title: Observation of direction-dependent mechanical properties in the human brain with multi-excitation MR elastography.
abstract: Magnetic resonance elastography (MRE) has shown promise in noninvasively capturing changes in mechanical properties of the human brain caused by neurodegenerative conditions. MRE involves vibrating the brain to generate shear waves, imaging those waves with MRI, and solving an inverse problem to determine mechanical properties. Despite the known anisotropic nature of brain tissue, the inverse problem in brain MRE is based on an isotropic mechanical model. In this study, distinct wave patterns are generated in the brain through the use of multiple excitation directions in order to characterize the potential impact of anisotropic tissue mechanics on isotropic inversion methods. Isotropic inversions of two unique displacement fields result in mechanical property maps that vary locally in areas of highly aligned white matter. Investigation of the corpus callosum, corona radiata, and superior longitudinal fasciculus, three highly ordered white matter tracts, revealed differences in estimated properties between excitations of up to 33%. Using diffusion tensor imaging to identify dominant fiber orientation of bundles, relationships between estimated isotropic properties and shear asymmetry are revealed. This study has implications for future isotropic and anisotropic MRE studies of white matter tracts in the human brain.
authors.affiliation: Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. Electronic address: aandrsn3@illinois.edu.
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Anderson
authors.affiliation: Département de génie mécanique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K2R1; Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, USA. Electronic address: eew.vanhouten@usherbrooke.ca.
authors.forename: Elijah E W
authors.initials: EEW
authors.lastname: Van Houten
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, USA. Electronic address: matthew.d.mcgarry@dartmouth.edu.
authors.forename: Matthew D J
authors.initials: MDJ
authors.lastname: McGarry
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, USA; Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire 03756, USA. Electronic address: keith.d.paulsen@dartmouth.edu.
authors.forename: Keith D
authors.initials: KD
authors.lastname: Paulsen
authors.affiliation: Bioengineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA; Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. Electronic address: holtrop1@illinois.edu.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Holtrop
authors.affiliation: Bioengineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA; Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. Electronic address: bsutton@illinois.edu.
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Sutton
authors.affiliation: Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA; Biomedical Engineering Department, Illinois Institute of Technology, Chicago, Illinois 60616, USA. Electronic address: jgeorgia@iit.edu.
authors.forename: John G
authors.initials: JG
authors.lastname: Georgiadis
authors.affiliation: Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA; Department of Biomedical Engineering, University of Delaware, Newark, Delaware 19716, USA. Electronic address: clj@udel.edu.
authors.forename: Curtis L
authors.initials: CL
authors.lastname: Johnson
mesh_terms: D016880:Anisotropy; D001921:Brain / Q000502:physiology*; D056324:Diffusion Tensor Imaging; D054459:Elasticity Imaging Techniques; D006801:Humans; D008279:Magnetic Resonance Imaging
keywords: Anisotropic soft tissue; Human brain; Magnetic resonance elastography; Nonlinear inversion; Stiffness; White matter