. With this combined method, we demonstrate improved spatial resolution while also improving the overall scan efficiency the sequence.

 
2407.   
Spectral-Spatial Selectivity Using Spatiotemporal Encoding
Jean-Nicolas Dumez1, Rita Schmidt1, and Lucio Frydman1
1Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel

 
A mechanism based on spatiotemporal encoding is exploited to add spectral selectivity to a pair of slice-selective frequency-swept pulses. The SPEN-based SPSP selectivity is used for fat suppression in spin-echo imaging. It does not require fast oscillating gradients and provides high-quality slice profiles. It can also be used to acquire images for two chemical species simultaneously. These concepts are illustrated with phantom experiments at 7T. Examples of fat suppression and water/fat imaging are also shown for breast imaging of human volunteers at 3T.

 
2408.   A Systematic Evaluation of an Auto Regressive Moving Average (ARMA) Model for Fat-Water Quantification and Simultaneous T2* Mapping
Axel J. Krafft1, Brian Allen Taylor1, Hannah Lin1,2, Ralf B. Loeffler1, and Claudia M. Hillenbrand1
1Radiological Sciences, St. Jude Children's Research Hospital, Memphis, TN, United States, 2Rhodes College, Memphis, TN, United States

 
Iron overload assessment is one of the most prominent applications of multi-echo GRE-based quantitative T2* mapping. One of the major confounding factors arises in the presence of fat due to additional modulations of the mGRE signal. However, these modulations can be modeled and have led to dedicated techniques for fat-water quantification with T2* estimation. Here, we systematically analyze a recently proposed autoregressive moving average (ARMA) model for its ability to simultaneously quantify fat-water concentrations and the associated T2* times. The ARMA model is compared to conventional fitting approaches and evaluated in phantoms and volunteer data.

 
2409.   Single-Point Fat-Water Separation Using a Fuzzy C-Means Algorithm
Junmin Liu1, David W. Holdsworth1,2, and Maria Drangova1,2
1Imaging Research Laboratories, Robarts Research Institute, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada,2Department of Medical Biophysics, Shulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada

 
A single-point Dixon fat-water separation method is presented to address the concern of relative long scan times associated with multi-echo acquisition. The method derives field maps using the bias-corrected fuzzy C-means (BCFCM) algorithm from a single-echo data set. In vivo 3D experimental results demonstrate that the proposed technique offers robust fat-water separation from a single data set; the results are compared those generated by the three-point IDEAL technique.

 
2410.   A Geometric Interpretation of Water-Fat Identification in Two-Point Dixon Imaging Without Phase Correction
Olen Rambow1, John D. Hazle1, John Clark2, and Jingfei Ma1
1Imaging Physics Department, University of Texas MD Anderson Cancer Center, Houston, TX, United States, 2Department of Electrical Engineering, Rice University, Houston, TX, United States

 
The possible solutions to the signal equations in two-point Dixon imaging are the intersection points of two ellipses in the water-fat plane. When the multi-peak spectrum of fat is included in the signal model, the ellipses tilt in such a way that at certain echo time combinations only one solution remains in the region where water and fat are both non-negative. This makes it possible to select the correct solution without phase correction. Simulation, phantom, and in vivo data show that the accuracy achievable by this method depends on both SNR and the echo times.

 
2411.   Water/Fat Decomposition Using Globally Optimal Non-Iterative Graph Surface Estimation
Chen Cui1, Xiaodong Wu2, Milan Sonka2, and Mathews Jacob2
1Electrical and Computer Engineering, The University of Iowa, Iowa city, IA, United States, 2Electrical and Computer Engineering, The University of Iowa, Iowa city, Iowa, United States

 
We introduce a novel fat-water decomposition based on non-iterative graph surface estimation.Global optimum of solution is guaranteed through 3D graph searching scheme. Method is applicable to multi-fat peaks situtation. Method are tested on multiple clinical datasets successfully. Computation expense is saved significantly compared to other major algorithms.

 
2412.   Noniterative Closed Form Solution to Multipeak Proton-Density Fat Fraction Estimation
Takeshi Yokoo1,2, Qing Yuan1, and Ivan E. Dimitrov2,3
1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, 2Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States,3Phillips Medical Systems, Highland Heights, OH, United States

 
This proof of concept study shows that a closed form estimation of multipeak proton-density fat fraction is possible using multiecho gradient-echo imaging. It compares favorably to the conventional nonlinear least-square fitting methods.

 
2413.   Optimization of Fat-Water Separation Algorithm Selection and Options Using Image-Based Metrics with Validation by ISMRM Fat-Water Challenge Datasets
David S. Smith1, Johan Berglund2, Joel Kullberg3, Håkan Ahlström3, Malcolm J. Avison4, and E. Brian Welch5
1Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, United States, 2Philips Healthcare, Stockholm, Sweden, 3Department of Radiology, Uppsala University, Uppsala, Sweden, 4Department of Pharmacology, Vanderbilt University, Nashville, Tennessee, United States, 5Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, United States

 
This research describes a robust fat-water separation algorithm for multi-echo MRI applicable to datasets spanning a wide range of anatomy, magnetic field strengths and collected echo times. The algorithm is validated in the context of the 2012 ISMRM Fat-Water Challenge. We show evidence of the power of image-based metrics to predict the best (or nearly best) option among multiple results obtained with various advanced fat-water separation algorithms. No matter the contest outcome, we look forward to sharing the full details of our final algorithm and to seeing many excellent solutions developed by other teams participating in the ISMRM Fat-Water Challenge.

 
2414.   A Novel Tiered, Multi-Threaded Region Growing Algorithm for Improved Phase Correction for Two-Point Dixon Imaging
Jingfei Ma1 and John D. Hazle1
1Imaging Physics, MD Anderson Cancer Center, Houston, TX, United States

 
We present a novel tiered, multi-threaded region growing algorithm for two-point Dixon water and fat imaging that can overcome the difficulty in phase correction when regions of large noise, artefacts, or isolated tissues are present. Each thread of processing starts from an initial seed and covers only a high-quality region containing the initial seed. Tiered seed masks serve as a quality metric and allow more trusted regions to be processed first even when completely isolated regions are present. Successful application of the algorithm is demonstrated for processing in vivo two-point Dixon images.

 
2415.   Water-Fat Identification for Analytical Multipoint Dixon’s Method
Dinghui Wang1 and James G. Pipe1
1Neuroimaging Research, Barrow Neurological Institute, Phoenix, AZ, United States

 
The recently proposed analytical formula obtains two sets of solutions of the field map, water and fat from images acquired at multiple points with flexible TE increments. We propose a post-processing based on regional iteration and region growing to reliably extract the correct field map from the two solutions. The field map can then be used to recalculate water and fat, and correct imaging artifacts such as blurring in spiral imaging. Results of the implementation with 3D spiral imaging suggest the feasibility of the method for a wide range of field map using short, uneven TE increments.

 
2416.   Effects of Denoising in the Estimation of T2* from Images Acquired Through Dixon Imaging
Rodrigo Moreno1, Thobias Romu2, Olof Dahlqvist Leinhard1, Magnus Borga2, and Ebo de Muinck1
1Department of Medical and Health Sciences, Linköping University, Linköping, Östergötland, Sweden, 2Department of Biomedical Engineering, Linköping University, Linköping, Östergötland, Sweden

 
This abstract explores the effect of prefiltering in the estimation of T2* from images acquired through symmetric Dixon imaging. Non-stationary Gaussian noise is removed from 8-point Dixon images acquired from the abdomen. T2* is computed by curve fitting of the in-phase images and the improvement of the estimation is computed through R2. The mean of R2 in is improved with the filtering from 0.73 to 0.75, from 0.84 to 0.89 and from 0.84 to 0.93 for fat- and water-dominant regions and ROIs in the liver respectively. Results suggest that advanced signal model fitting is only necessary in the fat-dominant regions.

 
2417.   Comparison of Accuracy and Precision of Image-Based Fat Quantification with Different Flip Angle Approaches in Skeletal Muscle
Pernilla Peterson1 and Sven Månsson1
1Medical Radiation Physics, Malmö, Lund University, Malmö, Sweden

 
This study aims at investigating the potential gain in precision using large or dual flip angles (FAs) for quantification of fat fraction (FF) in skeletal muscles, compared to a small FA approach. The accuracy and precision within muscle tissue in the lower leg of five lymphedema patients was investigated using small, large, and dual FAs. There was no improvement in precision of FF quantification from using neither a large nor dual FA approach. The large FA approach also resulted in a clear overestimation of the FFs. In conclusion, a small FA approach is preferable for FF quantification in skeletal muscles.

 
2418.   Validation of a Convex Relaxation Approach for Field Map Estimation
Abraam S. Soliman1,2, Jing Yuan2, Terry M. Peters1,2, and Charles A. McKenzie1,3
1Biomedical Engineering, University of Western Ontario, London, Ontario, Canada, 2Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada,3Medical Biophysics, University of Western Ontario, London, Ontario, Canada

 
MRI provides a unique ability to distinguish fat and water signals based on their unique chemical shifts. A successful separation largely relies on the correct estimation of B0 magnetic field inhomogeneities. In this work, we validate a previously proposed approach for field map estimation using datasets provided by the ISMRM challenge for water-fat reconstruction. All the datasets acquired with equally-spaced echo-times were processed by our technique. The average online scoring was 98.78 %, demonstrating that our method can be reliably applied on a wide variety of anatomies in clinical practice.

 
2419.   Comparison of Hepatic Fat Measurements Using Dual-Echo MDIXON Imaging and 1H MRS with Fat Phantom Validation
Paul Begovatz1, Peter Nowotny1, Tomas Jelenik1, Bettina Nowotny1, Birgit Klüppelholz2, Guido Giani2, Juergen Bunke3, Michael Roden1,4, and Jong-Hee Hwang1
1Institute of Clinical Diabetology, German Diabetes Center, Duesseldorf, Germany, 2Institute for Biometry and Epidemiology, German Diabetes Center, Duesseldorf, Germany, 3Philips Healthcare, Hamburg, Germany, 4Department of Metabolic Diseases, University Clinics, Heinrich Heine University, Duesseldorf, Germany

 
DIXON imaging is increasingly being used for liver fat quantification with a flexible Dual-Echo (mDIXON) technique recently introduced that provides a higher SNR through very short echo times. Tests of mDIXON versus 1H-MRS were conducted in a set of fat phantoms and human subjects. mDIXON showed a good correlation (slope=1.00, r=0.99, p<.001, intercept=4.5%) in the fat phantoms, and between mDIXON and 1H-MRS in vivo hepatic fat (slope=1.07, r=0.96, p<.001, intercept=1.6%). This shows that mDIXON can be used to detect changes in liver fat due to intervention in diabetics, but more work must be done for accurate disease diagnosis.

 
2420.   IDEAL Fat-Water Separation for the Detection and Characterization of Subcutaneous Hemorrhage
Andreas Petrovic1, Clemens Diwoky2, Eva Hassler1, Kathrin Ogris1, and Eva Scheurer1
1Ludwig Boltzmann Institute for Clinical-Forensic Imaging, Graz, Austria, 2Institute for Medical Engineering, Graz University of Technology, Graz, Austria

 
In forensic medicine the morphological characterization of subcutaneous (s.c.) hemorrhage caused by violent events is highly desired. Detailed knowledge of the origin and age of injury can help to reconstruct the sequence of events. However, accurate dating of s.c. hemorrhage is still an unsolved problem. In this study we examined volunteers with artificially created hematomas at several points in time after hematoma creation using the IDEAL fat-water separation technique. We found that with this method excellent delineation of s.c. hemorrhage is possible. Additionally, ROI analysis of water fraction images indicates a systematic decrease of water fraction with time.

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
MR Elastography

2421.   in vivo Quantification of Local Transient Softening in the Juvenile Rat Brain After Cannabinoïd Treatment: First Indications for Neuronal Remodeling?
Simon Chatelin1, Marie Humbert-Claude2, Philippe Garteiser1, Valérie Vilgrain1,3, Bernard E. Van Beers1,3, Zsolt Lenkei2, and Ralph Sinkus1
1U773-CRB3, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Paris, France, 2Laboratoire de Neurobiologie, ESPCI-CNRS UMR 7637, ESPCI-ParisTech, Paris, France,3Department of Radiology, University Hospitals Paris Nord Val de Seine, Beaujon, Clichy, France

 
Recent studies suggest a significant influence of type-1 cannabinoïd receptors (CB1R) on the puberty maturation processes. A preliminary study showed a decrease of the hippocampus elasticity after CB1R agonist injection. The aim of this study is to assess the significance and causes of this effect in the hippocampus of juvenile rats. The first step consists in the comparison of hippocampus elasticity and cerebral blood flow (CBF) values, from MR–Elastography (MRE) and Flow-sensitive Alternating Inversion Recovery (FAIR) perfusion imaging respectively, after CB1R activation. In a second step, the sensitivity of MRE to CBF modifications is assessed using the vasodilator nicardipine.

 
2422.   Measuring the Characteristic Topography of Brain Stiffness with Magnetic Resonance Elastography
Matthew C. Murphy1, John Huston1, Clifford R. Jack1, Kevin J. Glaser1, Matthew L. Senjem1, Jun Chen1, Armando Manduca2, Joel P. Felmlee1, and Richard Leroy Ehman1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States, 2Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States

 
In this work, we present a novel MR elastography pipeline for measuring regional brain stiffness free of edge-related bias and with high test-retest reliability. Repeatability was measured in 10 healthy volunteers, and the results indicated that typical errors for measuring global and regional brain stiffness were <1% and <2%, respectively. Furthermore, the results show that the mechanical properties of the brain follow a characteristic topography. Considering the lobes of the brain, stiffness is greatest in the occipital lobes, followed by the frontal lobes, the temporal lobes and finally the parietal lobes.

 
2423.   Mechanical Properties of the Frontal Lobe Gray and White Matter Measured Using MR Elastography with Soft Prior Regularization
Matthew D.J. McGarry1, Curtis Jonhson2,3, Elijah Van Houten4, Bradley P. Sutton3,5, John G. Georgiadis2,3, John Weaver1,6, and Keith D. Paulsen1,7
1Thayer School of Engineering, Dartmouth College, Hanover, NH, United States, 2Department of Mechanical Science and Engineering, University of Illinois at Urbana Champaign, Urbana, Illinois, United States, 3Beckman institute for Advanced Science and Technology, University of Illinois at Urbana Champaign, Urbana, Illinois, United States, 4Department of Mechanical Engineering, University de Sherbrooke, Sherbrooke, Quebec, Canada, 5Department of Bioengineering, University of Illinois at Urbana Champaign, Urbana, Illinois, United States, 6Department of Radiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH, United States, 7Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, NH, United States

 
A method of including spatial information in MR elastography mechanical property reconstruction is presented. Soft prior regularization is implemented through the addition of a penalty term to the objective function of a non-linear inversion algorithm to favor solutions with homogeneous property values in predefined spatial regions. Viscoelastic properties of the gray and white matter of the frontal lobe are presented to demonstrate the technique.

 
2424.   in vivo Waveguide Elastography of the Corona Radiata
Anthony J. Romano1, Michael Scheel2, Sebastian Hirsch3, Juergen Braun4, and Ingolf Sack2
1Physical Acoustics, Naval Research Laboratory, Washington, DC, United States, 2Department of Radiology, Charite-Universitatsmedizin, Berlin, Germany, 3Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, 4Institute of Medical Informatics, Charite - University Medicine Berlin, Berlin, Germany

 
White matter is composed primarily of myelinated axons which form fibrous, organized structures and can act as waveguides for the anisotropic propagation of sound. The evaluation of their elastic properties reguires both knowledge of the orientation of these waveguides in space, as well as knowledge of the waves propagating along and through them. Here, we present waveguide elastography for the evaluation of the elastic properties of the Corona Radiata, In Vivo, using a fusion of MRE, DTI, and anisotropic inversions. It is shown that the Corona Radiata can be characterized by Orthotropic anisotropy.

 
2425.   
MR Elastography Reveals the Local Properties of White Matter Structures
Curtis L. Johnson1,2, Matthew D.J. McGarry3, John B. Weaver3,4, Keith D. Paulsen3,4, Huan Wang2,5, William C. Olivero2,5, Bradley P. Sutton2,6, and John G. Georgiadis1,2
1Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 2Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 3Thayer School of Engineering, Dartmouth College, Hanover, NH, United States, 4Dartmouth-Hitchcock Medical Center, Lebanon, NH, United States, 5Surgery, University of Illinois Medical School, Urbana, IL, United States, 6Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States

 
Multishot MRE sequences for the brain allow for the acquisition of high-resolution displacement data, which can be used to create shear modulus maps with spatial variations consistent with white matter architecture. Through atlas-based segmentation, the mechanical properties of the corpus callosum and corona radiata are quantified. Healthy subjects are used to show that these structures are distinct from each other and from the total white matter. The reliability of these local measures is demonstrated through multiple scans of a single subject. This work shows that localized differences in brain mechanical properties may be investigated using high-resolution MRE.

