Florian Dittmann¹, Sebastian Hirsch¹, Jing Guo¹, Jürgen Braun², and Ingolf Sack^1
1Institute of Radiology, Charité, Berlin, Germany, ²Department of Medical Informatics, Charité, Berlin, Germany

We propose a MRE method utilizing shear waves induced by continuous low frequency vibration (10 – 20 Hz). The method is demonstrated for high resolution elastography of the brain and liver, and compared to results obtained by standard MRE frequencies from 25 to 50 Hz. Through low attenuation of the waves, a homogenous illumination of the tissue is achieved and high resolution elastograms are reconstructed despite long wave lengths. This opens the possibility to investigate tissue behavior with low dynamic MRE e.g. for exploiting poroelastic tissue properties.

John L Schmidt¹, Dennis J Tweten¹, Maisie M Mahoney², Tally Portnoi³, Ruth J Okamoto¹, Joel R Garbow⁴, and Philip V Bayly^1,2
1Mechanical Engineering and Materials Science, Washington University, St. Louis, MO, United States, ²Biomedical Engineering, Washington University, St. Louis, MO, United States, ³Electrical Engineering, Massachusets Institute of Technology, Cambridge, MA, United States, ⁴Biomedical Magnetic Resonance Laboratory, Department of Radiology, Washington University, St. Louis, MO, United States

In magnetic resonance elastography (MRE), mechanical properties are estimated by inversion of shear wave fields. Tissue properties are usually assumed to be isotropic and nearly incompressible, so that only one parameter (shear modulus) is obtained. In fibrous tissue, such as muscle or CNS white matter, tissue is anisotropic. The simplest anisotropic model is an incompressible, transversely isotropic model with three parameters: shear modulus (µ_2), shear anisotropy (ϕ) and tensile anisotropy (ζ). In this study, measurement of slow and fast shear wave speeds was performed by MRE of waves at specific angles relative to fiber direction, allowing estimation of these parameters.

Steven P Kearney¹, Spencer T Brinker¹, David A Burns¹, Thomas J Royston², and Dieter Klatt^2
1Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, United States, ²Bioengineering, University of Illinois at Chicago, Chicago, IL, United States

SampLe Interval Modulation Magnetic Resonance Elastography (SLIM-MRE) enables the simultaneous acquisition of 3D displacement, however this normally requires an increase in the echo time due to the mutual shifting of the motion encoding gradients (MEG). This study proposes a method of circular shifting of the start phase of the MEG waveforms allowing for rapid multidirectional motion encoding without increase in echo time. The new implementation of SLIM-MRE was applied to in vivo mouse brain and the results agree well to the ones obtained using conventional MRE encoding schemes.

Temel Kaya Yasar¹, Yifei Liu², Dieter Klatt³, Richard L Magin³, and Thomas J Royston^3
1Radiology, Icahn School of Medicine at Mount Sinai, New York, New York, NY, United States, ²Mechanical Engineering Department, University of Illinois at Chicago, Chicago, IL, United States, ³Biomedical Engineering Department, University of Illinois at Chicago, Chicago, IL, United States

An optimal MR elastography motion encoding scheme applicable to any MRE pulse sequence is introduced in this study along with a new mathematical framework to support this method. An MRE pulse sequence based on this scheme would have at least 33% time efficiency compared to a conventional MRE pulse sequence. This improvement has clinical significance for increasing in the quality of elastograms by reducing the motion artifacts and image misregistration. The method was demonstrated on a phantom and an excellent agreement was observed between the proposed method and a conventional MRE method.

Guy Nir¹, Ramin S. Sahebjavaher¹, and Septimiu E. Salcudean^1
1Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada

We present an image processing approach for enhancing magnetic resonance elastography (MRE) data. The approach employs image registration to compensate for motion of patients during the, typically lengthy, acquisition process, in order to improve the accuracy of the reconstructed elastogram. Then, a super-resolution technique is employed to increase the resolution of the registered phase images. To this end, the proposed approach novelly utilizes unique properties of the MRE acquisition process. The proposed approach is tested on phantom and prostate cancer patients' data to evaluate its potential in improving visualization and cancer detection.

