Brain Imaging and Immune Changes During Remibrutinib Treatment in Multiple Sclerosis.

Inclusion Criteria * Capable of providing written informed consent for volunteering to undergo research procedures. * Male or female, any race * Age between 40 and 70 years of age, inclusive * Diagnosis of RMS according to revised 2017 McDonald criteria at screening 15 * EDSS score of 0 to 6.5 (inclusive) at screening * Treated with ocrelizumab according to routine clinical practice and at standard dose for at least 18 months. The last administration of ocrelizumab must have occurred within 5 to 9 months prior to randomization. * Neurologically stable within 30 days prior to screening, including no MS relapse during this period. * Suitable to be switched to remibrutinib based on physician judgement or patient preference. Exclusion Criteria: The exclusion criteria of the parent study are adapted and inherited under this section (See parent study protocol section 5.2). In addition, the following exclusion criteria apply: * Hypersensitivity to \[11C\]-DPA-713 or any of its excipients * Contraindications to PET or MRI (e.g. certain incompatible electronic medical devices, inability to lie still for extended periods) that make it potentially unsafe for the individual to participate * Presence of a low affinity binding TSPO polymorphism. * Any condition that, in the opinion of the Principal Investigator or his designee, could increase the risk to the participant or limits their ability to participate (e.g., liver or kidney disease, advanced cancer) * Current or recent (within 12 months prior to screening) participation in research studies involving radioactive agents such that the total research-related radiation dose to the participant in any given year would exceed the limits set forth in the U.S. Code of Federal Regulations (CFR) Title 21 Section 361.1. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=361.1.