Date of Award
Doctor of Philosophy (PhD)
Accurate mechanical properties of the intact, living brain are essential for modeling traumatic brain injury (TBI). However, the properties of brain tissue in vivo have traditionally been measured in ex vivo samples. Magnetic resonance elastography (MRE) can be used to measure motion and estimate material properties of soft tissues in vivo, but MRE typically assumes tissue isotropy and homogeneity. The objective of this thesis is to improve MRE of soft tissue, like the brain, by developing and evaluating methods for in vivo estimation of heterogeneous, anisotropic properties. This was achieved through pursuit of the following aims: (1) quantifying the differences between in vivo and ex vivo brain tissue, thereby clarifying the need for in vivo measurements; (2) introducing and applying a new approach to anisotropic MRE, using data obtained during external actuation of the porcine brain in vivo, which highlighted the need for new actuation methods; and (3) developing and evaluating a method for anisotropic property estimation using MRE with actuation by harmonic focused ultrasound (FUS). This research has led to new methods for anisotropic MRE, and improved material property estimates of the brain and other soft tissues.
Philip V. Bayly
Hong Chen, Joel R. Garbow, J. Mark Meacham, Ruth J. Okamoto,