 
2426.   Magnetic Resonance Elastography of the Upper Airways with Guided Pressure Waves
Pascal Hagot1, Emeline Lamain2, Tom Doel3, Xavier Maître1, Redouane Fodil4, and Luc Darrasse1
1IR4M(UMR8081), Univ Paris-Sud, CNRS, Orsay, France, 2Service de Neuroradiologie, Univ Paris-Sud, Hôpital Bicêtre, Le Kremlin-Bicêtre, France, 3Oxford University Computing Laboratory, Univ of Oxford, Oxford, United Kingdom, United Kingdom, 4IRMB, Univ Paris XII, INSERM (U955), Creteil, France

 
Localisation of collapses in the upper airways of patients woth obstructive sleep apnea syndrome is a critical issue to guide and individualize the potential surgical option and procedures. Acoustic measurements may provide valuable information on the upper airway conformation and allow discrimination of healthy and pathological region. Mean amplitudes per slice ranged between 13 and 42 μm along the anterior-posterior direction, 11 and 43 μm along the feet-head direction, 11 and 47 μm along the right-left direction. The generated pressure wave is efficiently guided through the upper airways from the mouth down to the end of the trachea.

 
2427.   Automated Analysis of Hepatic MR Elastography Images with Motion Artifacts and Signal Inhomogeneities
Bogdan Dzyubak1, Armando Manduca2, Kevin J. Glaser2, Meng Yin2, and Richard Leroy Ehman2
1Mayo Graduate School, Mayo Clinic, Rochester, MN, United States, 2Radiology, Mayo Clinic, Rochester, MN, United States

 
MR Elastography (MRE) is increasingly being adopted as a practical approach for clinical diagnosis and staging of hepatic fibrosis using noninvasive measurements of liver stiffness. A fully automated algorithm that determines appropriate ROIs from which to report tissue stiffness and agrees with expert readers has been presented previously. Improvements that enable the algorithm to analyze images with motion artifact, signal inhomogeneity, and low edge contrast are presented here. The stiffnesses calculated by the algorithm across 500 cases had a similar discrepancy with clinical readers as the inter-reader discrepancy reported by our previous study.

 
2428.   Multifrequency MRE of Human Liver Specimen: Sensitivity of Viscoelastic Powerlaw Constants to the Collagen Matrix in Hepatic Fibrosis
Ingolf Sack1, Rolf Reiter1, Korinna Joehrens2, Andreas Fehlner3, Sebastian Hirsch1, Jing Guo4, Rajan Somasundaram5, Daniel Seehofer6, Carsten Kamphues6, Abbas Samani7, and Juergen Braun8
1Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Berlin, Germany, 2Department of Pathology, Charité - Universitätsmedizin Berlin, Berlin, Berlin, Germany, 3Department of Radiology, Charité University Medicine, Berlin, Berlin, Germany, 4Department of Radiology, Charite - University Medicine Berlin, Berlin, Berlin, Germany, 5Interdisciplinary Rescue Center, Charité - Universitätsmedizin Berlin, Berlin, Berlin, Germany, 6Department of Transplantation Surgery, Charité - Universitätsmedizin Berlin, Berlin, Berlin, Germany, 7Department of Electrical & Computer Engineering, University of Western Ontario, London, Ontario, Canada, 8Institute of Medical Informatics, Charite - University Medicine Berlin, Berlin, Berlin, Germany

 
Elastography has been established for the clinical assessment of liver fibrosis. However, little is known about the relationship between viscoelastic constants and pathophysiological mechanisms in the liver. In this study, samples of the liver of 16 patients with different degrees of fibrosis, inflammation and steatosis were investigated by wide-range MRE and by static indentation for the interaction between mechanical constants and structural parameters of human liver according to histology, matrix protein quantification and function tests. As a main result, MRE was the most sensitive modality to the degree of fibrosis outperforming static indentation experiments and chemical quantification of matrix proteins.

 
2429.   MR Elastography of ex Vivo Prostate Cancer at Multiple Frequencies at 7T
Ramin S. Sahebjavaher1, Guy Nir1, Mohammad Honarvar1, Andrew Yung1, Piotr Kozlowski1, Louis O. Gagnon1, Edward C. Jones1, Garteiser Philippe2, Ralph Sinkus2, Silvia Chang1, Larry Goldenberg1, and Septimiu E. Salcudean1
1University of British Columbia, Vancouver, BC, Canada, 2Institut National de la Santé et de la Recherche Médicale (INSERM), Paris, Île-de-France, France

 
MR elastography (MRE) is performed on ex-vivo prostate cancer specimens. The viscoelastic properties are probed at three frequencies. The reconstructed maps of both the shear (Gd) and loss (Gl) moduli registered to whole-mount histopathology can distinguish cancerous from healthy tissue. The ability to extract frequency dependent information is also assessed.

 
2430.   3D Multifrequency Abdominal MR Elastography Using a Piezoelectric Driver, Single-Shot Wave-Field Acquisition, and Multifrequency Dual Parameter Inversion
Jing Guo1, Sebastian Hirsch2, Rolf Reiter1, Thomas Kroencke1, Patrick Asbach3, Juergen Braun4, and Ingolf Sack1
1Department of Radiology, Charite - University Medicine Berlin, Berlin, Berlin, Germany, 2Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Berlin, Germany, 3MVZ CBF Radiologie, Charite - University Medicine Berlin, Berlin, Berlin, Germany, 4Department of Medical Informatics, Charite - University Medicine Berlin, Berlin, Berlin, Germany

 
3D multifrequency MRE including nonmagnetic shear wave excitation and least-squares multifrequency inversion is introduced for improving the spatial resolution in abdominal-MRE viscoelasticity maps. The new method is demonstrated in health volunteers and patients with ascites and portal hypertension. All three technical key-points, driver, single-shot wave field acquisition and dual parameter inversion, are new in their application to abdominal MRE and contribute to an improved clinical protocol for the precise and spatially highly resolved mechanical assessment of the liver and the spleen.

 
2431.   Waveguide Magnetic Resonance Elastography of the Heart
Anthony J. Romano1, Ria Mazumder2, Seongjin Choi3, Bradley Dean Clymer4, Richard White5, and Arunark Kolipaka5
1Physical Acoustics, Naval Research Laboratory, Washington, DC, United States, 2Electrical and Computer Engineering, Ohio State University, Columbus, OH, United States,3Radiology, The Ohio State University, Columbus, OH, United States, 4Electrical and Computer Engineering, The Ohio State University, Columbus, OH, United States,5Radiology and Internal Medicine, Ohio State University Wexner Medical Center, Columbus, OH, United States

 
Previously, we implemented a method called Waveguide Elastography in the analysis of the orthotropic elastic parameters of the corticospinal tracts (CSTs) in the brains of five healthy volunteers. Here, we extend this method in the analysis of an ex-vivo, porcine heart. We used our method to evaluate the anisotropic shear coefficients C44and C55 within the three layers of myocardial fibers (i.e. the epicardial, myocardial, and endocardial). We found that there was significant variation within the shear coefficients indicating that the heart is, at a minimum, orthotropic, with stiffness values ranging from 40-60 kPa.

 
2432.   MR Elastography as a Method to Determine the Mechanical Properties of Fresh and Formalin Fixed Porcine Hearts
Ria Mazumder1, Bradley Dean Clymer1, Richard White2,3, and Arunark Kolipaka2,3
1Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH, United States, 2Deparment of Radiology, The Ohio State University, Columbus, OH, United States, 3Deptarment of Internal Medicine, Division of Cardiology, The Ohio State University, Columbus, OH, United States

 
Formalin fixed hearts have been actively used in research to study mechanical properties such as stiffness of left ventricular (LV) myocardium. However, the stiffness of the fresh hearts greatly differs from that of the formalin fixed hearts. Mechanical testing has been the gold standard to determine the stiffness of the myocardium. In this study MR Elastography is used to compare the stiffness of LV myocardium between fresh and formalin fixed hearts within the same animal specimen. We have observed that formalin fixed hearts are significantly stiffer than the fresh hearts.

 
2433.   Quantification of Aortic Stiffness Using MR Elastography and Its Comparison to Pulse Wave Velocity: Early Validation
Aniurdh Damughatla1, Brian Raterman2, Orlando P. Simonetti2,3, Travis Sharkey-Toppen4, Ning Jin5, Richard White2, and Arunark Kolipaka2,3
1Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States, 2Radiology, The Ohio State University, Columbus, Ohio, United States, 3Internal Medicine, Division of Cardiovascular Medicine, The Ohio State University, Columbus, Ohio, United States, 4Davis Heart & Lung Institute, The Ohio State University, Columbus, Ohio, United States, 5Siemens Medical Solutions, The Ohio State University, Columbus, Ohio, United States

 
In aortic aneurysm or Marfan syndrome the stiffness of the aorta varies spatially, however clinical techniques provide global measure of stiffness. Therefore, there is a need for spatial estimation of stiffness of aorta non-invasively. The purpose of the study is to compare the abdominal aortic stiffness obtained using MRI based pulse wave velocity (PWV) measurements against magnetic resonance elastography (MRE) based stiffness measurements in normal volunteers with increase in age. The MRE stiffness values and PWV values plotted against age resulted in similar correlation in the in initial pool of data demonstrating initial feasibility in the same imaging plane.

 
2434.   Motion Correction in MR-Elastography
Marion Tardieu1, Marie Poirier-Quinot1, Emeline Lamain1, Ralph Sinkus2, Luc Darrasse1, and Xavier Maître1
1IR4M (UMR8081), CNRS, Univ Paris-Sud, Orsay, France, 2Centre de Recherches Biomédicales Bichat-Beaujon (UMR773), CRB3, Inserm, Paris, France

 
MR-elastography (MRE) aims at characterizing the properties of tissues by motion sensitized phase measurements, and had to cope with the intrinsic motions of the patient itself. A method taking account a correction for both spatial and displacement field component is proposed and is evaluated on a numerical brain phantom: a degradation of a in vivo 3D MRE acquisition (without motion) by 3D rotations between the three spatial encoded directions. The standard deviation of the difference between the reference acquisition phase and the motion simulated one decreased of about a factor 3 to 6 for motion angle of 0.5° to 5°.

 
2435.   Noise Robust Inverse Laplacian Operator Based Reconstruction of Global Elastic Parameters in Magnetic Resonance Elastography.
Sebastian Papazoglou1,2, Heiko Tzschaetzsch1, Juergen Braun3, and Ingolf Sack1
1Radiology, Charité University Medicine, Berlin, Berlin, Germany, 2NeuroCure Clinical Research Center, Charité University Medicine, Berlin, Berlin, Germany, 3Medical Informatics, Charite - University Medicine Berlin, Berlin, Berlin, Germany

 
Magnetic resonance elastography (MRE) provides diagnostically significant average viscoelastic parameters in organs with good signal to noise ratio (SNR) such as, e.g. the human liver. Usually, parameter reconstruction in MRE requires the computation of noise amplifying derivatives and also involves the inversion of noisy wave data. Therefore this direct approach is ineffective in case of very low SNR, e.g. in MRE on the human lung. In this study we present an approach based on the wave equation featuring the inverse Laplace operator, which requires no inversion to robustly recover global viscoelastic parameters even in presence of strong noise.

 
2436.   MR Elastography Using Switching-Gradient-Induced Vibration of the Patient Table - Assessment of Reproducibility -
Mikio Suga1,2, Takayuki Obata2, Hajime Ikeda1, Atsuhisa Koyama1, Tetsuya Wakayama3, and Riwa Kishimoto2
1Graduate School of Engineering, Chiba University, Chiba, Chiba, Japan, 2National Institute of Radiological Sciences, Chiba, Chiba, Japan, 3GE Healthcare Japan, Hino, Tokyo, Japan

 
Magnetic resonance elastography (MRE) is a noninvasive technique for measuring tissue viscoelasticity. Switching-gradient(s)-induced vibration (SGIV) can be used as a mechanical driving mechanism for MRE. The advantage of this approach is that it can be easily adapted for clinical application, but the reproducibility of measurements has not been confirmed. To evaluate reproducibility of MRE scanning with SGIV (MREwSGIV), this study compared shear wave amplitudes in gel phantoms of different weight and measured the viscoelasticity of the human brain at specific mechanical resonance frequencies twice. The results suggest that MREwSGIV enables reproducible measurements of brain elasticity.

 
2437.   Simple MR Elastography: A Gradient-Echo Type Multiecho MR Sequence
Tomokazu Numano1,2, Junichi Hata3, Kazuyuki Mizuhara4, Kouichi Takamoto5, Toshikatsu Washio2, Hisao Nishijo6, Kazuo Yagi1, and Kazuhiro Homma2
1Radiological Science, Tokyo Metropolitan University, Arakawa-ku, Tokyo, Japan, 2Institute for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 3The University of Tokyo Hospital, Bunkyo-ku, Tokyo, Japan, 4Mechanical Engineering, Tokyo Denki University, Adachi-ku, Tokyo, Japan, 5Department of Judo Neurophysiotherapy, University of Toyama, Toyama, Toyama, Japan, 6System Emotional Science (Physiology), University of Toyama, Toyama, Toyama, Japan

 
In this work we report on the development of a new technique for non-MSG MR Elastography sequence based upon a gradient-echo type multiecho MR sequence. In contrast to multiecho imaging major benefit of shortening acquisition time, we use the other benefit; separate images are produced from each echo of the train with different TE. When the period of actuator-generated vibration and the multiecho readout gradient lobes are in agreement, the MSG-like effect serves as the maximum. Moreover, the later generated echo is the greater the MSG-like effect (1st<2nd<3rd...), the non-MSG MRE multiecho sequences include images with different MSG-like effects are used to obtain various simultaneously without increasing the acquisition time.

 
2438.   Diffusion Tensor Imaging Enhanced Anisotropic MRE of the Brain
Guangqiang Geng1, Michael Green1, Caroline Rae1,2, Ralph Sinkus3, Roland G. Henry4, and Lynne E. Bilston1,5
1Neuroscience Research Australia, Sydney, NSW, Australia, 2UNSW, Sydney, NSW, Australia, 3Centre de Recherches Biomédicales Bichat-Beaujon, Paris, France,4Departments of Radiology and Biomedical Imaging, Neurology, and Bioengineering Graduate Group, University of California, San Francisco, California, United States, 5Prince of Wales Clinical School, UNSW, Sydney, NSW, Australia

 
Magnetic Resonance Elastography (MRE) measures the mechanical properties of the brain in vivo. Most brain MRE studies have assumed isotropy regardless to the anisotropy shown by diffusion tensor imaging (DTI). We combine MRE and DTI to investigate the anisotropic viscoelasticity of human brains. In WM, shear modulus (µ┴=2.44±0.05kPa) and its anisotropy (µFA=0.32±0.01) were significantly greater (ANOVA, p=0.0107 and 0.0011) than in GM (µ┴= 2.02±0.07kPa, µFA=0.24±0.00), consistent with rheological measurements. Also, μFA increased significantly (p<0.0001) from 0.27 to 0.35 when DTI FA increased from 0.26 to 0.54. DTI enhanced MRE enabled a reliable mapping for the anisotropic viscoelasticity of human brains.

 
2439.   High Resolution 3D Multifrequency MR Elastography at 7T
Juergen Braun1, Ralf Lützkendorf2, Jing Guo3, Sebastian Hirsch4, Andreas Fehlner5, Ingolf Sack5, and Johannes Bernarding6
1Department of Medical Informatics, Charite - University Medicine Berlin, Berlin, Germany, 2Department for Biometry and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany, 3Department of Radiology, Charite - University Medicine Berlin, Berlin, Germany, 4Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, 5Department of Radiology, Charité University Medicine, Berlin, Germany, 6Department for Biometry and Medical Informatics, Otto von Guericke University, Magdeburg, Germany

 
3D multifrequency MRE at 7 T MRI combined with least-squares multifrequency inversion was applied to five healthy volunteers in order to demonstrate the capability of cerebral MRE for providing maps of viscoelastic parameters with high spatial resolution. Our results show that the spatial resolution of viscoelastic parameter maps can approach the resolution of anatomical MR images. Viscoelastic parameters are significantly higher for white matter compared to gray matter. Ultrahigh field 3D multifrequency MRE may be used in the clinic for the mechanical characterization of tumors or neurodegenerative processes.

 
2440.   Magnetic Resonance Elastography for the Measurement of the Bulk Modulus in Compressible Materials.
Sebastian Hirsch1, Frauke Beyer1, Sebastian Papazoglou1, Jing Guo2, Juergen Braun3, and Ingolf Sack1
1Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Berlin, Germany, 2Department of Radiology, Charite - University Medicine Berlin, Berlin, Berlin, Germany, 3Institute of Medical Informatics, Charite - University Medicine Berlin, Berlin, Berlin, Germany

 
Compressible phantoms comprising agarose gel with gas-filled cavities were examined by a rheometer device and MR Elastography (MRE). An effective medium model was used to explain the bulk modulus revealed by the rheometer. MRE was able to detect the relative order of compressibility in phantoms, while severely underestimating the absolute numbers of the bulk moduli. Numerical simulations revealed that compression MRE is sensitive to noise imposing the need of appropriate post-processing. In conclusion, MRE can measure compression properties of tissue, while a more noise-robust inversion method is required for quantitative measurements of bulk moduli.

