Suspected Limbic Predominant Age-related TDP-43 Encephalopathy (LATE)

The goal of this clinical trial is to test whether we can reliably and safely measure the accumulation of pathological protein TDP-43 \[involved in rare forms of dementia such as frontotemporal dementia (FTD) and in amyotrophic lateral sclerosis (ALS)\] using a new positron emission tomography (PET) tracer called \[18F\]ACI-19626. Both healthy people and people with (suspected) TDP-43 accumulation will participate to this trial. The main questions it aims to answer are: * whether \[18F\]ACI-19626 is safe and well tolerated when injected into participants * whether \[18F\]ACI-19626 reliably detects abnormal TDP-43 in the brain using PET technique. * whether there are differences in the amount of this protein between people with diseases related to TDP-43 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 MRI in some cases). * Visit the clinic to receive the tracer \[18F\]ACI-19626 intravenously and be scanned in a PET scanner, during which blood will be collected. * Receive a phone call from the clinic 2 to 4 days 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, allowing the researchers to determine if the measurements with the first PET scan are stable and reproducible.