Eric Barnhill¹, Ingolf Sack², Jürgen Braun³, Jens Würfel⁴, Colin Brown⁵, Edwin van Beek¹, and Neil Roberts^1
1Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, Scotland, United Kingdom, ²Radiological Sciences, Charité Universitätsmedizin, Berlin, Germany, ³Informatics, Charité Universitätsmedizin, Berlin, Germany, ⁴Neuroradiology, Charité Universitätsmedizin, Berlin, Germany, ⁵Research and Development, The Mentholatum Company, East Kilbride, Scotland, United Kingdom

Multifrequency Magnetic Resonance Elastography (MMRE) fuses MRE acquisitions at multiple frequencies to increase resolution and gain information about dispersion across frequencies. Here the Stationary Super-Resolution (SSR) technique was applied to MMRE images to map sub-voxel features. SSR was first validated with numerical simulations in which sub-voxel features are acquired of a downsampled image. SSR was then applied to a pilot study of three brains: one healthy, one with glioblastoma and one with metastasis. Subvoxel features such as gray matter-CSF and gliosis-oedema interfaces are identified in the recovered parameter maps.

Aaron T Anderson¹, Curtis L Johnson², Joseph L Holtrop^2,3, Elijah EW Van Houten^4,5, Mathew DJ McGarry⁵, Keith D Paulsen^5,6, Bradley P Sutton^2,3, and John G Georgiadis^1,2
1Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, ²Beckman Institute for Advanced Science, University of Illinois at Urbana-Champaign, Urbana, IL, United States, ³Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, ⁴Département de Génie Mécanique, Université de Sherbrooke, Sherbrooke, QC, Canada, ⁵Thayer School of Engineering, Dartmouth College, Hanover, NH, United States, ⁶Dartmouth-Hitchcock Medical Center, Lebanon, NH, United States

Magnetic resonance elastography (MRE) is an emerging technique for characterizing the mechanical property changes in the brain during aging or when it is affected by a neurodegenerative disease. The success of MRE as a diagnostic technique relies on improving the fidelity of material property reconstructions. The isotropic-based nonlinear inversion of the material property maps predicts significant differences when distinctly different wave propagation fields are used. Analyzing the wave direction relative to neuron bundle orientation informs our understanding of the effects on the isotropic model and points to the need for improved material models characterizing the microstructure.

Curtis L Johnson¹, Hillary Schwarb¹, Matthew DJ McGarry², Bradley P Sutton¹, and Neal J Cohen^1
1Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, United States, ²Thayer School of Engineering, Dartmouth College, Hanover, NH, United States

The mechanical properties of specific neuroanatomical regions estimated with magnetic resonance elastography (MRE) have shown promise in reflecting the presence of disease. In this work, we introduce a high-resolution MRE method for examining subcortical gray matter structures that is specifically designed to overcome issues arising from inadequate spatial resolution and proximity to cerebrospinal fluid. In a group of healthy young participants, we find differences in viscoelasticity between the hippocampus, thalamus, and putamen. Ultimately, such measurements may be critical for improved evaluation of aging and neurological disease by studying regions linked to functional decline.

Najat Salameh^1,2, Mathieu Sarracanie^1,2, Christian Farrar¹, David E J Waddington^1,3, Bo Zhu^1,4, Arnaud Comment⁵, and Matthew S Rosen^1,2
1MGH/A.A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ²Department of Physics, Harvard University, Cambridge, MA, United States, ³ARC Centre of Excellence for Engineered Quantum Systems, University of Sydney, Sydney, NSW, Australia, ⁴Harvard-MIT, Division of Health Sciences and Technology, Cambridge, MA, United States, ⁵Institute of Physics of Biological Systems, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

MR elastography cannot be performed in subjects with iron overload due to both a dramatic drop of signal on the MR images, and strong magnetic susceptibility artifacts. We propose in this work an alternative to biopsy for patients with chronic liver diseases where MRE has already shown its robustness in staging liver fibrosis and even in the diagnosis of steatohepatitis before fibrosis appears. For that purpose, we implemented a high performance MRE sequence on a 6.5 mT scanner. We successfully performed MRE in samples prepared with different iron content and compared our performance to standard clinical 1.5 T scanners.

Joshua Trzasko¹, Jennifer Kugel¹, Roger Grimm¹, Kevin Glaser¹, Armando Manduca¹, Philip Araoz¹, and Richard Ehman^1
1Mayo Clinic, Rochester, MN, United States

Having access to a wide variety of information improves a physician’s ability to differentially diagnose complex disease. In this work, we demonstrate that a simple modification to a standard MR elastography (MRE) protocol enables simultaneous stiffness and fat+water estimation from a single data set, which may offer improved image SNR and mitigation of motion misregistration. After describing the MRE sequence modification and image reconstruction pipeline, we present experimental results that demonstrate this new capability.