Anisotropic Mechanical Properties of White Matter Tracts in Aging via Transversely Isotropic MR Elastography

Abstract

This study combined multi-excitation MR Elastography (ME-MRE) with a transversely isotropic inversion nonlinear inversion algorithm and diffusion tensor imaging (DTI) fiber directions to investigate anisotropic white matter tract integrity in aging. Participants were 5 older adults and 17 young adults. MRE outcomes include substrate shear modulus, μ, shear anisotropy, φ, tensile anisotropy, ζ, and DTI measures were also examined. Shear and tensile anisotropies were significantly different in the Corona Radiata and Superior Longitudinal Fasciculus. Diffusion measures were significantly different between groups in most tracts. These results suggest sensitivity of anisotropic properties to biological changes along white matter tracts in aging.

Mechanical Properties of White Matter Tracts in Aging Assessed via Anisotropic MR Elastography

“…Mechanical shear waves were introduced into the brain at 50 Hz using a pneumatic system (Resoundant, Inc.; Rochester, MN) with two vibration sources: a pillow driver that applies anterior-posterior (AP) motion and a custom designed left-right (LR) actuator highlighted in Figure 1A, applied separately, resulting in two distinct, three-dimensional wave fields for inversion (Figure 1C) (Smith et al, 2020). The LR actuator combines a silicone bottle driver with 3D printed components that affix the actuator to the head coil to enable stable vibrations and optimal coupling against the participants' temple (Caban-Rivera et al, 2022;Kailash et al, 2019). Wave fields from both actuations were captured with a 3D multiband, multishot spiral sequence (Johnson et al, 2016;) that encodes the full vector displacement fields generated in the brain by external actuation.…”