Quantitative Mapping of Substantia Nigra Iron in Parkinson's Disease (Stages I-IV, REM Sleep Behavior Disorder) and Controls

Inclusion Criteria: * 1\. Idiopathic Parkinson's Disease, REM Sleep Behavior Disorder subjects without signs of Parkinsonism and normal healthy controls a. If tremor is not present, subjects must have unilateral onset and persistent asymmetry of the symptoms. b. For PD Subjects only: Age \> 30 years at time of diagnosis of PD with a maximum age of 100 years old c. Hoehn \& Yahr stage \< V (if PD) * 2\. For PD subjects only: Receiving an optimized dopaminergic regimen (i.e., either MAO-B inhibitor, a dopamine agonist and/or low doses of L-dopa, with dose change no more frequent than every 6-month in the course of the study); or medications naive * 3\. No overt anemia, iron deficiency, or other hematological disorders * 4\. Deemed healthy and able to undergo MRI and PE2i PET imaging by the Site Investigator, based on screening assessments-- medical history, physical examination 5. For Controls \& REM Sleep Behavior Disorder Subjects Only: Age 20-80; willing to undergo multiple imaging sessions 6. Signed informed consent form Exclusion Criteria: * 1\. Patient with atypical parkinsonism (such as suspected Progressive Supranuclear Palsy, Multiple System Atrophy) and secondary parkinsonism (such as normal pressure hydrocephalus, drug-induced, or vascular parkinsonism) * 2\. Patients with uncertainty as to having classical Parkinson's disease, such as those who might have scans without evidence of dopaminergic deficits (SWEDDs) * 3\. Presence of a medical or psychiatric comorbidi…