Anna Morr¹, Marcin Nowicki², Gergely Bertalan¹, Rafaela Vieira da Silva¹, Carmen Infante Duarte¹, Stefan Paul Koch¹, Philipp Boehm-Sturm¹, Ute Krügel², Jürgen Braun¹, Barbara Steiner¹, Josef Käs², Thomas Fuhs², and Ingolf Sack^1
1Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Universität Leipzig, Leipzig, Germany

In this study, we investigated the mechanical properties of subregions of the murine dentate gyrus in vivo using MR elastography (MRE) and ex vivo with atomic force microscopy (AFM). Consistent with AFM, subregional analysis of the dentate gyrus by MRE revealed that the subgranular zone (SGZ), in which adult neurogenesis takes place, is characterized by marked soft-solid properties. We conclude that MRE is sensitive to micromechanical properties beyond the image resolution. The observed soft-solid material properties of the SGZ quantified by AFM and MRE might be of functional relevance for neurogenesis in the mouse brain.

Helge Herthum¹, Stefan Hetzer², Michael Scheel¹, Friedemann Paul³, Heiko Tzschätzsch¹, Tom Meyer¹, Mehrgan Shahryari¹, Jürgen Braun⁴, and Ingolf Sack^1
1Experimentelle Radiologie, Charité Universitätsmedizin Berlin, Berlin, Germany, ²Berlin Center for Advanced Neuroimaging (BCAN), Berlin, Germany, ³NeuroCure Clinical Research Center and Clinical and Experimental Multiple Sclerosis Research Center, Berlin, Germany, ⁴Institut für medizinische Informatik, Charité Universitätsmedizin Berlin, Berlin, Germany

Using multifrequency MR elastography with 2- and 1.5mm resolutions in a cohort of 19 patients with multiple sclerosis and a total 206 analyzed lesions we found no evidence for systematic differences in the viscoelastic properties between MS lesions and surrounding brain tissue. Although future technical improvements in MRE resolution and parameter reconstruction methods might reveal significant differences between lesion and brain properties, our results indicate that those differences are minor compared to other published changes in brain viscoelasticity of the human brain.

Fatiha Andoh¹, Claire Pellot-Barakat¹, and Xavier Maître^1
1Université Paris-Saclay, CEA, CNRS, Inserm, BioMaps, Orsay, France

The head down tilt (HDT) position is commonly used to simulate vascular and tissue fluid dynamics during spaceflights. In HDT position, the cerebral autoregulation faces difficulties to adjust the vascular tone while the cephalad fluid shifts may yield increased intracranial pressures and altered mechanical properties. MRI T₂ mapping in HDT position have shown fluid overpressure in the brain and resulting loss of water contents in the CSF and orbital compartments. Whole brain MRE was performed here in similar HDT conditions. It was sensitive enough to provide new insights on the overall mechanical response of brain tissues in microgravity analogous conditions.

Jakob Jordan¹, Gergely Bertalan¹, Heiko Tzschätzsch¹, Tom Meyer¹, Anton Gauert², Anja Heeren-Hagemann², Jürgen Braun³, and Ingolf Sack^1
1Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Department of Hematology/Oncology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ³Institute of Medical Informatic, Charité - Universitätsmedizin Berlin, Berlin, Germany

Zebrafish have emerged as a versatile, cost-efficient and easy-to-handle animal model in many areas of biomedical research. Using multifrequency MR elastography at 7-Tesla and 1000 to 1400 Hz excitation frequency, we analyzed the viscoelastic properties of the post-mortem zebrafish brain. Shear wave speed as a surrogate marker of stiffness was mapped with an in-plane resolution of 40 microns showing stiffer properties (1.2±0.3 m/s) of the brain than skeletal muscle (0.89±0.09 m/s). Furthermore, sub-regions showed distinct stiffness properties, which, however, lacked significance in this preliminary feasibility study.

Rolf Reiter^1,2, Shreyan Majumdar², Steven Kearney², Andre Kajdacsy‐Balla³, Virgilia Macias³, Michael Abern⁴, Simone Crivellaro⁴, Thomas J. Royston², and Dieter Klatt^2
1Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Bioengineering, University of Illinois at Chicago, Chicago, IL, United States, ³Pathology, University of Illinois at Chicago, Chicago, IL, United States, ⁴Urology, University of Illinois at Chicago, Chicago, IL, United States

We aimed to evaluate the heterogeneity of viscoelastic tissue properties of fresh prostatectomy specimens of men with prostate cancer using MR elastography and histopathology as a reference. Our results suggest that prostate cancer is characterized by a stiff yet homogeneous biomechanical signature. A possible explanation for this finding might be differences of healthy vs. cancerous tissue based on anatomical zones and their specific nonmalignant pathologies (prostatitis in the peripheral zone and benign prostatic hyperplasia in the central gland), and the unique nondestructive growth pattern of PC with intervening stroma which might provide a rigid scaffold.

