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Introduction T1-dark rim, a hypointense ring surrounding lesions on T1-weighted MRI, was recently proposed as a marker of paramagnetic rim lesions(PRLs) in a cross-sectional study. No studies have explored T1-dark rims longitudinally.Aims Explore prevalence and evolution of T1-dark rims in nascent and existing white matter lesions using 7T and clinical 3T MRI.Methods Prevalence and short-term(36weeks) evolution of nascent and existing T1-dark rim lesions was assessed in four patients using 7T MRI (T1-MP2RAGE) and compared to PRLs on quantitative susceptibility-weighted imaging(qSWI). To verify clinical detectability, T1-dark rims were assessed in 22 people with early MS using 3T T1(MPRAGE) MRI with follow-up at 6,12, 24, 36 months.Results At 7T, 75% of patients had ≥1 T1-dark rim representing 14% of lesions, compared to 7% PRLs on qSWI. 16/20 (80%) new lesions had a T1-dark rim; the remaining lesions were small(<100mm3). The largest T1-rim lesions were all PRLs.At 3T, 95% of patients had ≥1T1-dark rims, representing 10% of lesions. 5/20(25%) of new lesions(>100 mm3) had T1-dark rim.Conclusion T1-dark rims, present in most people with MS, are more frequent than susceptibility-based PRLs. They may be a more sensitive marker of lesion activity that could be easily incorporated into clinical practice.margareta.clarke2@nottingham.ac.uk