Inclusion Criteria:

1. Patient 18 years of age or older
2. Presenting for a 4th semi-annual cycle of ocrelizumab (minimum)
3. Requires follow-up MRI as part of treatment.
4. Initial indication for ocrelizumab according to the marketing authorization (active MS, RR or SP form)
5. Absence of relapse for at least 18 months (a relapse being defined as the appearance of new symptoms or worsening of existing symptoms, lasting more than 24 hours and outside a period of fever or an infectious episode; notified as a validated relapse by the neurologist in the patient's file, treated or not with boluses of Solu-Medrol).
6. EDSS between 0 and 6 inclusive
7. Having received informed information about the study and having signed a consent to participate in the study
8. French language proficiency
9. Affiliated or beneficiary of a social insurance scheme

Exclusion Criteria:

1. Clinical forms of primary progressive MS
2. Patients already receiving systematically spaced doses of ocrelizumab ≥ 9 months apart
3. Contraindication to continued treatment with ocrelizumab (hypersensitivity reaction, ongoing active infection, development of malignancy since previous injection, development of severe immune deficiency)
4. Planned pregnancy within 3 years
5. Contraindication to MRI
6. Contraindication to injection of contrast media
7. Subject with severe or uncontrolled symptoms of renal, hepatic, hematological, gastrointestinal, pulmonary, psychiatric or cardiac disease, or any uncontrolled intercurrent pathology.
8. Patient under legal protection
9. Patients of childbearing age who do not wish to use effective contraception
10. Pregnant or breast-feeding women