Yi Sui¹, Jiahui Li¹, Zheng Zhu¹, Kevin J Glaser¹, Nana K Owusu¹, Joshua D Trzasko¹, Arvin Arani¹, Ziying Yin¹, Phillip J Rossman¹, Meng Yin¹, and Richard L Ehman^1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States

A free-breathing hybrid radial-cartesian 3D MR elastography technique (TURBINE-MRE) was extended for kidneys with a dual driver system. This technique provides wave images and stiffness maps in a single 3.5-minute free-breathing acquisition. The feasibility of the new technique was demonstrated in a healthy volunteer.

Quanshangze DU¹, Simon Auguste LAMBERT², Nahiène HAMILA³, and Aline BEL-BRUNON^1
1Univ Lyon, INSA Lyon, CNRS, LaMCoS, UMR5259, 69621 Villeurbanne, France, ²Université de Lyon, INSA Lyon, Université Claude Bernard Lyon 1, Ecole Centrale de Lyon, CNRS, Ampère UMR5005, Villeurbanne, France, ³ENI Brest, UMR CNRS 6027, IRDL, F-29200 Brest, France

The finite element method (FEM) is widely used for modeling wave propagation and stiffness reconstruction in magnetic resonance elastography (MRE). However, it is not that efficient for modeling inclusions with complex interfaces. Here, we propose a formulation of FEM known as the eXtended FEM (XFEM), and investigate this method in two studies: wave propagation across an oblique linear interface and stiffness reconstruction of a random-shape inclusion. XFEM results present good agreement with the theoretical predictions and FEM simulation results. XFEM can be regarded as an ideal alternative to FEM for inclusion modeling in MRE.

Gwenaël Pagé¹, Félicia Juléa¹, Valérie Paradis², Valérie Vilgrain^1,3, Dominique Valla⁴, Bernard E. Van Beers^1,3, and Philippe Garteiser^1
1Laboratory of imaging biomarkers, INSERM UMR 1149, Paris, France, ²Center for research on inflammation, INSERM UMR 1149, Paris, France, ³Department of Radiology, University Hospital Paris Nord, Clichy, France, ⁴Hepatology service, University Hospital Paris Nord, Clichy, France

In this study we propose using a MR elastography reconstruction method adjust the ratio between wavelength and spatial resolution, by resampling the matrix of shear displacement locally, to optimize the quality of the reconstruction. This reconstruction algorithm was compared to existing direct inversion algorithms in phantoms, healthy volunteers and patients with liver fibrosis. We observed that the algorithm k-MDEV showing the best performance in phantoms and patients did not have the best repeatability. Our proposed method improved the diagnostic performance for advanced fibrosis, compared to classical direct inversion method, without a negative effect on repeatability.

Yasmine Safraou¹, Karolina Graczynska¹, Tom Meyer¹, Heiko Tzschätzsch¹, Thomas Fischer¹, Jürgen Braun¹, Ingolf Sack¹, and Jing Guo^2
1Radiology, Charité – Universitätsmedizin Berlin, Berlin, Germany, ²Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany

To investigate the effect of perfusion pressure on liver stiffness, 13 ex-vivo rat livers were studied by volumetric MRI, MR elastography (MRE) and diffusion MRI under controlled portal pressures between 0 and 15 cmH₂O. Liver volume, tissue-vascular volume fraction, stiffness and bulk modulus decreased while water diffusivity increased with increasing portal pressure. Collectively, our findings suggest that liver softening is caused by a relative increase in fluid volume while an increased vascular pressure, potentially increasing liver stiffness, is of minor importance when tissue can freely expand, as in our scenario.

