Parkinson’s disease (PD) is a neurodegenerative disease for which there is currently no curative treatment. At a time when many innovative treatments are being developed, it urges to fill the gap concerning the identification of early biomarkers of neurodegeneration to detect the disease and treat it as early as possible. Ultra-high field 7 Tesla MRI offers the possibility to perform a quantitative analysis of structural and functional abnormalities occurring in the brain. Thus, the aim of this thesis, after reviewing the literature to summarize the known MRI abnormalities at the premotor stage of PD, is to search for microstructural abnormalities, ionic homeostasis, and iron accumulation at the early stage of PD (motor symptoms lasting less than three years). First, thanks to sodium MRI (23Na), well show that there is an abnormal accumulation of sodium within the substantia nigra (SN) in patients with PD in the absence of atrophy compared with a control group. In a second step, what well observe in these same patients, with proton MRI (1H), is that there is, no difference between the groups regarding iron accumulation in the SN. For microstructural alteration parameters such as mean diffusivity and T1 relaxometry, a trend towards alteration is observed in patients with PD but does not reach the statistical threshold in multiple corrections. Thus, this thesis brings to light for the first time the interest of intracerebral sodium quantification as an early marker of neurodegeneration in PD and its possible decoupling from iron accumulation at the early stage of the disease. Other studies are warranted to confirm these results but also to investigate this accumulation of sodium at a premotor stage of the disease.