 
2441.   Evaluation of Commonly Available Materials for MR Elastography Phantoms
Loribeth Q. Evertz1, Jun Chen1, Jennifer L. Kugel1, and Richard Leroy Ehman1
1Mayo Clinic, Rochester, MN, United States

 
Commercial phantoms for system calibration and validation are common for imaging modalities like CT and MRI, including resolution and flow phantoms. However, there currently are no commercial sources for a suitable liver-mimicking test phantom for MRE. The purpose of this study was to identify and test readily available and inexpensive materials that might be useful as simple test phantoms for hepatic MRE.

 
2442.   Fast, Whole-Brain MR Elastography Using a 3D Multislab Acquisition
Curtis L. Johnson1,2, Joseph L. Holtrop2,3, Matthew D.J. McGarry4, John B. Weaver4,5, Keith D. Paulsen4,5, Bradley P. Sutton2,3, and John G. Georgiadis1,2
1Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 2Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 3Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 4Thayer School of Engineering, Dartmouth College, Hanover, NH, United States, 5Dartmouth-Hitchcock Medical Center, Lebanon, NH, United States

 
Most estimates of the mechanical properties of brain tissue from MRE are average values computed over only a small number of slices. This is derived from the need to keep scan times short for subject comfort and safety, which leads to acquisitions exhibiting low spatial resolution or poor brain coverage. In this work we take advantage of the SNR efficiency of 3D multislab acquisitions to develop an MRE sequence capable of acquiring high-resolution MRE displacement data with whole-brain coverage in a reasonable scan time.

 
2443.   Title: a Novel Method for Dynamic Mechanical Analysis of Soft Viscoelastic Materials and Comparison to Magnetic Resonance Elastography.
Phillip J. Rossman1 and Jun Chen1
1Mayo Clinic, Rochester, MN, United States

 
A new method for measuring the complex modulus of soft "tissue-like" materials using the basic principles of Dynamic Mechanical Analysis (DMA) is presented. Results are compared to to those obtiained using Magnetic Resonance Elastography (MRE).

 
2444.   Introduction of Sample Interval Modulation for the Simultaneous Acquisition of 3D Displacement Data in MR Elastography
Dieter Klatt1, Temel Kaya Yasar2, Thomas J. Royston1, and Richard L. Magin1
1Department of Bioengineering, The University of Illinois at Chicago, Chicago, Illinois, United States, 2Department of Mechanical & Industrial Engineering, The University of Illinois at Chicago, Chicago, Illinois, United States

 
Sampling interval modulation (SLIM)-MRE is introduced as new recipe for the arrangement of the motion encoding gradients (MEG). SLIM-MRE is independent of the type of MRE sequence and enables complete acquisition of 3D displacements of a monofrequency vibration within a single temporally-resolved MRE experiment. The displacement components are sampled using different time intervals and, in doing so, they are encoded as different apparent frequencies in the MRE signal phase. Thus, all three spatial components are stored in the same k-space and can be decomposed from eight temporally-resolved MRE experiments instead of 12-24 experiments, as is commonly performed in conventional MRE.

 
2445.   Highly Accelerated MR Elastography
John C. Bosshard1 and Steven M. Wright1
1Electrical & Computer Engineering, Texas A&M University, College Station, TX, United States

 
Highly parallel imaging with a 64 channel receive array in a "sandwich" configuration was used to capture MR elastography images of an emerging mechanical wave at 156 x 125 lower case Greek mum resolution. The same system was also used to perform simultaneous single echo acquisition imaging at the top and bottom boundaries of the sample using a non-linear gradient coil for compensation of RF coil phase. This method may have applications in microscopic MRE or for monitoring of elastic properties during single-shot events.

 
2446.   Matching Motion Sensitivity with TE and TR in Elastography for Faster Scans
Roger C. Grimm1, Jun Chen1, Scott A. Kruse1, and Richard Leroy Ehman1
1Mayo Clinic, Rochester, MN, United States

 
Elastography acquisitions measure a propagating complex shear wave field at multiple phase points to estimate stiffness. In general there are 3 polarizations, x, y, z. Using the TR to advance the phase in a multi-frequency acquisition has been previously described. The purpose of this work is to examine timing options where the TR provides the phase advance in interleaved 3 polarization acquisitions. This eliminates misregistration of the wave fields images. When there is no gradient dead time, this results in discrete TE/TR and motion sensitivity values.

 
2447.   Sub-Voxel Micro-Architecture Assessment by Scattering of Mechanical Shear Waves
Simon Auguste Lambert1, Simon Chatelin1, Peter Nasholm2, Lauriane Juge1, Philippe Garteiser1, Leon Ter Beek3, Valérie Vilgrain1, Bernard E. Van Beers1, Lynne E. Bilston4, Bojan Guzina5, Sverre Holm2, and Ralph Sinkus1
1CRB3- INSERM U773, Univ Paris Diderot, Sorbonne Paris Cité, Clichy, Paris, France, 2Informatics Department, University of Oslo, Oslo, oslo, Norway, 3Philips Healthcare, Best, best, Netherlands, 4Neuroscience Research Australia, University of New South Wales, Randwick, NSW, Australia, 5Civil Engineering, University of Minnesota, Minneapolis, Mn, United States

 
Recently, it has been hypothesized that propagation of waves at a macroscopic scale might be influenced by the presence of micro-obstacles and hence lead to an apparent viscosity that can be revealed when exploring the tissue at different frequency. We demonstrated on calibrated phantoms by simulation, experiment, and theory that the frequency-dependence of mechanical shear wave scattering can reveal the underlying micro-architecture even within one single voxel. This technique opens perspective of measuring at the macroscopic level information about micro vasculature of tumors, which is crucial for efficacy monitoring during cancer therapy.

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
Relaxometry

2448.   Combined Extended Two Point Dixon/Look Locker Technique for Mapping of Lipid Spin-Lattice (T1) Relaxation Time
Jihyun Annie Park1, Andrew Yung2, Stefan A. Reinsberg1, and Piotr Kozlowski2
1Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada, 2UBC MRI Research Center, Vancouver, BC, Canada

 
Tumour oxygenation can be measured from changes in lipid T1. Here, we combined the extended two point Dixon and Look Locker technique for a rapid T1 measurement of fat. After simulation studies, the method was first applied in a phantom and in vivo. The T1 recovery curves of fat and water for three regions (subcutaneous fat, external oblique muscle, and femoral muscle) were compared. The T1 values of fat were 442ms and 454ms in subcutaneous fat and external oblique muscle, respectively. We have successfully employed the technique in-vivo to spatially map T1.

 
2449.   
Single Breath-Hold 3D Radial Imaging for R2* and Fat Fraction Quantification in the Liver
Valentina Taviani1, Kevin M. Johnson1, Diego Hernando2, and Scott B. Reeder1,3
1Radiology, University of Wisconsin, Madison, WI, United States, 2Radiology, University of Wisconsin-Madison, Madison, WI, United States, 3Medical Physics, University of Wisconsin, Madison, WI, United States

 
In the presence of hepatic iron overload, quantification of R2* and fat fraction (FF) can be limited by the rapidly decaying signal. In this work, we propose a multi-echo 3D radial acquisition with angular undersampling and non-Cartesian parallel imaging reconstruction for hepatic R2* and FF quantification in a single breath hold. Phantom experiments and a preliminary evaluation in healthy volunteers and patients with hepatic iron overload are reported, including a comparison with a hybrid (in-plane radial, through-plane Cartesian) 3D sampling scheme and conventional 3D Cartesian sampling.

 
2450.   Mono-Exponential T2-Analysis of a Two-Pool System – Does Echo-Spacing Matter?
Hendrikus Joseph Alphons Crooijmans1 and Oliver Bieri1
1Radiological Physics, University of Basel Hospital, Basel, Switzerland

 
It is generally well accepted that tissue exists of multiple relaxation components, such as for example the free water protons and myelin-bound water protons in brain tissue. However, the spin-echo based quantification of a single T2 on such tissues is commonly considered being the gold standard. Within such an approach, the echo-spacing is believed to be of influence on the obtained T2. By means of simulations, we have shown that the echo spacing in a spin-echo acquisition for T2-quantification does not matter when performing a mono-exponential analysis of a two-pool system.

 
2451.   Complete T1, T2* and Proton-Density Maps of Bone and Soft Tissues from UTE and Standard FLASH
Jean-David Jutras1, Keith Wachowicz1,2, B. Gino Fallone1,2, and Nicola DeZanche1,2
1Dept. of Oncology, University of Alberta, Edmonton, Alberta, Canada, 2Dept. of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada

 
Achieving bone and soft-tissue contrast simultaneously is challenging. The traditional solution consists of co-registering a MRI dataset with a CT dataset; the MRI provides the soft-tissue contrast with high SNR, while CT yields the bone structural information. In this work, a combination of two similar MRI datasets is proposed: quantitative FLASH UTE and Standard FLASH. Bone T1, T2* and proton-density are segmented from the UTE datasets and combined with the standard datasets to form complete quantitative maps. The technique has the advantage of providing the same quantitative information in all tissue types, with three different contrast mechanisms.

 
2452.   A Flip-Angle-Optimized 3D FLASH Sequence for Fast Dynamic T1 Mapping
Maximilian Freiermuth1, Linus Willerding2, Maximilian F. Reiser1, Michael Peller1, and Olaf Dietrich1
1Josef Lissner Laboratory for Biomedical Imaging, Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany, 2Department of Internal Medicine III, Ludwig-Maximilians-University Hospital Munich, Munich, Germany

 
The purpose of the present study was to optimize and evaluate a fast three-dimensional T1 mapping approach based on the variable flip angle (VFA) technique. The proposed method requires only a single 3D FLASH data set for each time point combined with a longer baseline measurement. The optimal flip angle for the dynamic series can be shown to be αdyn,opt = arccos[(2E1–1)/(2–E1)], which was also confirmed experimentally. The proposed single-flip-angle technique provides accurate T1 values (within ±5%) in phantom measurements.

 
2453.   A New Model-Based Technique for Accurate Reconstruction of T2 Relaxation Maps from Fast Spin-Echo Data
Noam Ben-Eliezer1, Daniel K. Sodickson1, and Kai Tobias Block2
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, NYU Langone Medical Center, New York, NY, United States

 
T2 contrast is one of the most clinically useful tools for non-invasive diagnosis and prognosis. Genuine T2 quantification, however, is impractical due to the long acquisition times associated with full Spin-Echo (SE) acquisitions, or, for fast multi-echo SE sequences, is severely hampered by field inhomogeneities, non-rectangular slice profiles, diffusion effects, and by an inherent bias caused by stimulated echoes. We present a new technique for generating T2 maps from multi-echo data, based on full Bloch simulation of the experimental pulse-sequence. The technique is assumption free and can further incorporate any experimental factors, e.g., pulse shapes, multiple T2components and more.

 
2454.   A Model-Based Reconstruction Technique for Inversion Recovery Prepared Radially Acquired Data
Johannes Tran-Gia1, Dietbert Hahn1, and Herbert Köstler1
1Institute of Radiology, University of Würzburg, Würzburg, Germany

 
In this work, the previously presented Model-based Acceleration of Parameter mapping (MAP) algorithm for saturation prepared radially acquired datasets is extended for Inversion Recovery (IR) prepared datasets. By incorporating an exponential signal model into the image reconstruction, the proposed IR-MAP algorithm allows quantifying the longitudinal relaxation parameter T1 from a dataset acquired after one single magnetization preparation, leading to extremely short acquisition times of about 7 seconds for one slice of the human brain. The functionality of the algorithm is demonstrated in phantom experiments as well as in-vivo.

 
2455.   Accelerated 3D UTE Relaxometry for Quantification of Iron-Oxide Labeled Cells
Bo Zhao1,2, T Kevin Hitchens3,4, Anthony G. Christodoulou1,2, Fan Lam1,2, Yijen Wu3,4, Chien Ho3,4, and Zhi-Pei Liang1,2
1Department of Eletrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 2Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 3Pittsburgh NMR Center for Biomedical Research, Carnegie Mellon University, Pittsburgh, PA, United States, 4Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, United States

 
A new model-based reconstruction method is presented for accelerating 3D ultra-short echo time (UTE) parametric mapping. The proposed method enables accurate parameter mapping with significantly reduced data acquisition times. It should prove useful for 3D UTE relaxometry and various related applications (e.g., labeled cell tracking).

 
2456.   Bayesian Estimation of Multicomponent T2 Distributions with Stimulated Echo Compensation
Kelvin J. Layton1,2, Mark Morelande1, David Wright3, Peter M. Farrell1, Bill Moran1, and Leigh A. Johnston1,3
1Electrical and Electronic Engineering, The University of Melbourne, Parkville, Victoria, Australia, 2National ICT Australia, Parkville, Victoria, Australia, 3Florey Neuroscience Institutes, Parkville, Victoria, Australia

 
This work extends an existing algorithm for multicomponent T2 estimation to account for stimulated echoes using the extended phase graph (EPG) algorithm. The resulting Bayesian algorithm produces reliable multicomponent T2 maps in the presence of dramatic flip angle variation, such as those produced by a transceive surface coil. The method is validated using experimental data acquired on a 4.7T small-bore scanner. Multicomponent T2 maps are generated with and without stimulated echo correction, to demonstrate the importance of the correction. The proposed algorithm is also compared to the commonly used non-negative least squares (NNLS) algorithm and differences are highlighted.

 
2457.   Accelerating T2 Mapping Via Under-Sampled Low-Dimensional-Structure Self-Learning and Thresholding (LOST) Reconstruction
Tri Minh Ngo1, Haiyan Ding2, Mehmet Akçakaya3, Elliot R. McVeigh1, and Daniel A. Herzka4
1Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, United States, 2Biomedical Engineering, Tsinghua University, Beijing, China, 3Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States, 4Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States

 
Myocardial 3D T2 mapping is useful for differentiating between infarct, edema and normal tissue but currently requires prohibitively long acquisition times to be clinically useful. We apply Low-dimensional-structure self-learning and thresholding (LOST) to reconstruct an under-sampled T2 mapping dataset and compare with SENSE reconstruction of equivalent acceleration rates. For rates R3, R3.9, the mean T2 error is lower for LOST than SENSE. At rate R3 SENSE reconstructs edge details better than LOST even though SENSE’s mean T2 error is higher. At rate R3.9, SENSE exhibits high noise amplification while LOST exhibits blurring of high frequency details.

 
2458.   Accelerating Parameter Mapping with a Locally Low Rank Constraint
Tao Zhang1, John M. Pauly1, and Ives R. Levesque2
1Electrical Engineering, Stanford University, Stanford, California, United States, 2Radiology, Stanford University, Stanford, California, United States

 
Parameter mapping can provide intrinsic tissue information to detect pathological changes. Previous studies have shown that compressed sensing with a low-rank constraint can be used to accelerate the lengthy scan time required in parameter mapping. In this work, a locally low rank constraint is applied to parameter mapping. As examples, inversion recovery T1 mapping and multiple-echo T2 mapping are studied. Reconstruction with a locally low rank constraint can provide better accuracy and precision than that with a global low rank constraint.

 
2459.   Model-Based MR Parameter Mapping with Sparsity Constraint
Bo Zhao1,2, Fan Lam1,2, Wenmiao Lu2, and Zhi-Pei Liang1,2
1Department of Eletrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 2Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States

 
A new model-based reconstruction method is presented to directly reconstruct parameter maps from highly undersampled, noisy k-space data. Some representative results of T2 brain mapping are shown to illustrate the performance of the proposed method. It should prove useful for fast MR parameter mapping with sparse sampling.

 
2460.   A Novel Algorithm for Improved Pixel-By-Pixel T2* Mapping
Yanqiu Feng1, Peter David Gatehouse2,3, David N. Firmin2,3, Dudley J. Pennell2,3, Wufan Chen1, and Taigang He2,3
1School of Biomedical Engineering, Southern Medical University, Guangzhou, China, 2Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, United Kingdom, 3National Heart and Lung Institute, Imperial College, London, United Kingdom

 
MRI relaxometry mapping (pixel-by-pixel) is sensitive to the noise especially when high-resolution or rapid scans are required. Considering decay signals as the objects to be averaged, we aimed at improving the precision of T2* mapping through selectively Averaging the Decay signals with Similar Underlying Relaxation rates (ADSUR) before curve fitting. This novel algorithm was tested on T2* mapping of simulation data and an ex vivo heart with iron overload. The results demonstrate that the T2* relaxometry mapping can be improved by filtering the serial images with the proposed ADSUR algorithm, independent of curve-fitting models used.

 
2461.   Fast, Artifact-Free T2 Mapping with Fast Spin Echo Using the Extended Phase Graph and Joint Parameter Reconstruction
Christopher L. Lankford1,2 and Mark D. Does1,2
1Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, United States, 2Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, United States

 
Fast spin-echo images contain artifacts related to relaxation and imperfect refocusing. These artifacts are explained by well-known signal equations, and the sources of these artifacts can be accounted for if fit as a free parameter during image reconstruction. This abstract demonstrates the potential of this approach for artifact-free T2 mapping in comparison maps derived from Fourier-reconstructed images and voxelwise parameter fits.