Dilyana B. Mangarova^1,2, Julia Brangsch¹, Marcus R. Makowski^1,3, Bernd Hamm¹, Ingolf Sack¹, Jürgen Braun ⁴, and Gergely Bertalan^1
1Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Department of Veterinary Pathology, Free University of Berlin, Berlin, Germany, ³Department of Diagnostic and Interventional Radiology, Technical University of Munich, Berlin, Germany, ⁴Institute for Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany

Abdominal aortic aneurysms (AAA) are among the worldwide leading causes of death. Standard MRI and ultrasonography cannot predict the risk of life-threatening AAA rupture. The ECM composition and therefore the stiffness of the aortic wall changes during AAA development and progression. Therefore, we investigated AAA stiffness in murine tissue samples using MR elastography with an in-plane resolution of 40 microns. Compared to healthy aorta, we found an increase of vessel wall stiffness in AAA of approximately 20% and an excellent correlation of histology-quantified ECM accumulation with thrombus stiffness. 

Shruti Mishra^1,2, Bin Deng^2,3,4, W. Scott Hoge^1,2,3, Giacomo Annio⁵, Ralph Sinkus⁵, and Samuel Patz^1,2
1Department of Radiology, Brigham & Women's Hospital, Boston, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Athinoula A. Marginos Center for Biomedical Imaging, Charlestown, MA, United States, ⁴Radiology, Massachusetts General Hospital, Boston, MA, United States, ⁵Laboratory for Vascular Translational Science (LVTS), Institut National de la Santé et de la Recherche Médicale (INSERM), Paris, France

Magnetic resonance elastography (MRE) was utilized to demonstrate differences in shear wavelength between human cortical gray matter and subcortical white matter and evaluate the effect of spatial resolution on wavelength estimation. Much greater brain architectural detail was discerned in the viscoelastic maps when going from 2.5 mm to 1.5 mm isotropic spatial resolution. We also demonstrate in individual healthy subjects, through two adjacent multi-voxel regions of interest, that cortical gray matter is stiffer than adjacent subcortical white matter, and that this difference is accentuated at higher resolutions. Furthermore, we show that the mean estimated wavelength increases with decreasing spatial resolution.

Jiahui Li¹, Prachi Singh², Marzanna Obrzut¹, Xin Lu¹, Kevin J. Glaser¹, Alina Allen³, Sudhakar K. Venkatesh¹, Taofic Mounajjed⁴, Jun Chen¹, Armando Manduca¹, Vijay Shah³, Richard L. Ehman¹, and Meng Yin^1
1Radiology, Mayo Clinic, Rochester, MN, United States, ²Sleep and Cardiometabolic Health, Pennington Biomedical Research Center, Baton Rouge, LA, United States, ³Gastroenterology, Mayo Clinic, Rochester, MN, United States, ⁴Anatomic Pathology, Mayo Clinic, Rochester, MN, United States

Multiparametric MRI and MRE was performed in 27 obese patients who had biopsies of liver and subcutaneous adipose tissues. We found significant correlations between the mechanical properties of liver and subcutaneous fat and their histological and biochemistry results. A model combining liver proton density fat fraction and subcutaneous fat stiffness had a slightly higher AUC for diagnosing nonalcoholic steatohepatitis than liver stiffness (AUC: 0.87 vs. 0.84, p=0.74). The results indicate that obesity-induced systemic inflammation affects both adipose and liver tissue mechanical properties and, therefore, models utilizing mechanical biomarkers from adipose tissue may improve the diagnosis of steatohepatitis in obese patients.   

Elijah Van Houten¹, Cyril Tous^2,3, Alexandre Jodoin⁴, Matthew McGarry⁵, Philip Bayly⁶, Keith Paulsen^5,7, Curtis Johnson⁸, and Nathalie Bureau^2,4
1Mechanical Engineering, Université de Sherbroke, Sherbrooke, QC, Canada, ²Centre de recherche du Centre hospitalier de l’Université de Montréal, Montréal, QC, Canada, ³Université de Montréal, Montréal, QC, Canada, ⁴Department of Radiology, Centre hospitalier de l’Université de Montréal, Montréal, QC, Canada, ⁵Thayer School of Engineering, Dartmouth College, Hanover, NH, United States, ⁶Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis, MO, United States, ⁷Dartmouth-Hitchcock Medical Center, Lebanon, NH, United States, ⁸Department of Biomedical Engineering, University of Delaware, Newark, DE, United States

Surgical planning for rotator cuff repair would benefit significantly from quantitative measures of the muscle stiffness to avoid re-tearing of the muscle after surgery. MR Elastography (MRE) can provide quantitative measures of soft tissue stiffness in-vivo, but repeatable, stable results require accurate tissue models capable of treating the specific geometry and highly anisotropic structure of muscle tissue. Here, MRE based on a nearly incompressible, transversely isotropic continuum model is developed and applied to the case of the supraspinatus muscle. Overall, results show good agreement between reconstructed anisotropic stiffness values and independently published results based on wavelength analysis.

