Study to Evaluate a Potential PET Radioligand for Imaging Alpha-synuclein Deposits in the Brain

The overall goal of this protocol is to evaluate \[18F\]MNI-1216 (also known as \[18F\]ACI-12589) as an α-synuclein targeted radiopharmaceutical in 3 parts as follows: * Part 1: first in human (FiH) imaging * Optional Part 2: expansion of FiH imaging * Optional Part 3: retest imaging A total of up to 30 participants may be enrolled and participate in the study. Part 1 of the study will include up to 10 participants (target of up to 5 healthy volunteers and up to 5 participants with idiopathic Parkinson's Disease). There will be an ongoing review of study data in Part 1 to evaluate the characteristics of tracer binding and safety. If the study results are deemed adequate in Part 1, Part 2 and/or Part 3 may be initiated. The decision to initiate Part 3 may also include a review of data from Part 2, if Part 2 is performed and the data are available. If performed, Part 2 will include up to 20 participants, including health volunteers and participants with α-synucleinopathies to acquire additional tracer-related data. If performed, Part 3 will include up to 10 participants from in Part 1 and/or Part 2 (including health volunteers and participants with α-synucleinopathies) to evaluate the reliability of \[18F\]MNI-1216 (\[18F\]ACI-12589) Positron Emission Tomography (PET) imaging.