 
2462.   An Indirect Echo Compensated Reconstruction Algorithm for T2 Mapping of the Liver from Highly Undersampled Radial FSE Data
Chuan Huang1,2, Abhishek Pandey3, Tomoe Barr4, Ali Bilgin3,4, and Maria I. Altbach1
1Department of Medical Imaging, University of Arizona, Tucson, AZ, United States, 2Center for Advanced Radiological Sciences, Department of Radiology, Massachusetts General Hospital, Boston, MA, United States, 3Electrical and Computer Engineering, University of Arizona, Tucson, AZ, United States, 4Biomedical Engineering, University of Arizona, Tucson, AZ, United States

 
Early detection and classification of hepatic tumors and chronic liver disease are two important clinical problems. T2 mapping has been used to improve the characterization of pathologies in the liver. One promising sequence for fast T2 mapping is radial FSE. Most of the reconstruction methods for undersampled radFSE data do not take into account the effects of indirect echoes; this leads to T2 estimates that are dependent on the refocusing pulse slice profile and/or B1 inhomogeneities. Recently, we proposed a reconstruction algorithm – CURLIE (CUrve Reconstruction via pca-based Linearization with Indirect Echo compensation) – combines a principal component model-based algorithm with a slice-resolved extended phase graph signal model. In this work, we demonstrate the ability to obtain accurate T2 maps with indirect echo compensated from liver radFSE data acquired in a single breath hold. The algorithm is also evaluated using phantom and in vivo data. It is also shown that this technique is immune to B1 inhomogeneities and B1 mis-calibration.

 
2463.   Correction of B1 and Estimation of Oversampling Effect to Enable Accurate T1 Mapping Using 3D Variable Flip Angle Technique
Kosuke Morita1,2, Tomoyuki Okuaki3, Masanori Komi1, Akiko Kuraoka1, Daisuke Utsunomiya2, Mika Kitajima2, Masahiro Hashida1, and Yasuyuki Yamashita2
1Radiology, Kumamoto University Hospital, Kumamoto, Kumamoto, Japan, 2Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University Hospital, Kumamoto, Kumamoto, Japan, 3Philips Electronics Japan, 13-37, Kohnan 2-chome, tokyo, Japan

 
The purpose of our study was to acquire precise 3D T1maps by variable flip angle DESPOT1 method with B1 correction for clinical MR imaging. Moreover, the T1 value of outer-slice regions on 3D acquisition using the ordinary slice selective RF pulse with imperfect rectangular shape is not accurate. To resolve this problem, we evaluated the effect of the B1 inhomogeneity and slice-oversampling factor on 3D T1maps using a phantom and volunteers. Our experiments showed that the T1 value was improved by B1 correction using variable flip angle method and T1 value for 3D T1mapping was improved by optimizing slice-oversampling factor.

 
2464.   Relaxation Parameter Mapping Adapted for 7T and Validation Against Optimized Single Voxel MRS
Michael Wyss1, Thomas Kirchner1, Alex Ringenbach2, Klaas P. Prüssmann1, and Anke Henning1,3
1Institute for Biomedical Engineering, University and ETH Zürich, Zürich, Switzerland, 2Institute for Medical and Analytical Technologies, University of Applied Sciences of Northwestern Switzerland, Muttenz, Switzerland, 3Max Planck Institute for Biological Cybernetics, Tübingen, Germany

 
Previously published T1 relaxation times for brain tissue at 7T vary greatly in results and in methods. Only two publications have assessed in vivo T2 relaxation times in the human brain at 7T so far. We present the development and validation of T1 and T2 mapping sequences applicable at 7T in the presence of B1 inhomogeneity. For T1 mapping, a Look-Locker sequence with an adiabatic inversion prepulse and a modified fitting routine was implemented. For T2 mapping the vendor pre-implemented mixed imaging sequence was validated. For cross validation purpose T1 and T2 relaxation times were measured at selected anatomical locations by optimized SV-MRS parameter series.

 
2465.   High Resolution Quantitative Imaging of Rodent Brains at 7T
Tobias C. Wood1, Samuel A. Hurley2, Anthony Vernon3, and Steven C.R. Williams1
1Neuroimaging, King's College London, Institute of Psychiatry, London, United Kingdom, 2Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3Psychosis Studies, King's College London, Institute of Psychiatry, London, United Kingdom

 
High-resolution, whole rodent brain, quantitative T1&T2 maps were obtained at 7T using DESPOT techniques, including using a multi-component model to recover the Myelin Water Fraction.

 
2466.   Value of Independent Flip Angle Mapping for Transverse Relaxometry with Stimulated Echo Compensation
Dylan Breitkreutz1,2, Kelly C. McPhee1, R. Marc Lebel2, and Alan H. Wilman1,2
1Department of Physics, University of Alberta, Edmonton, Alberta, Canada, 2Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada

 
Stimulated echo compensation enables accurate single component T2 quantification by accounting for both stimulated-echo and spin-echo pathways to produce both T2 and flip angle maps from multi-echo data. In order to avoid non-unique solutions, the algorithm constrains refocusing angles to ≤ 180˚. This work demonstrates the limitations of this assumption, and examines the value of an independent and accurate flip angle map. The results indicate the independent flip angle map is particularly valuable in 2D experiments where refocusing angles exceed 180˚.

 
2467.   Effects of Flip Angle Profile in T2 Quantification Using 3D Dual Echo Steady-State (DESS)
Pei-Hsin Wu1, Cheng-Wen Ko2, Ming-Long Wu3, and Hsiao-Wen Chung1,4
1Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, 2Department of Computer Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan, 3Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan, 4Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan

 
Previous studies demonstrate that DESS provides quantitative T2 imaging. While using 3D acquisition, however, distinct estimated T2 values along section direction are found, particularly at larger flip angles. In this study, we investigate the influence of the uniformity of flip angle distribution in T2 quantification using 3D DESS. Simulation and experiment results suggest that the reliability of T2 quantification across slices within one slab could be improved with appropriate setting of RF flip angle profile, which provides benefit for clinical applications especially when slices comparison is required.

 
2468.   Challenges in Ultrashort Echo Time Relaxometry of the Human Brain
Ece Ercan1, Peter Börnert2, Maarten J. Versluis1, Tom Geraedts3, Andrew Webb1, and Itamar Ronen1
1C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands, 2Philips Research Laboratory, Hamburg, Germany,3Philips Healthcare, Best, Netherlands

 
Ultrashort echo time (UTE) imaging is recently suggested as a potential method to probe the signal from myelin. In this study, we investigate the challenges in UTE relaxometry of the human brain through phantom experiments and UTE acquisitions from the brain white matter. We suggest an improved long T2 suppression scheme for such experiments. We report the non-exponential behavior that we observed in the relaxometric data from the phantom with a T2* value of 30 ms as well as in the data from human brain, which is possibly caused by non-fully suppressed tissue constituents with a T2* value of 10-30 ms (such as myelin water).

 
2469.   Investigation of Temperature Dependence of Tissue Relaxation Parameters for Post-Mortem Imaging
Julia Kruisz1, Andreas Petrovic2, Rudolf Stollberger1, and Eva Scheurer2
1Institute for Medical Engineering, University of Technology Graz, Graz, Austria, 2Ludwig Boltzmann Institute for Clinical-Forensic Imaging, Graz, Austria

 
MRI in forensics is becoming increasingly important for a non-invasive and objective documentation before autopsy. However, the usually lower temperatures alter the tissues’ relaxation times which often leads to poor image contrast. In this study we investigated T1 and T2 of various tissues from 4° to 38°C. For most investigated samples a linear relationship describes the temperature dependence of relaxation times. Regarding the contrast of a spin echo sequence we found that for certain tissues it is impossible to obtain the same contrast as in vivo by adjusting the repetition time.

 
2470.   Field Dependence of Relaxivity of Gd Chelates as a Function of Macromolecular Content
Henry H. Ong1,2, Hua Li1,3, and John C . Gore2,4
1Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, 2Department of Radiology and Radiologic Sciences, Vanderbilt University, Nashville, TN, United States, 3Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, United States, 4Vanderbilt University, Nashville, TN, United States

 
Gd-DTPA is a common MRI contrast agent used in a variety of applications such as tumor imaging. Its T1 relaxivity (r1) is a fundamental property important for quantitative analyses. Previous studies did not address the behavior of r1 at ultra-high B0 or how r1 may be modified in the presence of realistic media to different extents at different fields which is expected from the Solomon-Bloembergen-Morgan equations. Here, we report Gd-DTPA r1 measurements as a function of macromolecular content and different high B0 (up to 15.2T) and found that the effect of macromolecular content disappears at 15.2T in agreement with theory.

 
2471.   Effect of Molecular Oxygen on Relaxation Times at Clinical Field Strengths
Harald Kramer1,2, Amanda R. Corcos3, Diego Hernando4, John F. Berry3, Mark L. Schiebler1, and Scott B. Reeder1
1Department of Radiology, University of Wisconsin - Madison, Madison, Wisconsin, United States, 2Institute for Clinical Radiology, Ludwig-Maximilians-University Munich, Munich, Bavaria, Germany, 3Department of Chemistry, University of Wisconsin - Madison, Madison, Wisconsin, United States, 4Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin, United States

 
Oxygen is paramagnetic and known to influence the relaxation properties of tissues in MRI. Little is known regarding the dependence of oxygen partial pressure on relaxation times (T1 and T2) in fluids. We performed relaxometry experiments in a phantom with varying oxygen partial pressure ranging from 0-760mmHg at clinical field strength. Using measured values of T1 and T2 at different oxygen tensions permitted calculation of the relaxivities (r1 and r2) of oxygen. Differences in oxygen tension can be visualized and quantified with MRI. The results suggest that the injection of oxygen saturated/desaturated saline could be used as a contrast agent.

 
2472.   
In Vivo Estimation of the Transverse Relaxation Time Dependence of Blood on Oxygenation at 7 Tesla
Dimo Ivanov1,2, Andreas Schäfer2, Andreas Deistung3, Markus N. Streicher2, Stefan Kabisch2, Ilona Henseler2, Elisabeth Roggenhofer2, Thies H. Jochimsen4, Ferdinand Schweser5, Jürgen R. Reichenbach5, Kamil Uludag1, and Robert Turner2
1Maastricht Brain Imaging Centre, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands, 2Max Planck Institute for Human Cognitive & Brain Sciences, Leipzig, Germany, 3Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 4Department of Nuclear Medicine, University of Leipzig, Leipzig, Germany, 5Medical Physics Group, Jena University Hospital - Friedrich Schiller University, Jena, Germany

 
The precise knowledge of the oxygenation dependence of the effective transverse relaxation time (T2*) of blood, within the physiologically relevant range will improve the quantitative understanding of the BOLD effect in gradient echo MRI at 7T along the vascular tree. Previous measurements of this dependence have been only reported in vitro and may be confounded by uncompensated susceptibility gradients between the sample and its surroundings. We present an approach of combining T2* and magnetic susceptibility mapping during different respiratory challenges for reliable determination of the change in the T2* of blood with oxygenation in vivo at 7T.

 
2473.   Ex Vivo Mapping of Sodium T 1 and T2* Relaxation Times in Human Lumbar Intervertebral Discs at 7 Tesla
Stefan Zbýn1, Sebastian Apprich1, Vladimir Juras1, Pavol Szomolanyi1, Sonja M. Walzer2, Xeni Deligianni3, Hannes Traxler4, Oliver Bieri3, and Siegfried Trattnig1
1MR Center of Excellence, Department of Radiology, Medical University of Vienna, Vienna, Austria, 2Department of Orthopaedic Surgery, Medical University of Vienna, Vienna, Austria, 3Division of Radiological Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland, 4Center for Anatomy and Cell Biology, Department of Applied Anatomy, Medical University of Vienna, Vienna, Austria

 
Previous studies on 23Na relaxation times in the intervertebral discs (IVD) reported different values. In this study, we employed novel gradient-echo sequence with variable echo time scheme at 7T for the ex vivo measurements of T1, T2*, fast (T2*F) and slow (T2*S) components of biexponential transversal relaxation times in human lumbar IVDs with different degree of degeneration. Our results suggesting shorter relaxation times in IVDs with higher degree of degeneration compared to less degenerated IVDs. Presented findings may provide the basis for quantification of 23Na content in human IVDs and could help to understand processes associated with degeneration of IVDs.

 
2474.   
Can Modified Look Locker Imaging (MOLLI) Provide Accurate T1 Values?
Mitchell Anthony Cooper1,2, Thanh Nguyen2, Pascal Spincemaille2, Martin R. Prince2, Jonathan W. Weinsaft3, and Yi Wang1,2
1Biomedical Engineering, Cornell University, Ithaca, New York, United States, 2Radiology, Weill Cornell Medical College, New York, New York, United States, 3Cardiology, Weill Cornell Medical College, New York, New York, United States

 
Here we systematically evaluate the inaccuracies of the MOLLI fitting method. We propose a new fitting method, bMOLLI, that utilizes the Bloch equations to model the SSFP signal evolution and account for the flip angle profile and inversion efficiency to provide accurate T1 estimates.

 
2475.   Experimental Analysis of Three Spoiling Mechanisms Used in Variable-Flip-Angle T1 Mapping
Martin Ott1, Thomas Benkert1, Martin Blaimer1, Peter M. Jakob1,2, and Felix A. Breuer1
1MRB Forschungszentrum für Magnet-Resonanz-Bayern e.V., Würzburg, Germany, 2Department of Experimental Physics 5, Institute of Physics, Würzburg, Germany

 
A comparison of different VFA-methods for T1-mapping is shown. This results that none of the common techniques can produce reliable data.

 
2476.   Highly Reproducible in vivo T1 Maps in Brain at 3T
Sofia Chavez1,2, Stephen Kish1,2, Tina McCluskey1, and Nancy Lobaugh1,3
1Research Imaging Centre, Centre for Addiction and Mental Health, Toronto, ON, Canada, 2Psychiatry, University of Toronto, Toronto, ON, Canada, 3Neurology, University of Toronto, Toronto, ON, Canada

 
The Method of Slopes (MoS), which accounts for spatial variations in flip angle, has been shown to yield accurate in vivo 3D T1 maps in brain at 3T. However, several factors may cause variations in the measurement within a subject across time. In this work, we assess the intra-subject reproducibility of T1 mapping with the MoS by repeating scans on five healthy subjects, at three time points on two consecutive days: morning, afternoon, morning. We find very small intra-subject coefficients of variation (CV<8%) in all brain regions, making these T1 maps suitable for the detection of short-term effects(eg. drug-induced).

 
2477.   ex-vivo MRI of the Brain: Effects of Long-Term Formalin Exposure on T1 Relaxation Times
Mekala R. Raman1, Yunhong Shu1, John D. Port1, Jan-Mendelt Tillema1, Istvan Pirko1, Clifford R. Jack1, and Kejal Kantarci1
1Mayo Clinic, Rochester, MN, United States

 
Our objective was to determine the effects of fixation on T1 relaxation of gray matter and white matter in ex vivo brain MRI for optimization of MPRAGE and DIR sequences. We found that T1 relaxation times of fixed brain tissue attenuate over time. Effects of formalin exposure on tissue relaxation time appear to be greater for gray matter than white matter.

 
2478.   Optimizing the Accuracy of T1 Mapping Accounting for RF Non-Linearities and Spoiling Characteristics in FLASH Imaging
Antoine Lutti1 and Nikolaus Weiskopf1
1Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, United Kingdom

 
The accuracy of T1 maps obtained with FLASH-based Variable Flip Angle (VFA) methods is affected by residual transverse coherences, spatial inhomogeneities of the transmit field B1 and non-linearities of the RF transmit chain. Here we address all these issues simultaneously and present an acquisition protocol with very high accuracy and precision. The accuracy was improved by ~40% in-vivo compared to a conventional VFA protocol, enabling cutting-edge applications such as mapping of myeloarchitecture.

 
2479.   T1 Mapping: Should We Agree to Disagree?
Mathieu Boudreau1, Nikola Stikov1, and Bruce G. Pike1
1Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada

 
A recent study reported that three commonly used methods for T1 mapping (Inversion Recovery, Look-Locker, Variable Flip Angle) measure similar T1 values in phantoms, but disagree in vivo at 3T (VFA overestimated and LL underestimated relative to IR). This work investigates possible confounding factors that may explain the T1 trends observed in vivo. Bloch simulations tested the effects of inaccurate B1 mapping and spoiling on T1 for all three sequences. These simulations predict a systematic bias in VFA and LL due to these effects, consistent with trends observed in vivo, highlighting the importance of proper calibration with the IR gold standard.

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
Susceptibility

2480.   Susceptibility-Weighted Imaging Using Susceptibility Map Estimated by L1 Norm Regularization
Ryota Sato1, Toru Shirai1, Yo Taniguchi1, Yoshihisa Soutome1, and Yoshitaka Bito1
1Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo, Japan

 
A method for susceptibility-weighted imaging, which can enhance contrast of regions with high susceptibility in arbitrary slice orientation, was developed. To enhance contrast in arbitrary slice orientation clearly, this method uses a susceptibility map estimated by L1 norm regularization. In contrast to conventional methods, the proposed method can enhance contrast of veins and iron depositions without causing streaking artifacts in arbitrary slice orientation. A numerical simulation and experiments on healthy volunteers show this method can enhance contrast of regions with high susceptibility in arbitrary slice orientation.

