Inclusion Criteria:
1. Cognitive unimpaired(CU) controls:
(1) Aged between 45 and 90 years; no gender restrictions； (2) Cognitive function is assessed as normal by the researcher based on cognitive tests, with a Clinical Dementia Rating (CDR) score of 0; (3) Confirmed by the researcher to have no neurological diseases, major chronic illnesses, malignant tumors, or acute infectious diseases; (4) No family history of Alzheimer's disease (AD) or other neurological diseases related to cognitive impairment and movement disorders; (5) Able to understand and provide written informed consent before any assessment; (6) Female subjects must provide medical documentation proving they have undergone surgical sterilization (e.g., hysterectomy, bilateral oophorectomy, or tubal ligation) or have been menopausal for over one year. If they are still of childbearing potential, they must use effective contraceptive measures during the study; (7) Male subjects must use effective contraceptive measures during the study period and are prohibited from donating sperm during this time; (8) Willing and able to comply with all study procedures. 2. Cognitive impaired(CI) patients:
1. Aged between 45 and 90 years; no gender restrictions;
2. CDR score ≥ 0.5;
3. MMSE score ≤ 24;
4. Brain MRI findings support the diagnosis of AD, with no evidence of other neurological diseases;
5. Any medications taken to alleviate AD symptoms must be maintained at a stable dose for at least 30 days before study participation;
6. Written informed consent must be provided by the subject or their legal guardian/caregiver;
7. If necessary, subjects may be accompanied by a caregiver;
8. Before any assessment, the subject or their legal representative must understand and sign a written informed consent form;
9. Female subjects must provide medical documentation confirming surgical sterilization (e.g., hysterectomy, bilateral oophorectomy, or tubal ligation).
Exclusion Criteria:
* All subjects:
1. Presence of severe neurological diseases or serious disorders affecting the gastrointestinal, cardiovascular, hepatic, renal, hematologic, oncologic, endocrine, respiratory, or immune systems;
2. Presence of MRI-incompatible metal implants, including cardiac pacemakers, intravascular metal devices, insulin pumps, cochlear implants, nerve stimulators, or cerebral aneurysm clips;
3. Inability to tolerate MRI noise or a history of claustrophobia;
4. Exposure to ionizing radiation exceeding 50 mSv within the past year due to participation in other clinical or scientific research;
5. History of drug or alcohol abuse;
6. Pregnancy or lactation;
7. Poor venous access, making repeated venipuncture infeasible;
8. Use of experimental drugs or devices with unknown efficacy or safety within the past month;
9. Allergy to any components of the tracer injection;
10. Any condition that, in the investigator's judgment, may pose a risk or compromise the integrity of the study.
