Extreme Encoding Methods

Monday 22 April 2013

Emre Kopanoglu¹, Ergin Atalar², and Robert Todd Constable^3
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.

Gigi Galiana¹ and Robert Todd Constable^1
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.

Jonathan C. Sharp¹, Qunli Deng¹, Scott B. King², Vyacheslav Volotovskyy², and Boguslaw Tomanek^1
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.

Esra Turk^1,2, Yusuf Ziya Ider¹, Arif Sanli Ergun³, Taner Demir², and Ergin Atalar^1,2
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.

Maxim Zaitsev¹, Sebastian Littin¹, Anna M. Welz¹, Feng Jia¹, Chris A. Cocosco¹, Andrew Dewdney², Gerrit Schultz¹, and Jürgen Hennig^1
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.

Angela Lynn Styczynski Snyder¹, Curtis Andrew Corum¹, Steen Moeller¹, Nathaniel J. Powell², and Michael Garwood^1
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.

Dan Ma¹, Vikas Gulani², Nicole Seiberlich¹, Jeffrey Duerk³, and Mark A. Griswold^2
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.

Yun Jiang¹, Dan Ma¹, Renate Jerecic², Vikas Gulani^1,3, Nicole Seiberlich¹, Jeffrey Durek^3,4, and Mark A. Griswold^1,3
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.

Najat Salameh^1,2, Mathieu Sarracanie^2,3, Brandon Dean Armstrong^2,3, Arnaud Comment⁴, and Matthew S. Rosen^2,3
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.

Ahmed A. Harouni¹, Ahmed M. Gharib², Nael F. Osman³, Roderic I. Pettigrew², and Khaled Z. Abd-Elmoniem^2
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.