 
2481.   Comparisons of Quantitative Susceptibility Mapping (QSM) by Using Restricted Oversampled Spatial Unit Dipole Field
Mai Murashima1, Tomohiro Ueno1, and Naozo Sugimoto1
1Human Health Science, Graduate School of Medicine, Kyoto University, Kyoto, Japan

 
In Quantitative susceptibility mapping (QSM), measured magnetic field distributions have to be deconvolved with a dipole field. The dipole field is effective even in a long range, and a rapidly changing function of a position in a short range. In order to access these problems, we performed numerical simulations taking into account partial volume effects in QSM by using the dipole fields with various field sizes and oversampling factors. We found that the diameter 21voxels was enough for the field size, and that the oversampled dipole field of factor 3 was sufficient for observing effects on the susceptibility estimation.

 
2482.   Differentiation of Fe2+ and Fe3+ with Iron-Sensitive MRI
Olaf Dietrich1, Johannes Levin2, Armin Giese3, Annika Plate2, Kai Bötzel2, Maximilian F. Reiser1,4, and Birgit Ertl-Wagner4
1Josef Lissner Laboratory for Biomedical Imaging, Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany, 2Department of Neurology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany, 3Center for Neuropathology and Prion Research, Ludwig-Maximilians-University Hospital Munich, Munich, Germany, 4Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany

 
The purpose of the present study is to demonstrate the different behaviors of ferric and ferrous iron ions in MRI and to suggest a technique to differentiate quantitatively between both forms of iron in tissue. A phantom consisting of tubes with different concentrations of ferrous and ferric chloride solutions was examined on a 3-Tesla MRI system. A multi-echo gradient-echo was used for both T2* and quantitative susceptibility measurements. Ferrous and ferric chloride show markedly different relaxation behaviors in MRI, but similar influences on the susceptibility. These properties can be used to differentiate ferrous and ferric samples.

 
2483.   Susceptibility Mapping of the Sinuses in the Brain by Preserving Phase Information in the Skull Using Short Echo Times
Sagar Buch1, Saifeng Liu1, Yu-Chung Norman Cheng2, and Ewart Mark Haacke1,2
1McMaster University, Hamilton, Ontario, Canada, 2Academic Radiology, Wayne State University, Detroit, Michigan, United States

 
Susceptibility mapping is generally used to provide us with the distribution of magnetic susceptibility properties of the different tissues. This abstract introduces a new concept of mapping the susceptibility inside brain sinuses, which are usually discarded from the MR phase. One of our key advances is to include the tissues in the skull outside the sinuses in phase images, before applying the inverse filter. Because the susceptibility effects between air and tissue are so large, we are able to use short effective echo times, produced by complex division of the datasets at two different echo times, to extract the susceptibility.

 
2484.   Atlas-Based Segmentation of Quantitative Susceptibility Maps: Determining Iron Content in Deep Gray Matter Structures
Issel Anne L. Lim1,2, Andreia V. Faria1, Xu Li1,2, Johnny T.C. Hsu1, Raag D. Airan1, Susumu Mori1,2, and Peter C.M. van Zijl1,2
1Radiology, Johns Hopkins University, Baltimore, Maryland, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States

 
Quantitative Susceptibility Mapping (QSM) methods have correlated magnetic susceptibility and gray matter (GM) brain iron concentration. Typically, average susceptibility per structure is determined via manual delineation of ROIs, which is labor-intensive and subject to human error. We created a QSM template as part of the Eve atlas, along with an "Everything" Parcellation Map ("EvePM") containing deep GM ROIs drawn from QSM and white matter ROIs from DTI maps. Using automated segmentation, we derived a susceptibility-iron calibration curve for deep gray matter based on known iron values for three regions, which was used to determine iron concentration in six other regions.

 
2485.   MR-Visible Surgical Meshes: Optimization and Phantom Studies
Florian Lippus1, Kerstin Brocker2, Jens Groebner1, Peter Hallscheidt3, and Michael Bock1
1Dept. of Diagnostic Radiology / Medical Physics, University Medical Centre Freiburg, Freiburg, BW, Germany, 2Dept. of Gynaecology, Heidelberg University Hospital, Heidelberg, BW, Germany, 3Diagnostic and Interventional Radiology, Heidelberg University Hospital, Heidelberg, BW, Germany

 
Partially absorbable surgical mesh implants can be used to treat Pelvic organ prolapse, which is a common disease in elderly women. When it comes to post-operative complications, MRI could be used to qualify movement or deformation of the implant, but current available mesh implants are not visible in MR images. In this work MR measurements are presented to develop and optimize an MR-visible mesh-implant made of threads with magnetic particles. Particle concentrations were determined based on relaxometric evaluation, and thread material was tested for its MR visibility.

 
2486.   Quantitative Characterization of Spatial Variations of Intrinsic Susceptibility by T1lower case Greek rho Dispersion
John T. Spear1,2, Zhongliang Zu2,3, and John C. Gore3,4
1Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, United States, 2Vanderbilt University Institute of Imaging Science, Nashville, TN, United States, 3Department of Radiology, Vanderbilt University, Nashville, TN, United States, 4Vanderbilt University, Nashville, TN, United States

 
A new method is reported for quantifying the spatial scales of susceptibility variations based on the effect of diffusion through internal gradients on the spin-lattice relaxation rate in the rotating frame R1rho (=1/T1rho). Model systems with internal field gradients exhibited significant dispersions in R1rho and fastidious analysis of these dispersions revealed three important locking fields. Three images were subsequently taken at these locking fields and combined in a novel image subtraction technique to delineate the average spatial frequency of magnetic inhomogeneities. This technique has the potential to quantitatively characterize magnetically inhomogeneous regions of tissue such as microvasculature in vivo.

 
2487.   Investigating Anisotropic Magnetic Susceptibility Effects in Model Systems
Matthew Cronin1, Samuel J. Wharton1, and Richard W. Bowtell2
1Sir Peter Mansfield Magnetic Resonance Centre, The University of Nottingham, Nottingham, Notts, United Kingdom, 2Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, Notts, United Kingdom

 
Although correct mathematical expressions for calculating field perturbations due to anisotropic magnetic susceptibility have been described, its effects have often been modelled using a simplified approach in which the anisotropy is represented by allocating the material an isotropic susceptibility whose magnitude depends on orientation to the field. Here we demonstrate using theory and experiment that this approximation leads to errors in predicting the frequency perturbation due to anisotropic structures. We also show that correct calculations predict interesting behaviour in a hollow cylinder model of the myelin sheath, and go on to demonstrate this behaviour experimentally in a simple model system.

 
2488.   Longitudinal Investigation of Diffuse Hemorrhagic Lesions Using Using Quantitative Susceptibility Mapping (QSM)
Andreas Petrovic1, Ferdinand Schweser2, Andreas Deistung3, Eva Scheurer1, and Jürgen R. Reichenbach2
1Ludwig Boltzmann Institute for Clinical-Forensic Imaging, Graz, Austria, 2Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital – Friedrich Schiller University Jena, Jena, Germany, 3Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany

 
Dating of hemorrhage is important in clinical and forensic medicine. In this study we measured the susceptibility of artificially created hematomas in 6 volunteers at different times to investigate if susceptibility changes due to changes of the oxygenation state of hemoglobin could be used. Quantitative susceptibility mapping is a unique method to measure magnetic susceptibility in vivo. The suspected increase of magnetic susceptibility could not be observed. This could be caused by blood being already fully deoxygenated at the time of the first measurement. Additionally, confounding factors as an increase of the hematocrit and recurring fat during resorption influence the measured susceptibility values.

 
2489.   Origin of B0 Orientation Dependent R2* (=1/T2*) in White Matter: Magic Angle Effect Vs. Magnetic Susceptibility
Se-Hong Oh1 and Jongho Lee1
1Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States

 
Recent MRI studies have demonstrated that the relative orientation of white matter fibers to the B0 field significantly affects R2* measurement. In this work, the origin of this effect was investigated by measuring R2 and R2* in multiple orientations and fitting the results to a magnetic susceptibility-based model and a magic angle-based model. To further explore the source of magnetic susceptibility effect, the contribution of tissue iron to the orientation dependent R2* contrast was investigated. Additionally, R2* was measured in basal ganglia area to confirm there is no orientation dependence in deep gray matter. Our results suggest that myelin is a primary source for R2* contrast because of its highly oriented structure and large susceptibility value.

 
2490.   
Frequency Difference Mapping at 7 T Using Two- And Three-Echo Approaches
Samuel J. Wharton1 and Richard W. Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom

 
Frequency difference mapping is a recently proposed gradient-echo-based MRI technique for creating image contrast that is sensitive to the orientation of myelinated nerve fibers in white matter. Frequency difference maps (FDM) are created by calculating the difference in phase-based frequency maps acquired at short and long echo times. In this study, we use simulations to determine the optimum TE values for creating in vivo FDM at 7T using two- and three-echo acquisition schemes. Both approaches yield high quality FDM in a 6 minute scan time. The two-echo scheme yields higher SNR, but requires the use of a high-pass filtering step.

 
2491.   Improved Characterisation of White Matter Lesions in Multiple Sclerosis Patients Using Quantitative Susceptibility Mapping
Matthew Cronin1, Samuel J. Wharton1, Richard W. Bowtell2, and Penelope A. Gowland2
1Sir Peter Mansfield Magnetic Resonance Centre, The University of Nottingham, Nottingham, Notts, United Kingdom, 2Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, Notts, United Kingdom

 
Peripheral rings surrounding white matter (WM) lesions in multiple sclerosis are often analysed using phase images from T2*-weighted, gradient echo scans. The usefulness of this approach is limited by the non-local, dipolar nature of phase contrast. Quantitative susceptibility mapping (QSM) can be used to overcome this problem. Here, by comparison of images and analysis of 1D profiles of signal variation with respect to the distance from the lesion edge, we show that QSM offers a more accurate representation of WM lesions, which reflects the underlying tissue composition more closely than phase or T2*-weighted magnitude data.

 
2492.   Evaluation of Multiparametric QBOLD in White Matter: A Simulation Study
Julien Bouvier1,2, Sebastien Castellani1, Clément S. Debacker1,3, Nicolas Pannetier4, Irène Troprès1,5, Alexandre Krainik1, and Emmanuel Luc Barbier1
1INSERM U836, Grenoble Institute of Neurosciences, Grenoble, France, 2Philips Healthcare, Suresnes, France, 3Bruker Biospin MRI, Ettlingen, Germany, 4University of California San Francisco, San Francisco, CA, United States, 5Plate-forme IRMaGe, UJF – INSERM US17 – CNRS UMS 3552, Grenoble, France

 
Quantitative estimates of the tissue blood oxygen saturation (StO2) may be obtained using a multiparametric quantification of the blood oxygen level dependent effect (multiparametric qBOLD). This method, based on a model of the MR signal, yielded promising experimental results on rodents. However, the first estimates of StO2 obtained in humans with this method matched those reported in the literature for gray matter only. To obtain reliable StO2 estimates in white matter, this study evaluates a solution to account for the bias on StO2 estimate induced by myelin, a paramagnetic substance, using a numerical simulation approach.

 
2493.   Relevance of Morphological Binary Information for L2 and L1 Total Variation Methods in Quantitative Susceptibility Mapping and Reconstruction Quality Assessment Without Presence of the Ground Truth
Diana Khabipova1, Yves Wiaux2,3, Rolf Gruetter4,5, and José P. Marques1,5
1LIFMET, EPFL, Lausanne, Switzerland, 2Electrical Engineering, EPFL, Lausanne, Switzerland, 3Radiology, UniGe, Geneva, Switzerland, 4LIFMET, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 5Radiology, UNIL, Lausanne, Switzerland

 
Phase imaging has been demonstrated to achieve a good contrast between and within brain tissues at 7T. However, phase imaging suffers from a non-local contrast variation which can be overcome by calculating the underlying magnetic susceptibility maps. As this problem is ill-posed, many regularization methods have been proposed over the past years. In this abstract we do a thorough comparison of some of these methods, focus on the impact of the prior information on the reconstructed susceptibility maps and propose a method to evaluate the quality of the susceptibility reconstruction in the absence of a ground truth.

 
2494.   Quality-Based UnwRap of SUbdivided Large Arrays (URSULA) at 9.4T
Johannes Lindemeyer1, Ana-Maria Oros-Peusquens1, Kaveh Vahedipour1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine 4, Forschungszentrum Jülich, Jülich, Germany, 2Department of Neurology, Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

 
Unwrapping of MR phase data becomes very time consuming for high-resolution data acquired at ultra-high fields. We present a new algorithm, URSULA (UnwRap of SUbdivided Large Arrays), an approach splitting up the original matrix in smaller-sized 3D volumes which are unwrapped individually. The computed subsets are assembled into a whole volume result using a quality-based approach. Sequential or parallel computing is applicable, especially the latter allowing for a dramatic gain in computing speed. Simulations show good reliability for a moderate number of subsets. The performance of the algorithm is exemplified on a human in vivo dataset measured at 9.4T.

 
2495.   Laplacian Filtering: A Simple and Robust Technique for Reducing Artifacts in Susceptibility Weighted Imaging (SWI)
Ferdinand Schweser1,2, Andreas Deistung1, Martin Stenzel3, Hans-Joachim Mentzel3, and Jürgen R. Reichenbach1
1Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 2School of Medicine, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 3Section Pediatric Radiology, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany

 
Susceptibility weighted imaging (SWI) is a novel imaging technique that exploits the MR phase information to delineate venous vessels and brain lesions. Various approaches have been presented to avoid severe off-resonance artifacts in SWI due to the strong field gradients induced, e.g., by the air-tissue interfaces above the nasal cavities. However, all of these techniques involve rather complex and laborious data processing based on raw complex-valued MR images, which are usually not available in commercial SWI implementations. In this contribution we present a simple and robust post-processing technique that allows eliminating the wrap-artifacts in SWI. The technique may be applied both retrospectively on filtered phase images (commercial SWI) and prospectively on raw complex-valued images.

 
2496.   Background Field Removal Based on Local Complex Phase Unwrapping and Spherical Mean Value Property
Saifeng Liu1, Sagar Buch1, and Ewart Mark Haacke1,2
1School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada, 2Department of Radiology, Wayne State University, Detroit, Michigan, United States

 
The quality of Quantitative Susceptibility Mapping (QSM) relies on the accuracy in background field removal. In the SHARP method, phase unwrapping is generally required, which is usually a time-consuming procedure. It could be avoided by using the Laplacian of the field but there are errors in regions with sharp phase changes. Besides, using the Laplacian may lead to reduced accuracy in the processed phase images. We proposed a method which allows for using an optimal kernel size without explicit phase unwrapping. This helps to reduce the processing time and improve the accuracy in background field removal using SHARP.

 
2497.   Quantitative Susceptibility Mapping: A Potential Biomaker for Characterizing Cerebral Cavernous Malformation
Huan Tan1, Ying Wu1,2, Ryan Hutten1, Liu Tian3, Yi Wang3, Pottumarthi Vara Prasad1,2, Issam Awad2, and Robert R. Edelman1,4
1NorthShore University HealthSystem, Evanston, IL, United States, 2The University of Chicago Pritzker School of Medicine, Chicago, IL, United States, 3Weill Cornell Medical College, New York, NY, United States, 4Northwestern University Feinberg School of Medicine, Chicago, IL, United States

 
Susceptibility weighted imaging (SWI) was shown to have a high sensitivity for detecting iron-rich cerebral cavernous malformation lesions. However, SWI is a qualitative technique that does not provide a means to evaluate changes in iron distribution within individual lesions. Quantitative susceptibility mapping (QSM) allows quantitative evaluations of intra-lesional susceptibility changes related to leakage of iron-containing blood products. In this study, we performed QSM in nine patients with CCM to characterize lesion burden, and demonstrate the potential of QSM as a quantitative imaging marker for monitoring disease progression and/or responses to treatments.

 
2498.   Feasibility of in-vivo Quantitative Susceptibility Mapping (QSM) in the Kidneys
Huan Tan1, Jon Thacker2, Tian Liu3, Yi Wang3, and Pottumarthi Vara Prasad1,4
1NorthShore University HealthSystem, Evanston, IL, United States, 2Northwestern University, Evanston, IL, United States, 3Weill Cornell Medical College, New York, NY, United States, 4The University of Chicago Pritzker School of Medicine, Chicago, IL, United States

 
The magnetic susceptibility of tissue can be measured using quantitative susceptibility mapping (QSM), a novel MRI technique that utilizes a 3D multi-echo gradient echo sequence for data acquisition. Since the quantification of susceptibility is inherently based on the phase information and necessitates 3D acquisition, respiratory motion remains a key challenge. In this study, we implemented a prospective cross-pair navigator method to minimize motion effects. The technique was tested in five volunteers, and the preliminary analysis supports feasibility of acquiring QSM in vivo in human kidneys.

