The goal of this observational study is to learn about neuroimage and biomarkers in the Alzheimer's continuum. The main questions it aims to answer are:

• How is the neurovascular coupling during AD pathogenesis?
• How is the pattern/mapping of alterations in AD biomarkers? Participants will be observed and visit the research center annually to perform multi-modal MRI, PET, neuropsychological tests, and blood tests.

The observational study recruits participants from clinics and communities with cognitive impairment. Healthy volunteers will also be recruited as controls. Longitudinal observation of these participants will help demonstrate AD biomarkers' significance during AD pathogenesis.

The investigators aim to build an aging population cohort covering the AD continuum and explore key biomarkers for AD. All participants will have multi-modal MRI scanning, PET scanning with different tracers, and blood test. With MRI scanning, the investigators are exploring the effect of neurovascular coupling in AD pathogenesis. In addition, the investigators are trying to find patterns/mapping of AD biomarkers with PET and blood tests. Beyond this, more neuroimage markers and digital biomarkers will be tested in the cohort.

Inclusion Criteria:

1. Male and female aged 50 to 90 years old;
2. In accordance with the diagnostic criteria for "mild cognitive impairment due to Alzheimer's disease" and "Dementia" from the National Institutes of Health National Institute on Aging-Alzheimer's Association (NIA-AA) (2011);
3. The Hamilton depression rating scale/17 edition (HAMD) total score<10;
4. The clinical dementia rating (CDR) is 0.5 or above;
5. Neurological examination: no obvious signs;
6. Participants should have a caregiver stable and reliable.
7. Education: primary school (grade 6) or above. They have the ability to complete tests for cognitive ability and have the ability and time to complete regulation of cognitive training

Exclusion Criteria:

1. Other causes of cognitive decline: cerebrovascular disease, central nervous system infection, CJD, Huntington's and Parkinson's disease, DLB, traumatic brain dementia, other physical and chemical factors (such as drugs, alcohol, CO), systemic disease (hepatic encephalopathy, pulmonary encephalopathy, etc.), intracranial occupation (a subdural hematoma, brain tumor), the endocrine system disease (thyroid disease, parathyroid disease), and vitamins deficiency or any other causes of dementia.
2. The history of nervous system diseases, including stroke, optic myelitis, Parkinson's disease, epilepsy, etc.);
3. Psychiatric patients, including schizophrenia or other mental illnesses, bipolar disorder, major depression, or delirium;
4. There are unstable or serious heart, lung, liver, kidney, and hematopoietic system diseases; Poor prognosis because of malignant diseases such as tumors.
5. Vision or hearing problems that lead to poor performance on cognitive tests;
6. Two years history of severe alcoholism, and drug abuse;
7. The researchers believe that the subjects could not complete the study.
8. Contraindication of MRI or PET scanning.

The population consists of Alzheimer's disease, mild cognitive impairment, and cognitively normal participants.

There is not yet a plan to make IPD available to other researchers