Method for determination of an indicator representative of a change in the brain of an individual caused by a demyelinating or related disease, affecting the state of the myelin of the brain

A method for determining an indicator, representative of a brain alteration of an individual caused by a demyelinating pathology, the method comprising:

• a first step, for each region of interest of a set gathering several regions of interest of the brain, of determining a regional diffusion coefficient corresponding to an average, over said region of interest, of one of the following diffusion coefficients:
• radial diffusion, axial diffusion, mean diffusion, anisotropy fraction or a combination of several of these coefficients, the regional coefficients respectively associated with these different regions being determined from an image of the brain of the individual to be examined previously obtained by diffusion MRI;
• a second step of determining a number of altered regions, by counting the number of regions of interest for which a given condition is satisfied, said condition relating to the value of the regional diffusion coefficient associated with the region under consideration, compared with a reference regional coefficient which is equal to an average of the regional diffusion coefficient for this region for a cohort of healthy patients;
• and
• a third step of determining said indicator as a function of the number of altered regions.