 The purpose of this study is to investigate the utility of dopamine transporter imaging in monitoring and predicting the progression of Parkinson disease. This study will be performed in the PRECEPT cohort, an already existing cohort of 806 subjects recruited to participate in the study called, A Randomized, Double-Blind, Placebo-Controlled, Dose-Finding Study to Assess the Efficacy and Safety of CEP-1347 in Patients With Early Parkinsons Disease - PRECEPT, sponsored by Cephalon and Lundbeck and coordinated by the Parkinson Study Group. The imaging data from this long-term PRECEPT follow-up study will allow us to evaluate the long-term progression of DAT loss in PD, the long-term follow-up of SWEDD subjects, the relationship between long-term clinical and imaging PD outcomes, and the relationship between long-term imaging outcomes and genetic and biochemical biomarkers of PD progression. 