Yuan Le¹, Jun Chen¹, Phillip J. Rossman¹, Ziying Yin¹, Kevin J. Glaser¹, Joshua D. Trzasko¹, Yi Sui¹, Stephan Kannengiesser², Bradley D. Bolster, Jr.³, Joel P. Felmlee¹, and Richard L. Ehman^1
1Radiology, Mayo Clinic, Rochester, MN, United States, ²Siemens Healthcare GmbH, Erlangen, Germany, ³Siemens Medical Solutions USA, Inc., Salt Lake City, UT, United States

This study is to test the feasibility of visualizing waves propagating in the spine and measuring the strain in the intervertebral discs (IVDs) in vivo with Magnetic Resonance Elastography (MRE). Our results show that waves can be visualized, and that IVD shear strain can be quantitatively assessed. Degeneration of the IVD is thought to decrease disc shear stiffness. Preliminary results in a series of volunteers demonstrated increasing IVD shear strain with age, consistent with the known gradual degradation of IVD function with age.

Giacomo Annio^1,2, Ahmed Hamimi³, Khaled Z. Abd-Elmoniem ³, Theo Heller³, Elliot Levy ³, David E. Kleiner⁴, Ohad Etzion⁵, Rabab Ali⁶, Ralph Sinkus^1,2, and Ahmed M. Gharib^3
1LVTS, INSERM U1148, Paris, France, ²Department of Biomedical Engineering, King's College London, London, United Kingdom, ³Biomedical and Metabolic Imaging Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD, United States, ⁴Center for Cancer Research, National Cancer Institute, Bethesda, MD, United States, ⁵Department of Gastroenterology and Liver Diseases, Ben-Gurion University of the Negev, Be'er Sheva, Israel, ⁶Department of Internal Medicine, Duke University, Durham, NC, United States

The assessment of liver fibrosis and inflammation is crucial to the clinical management of patients suffering from liver diseases. Portal venous pressure assessment has important prognostic implications for hepatic disease patients’ care. However, it can only be measured invasively.  In this work we show that liver stiffness quantified via 3DMRE is a strong independent predictor of DPVP compared to invasive biopsy. Moreover stiffness as evaluated with 3DMRE is an operator independent and non-invasive biomarker which could hence constitute an optimal method for diagnosis and fibrosis staging in all patients and a non-invasive surrogate of DPVP.

Huiming Dong¹, Prateek Kalra¹, Richard D White¹, and Arunark Kolipaka^1
1Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States

Aortic stiffness is a valuable imaging marker because of its association with a variety of cardiovascular conditions such as abdominal aortic aneurysm (AAA). Calculating AAA stiffness from aortic MRE data presents a unique challenge due to the relatively small size of an AAA compared to the liver. In the present study, we propose a new inversion strategy that consists of directional filters that are designed to extract the propagating waves along the axial direction of the AAA, and uses the wave information along the axial direction for stiffness calculation to reduce the impact of AAA geometry on stiffness estimation.

Abrar Faiyaz¹, Irteza Enan Kabir¹, Marvin M Doyley¹, Ingolf Sack², Md Nasir Uddin³, and Giovanni Schifitto^3
1Department of ECE, University of Rochester, Rochester, NY, United States, ²Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ³Department of Neurology, University of Rochester, Rochester, NY, United States

Neuroinflammation plays a crucial role in HIV-infected subjects at risk of cerebral small vessel disease. As MR-Elastography (MRE) has shown the potential to link inflammation with brain stiffness reduction, we investigated the brain viscoelastic properties of the HIV-infected and HIV-uninfected individuals. The preliminary results with MRE are promising, complementing other imaging modalities such as diffusion MRI (DTI, NODDI) to investigate brain microstructure integrity in HIV infection.

Jonathan M Trevathan¹, Jonathan M Scott¹, Joshua D Trzasko¹, Armando Manduca¹, John Huston¹, Richard L Ehman¹, and Matthew C Murphy^1
1Mayo Clinic, Rochester, MN, United States

Bulk motion during the motion encoding of multi-slice spin-echo EPI pulse sequences used to acquire 3D MRE data creates a slice-to-slice phase jitter. A 3D convolutional neural network was trained to estimate a phasor corresponding to noise-free displacements given noisy, complex-valued MRE data. The net outperformed its filtering counterpart in noisy and noise-free simulation data, and decreased test-retest repeatability error in vivo.