Parkinson disease (PD) is a progressive neurological disorder strongly linked to advancing age that results in decline in mobility and thinking. Based on prior research, the investigators think that small amounts of inflammation in the brain may contribute to the mobility and thinking problems in people with PD. They are trying to measure inflammation in the brain in order to understand how this inflammation could be contributing to the symptoms of PD. This study involves a brain positron emission tomography (PET) scan with a new, investigational radioactive tracer called [11C]-CS1P1 to identify inflammation in the brain.The goal of this project is to quantify neuroinflammation with [11C]-CS1P1 PET and compare to motor and cognitive function in participants with various stages of severity of PD compared to controls.

Inclusion Criteria:

• Parkinson Disease (PD) participants must be at least 50 years old and meet clinical diagnostic criteria of idiopathic PD.
• Control participants must be at least 50 years old and not have PD, no first-degree family member with PD, and no evidence of PD or dementia on examination.

Exclusion Criteria:

• any history of other neurologic illness (e.g. stroke, seizure, multiple sclerosis)
• history of brain surgery or major head trauma
• major medical/systemic illness
• severe psychiatric illness (e.g. bipolar disorder, schizophrenia)
• major drug abuse
• history of long term use of anti-dopaminergic medication
• chronic treatment with immunomodulatory or anti-inflammatory medications
• weight over 300 lbs
• contraindication to or inability to tolerate MRI

A total of 50 participants with idiopathic PD and up to 30 healthy control participants are to be studied. Some of these participants will be recruited from existing research studies. Others will be recruited from the clinic, the community, and a registry of healthy volunteers.