Owais Siddiqi¹, Jessica Winfield^1,2, Konstantinos Zormpas-Petridis¹, Emma Harris¹, Anand Ramkumar¹, Antonio Candito¹, Steffen Görner³, Christina Messiou^1,2, Matthew Blackledge¹, and Imogen Thrussell^1,2
1Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom, ²Department of Radiology, The Royal Marsden NHS Foundation Trust, London, United Kingdom, ³Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany

New measures of response are required that can capture the inherent heterogeneity and the heterogeneous changes observed in soft tissue tumours. Shear-wave Magnetic Resonance Elastography (MRE) measures stiffness of tissue by measuring the propagation of externally applied shear waves. In this study we explore the test-retest repeatability of Multifrequency MRE (MMRE), acquired using an echo-planar imaging readout applied to a soft gelatin phantom used to mimic the stiffness of soft-tissue tumours. Our results suggest MMRE is highly repeatable and supports further investigation in using MMRE to measure response in soft-tissue tumours.

Nienke P.M. Wassenaar¹, Anne-Sophie van Schelt¹, Eric M. Schrauben¹, Rémi van der Woude², Jamila E. de Jong², Jules L. Nelissen¹, Hanneke W.M. van Laarhoven³, Jing Guo⁴, Ingolf Sack⁴, Jurgen H. Runge¹, Aart J. Nederveen¹, and Jaap Stoker^1
1Radiology and Nuclear Medicine, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands, ²University of Twente, Enschede, Netherlands, ³Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands, ⁴Department of Radiology, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany

Free-breathing acquisition of pancreatic MR elastography can potentially introduce errors in stiffness reconstruction. In this study, breathing tasks are introduced during interleaved and reversed slice order MRE acquisition to determine if the quality of MRE increases. The shear-wave speed and octahedral shear strain signal-to-noise-ratio in the pancreas did not significantly change when using breathing tasks. However, the stability of the pancreas location over time increases when using breathing tasks combined with reversed slice ordering as well as the octahedral shear strain signal-to-noise-ratio in the whole abdomen. Future research should focus on comparing shear-wave speed reproducibility of both MRE methods.

Pilar Sango-Solanas¹, Kevin Tse-Ve-Koon¹, Eric Van Reeth^1,2, Cyrielle Caussy^3,4, and Olivier Beuf^1
1Univ Lyon, INSA-Lyon, Inserm, UCBL1, CNRS, CREATIS, UMR 5220, U1294, F-69621, Lyon, France, ²CPE Lyon, Département Sciences du Numérique, Lyon, France, ³Univ Lyon, CarMen Laboratory, INSERM, INRA, INSA Lyon, Université Claude Bernard Lyon 1,69495, Lyon, France, ⁴Hospices Civils de Lyon, Département Endocrinologie, Diabète et Nutrition, Hôpital Lyon Sud, 6949, Lyon, France

Magnetic Resonance Elastography (MRE) allows the quantitative characterization of mechanical properties of tissues based on the properties of shear wave propagation. MRE uses mostly oscillating motion encoding gradients (MEGs) to encode motion. Their presence involves  long echo times, limiting the application of MEGs to very short T2 tissues. RF pulses designed with an optimal control (OC) algorithm applied with a constant gradient can simultaneously perform slice selection and motion encoding, enabling short echo times. In this study, we used OC pulses to mechanically quantify by MRI for the first time a very short T2 tissue such as the Achilles tendon.

Tom Meyer¹, Stephan Rodrigo Marticorena Garcia¹, Heiko Tzschätzsch¹, Helge Herthum², Mehrgan Shahryari¹, Jürgen Braun², Prateek Kalra^3,4, Arunark Kolipaka^3,4, and Ingolf Sack^1
1Department of Radiology, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany, ³Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States, ⁴Department of Radiology, The Ohio State University, Columbus, OH, United States

Magnetic resonance elastography (MRE) depicts the viscoelastic properties of soft tissues for diagnosis of various diseases such as tumors or fibrosis. However, different MRE inversion methods yield different results. This lack of comparability of different MRE inversion results hinders the dissemination of advanced reconstruction methods. Therefore, we here introduce an extensible, open-access web platform that offers multiple inversion techniques for multifrequency, three-dimensional MRE to promote comparison of values. We demonstrate the utility of the platform in phantom data and in vivo free-breathing multifrequency MRE data of the kidneys of healthy volunteers.

