Cross-validating magnetic resonance elastography and ultrasound time-harmonic elastography of the brain by using a 3D optical tracker

Motivation: Magnetic resonance elastography (MRE) and ultrasound time-harmonic elastography (USE-THE) have not been cross-validated yet. Since their results are in 3D and 2D, respectively, aligning them is difficult. Goal(s): To cross-validate MRE and USE-THE in the brain based on a common atlas space. Approach: An optical system tracked the position of fiducial markers derived from MRE during USE-THE measurements. Consequently, the resulting spatial alignment of both measurements allowed direct comparison. Results: Stiffness was averaged over the whole field-of-view and over five anatomical regions. Globally, agreement was good (ICC=0.6982) and regionally, it was acceptable based on a Wilcoxon signed test (p>0.05). Impact: Agreement between cerebral MRE and USE will facilitate multi-modal neural tissue characterization. Combined MRE-USE could benefit from high spatial resolution of MRE and high temporal resolution of USE-THE.