Fast Whole-Brain Three-dimensional Macromolecular Proton Fraction Mapping in Multiple Sclerosis

Purpose: To evaluate the clinical utility of fast whole-brain macromolecular proton fraction (MPF) mapping in multiple sclerosis (MS) and compare MPF with established quantitative magnetic resonance (MR) imaging measures of tissue damage including magnetization transfer (MT) ratio and relaxation rate (R1). Materials and Methods: In this institutional review board-approved and HIPAA-compliant study, 14 healthy control participants, 18 relapsing-remitting MS (RRMS) patients, and 12 secondary progressive MS (SPMS) patients provided written informed consent and underwent 3-T MR imaging. Three-dimensional MPF maps were reconstructed from MT-weighted images and R1 maps by the single-point method. Mean MPF, R1, and MT ratio in normal-appearing white matter (WM), gray matter (GM), and lesions were compared between subject groups by using analysis of variance. Correlations (Pearson r) between imaging data and clinical scores (Expanded Disability Status Scale [EDSS] and MS Functional Composite [MSFC]) were compared by using Hotelling-Williams test. Results: RRMS patients had lower WM and GM MPF than controls, with percentage decreases of 6.5% (P < .005) and 5.4% (P < .05). MPF in SPMS was reduced relative to RRMS in WM, GM, and lesions by 6.4% (P < .005), 13.4% (P < .005), and 11.7% (P < .05), respectively. EDSS and MSFC demonstrated strongest correlations with MPF in GM (r = -0.74 and 0.81; P < .001) followed by WM (r = -0.57 and 0.72; P < .01) and lesions (r = -0.42 and 0.50; P < .05). R1 and MT ratio in all tissues were significantly less correlated with clinical scores than GM MPF (P < .05). Conclusion: MPF mapping enables quantitative assessment of demyelination in normal-appearing brain tissues and shows primary clinical relevance of GM damage in MS. MPF outperforms MT ratio and R1 in detection of MS-related tissue changes. (C) RSNA, 2014