Contours of the basal ganglia and brainstem nuclei will be manually drawn in each subject in both hemispheres. These manual segmentations on healthy volunteers will be used to train the automatic algorithm described in paragraph 5.3.1. Then, the trained algorithm will be employed to automatically extract the contours of the ganglia and brainstem nuclei on the patient database.
Volumes of the STN is 300 mm3 (box of 10x6x5 mm3) and of the PPN 14 (sphere of 3 mm diameter) to 30 mm3 (cubic shape). Using MRI and an isotropic voxel of 500 µm, the STN will comprise 2400 voxels and the PPN 100 to 200 voxels (as compared to 14 to 30 voxels at 1.5T). Statistical comparisons will be performed on volumes as well as several other morphological criteria (shape, orientation, radial diameter…) using in-house software.