The transition from relapsing-remitting multiple sclerosis to secondarily progressive multiple sclerosis (SPMS) is difficult to identify. Typically, SPMS is diagnosed retrospectively, with a significant delay, on the basis of a clinical history of progressive worsening, independent of relapses. Thus, SPMS is often associated with a considerable period of diagnostic uncertainty.

The use of ultra-high field imaging can shed light on the mechanisms of disability progression thanks to its better spatial resolution and advanced imaging techniques.

The new morphological imaging techniques make it possible to visualize chronic inflammatory lesions and to evaluate their evolution. It also allows for the precise measurement of brain atrophy, a reference in the evaluation of neurodegeneration.

Metabolic imaging via proton spectroscopy allows the analysis of several promising cerebral metabolites that can provide information on cellular energy metabolism, mitochondrial function, or oxidative stress, and can help identify tissues at risk of neurodegeneration. Sodium imaging can provide information on axonal energy metabolism before the occurrence of stable and irreversible axonal damage. This technique is promising as an early marker of neurodegeneration.

Inclusion Criteria:

• Age ≥ 18 years,
• Duration of disease ≤ 25 years,
• Irreversible disability ≤ 7 (permanent wheelchair use) on the EDSS scale

Exclusion Criteria:

• Other progressive neurological disease,
• Isolated radiologic syndrome (RIS),
• Severe psychiatric pathology not in balance,
• Change in dosage, discontinuation or initiation of a psychotropic treatment within the last month,
• Change in background MS treatment for less than 3 months,
• A course of corticosteroids (oral or intravenous) for less than one month,
• Patient with a contraindication to MRI: pregnancy, metallic ocular foreign body (accidental splinters or others), pacemaker, implantable defibrillator, neurostimulator not compatible with MRI 7.0 T, cochlear implants and in general any electronic medical equipment implanted in an irremovable way: metallic cardiac valve, vascular clips (formerly implanted on cranial aneurysm), metallic prosthesis...),
• Illiterate and non-French speaking patient: patient who is partially or completely unable to read and write French.
• Patient benefiting from reinforced protection, i.e. minor, subject deprived of liberty by a judicial or administrative decision, subject staying in a health or social establishment, adult under legal protection and finally patient in emergency situation,
• Pregnant or breastfeeding women, women of childbearing age who do not have effective contraception (hormonal/mechanical: per os, injectable, transcutaneous, implantable, intrauterine device, or surgical: tubal ligation, hysterectomy, total oophorectomy)