Quasi-static magnetic resonance elastography at 7 T to measure the effect of pathology before and after fixation on tissue biomechanical properties.

Evaluation of imaging for cancer detection and localization can be achieved by correlation of gold-standard histopathology with imaging data. Usage of a 3D biomechanical-based deformable registration for correlation of the histopathology of whole-tissue specimens with ex vivo imaging necessitates measurement of the distribution of biomechanical properties in the ex vivo tissue specimen and changes that occur during pathology fixation. To measure high-resolution 3D distributions of Young's modulus (E) prefixation and postfixation, a quasi-static magnetic resonance elastography method was developed at 7 T. Use of echo-planar imaging allowed for shorter imaging times, in line with limited time frames allowable for pathology specimens. The finite element modeling algorithm produced voxel-wise E measures, and mechanical indentation was used for comparison. An initial preclinical evaluation with canine prostate specimens (n = 5) demonstrated a consistent increase in E with fixation (P < 0.002) by a factor of 4 (± 1). Increases were a function of distance from the tissue edge and correlated with fixation time (ρ = 1, P < 0.02). The technique will be used to generate population-averaged data of E from clinical ex vivo specimens prefixation and postfixation to inform registration of whole-mount histopathology with in vivo imaging.