Introduction: Paramagnetic rim lesions (PRL)s, a class of MS lesions with chronic iron-laden inflammatory cells, are linked to more severe tissue injury, but their longitudinal behavior and factors that relate to their development are not well understood.

Objective: The aim of this study was to investigate patient level determinants that predict later PRL accumulation and whether newly forming PRLs follow distinct trajectories compared to non-PRLs using 7T MRI.

Methods: A cohort of 20 patients with MS who had new contrast enhancing lesions (CELs) on their clinical MRI were scanned on a 7T MRI at baseline, 3, 6, 9 months, and annually. Then scans were registered and the CELs were segmented manually on the MP2RAGE T1 map to obtain volume and T1 relaxation times of the specific lesions at each time point. Lesions were categorized as a new PRL or new nonPRL on the 6 month scan based on the presence of a hypointense rim on the T2* phase sequence. New lesions identified on subsequent 7T MRIs were also identified, segmented and characterized as new PRL or nonPRL.

Results: We found that higher baseline PRL and CEL burden (number and volume) predicted greater endpoint PRL burden. Additionally, across follow-up, new PRLs had larger volume and longer T1 relaxation times than new non-PRLs, with a trend of early expansion and partial decline later on.

Discussion: These findings support PRLs being markers of greater tissue injury and suggest that patient-level factors (i.e. baseline burden) has potential to be used as a prognostic index in patients at risk for developing future PRLs.