 
2499.   Fast Susceptibility Weighted Imaging (SWI) Using PROPELLER-EPI
Martin Krämer1, Andreas Deistung1, Ferdinand Schweser1, and Jürgen R. Reichenbach1
1Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany

 
The ability to perform phase correction during PROPELLER-EPI image reconstruction is highly advantageous making PROPELLER-EPI a robust segmentation scheme for fast high resolution echo planar imaging. However, only modified phase information is obtained after the complete image reconstruction, hampering further processing of the image phase. To avoid this issue and to make SWI processing of PROPELLER-EPI data possible we propose to perform the processing of phase information on the blade level, before image phase is modified in any way. We show that this reconstruction scheme enables high resolution susceptibility weighted imaging using a fast EPI readout.

 
2500.   Expansion of the GESFIDE Sequence for Simultaneous SWI, T1W Imaging and MR Angiography
Wei Feng1, Yang Xuan1, and Ewart Mark Haacke1
1Radiology, Wayne State University, Detroit, Michigan, United States

 
Gradient echo sampling of FID and echo (GESFIDE) and its variants have been studied to quantify tissue relaxation rates, including R2, R2* and R2’. In this abstract, we expand this sequence to also achieve susceptibility weighted imaging (SWI), T1W imaging, and MR angiography. Gradient echoes are placed before the refocusing pulse, after the refocusing pulse and even after the spin echo. A carefully selected flip angle, echo time and repetition time allow the unwrapping of multiecho phase images to generate improved SWI images. Furthermore, good T1 contrast can be achieved at short GRE echoes while MRA can be obtained at the spin echo.

 
2501.   Microhemorrhage Detection with Segmented EPI SWI: Comparison to 3D GRE SWI in a Series of TBI Patients
Wen-Tung Wang1, Ningzhi Li2, Dzung Pham2, and John Anthony Butman1,2
1Radiology and Imaging Sciences, Clinical Center of the National Institutes of Health, Bethesda, MD, United States, 2Center for Neuroscience and Regenerative Medicine, Bethesda, MD, United States

 
Susceptibility weighted imaging using segmented EPI dramatically accelerates aquisition as compared with traditional 3D GRE methods. In the context of TBI, the ability to cover the whole brain in 90 seconds with segmented EPI with microhemorrhage detection sensitivity comparable to the 9 minute 3D GRE method makes it attractive for routine clinical use.

 
2502.   Correlation of R2 and R2* with Quantitative Susceptibility Maps in Healthy Elderly Controls
Jeam Haroldo Oliveira Barbosa1, Saifeng Liu2, Jin Tang3, Manju Liu4, Weili Zheng4, Ewart Mark Haacke2,4, and Carlos Ernersto Garrido Salmon1
1Department of Phisics, University of Sao Paulo, Ribeirao Preto, Sao Paulo, Brazil, 2School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada, 3MRI Institute for Biomedical Research, Detroit, Michigan, United States, 4Wayne State University, Detroit, Michigan, United States

 
There are a variety of means by which iron content in vivo tissue can be measured. These include but are not limited to measuring: transverse relaxation rates (R2 and R2*) and quantitative magnetic susceptibility (QSM). However, the dependency of transverse relaxation rates with water content can confound the accuracy of iron quantification if R2 or R2* are used. To overcome this limitation, magnetic susceptibility mapping has been suggested to evaluate iron deposits in neurodegenerative diseases. In this study, we evaluated the correlation between iron concentration with R2 and R2* and magnetic susceptibility in vivo in the midbrain region for seven healthy elderly subjects.

 
2503.   
R2' Mapping of the Human Kidney Using Navigator Gated, Asymmetric Spin Echo, Multi-Shot EPI
Jon Thacker1, Huan Tan2, Shivraman Giri3, and Pottumarthi Vara Prasad2
1Biomedical Engineering, Northwestern, Evanston, Illinois, United States, 2Northshore University Health System, Evanston, Illinois, United States, 3Siemens Healthcare, Chicago, Il, United States

 
Renal oxygenation is typically assessed through R2* maps. However, it is well known that R2* is sensitive to physiological changes other than oxygenation. R2* is believed to be made up of two components: R2 and R2’. R2’ has been assessed as a potentially more specific indicator of oxygenation. Previous work has been done with asymmetric spin echo (ASE) EPI sequences for acquiring R2’ maps. These have been limited in spatial resolution and confined to breath-hold acquisitions. We have integrated a navigator gated, ASE segmented EPI sequence for increased resolution and removal of the inherent constraints with breath-hold scans.

 
2504.   Clinical Comparison Between PADRE and SWI for Susceptibility Weighted MRI
Karin Markenroth Bloch1,2, Stefanie Eriksson3, Roger Siemund4,5, Håkan Sjunnesson4,5, Emelie Lindgren2, and Danielle van Westen4,5
1Clinical science, Philips, Lund, Sweden, 2Dept. of Medical Radiation Physics, Lund University, Lund, Sweden, 3Dept. of Chemistry, Lund University, Lund, Sweden, 4Center for Medical Imaging and Physiology, Skane University Hospital Lund, Lund, Sweden, 5Dept. of Diagnostic Radiology, Lund University, Lund, Sweden

 
The aim of this study was to quantitatively compare two techniques for susceptibility weighted imaging (PADRE and SWI) with regard to hemorrhagic lesion detection and contrast of hemorrhages, as well as to qualitatively compare the image quality.

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
Contrast Mechanism: From Exotic to Clinical Applications

2505.   Quantitative Water Content Assessment Using a Single-Scan Multi-Parameter Mapping Technique and Spectral Processing of a Multiple Gradient Echo Acquisition
Ken-Pin Hwang1, Marcel Warntjes2, R. Jason Stafford3, Wolfgang Stefan3, Edward F. Jackson3, John E. Madewell4, John D. Hazle3, Zachary W. Slavens5, and Tzehping L. Chi4
1Global Applied Science Laboratory, General Electric Healthcare, Houston, TX, United States, 2Center for Medical Imaging Science and Visualisation, Linköping University, Linköping, Sweden, 3Department of Imaging Physics, University of Texas MD Anderson Cancer Center, Houston, TX, United States, 4Department of Radiology, University of Texas MD Anderson Cancer Center, Houston, TX, United States, 5MR Engineering, General Electric Healthcare, Waukesha, WI, United States

 
Brain water content may be assessed with a proton density measurement as derived from a multiple gradient echo sequence, where all causes of signal inhomogeneity are properly corrected. Typically, the effective flip angle of the transmit field and T1 of tissues are mapped with multiple dedicated sequences. Here, we base our corrections on parameters produced from a single multi-parameter mapping technique. We also extrapolate the gradient echo signal using a spectral modeling technique instead of fitting the signal magnitudes. Thus absolute water content assessment is performed with two complementary sequences which provide other quantitative measurements as well.

 
2506.   Specific Inhomogeneous MT Contrast in White Matter. Application to Spinal Cord Imaging.
Olivier M. Girard1, Virginie Callot2, Alexandre Vignaud3, Gopal Varma4, Patrick J. Cozzone5, David C. Alsop4, and Guillaume Duhamel2
1CRMBM UMR 7339, CNRS / Aix-Marseille Université, Marseille, France, 2CRMBM UMR 7339, Aix-Marseille University, Marseille, France, 3Siemens Healthcare, Saint-Denis, France,4Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States, 5CRMBM UMR 7339, Aix-Marseille Université, Marseille, France

 
Myelin specific imaging has become an abounding research area because of the high clinical relevance of myelin-associated diseases such as multiple sclerosis (MS). Recently a novel MT contrast, known as inhomogeneous MT - ihMT, has demonstrated high specificity toward brain WM tissue. In this work an ihMT sequence was developed on a 1.5T clinical scanner and applied on the human cervical spinal cord. This new endogenous contrast demonstrated tremendous specificity towards spinal cord WM. This holds great promise for future clinical applications on SC pathologies such as trauma or MS.

 
2507.   Simultaneous Fat Saturation and Magnetization Transfer Preparation with 2D Small-Tip Fast Recovery Imaging
Feng Zhao1, Scott D. Swanson2, Jon-Fredrik Nielsen1, Jeffrey A. Fessler3, and Douglas C. Noll1
1Biomedical Engineering, The University of Michigan, Ann Arbor, MI, United States, 2Radiology, The University of Michigan, Ann Arbor, MI, United States, 3EECS, University of Michigan, Ann Arbor, MI, United States

 
We propose to do simultaneous fat saturation and magnetization transfer (MT) preparation with small-tip fast recovery imaging (STFR) which produces high SNR bSSFP-like images free of banding artifacts. This sequence requires much less SAR for MT preparation due to its much higher sensitivity to MT effect than regular non-steady-state MT sequence.

 
2508.   Tissue Border Enhancement by Inversion Recovery Acquisition
Mauro Costagli1, Douglas A.C. Kelley2, Riccardo Stara3, Gianluigi Tiberi1, Mirco Cosottini1,3, and Michela Tosetti1,4
1IMAGO7, Calambrone, Pisa, Italy, 2GE Healthcare Technologies, San Francisco, California, United States, 3University of Pisa, Pisa, Pisa, Italy, 4IRCCS Stella Maris, Pisa, Pisa, Italy

 
This study presents an IR sequence that enhances the border between two tissues of interest by employing an inversion time such that magnetizations of the two tissues have same magnitude and opposite sign, hence their interface results nulled and highlighted in the image by a dark line. The most obvious advantage of this technique is that it allows for immediate, enhanced visualization of borders between two tissues of interest without any additional postprocessing procedure, hence images are immediately visible to the neuroradiologist in real time. This technique is feasible on both standard and ultra-high field MRI systems.

 
2509.   Short Echo Times and Multiple Echoes to Image, Quantitate and Classify Fast-Relaxing Anatomy
Ethan M. Johnson1, Jinyi Qi2, Urvi Vyas1, Kim R. Butts Pauly1, and John M. Pauly1
1Stanford University, Stanford, CA, United States, 2UC Davis, Davis, CA, United States

 
Pulse sequences using very short echo times (‘UTE’, ‘CUTE’, ‘DUTE’, etc.) have been applied variously to image tissues with short spin-spin relaxation (T2) times. With consideration of the consequences short-T2 times have for excitation and encoding, a UTE-style pulse sequence capable of visualising bone and other fast-relaxing structures is developed. The acquired images show features that facilitate tissue classification, which is useful, e.g., for MR-PET and high-frequency focussed-ultrasound. To demonstrate, bone, soft tissue and air are classified from 1/T2 and signal level, from which a linear attenuation coefficient map useful for PET reconstruction is generated.

 
2510.   Inversion Recovery Prepared PSIF for FLAIR at 7T
Yiu-Cho Chung1, Yanjie Zhu1, Xin Liu1, and Chao Zou1
1Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Key Laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China

 
TSE based FLAIR at 7T is challenging due to B1 transmit field inhomogeneity and SAR limitation. We propose inversion recovery prepared PSIF (IR-PSIF) for FLAIR imaging at 7T. The short TR in PSIF shortens scan time (~5s per slice) and eliminates the need for segmentation. Use of excitation pulses instead of refocusing pulses makes PSIF less sensitive to hardware imperfections. The SNR of white matter from an IR-PSIF image is about 44, and is half that of FLAIR. Such SNR would be sufficient for diagnostic purposes. We believe IR-PSIF may be a fast and robust alternative for FLAIR at 7T.

 
2511.   T1rho and T2rho Mapping with Gradient Offset Independent Adiabatic Pulse Trains
Ovidiu C. Andronesi1, Himanshu Bhat2, Shreya Mukherjee1, Peter Caravan1, and Bruce R. Rosen1
1Martinos Center, Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, United States, 2Siemens Medical Solutions, Charlestown, Massachusetts, United States

 
T1 and T2 relaxation in the rotating frame (T1rho, T2rho) are sensitive to slow molecular dynamics on the ms time scale, relevant for interaction of water with important biological systems such as proteins, glycosaminoglycans and cell membranes. T1rho and T2rho have been used to investigate pathology of stroke, Alzheimer’s Disease, Parkinson Disease, liver cirrhosis and cartilage damage. Because T1rho and T2rho contrasts are created by the application of a long spin lock RF field, or by a train of adiabatic inversion pulses this results in sequences that have high specific absorption rate (SAR). Here we propose a pulse sequence based on low power gradient offset independent adiabatic pulses (GOIA-W(n,m))for decreasing SAR and performing slice selective T1rho and T2rho mapping.

 
2512.   A T2-Diffusion-Prepared Cube Sequence for Brain Lesion Detection at 7T
Eric K. Gibbons1, Manoj Saranathan2, Brian K. Rutt2, John M. Pauly3, and Adam B. Kerr3
1Department of Bioengineering, Stanford University, Stanford, California, United States, 2Department of Radiology, Stanford University, Stanford, California, United States,3Department of Electrical Engineering, Stanford University, Stanford, California, United States

 
Brain lesion detection at 7T is complicated by the T1 lengthening observed for white and grey matter without a corresponding increase in CSF T1. As a consequence, there is lower SNR and contrast for grey and white matter in FLAIR sequences designed to null CSF signal. The recently developed MP-FLAIR 3D FSE sequence introduced a magnetization preparation sequence to initially saturate white/grey matter Mz so as to allow for greater recovery during the FLAIR inversion period. In this preliminary work, we examine the possibility of eliminating the inversion preparation entirely, using instead a T2 and diffusion preparation sequence, with the goal being CSF signal suppression due to it’s higher diffusion, and simultaneous introduction of combined T2/diffusion contrast between white/grey matter and lesions.

 
2513.   Quantitative Proton Density Mapping in Pathological Tissue: Comparison of Two Receiver Profile Correction Methods
Steffen Volz1, Ulrike Nöth1, Alina Jurcoane2, Ulf Ziemann3, Elke Hattingen2, and Ralf Deichmann1
1Brain Imaging Center, University Frankfurt, Frankfurt, Germany, 2Department of Neuroradiology, University Frankfurt, Frankfurt, Germany, 3Department of Neurology, University Frankfurt, Frankfurt, Germany

 
Correcting for the receiver profile (RP) of the RF coil is a crucial step in quantitative proton density (PD) mapping. Two new RP correction methods were compared for pathological tissue: (1) bias field correction method and (2) pseudo PD calculation method assuming a linear relationship between T1 and PD in white and grey matter. Results were consistent for multiple sclerosis and stroke patients (small lesions). However, differences between the two RP correction methods were found in tumour tissue with results from the pseudo PD method being more plausible.

 
2514.   Robust Susceptibility Weighted Imaging Using Single-Slab 3D GRASE with Removal of Background Phase Variation
Hahnsung Kim1, Dong-Hyun Kim1, and Jaeseok Park2
1Yonsei University, Seoul, Korea, 2Korea University, Seoul, Korea

 
In susceptibility weighted imaging, it is important to remove background phase variations while retaining only local field information. The projection onto dipole field method was recently introduced, employing image-based convolution with ROI masks to decompose a background field within the ROI into one originating from dipoles outside the ROI. However, the image-based convolution is sensitive to rapid field variations at the boundaries of the ROI, leading to loss of important phase information particularly at the air-tissue interfaces. To regionally correct rapid phase aliasing at the boundaries while locally removing smoothly varying background phases, we develop a robust SWI method employing: 1) Single-slab 3D GRASE to simultaneously acquire both artifact-free magnitude images from spin echo and phase images from free induction decay signals, 2) Removal of rapid background field at the boundaries using forward field calculation, and 3) Removal of local background field with the ROI extended to the boundaries to preserve susceptibility induced phase information over the entire image.

 
2515.   Phase and Diffusion Tensor Imaging at Ultra-High Magnetic Field: Differences and Similarities
Yohan van de Looij1,2, Rajika Maddage2, Nicolas Kunz1,2, Petra Susan Hüppi1, Rolf Gruetter3,4, and Stéphane V. Sizonenko1
1Division of Child Growth & Development, University of Geneva, Geneva, Switzerland, 2Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 3Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, 4Department of Radiology, University of Geneva and Lausanne, Geneva and Lausanne, Switzerland

 
DTI gives useful white matter information such as fiber direction and integrity. The phase of gradient echo images (PI) has been used to create anatomical images with excellent grey/white matter contrast. In this work the potential correlations between DTI and PI in the rat brain were investigated. We show that PI contrast is influenced by degree of anisotropy and fiber orientation. A correlation between DTI derived parameters and frequency shift of PI was also observed. Further experiments are in progress to quantify more accurately these results by an assessment of the correlations between DTI and susceptibility maps.

 
2516.   Collagen Composition and Content-Dependent Contrast in Porcine Annulus Fibrosus Using Double-Quantum Filtering Combined with Magnetization-Transfer and UTE MRI
Uzi Eliav1, Michal E. Komlosh2, Peter J. Basser2, and Gil Navon1
1School of Chemistry, Tel Aviv University, Tel Aviv, Israel, 2STBB/PPITS/NICHD/NIH, NIH, Bethesda, MD, United States

 
The combined double quantum (DQ) filtering and magnetization transfer (DQF-MT) and Ultra-Short TE (UTE) MRI (DQF-MT/UTE) pulse sequence was applied for the study of the annulus fibrosus in porcine intervertebral disc (IVD). It was shown that unlike the UTE that gives the same intensity throughout the tissue the intensity in the DQF-MT/UTE image declines from the outer layers towards the inner ones (closer to the nucleus pulposus). The latter result was interpreted as a combined effect of the declined concentration of collagen and the ratio of collagen type I to type II going from the outer into the inner layers.

