White and Gray Matter Multiple Sclerosis Spinal Cord Lesion Characteristics and Individualized Tissue Damage Assessment Using 7 T T1 Mapping

OBJECTIVES: The aim of this exploratory study was to demonstrate how 7 T MP2RAGE T1 mapping can be used to evaluate spinal cord (SC) tissue damage and lesion characteristics in multiple sclerosis (MS) at both subregional and individual levels. MATERIALS AND METHODS: Fifteen patients with relapsing-remitting MS (pwRRMS; mean disease duration = 32 ± 24.9 mo) and 15 age-matched healthy controls (HC) underwent 7 T cervical 3D MP2RAGE imaging with submillimetric spatial resolution. Automatic SC and lesion segmentations were obtained and manually corrected when necessary. Images were registered to the AMU7T template space to extract T1 values from specific regions of interest (ROIs), including white matter (WM) tracts: corticospinal (CST), lateral sensory (LST), posterior sensory (PST), ventral motor (VMT), and gray matter (GM) subregions: ventral, intermediate, and dorsal. Individual Z-score maps were computed and used to derive a global index of tissue impairment (patient-specific Z-score barplot) for lesion and normal appearing tissues (NAT). Finally, MS lesions were further characterized by their relative lesion load (RLL%), frequency maps, and topography across ROIs. RESULTS: Lesions were predominantly located in the posterior half of the cord, with GM showing the highest RLL. However, no lesions were observed exclusively in GM.An increasing gradient in T1 values was observed, with T1_HC <T1_NAT <T1_lesion (P < 0.01). Mixed GM-WM lesions exhibited higher T1 values and larger volumes than WM-only lesions. Elevated T1 values were also detected in NATs of SC lesion-free patients relative to HC, suggesting diffuse microstructural injury beyond visible lesions.The Z-score barplots provided individualized visualization of tissue damage, revealing more than 10% of abnormal SC voxels in 8/15 pwRRMS. CONCLUSION: This exploratory study demonstrates the potential and sensitivity of 7 T MP2RAGE T1 mapping for characterizing both focal and diffuse WM/GM SC tissue damage in MS. When combined with Z-score metrics, it provides a quantitative and individualized framework for assessing tissue integrity, grading the extent of microstructural impairment, and potentially monitoring neuroprotective treatment effects over time.