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