New brain scan technique could reveal hidden inflammation in MS patients

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: RRMS patients: * Age between 18 and 55 years old * RRMS according to the 2017 Mc Donald criteria * At least 9 supra-tentorial white matter lesions on T2/FLAIR MRI * Last treatment with methylprednisolone should have been performed at least 1 month before PET examinations * No current disease modifying therapy * Indication for a highly active disease modifying treatment: Natalizumab, anti CD20 antibody, Alemtuzumab, sphingosine-1 phosphate modulator, or cladribine. This will consist either as patients with an active form of relapsing MS or patients who have experienced two relapses during the previous year * Affiliation to a social security scheme or beneficiary of such a scheme (except "Aide Médicale d'Etat") Healthy Volunteers: * Age between 18 and 55 years old * Without any evolutive pathology * Able to understand the study objectives and procedures * Affiliation to a social security scheme or beneficiary of such a scheme (except "Aide Médicale d'Etat") Exclusion Criteria: For all participants: * Any reasons, which does not allow to perform MRI, including claustrophobia, the implant of a pace-maker or the presence of an intra-ocular foreign body, (a contra-indication questionnaire will be filled in beforehand) * Realization of any test using radioactivity within the last 12 months * Low Affinity Binding profile (analyse of TSPO polymorphism done at screening visit) * Pregnancy, breast-feeding, lack of efficient contraception for women of childbearing potential * Current symptoms of severe or uncontrolled renal, hepatic, hematological, gastrointestinal, pulmonary or cardiac disease, or any other chronic neurological diseases * Unwillingness to be informed in case of unexpected MRI abnormality (with a significant medical anomaly) * Patient under legal protection * Participation in another interventional study or being in the exclusion period at the end of a previous study RRMS patients: * Hypersensitivity to gadoteric acid * Meglumine or any drug containing gadolinium * Severe renal insufficiency (creatinine clearance \< 60mL/min and GFR \<30ml / min / 1.73m2).