The goal of this clinical trial is to test whether we can reliably and safely measure the accumulation of pathological protein α-synuclein \[involved in some diseases such as Parkinson's disease, Lewy body dementia and Multiple System Atrophy (MSA), collectively named α-synucleinopathies\] using a new positron emission tomography (PET) tracer called \[18F\]ACI-15916. Both healthy people and people with (suspected) α-synuclein pathology will participate to this trial. The main questions it aims to answer are: * whether \[18F\]ACI-15916 is safe and well tolerated when injected into participants * whether \[18F\]ACI-15916 reliably detects α-synuclein in the brain using PET technique. * whether there are differences in the amount of this protein between people with diseases related to α-synuclein accumulation in the brain and people without these diseases. Participants will: * Visit the clinic to consent to their participation and to ensure they are eligible \[physical and neurological examinations, questionnaires, blood and urine tests, ECG and in some cases a MRI and a PET scan with a licensed tracer (\[18F\]FE-PE2I) to confirm or not the disease\]. * Visit the clinic to receive the tracer \[18F\]ACI-15916 intravenously and be scanned in a PET scanner, during which blood will be collected (and optionally spinal fluid). * Receive a phone call from the clinic 1 week after the PET scan to report any symptoms and side-effects that they may be having. Some of the participants may be asked to come again to the clinic for a second PET scan with \[18F\]ACI-15916, allowing the researchers to determine if the measurements with the first PET scan are stable and reproducible. Some of the participants will participate in a specific part of the study to evaluate the distribution of the PET ligand in the whole body, with a similar visit schedule.
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Number of participants with Adverse Events (AEs) assessed by severity (mild, moderate, severe, life threatening, death) and causal relationship (not related, unlikely related, possibly related or related)
Timeframe: From Informed Consent Signature (screening) to safety phone call after PET scan (i.e. up to 14 weeks in total)
Number of participants with clinically significant changes in vital signs measurements
Timeframe: During PET scan visit (i.e. at Day 0): before [18F]ACI-15916 injection and after the PET scan is completed
Brain uptake of the tracer [18F]ACI-15916
Timeframe: At the time of the [18F]ACI-15916 PET scan (i.e. at Day 0): 0-93 minutes after injection
AC Immune SA Clinical Trial Information