Subvoxel quantitative susceptibility mapping reveals distinct susceptibility patterns and clinical associations of juxtacortical paramagnetic rims in multiple sclerosis.

BACKGROUND: Juxtacortical paramagnetic rims (JPRs) have emerged as potential biomarkers of cortical pathology in multiple sclerosis (MS), yet their susceptibility characteristics and clinical significance remain unclear. OBJECTIVES: To characterize the heterogeneity of cortical lesions (CLs), with a particular focus on JPRs and clinical relevance. METHODS: Sixty-four patients underwent 3T magnetic resonance imaging (MRI), including structural imaging, multi-echo gradient echo, and Magnetic Resonance Image Compilation (MAGiC) sequences. Paramagnetic (χpara) and diamagnetic (χdia) maps were reconstructed using subvoxel quantitative susceptibility mapping. CLs were identified, and those with JPRs were defined as JPR-associated CLs. Susceptibility metrics were compared across lesion subtypes and correlated with clinical and imaging measures. RESULTS: Among 499 CLs, 15% were JPR-associated CLs, which exhibited elevated χpara measurements and reduced χdia measurements. Patients with JPRs had a higher number of paramagnetic rim lesions (95% CI [2.445, 4.738], p < 0.001), annualized relapse rates (95% CI [0.130, 0.297], p < 0.001), and lower digit span test scores (95% CI [-2.504, -0.473], p = 0.004). The absolute χpara and χdia values in all CLs were correlated with longer disease duration (r = -0.461, p = 0.001; r = 0.457, p = 0.001). CONCLUSION: JPRs are a characteristic feature of CLs associated with greater clinical and radiological burden in MS.