Stiffness, strain and blood volume, unraveling three (mechanical) properties of the brain

Abstract

Mechanical properties of the brain can be indicators for different kinds of brain diseases. Separate measurements of different mechanical properties exist, however, little is known about their mutual influence. This study aims to unravel the influences of shear stiffness, volumetric strain, octahedral shear strain and cerebral blood volume (CBV) in the human brain. Repeated acquisitions of the intrinsic brain movement of 8 healthy subjects using a Displacement ENcoding with Stimulated Echos (DENSE) sequence in a 7T MRI were undertaken to calculate shear stiffness, volumetric strain and octahedral shear strain. Shear stiffness was estimated using intrinsic Magnetic Resonance Elastography (MRE) with nonlinear inversion. Volu- metric stain and octahedral shear strain were calculated directly form displacement measurements. CBV values were taken from a brain atlas. We calculated and compared average stiffness, strain and CBV values in 30 regions of interest located in the cortical gray matter (GM), subcortical GM and white matter (WM). The results show a correlation between CBV and strain values in WM regions as well as correlations between volumetric strain and octahedral shear strain. We did not find significant correlations between stiffness and strain. We assume that shear stiffness carries independent information from strain and could thus potentially be indicators for different types of disorders or diseases.