Anisotropic mechanical properties in the healthy human brain estimated with multi-excitation transversely isotropic MR elastography.
Daniel R Smith, Diego A Caban-Rivera, Matthew D J McGarry, L Tyler Williams, Grace McIlvain, Ruth J Okamoto, Elijah E W Van Houten, Philip V Bayly, Keith D Paulsen, Curtis L Johnson
Author Information
Daniel R Smith: Department of Biomedical Engineering, University of Delaware, Newark DE 19711.
Diego A Caban-Rivera: Department of Biomedical Engineering, University of Delaware, Newark DE 19711.
Matthew D J McGarry: Thayer School of Engineering, Dartmouth College, Hanover NH 03755.
L Tyler Williams: Department of Biomedical Engineering, University of Delaware, Newark DE 19711.
Grace McIlvain: Department of Biomedical Engineering, University of Delaware, Newark DE 19711.
Ruth J Okamoto: Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis MO 63130.
Elijah E W Van Houten: Département de génie mécanique, Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1.
Philip V Bayly: Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis MO 63130.
Keith D Paulsen: Thayer School of Engineering, Dartmouth College, Hanover NH 03755.
Curtis L Johnson: Department of Biomedical Engineering, University of Delaware, Newark DE 19711.
Magnetic resonance elastography (MRE) is an MRI technique for imaging the mechanical properties of brain in vivo, and has shown differences in properties between neuroanatomical regions and sensitivity to aging, neurological disorders, and normal brain function. Past MRE studies investigating these properties have typically assumed the brain is mechanically isotropic, though the aligned fibers of white matter suggest an anisotropic material model should be considered for more accurate parameter estimation. Here we used a transversely isotropic, nonlinear inversion algorithm (TI-NLI) and multiexcitation MRE to estimate the anisotropic material parameters of individual white matter tracts in healthy young adults. We found significant differences between individual tracts for three recovered anisotropic parameters: substrate shear stiffness, (range: 2.57 - 3.02 kPa), shear anisotropy, (range: -0.026 - 0.164), and tensile anisotropy, (range: 0.559 - 1.049). Additionally, we demonstrated the repeatability of these parameter estimates in terms of lower variability of repeated measures in a single subject relative to variability in our sample population. Further, we observed significant differences in anisotropic mechanical properties between segments of the corpus callosum (genu, body, and splenium), which is expected based on differences in axonal microstructure. This study shows the ability of MRE with TI-NLI to estimate anisotropic mechanical properties of white matter and presents reference properties for tracts throughout the healthy brain.