 
2517.   31P and 1H NMR Investigation of Liquid Crystal Phase Temperature Dependence in Rehydrated Myelin
Henry H. Ong1, Michael J. Wilhelm2, Suzanne L. Wehrli3, Edward James Delikatny4, and Felix W. Wehrli1
1Laboratory for Structural NMR Imaging, Department of Radiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, United States, 2Department of Chemistry, Temple University, Philadelphia, PA, United States, 3NMR Core Facility, Children's Hospital of Philadelphia, Philadelphia, PA, United States, 4Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

 
Understanding MR properties of myelin would provide valuable insight into current MRI methods for myelin imaging. Myelin forms a lamellar liquid crystal lipid system whose phase behavior is influenced by temperature. In recent work the MR properties of rehydrated myelin extracts have been studied at room temperature, but whether the results apply to physiological temperature is not currently understood. Here, we studied the temperature dependence (10-50°C) of the liquid crystal phase of rehydrated bovine myelin extract with 31P and 1H NMR. The results are consistent with myelin lipids exhibiting a lamellar liquid crystal phase over this temperature range

 
2518.   Bz-SNR-Enhanced Echo-Shifted Incoherent Steady State Imaging for Electrical Conductivity Mapping
Hyunyeol Lee1, Woo Chul Jeong2, Hyung Joong Kim2, Eung Je Woo2, and Jaeseok Park1
1Brain and Cognitive Engineering, Korea University, Seoul, Korea, 2Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi, Korea

 
Magnetic resonance electrical impedance tomography (MREIT) was recently introduced to achieve high spatial resolution, wherein the internal magnetic flux density (Bz) induced by current injection results from image phases and electrical conductivity is then calculated using the harmonic Bz algorithm. To achieve accurate conductivity distribution in tissues, a high signal-to-noise ratio (SNR) in Bz is critical, which is proportional to the product of current injection time (TC) and SNR in magnitude image. To effectively enhance the SNR of Bz in MREIT and speed up data acquisition, in this work we develop a Bz-SNR-optimized echo-shifted incoherent steady state imaging pulse sequence for accurate quantification of electrical conductivity, wherein free induction decay (FID) signals experience multiple current injections to form an echo without apparent loss of signals while retaining high imaging efficiency.

 
2519.   Tissue Thermal Property Tomography
Leeor Alon1,2, Christopher Collins1,2, Giuseppe Carluccio1, Dmitry S. Novikov1, Yudong Zhu1,2, and Daniel Sodickson1,2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University, New York, NY, United States

 
At last year’s ISMRM meeting, we introduced Local Maxwell Tomography (LMT) – a method for noninvasive mapping of electrical conductivity and permittivity using incomplete MR-based measurements of RF field curvature. Here, we apply a theoretical framework analogous to that of LMT to solve Pennes’ bio-heat equation, instead of Maxwell’s equations, and thereby to reconstruct tissue thermal property maps from MR thermometric measurements. We outline the theory and demonstrate reconstruction of thermal properties such as heat capacity, thermal conductivity, and metabolic energy rate.

 
2520.   Neuronal Current MRI in the Octopus Visual System
Xia Jiang1, Hanbing Lu2, Shuichi Shigeno3, Li-Hai Tan4, Yihong Yang2, Clifton W. Ragsdale3, and Jia-Hong Gao1
1Brain Research Imaging Center and Department of Radiology, University of Chicago, Chicago, IL, United States, 2Neuroimaging Research Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, United States, 3Department of Neurobiology, University of Chicago, Chicago, IL, United States, 4State Key Lab for Brain Research, University of Hong Kong, Hong Kong, China

 
Much effort has been made to determine the feasibility of neuronal current MRI (nc-MRI), where the small magnetic field change due to neuronal currents activity is mapped using MRI. However, most previous studies in nc-MRI were susceptible to the contamination of BOLD signal. In this study we tested nc-MRI in the octopus visual system, which is free from BOLD effect. In addition, electrophysiological recordings were used to confirm electrical activities. Scans with the EPI sequences indicated that no statistically significant nc-MRI effect could be detected at 0.2%/0.2° level for signal magnitude and phase respectively.

 
2521.   Imaging Chick Embryos with SPIO Nanoparticles Using SWIFT
Luning Wang1, Yangqing Lu2, Khan Hekmatyar3, Steve Stice2, and Qun Zhao1
1Department of Physics and Astronomy, University of Georgia, Athens, GA, United States, 2Department of Animal and Dairy Science, University of Georgia, Athens, GA, United States, 3BioImaging Research Center (BIRC), University of Georgia, Athens, GA, United States

 
Magnetic resonance imaging (MRI) has been used for studying the dynamics of chick embryo development and growth. This can be repeated observations on the same embryo on a longitudinal basis, using high resolution ultra-high-field (7 Tesla or higher) MR scanners. MRI-based cell tracking using super-paramagnetic iron oxide (SPIO) particles provide an excellent means of cell monitoring in in-vivo. In this work, a novel sweep imaging with Fourier transformation (SWIFT) sequence, compared with conventional fast spin echo (FSE) and gradient-recalled echo (GRE) sequences, will be used to scan a chick embryo injected with SPIO nanoparticles.

 
2522.   Optimal Partial Fourier Reconstructions in Electron Paramagnetic Resonance Imaging
Alan B. McMillan1, Hyungseok Jang1, Sankaran Subramanian2, and Murali C. Krishna2
1Radiology, University of Wisconsin, Madison, WI, United States, 2Radiation Biology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, MD, United States

 
Electron paramagnetic resonance imaging (EPRI) employed using single-point (SP) imaging techniques offers the capability to dynamically image in vivo tumor oxygenation. While highly specific, current capabilities for high spatial resolution dynamic imaging are limited. Recently, we have investigated partial k-space acceleration techniques for SP-EPRI. In this work, we show that the SP-EPRI imaging technique is highly suited to PF techniques due to its tractable phase characteristics, and that performance of each method is dependent upon image matrix size.

 
2523.   Characterization of EPR Spin-Echo Data for Accelerated Oximetry
Frank Golub1, Lee C. Potter1, and Rizwan Ahmad1
1The Ohio State University, Columbus, OH, United States

 
The current standard for evaluating the T2 decay constant in pulsed EPR oximetry employs peak-picking of spin echoes. This method is inefficient, because it only uses a small subset of the available echo data. In this work, we characterize a sequence of measured spin echoes using either a rank-one matrix or a train of parametric functions. Simulation results indicate that the proposed methods can significantly reduce the error variance in the estimation of T2 and hence the data acquisition time for EPR oximetry.

 
2524.   A Method to Improve Temporal Resolution in EPR Imaging of Tissue Oxygenation
Hyungseok Jang1, Sankaran Subramanian2, Nallathamby Devashayam2, Murali C. Krishna2, and Alan B. McMillan1
1Radiology, University of Wisconsin, Madison, WI, United States, 2Radiation Biology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, MD, United States

 
In EPRI acquired using single-point techniques, repeated imaging experiments with differing gradient amplitudes are used to calculate spectral linewidths necessary to quantify pO2. In this study, we propose a novel estimation method that enables direct calculation of linewidth within a single dataset. We investigate gridding reconstruction and image-based registration techniques to maintain image FOV, and enable pixelwise estimation of linewidth. In phantom experiments, we show that these methods allow quantification of pO2 within a single dataset, which will allow temporal resolution improvements of 3x compared to existing techniques.

 
2525.   Influence of Free Radicals Signal from Dental Resins on the Radio-Induced Signal in Teeth in Nuclear Retrospective Dosimetry : Kinetic Analysis Using EPR
Celine M. Desmet1, Philippe Leveque1, Gaetane Leloup2, and Bernard Gallez3
1Biomedical Magnetic Resonance, Universite catholique de Louvain, Brussels, Belgium, 2CRIBIO, Universite catholique de Louvain, Brussels, Belgium, 3Biomedical Magnetic Resonance, University of Louvain, Brussels, Belgium

 
Tooth enamel associated with EPR detection is a very promising natural dosimeter. When conducting retrospective dosimetry, attention should be paid to recent restorations on teeth (less than 6 month), specially for doses lower than 3Gy because dental resins exhibit intense EPR signals early after photopolymerization

 

TRADITIONAL POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION A
Tuesday, 23 April 2013 (13:30-15:30) Exhibition Hall
CEST, MT, APT

2526.   Amide Proton Transfer (APT) Imaging for Grading of Glioma
Ge Zhang1, Xianlong Wang1, Shilong Lu1, Jinyuan Zhou2, and Zhibo Wen1
1Department of Radiology, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China, 2Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States

 
We explored the imaging features of different grades of glioma using Amide Proton Transfer MR Imaging at 3 Tesla. Results showed that the average APT signal intensities of the viable tumor cores were significantly higher than those of peritumoral edema or normal-appearing white matter in both low-grade and high-grade glioma. The average APT signal intensities of the viable tumor cores were significantly higher than in low-grade glioma. APT imaging provides additional diagnostic information to characterize different grade of glioma.

 
2527.   APT and NOE Imaging Contrasts of Glioma with Different RF Saturation Powers
Jinyuan Zhou1,2 and Xiaohua Hong1
1Department of Radiology, Johns Hopkins University, Baltimore, Maryland, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States

 
We performed APT imaging and NOE imaging experiments on 9L tumor-bearing rats. The NOE effect is clearly visible at lower saturation powers and is larger in contralateral normal brain tissue. On the contrary, the APT effect is observed at relatively higher saturation powers and is larger in tumor. The NOE effect is a confounding factor for the quantification of APT and other CEST effects and may be exploited as a potentially new MR contrast.

 
2528.   in vivo Saturation Transfer Imaging of Nuclear Overhauser Effect from Aromatic and Aliphatic Protons: Implication to APT Quantification
Tao Jin1 and Seong-Gi Kim1,2
1Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States, 2Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, United States

 
Recent in vivo saturation transfer MRI studies have showed significant signals from the Nuclear Overhauser effect (NOE) from aliphatic protons of macromolecules. In this preliminary study, we found that the aromatic protons, with frequency range downfield of water and close to the amide frequencies, can also affect the water signal in a saturation transfer experiment through the NOE, and the effect is significant in vivo. Both aromatic and aliphatic NOE signals are not sensitive to tissue pH, while they impose difficulties to the quantification of amide proton transfer contrast, they may provide novel MRI contrast complementary to CEST.

 
2529.   Amide Proton Chemical Exchange Saturation Transfer at 9.4 T with Optimized RF Transmit Field Through B1 Shimming
Christian C. Mirkes1,2, Jens Hoffmann1, Gunamony Shajan1, Rolf Pohmann1, and Klaus Scheffler1,2
1High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 2Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany

 
Amide proton transfer imaging is very promising at ultra-high field due to the large spectral separation. Here we show that quantification of the chemical exchange saturation effect can be facilitated by homogenizing the transmit field through B1 shimming.

 
2530.   Contamination of Neurometabolite Amine-Water Proton Exchange to Amide Proton Transfer MRI
Xiaopeng Zong1, Ping Wang1, Seong-Gi Kim1, and Tao Jin1
1Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

 
Amide-water proton transfer (APT) can be exploited to provide useful MRI contrast under various disease conditions. However, the APT-weighted signals (APTw) might be contaminated by other chemical exchange processes, such as fast amine-water proton exchange. To investigate this issue, we measured APTw of nine major neurometabolites in phantoms and estimated their contributions to the in vivo APTw contrast in ischemic rat brain. We found significant contributions from several metabolites to the APTw, which showed pH dependence opposite to the APTw signal in vivo. Thus, possible contaminations from neurometabolites should be considered when interpreting the sources of APTw contrast.

 
2531.   Effect of Saturation Pulse Duration and Strength on Parallel Transmission Based Amide Proton Transfer MRI of the Prostate
Guang Jia1, Saba N. Elias1, Ronney Abaza2, Debra L. Zynger3, Zarine K. Shah1, Lai Wei4, Robert R. Bahnson2, and Michael V. Knopp1
1Department of Radiology, The Ohio State University, Columbus, OH, United States, 2Department of Urology, The Ohio State University, Columbus, OH, United States,3Department of Pathology, The Ohio State University, Columbus, OH, United States, 4Center for Biostatistics, The Ohio State University, Columbus, OH, United States

 
This study shows the importance of APT-MRI contrast optimization based on pulse duration and power strength in clinical prostate cancer patient examinations and its benefits to further develop this methodology into an imaging biomarker.

 
2532.   Prospectively Motion Compensated Amide Proton Transfer MRI for Body Oncology
Jochen Keupp1, Guang Jia2, Ivan E. Dimitrov3, Silke Hey4, and Michael V. Knopp2
1Philips Research, Hamburg, Germany, 2Department of Radiology, The Ohio State University, Columbus, OH, United States, 3Philips Healthcare, Cleveland, OH, United States, 4Philips Healthcare, Best, Netherlands

 
Endogenous contrast of exchangeable amide protons of intra-cellular proteins and peptides (amide proton transfer, APT) has been developed sucessfully and applied for first cinical studies in oncology applications. The work up to now has been mostly focused on the brain, with some extensions to e.g. prostate and breast APT. The organs addressed so far are not subject to respiratory motion. Body oncology applications in e.g. liver and kidney are challenging for APT, because the time scale of RF saturation needed for sensitive APT MRI (about 2s) is of the same order as typical respiratory intervals. A basic respiratory triggered saturation transfer technique was previously developed for contrast agent studies in human kidneys. In the current work, this approach was extended for improved stability of the contrast with varying respiratory cycles, scan time efficiency and SAR management. The novel technique was successfully tested in human volunteers with a focus on APT contrast in liver and kidney.

 
2533.   Amide Proton Transfer MR Imaging in Peritoneal Metastasis Evaluation
Xue Yu1, Elaine Yuen Phin Lee1, Queenie Chan2, and Mina Kim1
1Diagnostic Radiology, The University of Hong Kong, Hong Kong, China, 2Philips Healthcare, Hong Kong, China

 
Neoadjuvant treatment for peritoneal metastasis has emerged. Therefore evaluation of peritoneal metastasis is crucial for diagnosis and treatment planning. As APT MRI can provide complementary information to current MR sequences in clinical use, the purpose of this study is to assess APT MRI in peritoneal metastasis imaging. This pilot study demonstrates the feasibility of APT MRI in differentiating peritoneal metastasis from muscle and fat, which is clinically relevant as peritoneal metastases can be deposited in the area with abundant fat or adherent to soft tissue. The separation of these tissues will aid detection and assessment of peritoneal metastasis.

 
2534.   Isolating Chemical Exchange Contrast from Amide and Amine Protons in the Presence of Asymmetric Macromolecular Magnetization Transfer with Off-Resonance Spin Locking at 3T in the Human Brain
Rachel Scheidegger1,2 and David C. Alsop1,3
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States, 2Health Sciences and Technology, Harvard-MIT, Cambridge, MA, United States, 3Radiology, Harvard Medical School, Boston, MA, United States

 
We present spin-locking RF preparations schemes optimized to generate chemical exchange saturation transfer (CEST) contrast with reduced errors from multiple exchangeable protons and intrinsic magnetization transfer (MT) asymmetry for human imaging at 3T. Tuning both the spin-locking power and duration can be used to maximize signal from either amide or amine protons. We demonstrate, in healthy volunteers, how these methods allow clear and robust measurement of the amine proton peak with reduced MT asymmetry which could improve the feasibility of quantifying exchange rates in-vivo and measuring pH.

 
2535.   Specific Inhomogeneous MT Contrast in Mouse Brain White Matter
Guillaume Duhamel1, Olivier M. Girard1, Gopal Varma2, Patrick J. Cozzone1, Virginie Callot1, and David C. Alsop2
1CRMBM / CNRS 7339, Aix-Marseille University, Marseille, France, 2Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States

 
Specific imaging able to provide quantification of myelin concentration would be a very valuable tool for clinical and preclinical studies of white matter pathologies. While several advanced MR techniques are used to assess myelin content (short T2 imaging, MWF, MT …), they all are affected by confounding factors which limit their specificity to myelin. A new MT approach specific to the inhomogenous component of the MT spectrum was applied on human at 3T and appeared to be selectively sensitive to tissue with myelin. Here, we investigated the specificity of this inhomogenous MT sequence in mouse brain at 11.75T

 
2536.   Quantitative Evaluation of the Exchange Time and T2 Associated with an Inhomogeneous Component Using Inhomogeneous Magnetization Transfer Imaging
Gopal Varma1, Fotini Kourtelidis1, and David C. Alsop1
1Radiology, Division of MR Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States

 
Application of quantitative magnetization transfer (MT) to white matter in the brain is of interest, particularly in studies of degenerative diseases. A greater contrast and sensitivity has been shown from inhomogeneous MT (IHMT) imaging. A more quantitative analysis of the IHMT effect is applied in hair conditioner phantoms and in vivo based on a 2 pool model to elucidate exchange time and T2 parameters associated with an inhomogeneous component. An exchange time of ~6ms and T2 of ~200µs is found in healthy volunteers, which are distinct from the results in vitro.

