Test-retest Trial With [11C]MODAG-005 in PD or MSA and AMHC - Pilot Phase

This is an open-label, single-center Phase 1 study evaluating the safety, tolerability, and test-retest characteristics of \[11C\]MODAG-005, an investigational positron emission tomography/computed tomography (PET/CT) radioligand intended to image pathological alpha-synuclein deposition in the brain. The study will enroll participants with Parkinson's disease (PD), participants with multiple system atrophy (MSA), and age-matched healthy controls (AMHC). Participants with PD or MSA will undergo two \[11C\]MODAG-005 PET/CT imaging sessions: one baseline scan and one follow-up scan 7 to 48 days later. Age-matched healthy controls will undergo one baseline scan. A subset of PD and MSA participants will receive a single oral dose of anle138b (Emrusolmin) before the second scan to evaluate tracer uptake under blocking conditions. The primary objective is to assess the safety and tolerability of \[11C\]MODAG-005. Secondary objectives include evaluating whether \[11C\]MODAG-005 PET imaging can distinguish participants with MSA or PD from age-matched healthy controls, distinguish PD from MSA, and determine test-retest variability of PET outcome measures.