Several recent studies have shown an increase in the signal intensity of the unenhanced T1-weighted magnetic resonance images in the brain of patients with normal renal functions and a breakdown of the blood-brain barrier. This hyper-intensity was specifically related to an accumulation of gadolinium based contrast agent. These studies were mainly conducted in patients with primary or secondary brain tumor. Multiple sclerosis is a particular model since it involves patients with a break of the blood-brain barrier, a long life expectancy, and who received many injections of contrast enhancing agents. In this context, it appears fundamental to know whether contrast agents accumulate in the brain for this disease. The French Observatory of Multiple Sclerosis is particularly suited to test this hypothesis, with homogeneous MRI data over several centers in France, and optimized sequences of 3D-T1 without injection. The purpose of this study is to evaluate the accumulation of two commonly used gadolinium based contrast materials (Dotarem and Multihance) in patients with multiple sclerosis, who received at least 5 injection of exclusively one of these contrast material.

• Inclusion Criteria:
• Clinical diagnosis of Multiple sclerosis
• At least 5 MR imaging with the same Gadolinium based contrast agent (either Dotarem or Multihance)
• Have performed an unenhanced T1-weighted image before Gadolinium based contrast agent injection according to the OFSEP protocol
• Exclusion Criteria:
• Never experienced other contrast agent then the one specified by the group to which they belong (either Dotarem, or Multihance)

Patients from the French observatory of multiple sclerosis (www.ofsep.org/)