Inclusion Criteria:  Patients who meet the core clinical diagnostic criteria for Alzheimer's disease as defined by NIA-AA for mild cognitive decline or probable Alzheimer's disease. Subjects are able to understand and sign the informed consent voluntarily, with good compliance.  Exclusion Criteria:  Have contraindications to PET/MR examination. Clinically clear history of stroke. Have a history of bipolar disorder or depression. Patients with severe heart, liver, and kidney dysfunction. Pregnant or lactating women. Patients refuse to sign the informed consent.