 
2537.   Assessment of Interslice MT Signal Characteristics of BSSFP for MTR Imaging of the Human Brain
Jeffrey William Barker1,2, Kyongtae Ty Bae1, and Sung-Hong Park1,3
1Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3Bio and Brain Engineering, Korean Advanced Institute of Science and Technology, Daejeon, Yuseong-gu, Korea

 
For our newly developed MT ratio (MTR) imaging, we assessed characteristics of interslice MT signals, that are inherent to multi-slice bSSFP imaging for varying flip angle and phase encoding (PE) order. We compared in vivo MTR values to two-pool model simulations. Overall, MTR and SNR values increased with flip angle. Centric PE images showed higher MTR values, higher SNR, and better WM/GM contrast. Linear PE image contrast was influenced by relaxation effects. Simulations agreed well with in vivo data. Our study assessed characteristic factors of the interslice MTR method to be considered for MTR imaging in the brain.

 
2538.   Contributors to Contrast Between Glioma and Brain Tissue in Chemical Exchange Saturation Transfer Sensitive Imaging at 3 Tesla
Rachel Scheidegger1,2, Eric T. Wong3,4, and David C. Alsop1,5
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States, 2Health Sciences and Technology, Harvard-MIT, Cambridge, Massachusetts, United States,3Brain Tumor Center & Neuro-Oncology Unit, Beth Israel Deaconess Medical Center, Boston, MA, United States, 4Neurology, Harvard Medical School, Boston, MA, United States, 5Radiology, Harvard Medical School, Boston, MA, United States

 
We report a study targeted at separating the different saturation transfer signals from amide, amine, aliphatic protons and macromolecular magnetization transfer contrast (MTC) and identifying their relative contributions to CEST contrast in high grade glioma patients. Amide exchange could be detected with lower saturation power than has previously been reported in glioma but showed no detectable contrast in tumors. At high saturation powers, amine proton exchange was a major contributor to the observed signal but also showed no contrast in tumors. The loss of broad macromolecular MTC from normal brain tissue was responsible for the majority of contrast with glioma.

 
2539.   Quantitative Magnetization Transfer Imaging at 7 Tesla: Application in Multiple Sclerosis Patients and Validation in Postmortem Brain
Richard D. Dortch1,2, Adrienne N. Dula1,2, Francesca Bagnato1,2, David R. Pennell1,2, Siddharama Pawate3, Simon Hametner4, Hans Lassmann4, John C. Gore1,2, and Seth A. Smith1,2
1Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, 2Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 3Neurology, Vanderbilt University, Nashville, TN, United States, 4Center for Brain Research, Medical University, Vienna, Austria

 
We recently developed a selective inversion recovery (SIR) quantitative magnetization transfer (qMT) protocol that exploits the increased signal-to-noise ratio available at 7.0 T to reduce scan times. The goals of this study were: 1) to establish the relationship between the resulting SIR-derived metrics and pathological changes in relapsing-remitting multiple sclerosis (RRMS) patients and 2) to validate the SIR technique by comparing qMT parameter maps in postmortem brains to histological measurements of myelin. The in vivo results suggest that SIR-derived metrics are sensitive to RRMS pathology, and the postmortem results suggest that the method is reporting on changes in myelin content.

 
2540.   Sulcal and Gyral Crown Cortical Grey Matter Involvement in Multiple Sclerosis: A Magnetisation Transfer Ratio Study
Rebecca S. Samson1, Nils Muhlert2, Varun Sethi2, Claudia Angela M. Wheeler-Kingshott2, Maria A. Ron2, David H. Miller2, and Declan T. Chard2
1NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, London, England, United Kingdom, 2NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom

 
Histopathology has demonstrated extensive cortical grey matter (CGM) demyelination in multiple sclerosis (MS), and suggests that sulcal folds may be preferentially affected, particularly in secondary progressive (SP) MS. We measured sulcal and gyral crown magnetisation transfer ratio (MTR) in MS and healthy control CGM in vivo, and examined associations with clinical status. CGM MTR abnormalities were present in all MS subtypes and were most pronounced in SPMS. However, sulcal was lower than gyral MTR in all groups (including controls) except SPMS, indicating that there is not a clear sulcal predilection for these changes.

 
2541.   CEST Effect at 2ppm (CEST@2ppm): A Potential Biomarker for Grading Brain Tumor Malignancy
Kejia Cai1, Mohammad Haris1, Anup Singh1, Ravi Prakash Reddy Nanga1, Ranjit Ittyerah1, Damodar Reddy1, Harish Poptani1, Hari Hariharan1, and Ravinder Reddy1
1University of Pennsylvania, Philadelphia, PA, United States

 
The CEST effect at 2ppm (CEST@2ppm), quantified through fitting Z spectrum with Lorentzian functions, decreases in tumor compared to normal brain tissue and further reduces as tumor progresses, correlating to MRS quantification of creatine. Along with other justifications, we suggest creatine to be the major contribution to the CEST@2ppm. Our results show F98 tumors have significant lower CEST@2ppm effect compared to 9L tumors. Once validated, the high-resolution creatine mapping method could be used for grading brain tumors.

 
2542.   The CEST Effect of Guanidine and Hydroxyl Protons Can Be Used as a Positive Contrast in Ischemia
Tao Jin1 and Seong-Gi Kim1
1Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

 
CEST imaging utilizing the the endogenous amide-proton transfer (APT) effect has shown great potential in stroke studies. However, the APT contrast in stroke is negative which decreases at the lesion region. A positive pH-sensitive imaging contrast would be preferable. In this preliminary study, we investigated the chemical exchange effects of endogenous guanidine and hydroxyl protons and their potential application in stroke studies. Because guanidine and hydroxyl protons exchange with water at much faster rate than amide protons, a positive chemical exchange imaging contrast induced by tissue acidosis can be detected by judicious selection of the off-resonance irradiation pulse power.

 
2543.   Feasibility of in vivo CEST Imaging of Creatine (CrCEST) at 3T
Catherine DeBrosse1, Feliks Kogan1, Mohammad Haris1, Anup Singh1, Kejia Cai1, Ravi Prakash Reddy Nanga1, Hari Hariharan1, and Ravinder Reddy1
1Center for Magnetic Resonance and Optical Imaging, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States

 
The purpose of this study was to determine the feasibility of mapping creatine (Cr) in vivo using chemical exchange saturation transfer (CEST) on routine clinical scanners (3T). Mild plantar flexion exercise on healthy human subjects led to an increase in CrCESTasym that is correlated to the change in the PCr signal measured with 31P MRS.

 
2544.   
Imaging of Endogenous CEST Agents in the Human Brain Using Frequency Labeled Exchange (FLEX) Transfer
Nirbhay N. Yadav1,2, Craig K. Jones1,2, Jun Hua1,2, Jiadi Xu1,2, and Peter C.M. van Zijl1,2
1Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, 2FM Kirby Research Center, Kennedy Krieger Institute, Baltimore, MD, United States

 
It is shown that it is possible to image endogenous exchangeable proton signals in the human brain at 3T using the recently reported method of frequency labeled exchange transfer (FLEX) MRI. The results indicate that, compared to traditional CEST experiments, FLEX MRI preferentially detects more rapidly exchanging amide/amine protons, thereby changing the information content of the exchangeable proton spectrum. This has the potential to open up different types of endogenous applications as well as more easy detection of rapidly exchanging protons in diaCEST agents or fast exchanging units such as water molecules in paraCEST agents without interference of conventional MTC.

 
2545.   A Multi-Echo Length and Offset VARied Saturation (Me-LOVARS) CEST Method
Xiaolei Song1,2, Jiadi Xu1,2, Shuli Xia3, Nirbhay N. Yadav1,2, Bachchu Lal3, Jeff W.M. Bulte2,4, John Laterra3, Peter C.M. van Zijl1,2, and Michael T. McMahon1,2
1Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University, Baltimore, Maryland, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, 3Department of Neuro-Oncology, Kennedy Krieger Institute, Baltimore, MD, United States, 4Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, United States

 
Chemical Exchange Saturation Transfer (CEST) has become an important method to generate MRI contrast, with applications in the imaging of strokes and cancer. We present an efficient CEST imaging method, named Multi-echo Length and Offset VARied Saturation (Me-LOVARS), which allows acquiring a series of Z-spectra at multiple tsat values, without extra scan time cost. When using Me-LOVARS for imaging mice baring glioblastomas, 3 Z-spectra with saturation length of 0.8sec., 1.6sec. and 2.4sec were acquired, using same time as one conventional Zspectrum. The contrast-noise-ratio of B0-corrected MTRasym maps using Me-LOVARS is also comparable to the conventional method with the same tsat.

 
2546.   An Analytical Approach Towards Pulsed-SL/CEST Quantification
Volkert Brar Roeloffs1, Moritz Zaiss1, and Peter Bachert1
1Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Baden-Wuerttemberg, Germany

 
Chemical exchange saturation transfer (CEST) experiments provide a NMR-imaging technique capable of detecting dilute metabolite protons. Off-resonant spinlock experiments are in a similar way sensitive to chemical exchange. However, within the clinical context, RF pulse duration and power are limited due to SAR-restrictions. For this reason, in this work the effect of pulsed spinlock saturation has been modeled theoretically. The findings were validated experimentally and a method of quantifying exchange rates was proposed, which might be an important step towards a contrast-agent free imaging technique that allows in vivo quantification of physiological relevant exchange rates and metabolite concentrations.

 
2547.   The Non-Linearity of CEST and MT Signal Combination
Sheng-Min Huang1, Chih-Kuang Yeh1, and Fu-Nien Wang1
1Department of Biomedical Engineering & Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan

 
The interference from magnetization transfer (MT) in chemical exchange saturation transfer (CEST) complicates the issue of quantitative measurement. In this study, we performed both numerical simulation and phantom experiment to identify if linear combining assumption of CEST and MT signal is appropriate. Both our results showed that the mix signal of CEST and MT were overestimated approximately 25% by linear model, which indicates that linear combination fails to describe the relations between CEST and MT signal. Comprehensive study of CEST and MT relationship is needed for reducing the asymmetric MT effect.

 
2548.   MTRRex – a New Spillover and MT Correction Method for Quantitative Pulsed Steady-State CEST
Moritz Zaiss1, Steffen Goerke1, and Peter Bachert1
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, BW, Germany

 
CEST evaluation suffers from concomitant effects as direct water saturation (spillover) and MT. We present a new spillover correction for pulsed CEST which yields the exchange dependent relaxation in the rotating frame Rex. We proof our method at creatine model solutions and show additionally, that also quantification is possible and therefore calculation of pH and creatine concentration maps. Our method can simply be applied to clinical data of gagCEST, APT, glucoCEST and many more.

 
2549.   Simplified RF Spillover-Corrected Omega Plot for Simultaneous Determination of Labile Proton Ratio and Exchange Rate
Phillip Zhe Sun1, Gang Xiao2, and Renhua Wu3
1Radiology, Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 2Department of Math and Information Technology, Hanshan Normal University, Chaozhou, Guangdong, China, 3Department of Medical Imaging, Medical College of Shantou University, Chaozhou, Guangdong, China

 
Whereas CEST-weighted MRI has provided tremendous insights, it is important to develop quantitative CEST (qCEST) analysis to characterize the underlying CEST system. We here postulated that the concomitant RF spillover effects can be reasonably estimated for simplified qCEST analysis. Specifically, both the labile proton ratio and exchange rate can be determined from RF spillover factor corrected modified omega plot. The proposed qCEST analysis was validated both numerically and experimentally. In summary, our study established a simplified qCEST analysis algorithm, which remains promising to aid the ongoing development of qCEST MRI.

 
2550.   Off-Resonance Irradiation Power to Optimize the CEST Sensitivity Versus the Exchange Rate-Specificity
Tao Jin1 and Seong-Gi Kim1
1Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States

 
In CEST studies, the off-resonance irradiation power amplitude (B1) should be adjusted to optimize the sensitivity and/or specificity of chemical exchange contrast. If only one type of labile proton exist or is dominant, B1 can be optimized to maximize the sensitivity of chemical exchange contrast. If several types of labile protons have similar Larmor frequencies but very different exchange rates, B1 can also be optimized to selectively enhance the chemical exchange contrast from a specific labile proton. In this work we derived analytical solutions for B1 optimization of these two cases in the slow exchange regime.

 
2551.   A New Method for Quantifying Chemical Exchange Rates from CEST MRI Using the Solutions to the Time-Dependent Bloch Equations with and Without Spin Locking
Kenya Murase1, Junpei Ueda1, Koji Itagaki1, Shigeyoshi Saito1, and Atsuomi Kimura1
1Medical Physics and Engineering, Osaka University, Suita, Osaka, Japan

 
Recently, there have been an increasing number of studies that have used the chemical exchange effect to probe the tissue microenvironment. Most of these studies adopted either a chemical exchange saturation transfer (CEST) or a spin-locking (SL) approach. We presented a simple and fast method for solving the time-dependent Bloch equations in CEST MRI with SL, and proposed a new method for quantifying chemical exchange rates from CEST MRI with and without SL using this method. Our results suggest that the CEST MRI with SL is more reliable than that without SL for quantifying chemical exchange rates.

 
2552.   Optimization of Spin-Lock Parameters for Chemical Exchange Imaging Contrast Enhancement by Maximizing Asymmetric Magnetization Transfer Ratio: A Theoretical Study
Jing Yuan1, Qinwei Zhang1, Anil T. Ahuja1, and Yi-Xiang Wang1
1Department of Imaging and Interventional Radiology, Chinese University of Hong Kong, Shatin, NT, Hong Kong

 
Spin-lock technique, which is traditionally used to measure T1£l relaxation time, can also be used for chemical exchange (CE) imaging. This study theoretically investigates the optimization of spin-lock frequency (FSL) and spin-lock time (TSL) to maximize the asymmetric magnetization transfer ratio for different proton exchange rates, by numerical simulations based on a two-pool R1£l relaxation model derived from the Bloch-McConnell equations. Results show that spin-lock pulse with low FSL and long TSL is sensitive to detect slow CE processes while spin-lock pulse with high FSL and short TSL is useful for fast CE process study.

 
2553.   Differentiation and Quantification of Exchanging Protons in Different Pool Resonating at the Same Frequency in CEST
Olivier E. Mougin1 and Penelope A. Gowland2
1SPMMRC, School of Physics and Astronomy, University of Nottingham, Nottingham, Select, United Kingdom, 2SPMMRC, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

 
CEST is increasingly used to study a wide range of endogenous and exogenous species. However different species of interest overlap in the z-spectra even at high field due to line broadening caused by exchange. Here we propose a new combination of acquisition and analysis approaches to separate fast and slow exchanging species. Simulation and experimentation of a z-spectra database for two pools exchanging at different rates is presented here, and was used successfully in fitting pool protons overlapping on the z-spectra, both numerically and empirically.

 
2554.   Contribution of Tissue Perfusion to the CEST Effect from Creatine in Skeletal Muscle
Feliks Kogan1, Randall B. Stafford2, Mohammad Haris1, Erin K. Englund2, Anup Singh1, Kejia Cai1, Catherine DeBrosse1, Ravi Prakash Reddy Nanga1, Hari Hariharan1, John A. Detre3, and Ravinder Reddy1
1Center for Magnetic Resonance and Optical Imaging (CMROI), University of Pennsylvania, Philadelphia, PA, United States, 2Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States, 3Center for Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA, United States

 
The objective of this work was to determine the contribution of perfused blood on the chemical exchange saturation transfer (CEST) from creatine. Perfusion changes were produced by a combination of cuff inflation and deflation. Reactive hyperemia resulted in substantial increases in perfusion as measured by arterial spin labeling (ASL) mean percent difference maps but negligible changes in CrCEST maps. This demonstrates that the CEST effect from perfused blood is negligible and does not confound CrCEST measurements.

 
2555.   Variable Delay Pulse Train for Fast CEST and NOE-CEST MRI
Jiadi Xu1, Nirbhay N. Yadav1, Amnon Bar-Shir2, Craig Jones1,2, Kannie W.Y. Chan1, Jingyang Zhang2, Piotr Walczak2, Michael T. McMahon1, and Peter C.M. van Zijl1
1F. M. Kirby Center, Kennedy Krieger Institute, Baltimore, MD, United States, 2Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States

 
We propose a new technique, variable delay pulsed CEST (VDP CEST), which eliminates the need for performing asymmetry analysis in CEST imaging. The scheme involves acquiring images with variable delay times between RF saturation pulses in pulsed CEST, producing a series of CEST images sensitive to the speed of saturation transfer. Subtracting two images or fitting a time series produces CEST and NOE-relayed CEST maps without effects of direct saturation and strongly reduced influence of semi-solid magnetization transfer. This technique, which can provide very short scan times when using a single RF frequency, is demonstrated in vivo on rat brain.