ISMRM 21st Annual Meeting & Exhibition ○ 20-26 April 2013 ○ Salt Lake City, Utah, USA
SCIENTIFIC SESSION
Extreme Encoding Methods Monday 22 April 2013
Room 151 AG | 10:45 - 12:45 | Moderators: | R. Todd Constable, Mark A. Griswold
10:45 | 0012. | Reduced-FOV Imaging with Excitation Using Nonlinear Gradient Magnetic Fields (ENiGMa) Emre Kopanoglu1, Ergin Atalar2, and Robert Todd Constable3 1Diagnostic Radiology, Yale University School of Medicine, New Haven, CT, United States, 2UMRAM, Bilkent University, Ankara, Turkey, 3Diagnostic Radiology, Yale University, New Haven, CT, United States A reduced-FOV imaging method that employs nonlinear gradient fields for excitation is demonstrated using an additional gradient amplifier, a transmit array architecture and a head-sized nonlinear gradient coil. The method makes use of the non-Cartesian shape of the excitation profile to channel folding artifacts to outer sections of the image. Although scan time reduction is application specific, for a given example, around 60% reduction is shown. The main advantage of the proposed method is that the echo and repetition times, as well as the SAR are kept unaltered, compared to a conventional excitation approach.
10:57 | 0013. | Ultrafast Single Shot Imaging with Rotating Nonlinear Fields Gigi Galiana1 and Robert Todd Constable1 1Diagnostic Radiology, Yale University, New Haven, Connecticut, United States We present a novel approach whereby nonlinear gradient encoding can facilitate extremely fast imaging. We describe a trajectory that encodes the entire 2D image with a single rotation of a strong nonlinear field. Because this entails ramping through just one sine/cosine-shaped gradient pulse on each channel, the slew requirements of a single shot acquisition are minimal, and the acquisition can be compressed to a very short acquisition time without violating PNS limits. Our calculations show that the rotating gradient strategy could potentially allow us to acquire a full 20cm 642 image in as little as 2ms.
11:09 | 0014. | A 3-Axis Phase Gradient Array for RF Encoded MRI Using the TRASE Method Jonathan C. Sharp1, Qunli Deng1, Scott B. King2, Vyacheslav Volotovskyy2, and Boguslaw Tomanek1 1National Research Council of Canada, Calgary, Alberta, Canada, 2National Research Council of Canada, Winnipeg, Manitoba, Canada The first 3-axis encoded RF transmit array for TRASE (Transmit Array Spatial Encoding) B1 imaging is presented. TRASE is a novel MRI method in which the spatial encoding is achieved by repeated refocusing by 180 deg pulses, where all B1 transmit fields are a phase gradient. The transmit array is capable of producing any one of 6 phase gradient fields (+X, -X, +Y, -Y, +Z, -Z). Imaging results in all three orthogonal planes are presented. Some possible applications of this new form of encoding include low-cost MRI (due to the elimination of the B0 gradient system) and microscopy.
11:21 | 0015. | Shear Wave Imaging by Using B1 Gradients Esra Turk1,2, Yusuf Ziya Ider1, Arif Sanli Ergun3, Taner Demir2, and Ergin Atalar1,2 1Electrical and Electronics Engineering Department, Bilkent University, Ankara, Turkey, 2National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey, 3Electrical and Electronics Engineering Department, TOBB-University of Economics and Technology, Ankara, Turkey In this study, the feasibility of using B1 gradients in detecting the shear properties of tissues at kilohertz range frequencies is shown. With this method, shear waves on stiff and small tissues can be detected with high resolution without frequency limitation faced up with in methods using B0 gradient coils due to the slow gradient switching times.
11:33 | 0016. | 3D Imaging with Multidimensional Nonlinear Encoding Maxim Zaitsev1, Sebastian Littin1, Anna M. Welz1, Feng Jia1, Chris A. Cocosco1, Andrew Dewdney2, Gerrit Schultz1, and Jürgen Hennig1 1Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Healthcare Sector, Siemens AG, Erlangen, Germany To overcome present limitations of gradient performance and investigate unconventional encoding topologies a PatLoc (parallel imaging technique using localized gradients) concept was proposed recently. PatLoc relaxes requirements of gradient homogeneity in favour of local gradient strength. Multidimensional encoding (MDE) combines nonlinear PatLoc fields with traditional linear gradients and holds a great promise for accelerated imaging. In this work we propose using MDE for two phase encoding directions in 3D imaging, where a traditional linear gradient is used for the signal read out. We demonstrate a feasibility of this approach by implementing a radial-in-out scheme as a pure phase encoding strategy.
