Inclusion Criteria:  RRMS patients:  Age between 18 and 55 years old RRMS according to the 2017 Mc Donald criteria Less than 5 years of disease duration 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 Interferon-beta, glatiramere acetate and oral first line therapy will such as dimethylfumarate or teriflunomide will be admitted Affiliation to a social security scheme or beneficiary of such a scheme (Except "Aide Médicale d'Etat")  Progressive MS patients:  Age between 18 and 55 years old Progressive MS (primary or secondary progressive MS) according to the 2017 Mc Donald criteria Less than 10 years of disease duration in the progressive phase At least 9 supra-tentorial white matter lesions on T2/FLAIR MRI Interferon-beta, glatiramere acetate and oral first line therapy will such as dimethylfumarate or teriflunomide will be admitted 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) PET for clinical research already done within the last 12 months Low Affinity Binding profile (TSPO polymorphism analyzed at screening visit) Pregnancy, breast-feeding, lack of efficient contraception 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 abnormal MRI (with a significant medical anomaly) Know hypersensitivity to Myelin PET : [18F]-Florbetaben Patient under legal protection  Additional exclusion criteria for patients:  Treatment with cyclophosphamide, mitoxantrone, fingolimod, cladribine, alemtuzumab, anti CD20 antibodies or natalizumab will not be admitted. These treatments may be administered after the Baseline visit. Known allergy to gadoteric acid Allergies (seafood, pollinosis, urticarial) having required a medical intervention Severe renal insufficiency (creatinine clearance < 60mL/min).