Multi-scale MRI spectrum detects differences in myelin integrity between MS lesion types

Background: Lesions with different extents of myelin pathology are found at autopsy in multiple sclerosis (MS), but the differences are not discernible in magnetic resonance imaging (MRI). Objective: To determine whether analysis of the local spectrum in MRI is sensitive to lesion differences in myelin integrity. Methods: We imaged fresh brain slices from 21 MS patients using 1.5T scanners. White matter lesions were identified in T2-weighted MRI, matched to corresponding specimens, and then classified into five categories in histology: pre-active (intact myelin); active, chronic active, chronic inactive (complete demyelination); and remyelinated lesions. Voxel-based frequency spectrum was calculated using T2-weighted MRI to characterize lesion structure (image texture). Results: MRI texture heterogeneity resulting from all spectral scales was greater in completely demyelinated lesions than in myelin-preserved lesions (p = 0.02) and normal-appearing white matter (p < 0.01). Moreover, the spectral distribution pattern over low-frequency scales differentiated demyelinated lesions from remyelinated and pre-active lesions (p < 0.01), where different lesion types also showed distinct texture scales. Conclusion: Using multi-scale spectral analysis, it may be possible for standard MRI to evaluate myelin integrity in MS lesions. This can be critical for monitoring disease activity and assessing remyelination therapies for MS patients.