11:45 | 0017. | MRI by Steering Resonance Through Space Angela Lynn Styczynski Snyder1, Curtis Andrew Corum1, Steen Moeller1, Nathaniel J. Powell2, and Michael Garwood1 1Department of Radiology, University of Minnesota, Minneapolis, MN, United States, 2Department of Neuroscience, University of Minnesota, Minneapolis, MN, United States MR images are typically created by Fourier transforming signals that have been spatially encoded using frequency- and phase-encoding gradients. Recently, new spatiotemporal-encoding strategies allow direct image formation without FT by sweeping a resonance plane through time and space. Alternatively, it is demonstrated here that a combination of RF and gradient modulation can move a relatively isolated resonance region sequentially through space allowing for time-dependent echo formation and 2D imaging without FT. The method, called steering resonance (STEREO), has the unique capability to treat each region in space independently, which can potentially be exploited to compensate extreme B1and B0 inhomogeneity.
11:57 | 0018. | MR Fingerprinting: Rapid Simultaneous Quantification of T1, T2, Proton Density and Off-Resonance Using a Spiral Trajectory Dan Ma1, Vikas Gulani2, Nicole Seiberlich1, Jeffrey Duerk3, and Mark A. Griswold2 1Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 2Radiology, Case Western Reserve University, Cleveland, OH, United States, 3School of Engineering, Case Western Reserve University, Cleveland, OH, United States The purpose of this study is to quantify multiple MR parameters in a single acquisition in a short acquisition time by combining the MR Fingerprinting (MRF) with a rapid spiral readout. MRF is a novel approach that can quantify multiple parameters (e.g. T1, T2, proton density and off-resonance) of a material or tissue simultaneously. This study uses single-shot spiral MRF method to reduce the acquisition time to around 10 seconds. Because of the robustness of pattern recognition, the parameter maps have shown high rejection of severe undersampling artifacts.
12:09 | 0019. | MR Fingerprinting Using Spiral QUEST Yun Jiang1, Dan Ma1, Renate Jerecic2, Vikas Gulani1,3, Nicole Seiberlich1, Jeffrey Durek3,4, and Mark A. Griswold1,3 1Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2Siemens AG,Healthcare Sector, Erlangen, Germany, 3Department of Radiology, Case Western Reserve University, Cleveland, Ohio, United States, 4Case School of Engineering, Case Western Reserve University, Cleveland, Ohio, United States MR Fingerprinting is a novel imaging concept to generate multiple parametric maps simultaneously by matching spatially and temporally incoherent signals to a pre-calculated dictionary. Here we explore MR fingerprinting using a QUick Echo Split Technique (QUEST) with a spiral trajectory to simultaneously generate T1, T2 and M0 maps. QUEST MRF achieves unique signal evolution by acquiring the maximum possible number of echoes for a small number of RF pulses. The results show that this method can be used to generate accurate quantitative maps and demonstrates the potential of MRF to explore unlimited pulse sequence designs.
12:21 | 0020. | Overhauser Enhanced MR Elastography at Very Low Field Najat Salameh1,2, Mathieu Sarracanie2,3, Brandon Dean Armstrong2,3, Arnaud Comment4, and Matthew S. Rosen2,3 1Institut de Physique des Systèmes Biologiques, EPFL, Lausanne, Switzerland, 2Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 3Department of Physics, Harvard University, Cambridge, MA, United States, 4Institut de Physique des Systèmes Biologiques, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland MR Elastography (MRE) suffers from a major limitation: its low sensitivity due to the use of long TE's leading to long acquisition times. This drawback hinders its use in daily routine by radiologists. The aim of the present study was to show the feasibility of enhancing the signal via the Overhauser effect to shorten MRE acquisition times.
12:33 | 0021. | Driver-Free Assessment of Liver Stiffness Using Fast Strain-Encoded (FSENC) MRI Ahmed A. Harouni1, Ahmed M. Gharib2, Nael F. Osman3, Roderic I. Pettigrew2, and Khaled Z. Abd-Elmoniem2 1Clinical Center, National Institutes of Health, Bethesda, Maryland, United States, 2NIDDK, National Institutes of Health, Bethesda, Maryland, United States, 3Russell H. Morgan Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States Liver fibroses is a major health concern in the US. and is reversible in early stages. Therefore, there is a need for a non-invasive screening tool. We propose to use the myocardium’s intrinsic motion as a source of vibration with fast strain-encoded MRI to measure the strain through the liver’s left lobe adjacent to the myocardium. Phantom experiments and in-vivo experiments were conducted. Results show significant difference between healthy subjects and fibrotic patient (p<0.0001). Peak strain was 13.5% ± 0.86%, 4.35% ± 2.88% for healthy subjects and fibrotic patient, respectively. Reproducibility experiments were also performed and showed no significant difference between repeated measured peak strain.