Multimodal Biomarkers for Diagnosis and Prognosis in VCI

Inclusion Criteria: \- I. Vascular cognitive impairment patients: 1. Age older than 20 years. 2. Clinical diagnosis: 1. At least one obstacle to executive function, attention, memory, language and visual space function. 2. Affected activities of daily living. 3. Brain MRI showing cerebrovascular disease. 3. Patient agrees to participate in the study and is willing to receive 11C-PiB PET. II. Alzheimer's disease (AD) patients: 1. Age older than 20 years. 2. Clinical diagnosis: 1. Amnesia or non-amnesia (language, visual space, executive ability) performance. 2. Affected activities of daily living. 3. Patient agrees to participate in the study and is willing to receive 11C-PiB PET. III. Normal controls: 1. Age older than 20 years. 2. No neurological or psychiatric history. 3. Patient agrees to participate in the study and is willing to receive 11C-PiB PET. Exclusion Criteria: \- I. Vascular cognitive impairment patients: 1. Have other illnesses, including people with drug / alcohol abuse / addictivity within three months. 2. Patient cannot accept brain magnetic resonance imaging or 11C-PiB PET, such as agitation and inability to cooperate, allergy to contrast agents, hemodynamic instability (blood pressure, pulse, or blood oxygen is not in the normal range), and a heart rhythm regulator has been implanted , Have ever undergone intracranial aneurysm clamp surgery, claustrophobia and hemodynamic instability. 3. Pregnant woman or intends to be pregnant in the near future. 4. Patient who is breast feeding or intends to. 5. Allergic to 11C-PiB, or with severe drug allergy history. 6. Patient or the family refuses to participate in the study. II. Alzheimer's disease (AD) patients: 1. Have other illnesses, including: 1. Cognitive disorders caused by cerebrovascular diseases (the decline in cognitive function is closely related to the time of stroke, multiple large-scale necrosis, and severe white matter lesions). 2. The main manifestation of dementia is Lewy body dementia 3. Symptoms are behavioral variation of frontotemporal dementia. 4. The symptoms are obviously semantic progressive aphasia. 5. Symptoms are not fluent in primary progressive aphasia. 6. Other comorbidities that affect cognitive function (including other active neurological diseases, or non-neurological diseases but the disease or the treatment used will affect cognitive function) 2. Patient cannot accept brain magnetic resonance imaging or 11C-PiB PET, such as agitation and inability to cooperate, allergy to contrast agents, hemodynamic instability (blood pressure, pulse, or blood oxygen is not in the normal range), and a heart rhythm regulator has been implanted , Have ever undergone intracranial aneurysm clamp surgery, claustrophobia and hemodynamic instability. 3. Pregnant woman or intends to be pregnant in the near future. 4. Patient who is breast feeding or intends to. 5. Allergic to 11C-PiB, or with severe drug allergy history. 6. Patient or the family refuses to participate in the study. III. Normal controls: 1. Patient cannot accept brain magnetic resonance imaging or 11C-PiB PET, such as agitation and inability to cooperate, allergy to contrast agents, hemodynamic instability (blood pressure, pulse, or blood oxygen is not in the normal range), and a heart rhythm regulator has been implanted , Have ever undergone intracranial aneurysm clamp surgery, claustrophobia and hemodynamic instability. 2. Pregnant woman or intends to be pregnant in the near future. 3. Patient who is breast feeding or intends to. 4. Allergic to 11C-PiB, or with severe drug allergy history. 5. Patient or the family refuses to participate in the study. 6. high risk as assessed by a doctor.