Characterization of the Serotonin 2A Receptor Selective PET Tracer [18F]MH.MZ in Patients With Neurodegenerative Diseases

Inclusion Criteria:

* Patient arm - clinical diagnosis of Parkinson disease, diffuse Lewy body disease, multiple systems atrophy, Huntington's Disease, Frontotemporal Dementia, and other variants
* Healthy arm - age and gender matched to patient arm
* Psychosis (presence of hallucinations or delusions) starting after the diagnosis of Parkinson's disease, occurring at least weekly for 4 weeks, severe enough to warrant treatment.
* Study partner available for study visits

Exclusion Criteria:

* Prior stroke or other uncontrolled serious neurological or medical illness
* Contra-indication or inability to tolerate MRI scan
* Use of serotonergic medications in the last 6 weeks
* Incapable of providing independent consent.
* Pregnant or breastfeeding women
* psychosis due to a metabolic, toxic, or primary psychiatric disease
* Deemed unable to complete neurocognitive testing
* For PD Participants: current or prior use of pimavanserin
* Use of antipsychotics in the last 2 weeks