In the field of diagnosing brain neurodegenerative diseases, it is now a well-established practice to inject positron-emitting tracers into the human body. These tracers bind to specific target proteins, allowing their distribution to be visualized via PET imaging. Currently, several research groups worldwide are engaged in developing and clinically validating their own tau imaging agents.

This clinical research project aims to visualize abnormal tau pathology in the living human brain using [18F]NIDF PET imaging. [18F]NIDF is a 2-arene-azaindole-based tracer that offers stronger binding affinity to tau neurofibrillary tangles and reduced non-specific/off-target binding compared to existing tau-PET imaging agents. The study primarily focuses on evaluating the safety and diagnostic efficacy of [18F]NIDF PET imaging in human subjects.

Inclusion Criteria:

1. Between 18 and 90 years old;
2. No gender limitation;
3. Clinical diagnositic rerults supported the diagnosis of neurodegeneration, and there was no evidence of other neurological diseases;
4. Healthy participants or patients with probable Alzheimer's disease or with dementia due to other causes;
5. Informed consent signed in person by the subject or his legal guardian or caregiver.

Exclusion Criteria:

1. Has allergy to [18F]NIDF or any of its excipients;
2. Incapable of providing written informed consent or lacking a legally authorized representative (LAR) to provide informed consent ;
3. Unwilling or unable to undergo PET scans tracer injections;
4. Any condition that, in the Investigator's opinion, could increase the risk to the participant, limit the participant's ability to tolerate the research procedures, or interfere with the collection/analysis of the data (e.g., renal or liver failure, advanced cancer);
5. Received an experimental drug or device within 1 month (whose efficacy or safety is unclear);
6. Have other serious neurological disorders, or gastrointestinal, cardiovascular, liver, kidney, blood system, tumor, endocrine, respiratory, immune deficiency, and other serious diseases;
7. Women who are currently pregnant or breastfeeding.

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.