MRI issue.

Many central nervous system pathologies have an inflammatory component, often associated with an accumulation of disability and more severe tissue damage.

In multiple sclerosis, the inflammatory process is in part characterized by the activation of microglia, an entity of the innate inflammatory system, as well as a breakdown of the blood-brain barrier. During inflammation, activated microglia may contain high levels of iron, characterizing its activated state.

Several MRI imaging tools are known to be highly sensitive to tissue iron content and have become the method of choice to study brain iron, including in a pathological context such as multiple sclerosis.

Quantitative magnetic susceptibility mapping (QSM) is an emerging technique to access non-invasively the iron content in brain tissue. For some years this technique has been used in MS to characterize white matter lesions. Changes in the QSM value of the lesions have made it possible to describe lesions surrounded by an iron ring. Susceptibility MRI has also been proposed to highlight lesions according to their chronology.

The study of reproducibility is of particular importance when using QSM in longitudinal studies or in therapeutic trials. A better understanding of intra- and inter-subject variation in QSM measurements may also allow a more accurate estimate of the number of subjects needed to detect changes in studies. In order to be widely applied to various pathologies, it is therefore necessary to evaluate its reproducibility by estimating the intra- and inter-subject variability for future dissemination in clinical and pharmaceutical studies.

In this project, the invstigators propose to study the reproducibility of QSM acquisition.

Inclusion Criteria:

• Subject over 18 years old
• Consent to participate in the study
• Beneficiary of a social protection scheme
• Healthy volunteers: Consent to be informed if an unexpected anomaly is revealed by the imagery.
• Patients: With MS defined according to McDonald's revised criteria for spatial dissemination and temporal or clinical or radiological temporal dissemination and who should benefit from MRI in the imaging department

Exclusion Criteria:

• Absolute contraindication to 3T MRI
• Realization of an injected MRI (gadolinium) in the previous year
• Patient benefiting from a legal protection measure
• Pregnant or breastfeeding woman
• For healthy volunteers: History of neurological pathology or neurological pathology in progress

Participation in the study will be offered to patients with MS (the primary indication for which QSM is studied) as well as to healthy volunteers among staff.