Helge Herthum¹, Heiko Tzschätzsch¹, Mehrgan Shahryari¹, Bernhard Kreft¹, Steffen Görner¹, Stefan Hetzer², Jürgen Braun¹, and Ingolf Sack^1
1Charité Universitätsmedizin Berlin, Berlin, Germany, ²Berlin Center for Advanced Neuroimaging, Berlin, Germany

MR elastography(MRE) measures in vivo soft-tissue mechanical parameters which are sensitive to various diseases. Robust and reliable measurements are critical for clinical translation; however, the variability of reported values, especially for MRE in the brain, remains a challenge. We here introduce an optimized setup for high-resolution brain MRE and compare the consistency of values obtained from 2D- and 3D-analysis in a group of healthy subjects studied in the follow-up of a year. Both 2D- and 3D-MRE values agreed very well between the two measurements. Intersubject variability was lower in 2D than in 3D while intrasubject variability was lower in 3D. 

Yuan Le¹, Jun Chen¹, Phillip J. Rossman¹, Bradley D. Bolster Jr.², Stephan Kannengiesser³, and Richard L. Ehman^1
1Radiology, Mayo Clinic, Rochester, MN, United States, ²MR Collaborations, Siemens Medical Solutions USA, Inc., Salt Lake City, UT, United States, ³MR Application Predevelopment, Siemens Healthcare GmbH, Erlangen, Germany

The goal of this study was to better detect cyclic motion with multiple frequencies in tissue. A novel MRE technique was developed using motion encoding gradient (MEG) pulses of multiple scales (multi-scale MRE). These MEG pulses were designed and timed to approximate a complete basis of Haar wavelet system. Our hypothesis was that a set of orthogonal MEG pulses can capture the tissue motion more efficiently and tissue motion can be reconstructed by a simple inverse transform. Initial tests were performed on a phantom and a volunteer.

Anne-Sophie van Schelt¹, Nienke P.M. Wassenaar¹, Eric M. Schrauben¹, Jules L. Nelissen¹, Jing Guo², Ingolf Sack², Jaap Stoker¹, Aart J. Nederveen¹, and Jurgen H. Runge^1
1Radiology and Nuclear Medicine, Amsterdam UMC location AMC, Amsterdam, Netherlands, ²Department of Radiology, Charité – Universitätsmedizin Berlin, Berlin, Germany

Pancreas magnetic resonance elastography (MRE) allows non-invasice estimation of tissue stiffness for multiple pathophysiological diseases. MRE reproducibility and the effect of bowel-preparation (butylscopolaminebromide and drinking water) for increased MRE data quality were assessed for the pancreas. Shear wave speed and MRE quality were determined for the pancreas, liver and kidneys. Intrasession and intersession reproducibility showed a coefficient-of-variation of 6.59% and 13.10%. Repeated measures ANOVA showed no significant difference in SWS of all organs (f=3/11,p>0.05). Bowel-preparation methods for pancreatic MRE do not increase MRE quality. Drinking water increases the MRE quality for kidneys and liver whilst not altering the measured SWS.

Jiahao Zhou¹, Ruokun Li², Yikun Wang², Jing Guo³, Ingolf Sack³, and Fuhua Yan^2
1radiology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China, ²Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China, ³Department of Radiology, Charité–Universitätsmedizin Berlin, Berlin, Germany, Berlin, Germany

Tumor-liver biomechanical interaction investigated by multifrequency MR elastography in patients with HCC

Alexa M. Diano¹, Grace McIlvain¹, Andrew K. Knutsen², Suhas Vidhate³, Dzung L. Pham², and Curtis L. Johnson^1
1Biomedical Engineering, University of Delaware, Newark, DE, United States, ²Henry M. Jackson Foundation, Bethesda, MD, United States, ³National Institutes of Health, Bethesda, MD, United States

This study uses a novel multishot spiral magnetic resonance elastography (MRE) pulse sequence to simultaneously measure skull and brain motion in vivo in a single acquisition. Results in a healthy volunteer and a fat-water phantom showed a reduced transmission of motion from the skull to the brain in all three directions of motion. Additionally, the skull and brain appear to be out of phase in motion in both the x (left-right) and z (superior-inferior) directions. This research provides a basis for future studies quantifying skull-brain coupling including with multiple actuation frequencies and excitation directions.

