Evaluation of Early Changes Visible to the Diffusion MRI in Response to Two Years of Treatment With Tysabri in Patients With Multiple Sclerosis

Inclusion Criteria: * Major Patient * Patient with relapsing remitting multiple sclerosis and eligible for treatment with Tysabri * Patient affiliated to a social security scheme * Patient who signed informed consent * Patient who have been informed of the results of the prior medical examination Exclusion Criteria: * Patient not currently eligible for treatment with Tysabri * Contraindication to MRI scanning * Unability to provide informed consent (subject in an emergency situation, difficulties in understanding , ...) * Patient under judicial protection * Patient under guardianship or curatorship * Pregnancy (women of childbearing age in the absence of effective contraception) * Breastfeeding