As the decrease of dopamine transporter (DAT) binding capacity and dopamine concentration are the neuropathological hallmarks of PD due to degeneration of dopaminergic neurons (Uhl, 2003), the secondary aim of this study is to investigate the association between the NBM degeneration (i.e., free water and volume changes) and DAT binding. Here, SLC6A3 is linked to Parkinson disease.