Mehrgan Shahryari¹, Pablo Gottheil², Elisabeth Gertrud Hain³, Helge Herthum⁴, Heiko Tzschätzsch¹, Tom Meyer¹, Josef Alfons Käs², Eberhard Siebert⁵, Vincent Prinz^6,7, and Ingolf Sack^1
1Department of Radiology, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany, ²Faculty of Physics and Earth Sciences, Peter Debye Institute, Leipzig University, Leipzig, Germany, ³Department of Neuropathology, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany, ⁴Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany, ⁵Institute of Neuroradiology, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany, ⁶Department of Neurosurgery, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany, ⁷Department of Neurosurgery, University Hospital Frankfurt, Frankfurt am Main, Germany

Clinical MRI is an important method for the delineation and characterization of gliomas for resection planning and therapy monitoring in neurosurgery. Here, we used a 3D curl- and phase-gradient based inversion algorithm in multifrequency magnetic resonance elastography (MRE) to generate maps of the mechanical tumor properties, wave speed and wave damping. Overall, our method improved the spatial resolution of MRE maps in glioma patients and allowed precise measurement of tumor mechanical properties. In the future, the method could help with characterization, surgical planning and treatment monitoring of neuro tumors.

Jakob Seja¹, Bernhard Kreft², Helge Herthum², Mehrgan Shahryari³, Jürgen Braun², Ingolf Sack³, and Stefan Hetzer^1
1Berlin Center for Advanced Neuroimaging, Charité - Universitätsmedizin Berlin, Berlin, Germany, ²Institute of Medical Informatics, Charité - Universitätsmedizin Berlin, Berlin, Germany, ³Radiology department, Charité - Universitätsmedizin Berlin, Berlin, Germany

The viscosity of blood scales with the concentration of red blood cells (hematocrit) and potentially influences the viscoelasticity of the perfused tissue. In this study, cerebral MR elastography (MRE) was applied to a group of healthy subjects to analyze the interrelation between mechanical properties of brain tissue and the hematocrit. We found a highly significant positive correlation between in-vivo mechanical properties of cerebral tissue and hematocrit level (p<0.0001).

Mary K Kramer¹, Grace McIlvain¹, Faria Sanjana², Fiona Horvat², Christopher R Martens², and Curtis L Johnson^1
1Biomedical Engineering, University of Delaware, Newark, DE, United States, ²Kinesiology and Applied Physiology, University of Delaware, Newark, DE, United States

Lower body negative pressure (LBNP) is a non-invasive physiological method known to decrease cerebral blood flow. This technique was used to study the brain’s response to altered cerebrovascular hemodynamics and showed that, on average, brain stiffness decreases by 2.28% in response to ten minutes of LBNP application and decreased cerebral blood flow. By decreasing and increasing cerebral blood flow by turning the LBNP on and off repeatedly in 10-minute blocks, brain stiffness was shown to increase by 3.02% on average from the initial application of LBNP to the final application of LBNP.

Alicia Palomar Garcia¹, Valentin H. Prevost², Alba Iruela Sanchez¹, Wolter de Graaf³, and Bruno Triaire^2
1Canon Medical Systems Spain and Portugal, Barcelona, Spain, ²Canon Medical Systems Corporation, Tochigi, Japan, ³Canon Medical Systems Europe, Zoetermeer, Netherlands

This study evaluated the feasibility of performing virtual elastography based on diffusion-weighted MRI (vMRE) on a 1.5T system with two different acceleration methods, SPEEDER and EXSPER. Proton density fat fraction (PDFF) imaging was also acquired. The vMRE and PDFF measurements were consistent with healthy values that can be found in the literature. This study demonstrated the feasibility of performing vMRE at 1.5T for the estimation of overall liver elasticity. SPEEDER and EXSPER vMRE implementations provided consistent stiffness estimations and both would be adequate for conducting future studies at 1.5T systems on patients.