Patients underwent PET molecular imaging at baseline, at six months (data not presented), and at one year after hfSC implantation. Radiopharmaceuticals utilized were (+)-alpha-[11C]Dihidrotetrabenazine (DTBZ), 6-[18F]Fluoro-L-DOPA (FDOPA), and [11C]Raclopride (RAC). All patients underwent DTBZ-PET scans and one additional study with either FDOPA or RAC, at least one week apart. Patients were asked to discontinue antiparkinsonian medications at least 12h before each study. Scans were acquired on a Siemens Biograph 64 PET/CT. Thirty-minute brain emission scans were acquired 20 minutes post-injection of DTBZ or RAC, while 15 min scans were acquired for FDOPA 75 min post-injection. All patients studied with FDOPA were pre-medicated with 150 mg of carbidopa to prevent peripheral decarboxylation. Images were reconstructed using an OSEM-2D algorithm and analyzed with the software Statistical Parametric Mapping (SPM v.12). Each individual PET brain image was normalized on an anatomical MRI atlas to be evaluated within a standard space. Following normalization, FSL structural atlases were used for definition of the regions of interest. To facilitate the quantitative analysis, specific uptake ratios (SUR) in the caudate and putamen were calculated by subtracting the background signal of a reference region with nonspecific uptake from striatal activity and dividing by reference region activity [(target uptake - reference uptake)/reference uptake], using occipital cortex (DTBZ and FDOPA) and cerebellum (RAC), as reference regions.