Post-Mortem Changes of Anisotropic Mechanical Properties in the Porcine Brain Assessed by MR Elastography

Motivation: Anisotropic mechanical properties of brain tissue define the mechanobiology of injury and disease, but most measurements of direction-dependent properties have been performed post-mortem. Goal(s): To characterize the post-mortem changesApproach: We use magnetic resonance elastography and diffusion tensor imaging with a transversely-isotropic nonlinear inversion algorithm to estimate anisotropic mechanical properties of minipig brain, both in vivo and at specific times after death. Results: White matter is stiffer, more dissipative, and more anisotropic than gray matter when the minipig is alive, but except for tensile anisotropy, these differences largely disappear post-mortem. Overall, brain tissue becomes stiffer, less dissipative, and less mechanically anisotropic after death. Impact: Our demonstration of significantly different mechanical properties in living versus post-mortem minipig brains is critical to improving computational models of TBI and correctly interpreting their predictions, which have relied on post-mortem measurements of brain material properties for several decades.