The size of the deep structures of the brain stem involved in the Parkinsonian syndrome (SN, STN, RN, PPN) is relatively small compared to the millimeter resolution of the MRI data obtained at low field (1.5T). It also explains why most studies based on MRI only provided partial answers to questions of interest for the clinician.
Today, the major improvement of the spatial resolution resulting from the use of ultra-high field MRI systems offers new perspectives of imaging of these deep structures. The use of the human 7T system now allows the acquisition of high resolution structural data at 250 um x 250 um x 1mm, as depicted on figure 1. In this project, we will rather use a 400 um isotropic resolution in the future, keeping the same voxel volume and preserving the signal to noise ratio. Not only the spatial resolution is improved, but the standard T2*-weighted gradient-echo imaging provides some new contrasts mechanisms especially in the deep nuclei linked to the presence of iron in these structures with different concentrations. The top-left part of the figure 1 shows some preliminaries T2* data depicting a very good contrast in the SN, the STN and the RN allowing the study of their morphometry, which was almost impossible at low field (1.5T). In the case of the SN, this contrast mechanism will probably become a new biomarker of the Parkinsonian syndromes.