SELECTIVE INVERSION RECOVERY QUANTITATIVE MAGNETIZATION TRANSFER BRAIN MRI AT 7T: CLINICAL AND POST-MORTEM VALIDATION IN MULTIPLE SCLEROSIS

BACKGROUND AND PURPOSE: An imaging biomarker of myelin integrity is an unmet need in multiple sclerosis (MS). Selective inversion recovery (SIR) quantitative magnetization transfer imaging (qMT) provides assays of myelin content in the human brain. We previously translated the SIR method to 7T and incorporated a rapid turbo field echo (TFE) readout for whole-brain imaging within clinically acceptable scan times. We herein provide histological validation and test in vivo feasibility and applicability of the SIR-TFE protocol in MS. METHODS: Clinical (T(1)- and T(2)-weighted) and SIR-TFE MRI scans were performed at 7T in a post mortem MS brain and MRI data were acquired in 10 MS patients and 14 heathy volunteers to test in vivo. The following parameters were estimated from SIR data: the macromolecular-to-free water pool-size-ratio (PSR), spin-lattice relaxation rate of water (R(1f)), and the MT exchange rate (k(mf)). Differences in SIR parameters across tissue types e.g., white matter lesions (WM-Ls) and normal appearing WM (NAWM) in patients, and normal white matter (NWM) in heathy volunteers were evaluated. Associations between SIR parameters and disability scores were assessed. RESULTS: For post mortem scans, correspondence was observed between WM-Ls and NAWM from histology and PSR/R(1f) values. In vivo differences were detected for PSR, R(1f), and k(mf) between WM-Ls and NWM (p≤0.041). Associations were seen between WM-Ls/NAWM PSR and disability scores (r≤−0.671, p≤0.048). CONCLUSIONS: SIR-qMT at 7T provides sensitive, quantitative measures of myelin integrity for clinical and research applications.