Outcome measures. The primary outcome measure is the presence or absence, on the week-13 7-tesla scan, of a hypointense phase rim in each of the lesions followed over time. Secondary outcome measures include the presence or absence of a hypointense phase rim at week 25, as well as the lesion volume and intralesional median R1 relaxation rate at weeks 13 and 25. From 3-tesla scans, we will measure the change in normalized intralesional proton density-weighted and T1-weighted signal, as well as the R1 relaxation rate, between baseline and week 25. We will also assess for the presence or absence of a hypointense phase at 3T. Additional exploratory outcome measures, including clinical and immunological assessments, will also be collected.