Inclusion Criteria:
1 1. Men or women aged ≥ 40 years (including the threshold age). 2. Men or women with fertility must use effective contraceptive measures during the study period. Effective contraceptive measures include sterilization, intrauterine hormone devices, condoms, birth control pills, abstinence, or vasectomy.
3\. Meet the diagnostic criteria for normal cognitive function, Mild Cognitive Impairment (MCI), or Alzheimer's disease (AD).
4\. Participants voluntarily join the study, can cooperate with the experimental observations, and sign a written informed consent form. For participants with AD dementia, the informed consent form must be signed together with their legal guardian. If the participant is unable to sign the informed consent form due to limited cognitive ability or other reasons, the participant's signature space may be left blank, with the reason documented. The guardian should sign in the designated space for explanation.
Exclusion Criteria:
1. Known allergy to \[18F\]Fluorbetazine injection or its excipients.
2. Presence of previously implanted metal devices that are incompatible with MRI examinations, including pacemakers, defibrillators, insulin pumps, cochlear implants, intraocular metal implants, nerve stimulators, or CNS aneurysm clips; or suffering from claustrophobia or intolerance to imaging procedures for other reasons.
3. Cognitive impairment caused by reasons other than Alzheimer's disease (AD).
4. Cranial MRI scan shows one or more of the following results:
* More than 2 infarctions with a diameter greater than 2 cm in any part of the brain;
* Infarctions of any diameter in key areas such as the thalamus, hippocampus, entorhinal cortex, hippocampal gyrus, gyrus, cortex, or other subcortical gray matter nuclei;
* Fazekas Scale grading of white matter lesions \> 2;
* Presence of brain tumors, intracranial infections, or cerebral hemorrhage, and deemed unsuitable for participation in this study by the researchers.
5. Current clinically significant psychiatric illnesses, such as severe depression or schizophrenia, based on medical history, and the researchers have assessed that the imaging process cannot be completed. Researchers should carefully consider whether participants with dementia and behavioral disorders who may require psychiatric medication can complete the imaging process.
6. Received radiopharmaceutical imaging or treatment within at least 5 half-lives prior to screening.
7. Suffering from other serious and/or poorly controlled and/or unstable diseases, and deemed unsuitable for participation in this study by the researcher.
8. Positive test results for human immunodeficiency virus (HIV) antibodies or Treponema pallidum antibodies.
9. History of alcohol or drug abuse.
10. Pregnant or lactating women with positive pregnancy test results during the screening period (including premenopausal women who have not undergone surgical sterilization and women within one year after menopause).
11. Participated in any clinical trials within 4 weeks prior to enrollment and used investigational drugs; or those who plan to participate in any clinical trials during the study period.
12. Other situations deemed unsuitable for participating in this clinical trial by the researchers.
Participants with Normal Cognitive Function
1\. Any evidence suggesting the possibility of AD from previous MRI, CT, or other biomarker studies.
MCI and AD Dementia Participants
1. Received anti-Aβ targeted therapy drugs, such as lecanemab monoclonal antibody, or treated or prophylactic anti-Aβ vaccines.
2. Suffering from neurodegenerative diseases other than AD, including but not limited to Parkinson's disease, Pick's disease, frontotemporal degeneration (FTLD), Huntington's disease, Down syndrome, Creutzfeldt-Jakob disease, normal pressure hydrocephalus, or progressive supranuclear palsy (PSP).
3. Previously or currently diagnosed with dementia other than AD, including but not limited to Parkinson's disease dementia, Lewy body dementia, frontotemporal dementia, vascular dementia, mixed dementia, etc.
