This study will recruit a total of 150 evaluable subjects (30 cognitively normal volunteers, and 60 MCI(Mild cognitive impairment), and 60 AD(Alzheimer's disease), respectively) Each evaluable subject involved in this study must fulfill all the inclusion and exclusion criteria according the subject grouping.

Safety measurement will be evaluated by medical history, vital signs, physical examinations, laboratory examinations and collecting of adverse events.

This study is expected to be completed in a period of 3 years.

The primary objective of this protocol is to address the feasibility of clinical utilization of [18F]AV-45 in various neurodegenerative diseases. Specifically, we will expand the database of [18F]AV-45 PET imaging in Alzheimer's disease and MCI patients to refine the definition of a positive scan in patient with AD and MCI as compared to healthy control. Secondary, we will expand the safety database of [18F]AV-45 PET imaging. In addition, the image characteristics and prevalence of Aß positivity will be evaluated in different subsets of MCI and AD patients.

Inclusion Criteria:

• Both genders ≥ 50 years old.
• Written and dated informed consent by self or by legal representative, to be obtained before any of the study procedures.
• 30 cognitively normal volunteers with no evidence of significant cognitive impairment by history and psychometrictesting (MMSE > 24).
• 60 subjects with a diagnosis of AD according to the NINCDS-ADRDA criteria.
• 60 subjects with a diagnosis of MCI

Exclusion Criteria:

1. Pregnant or becoming pregnant during the study (as documented by pregnancy testing at screening or at any date during the study according to the PI discretion) or current breast feeding.

2. Modified Hachinski ischemic score of >4 or those who meet the NINDS-AIREN criteria for vascular dementia.

3. Any subject who has a clinically significant abnormal laboratory values, and/or clinically significant or unstable medical or psychiatric illness.

   • Clinically significant hepatic, renal, pulmonary, metabolic, or endocrine disturbances, especially thyroid disease;

   • Current clinically significant cardiovascular disease. Clinically significant cardiovascular disease usually includes one or more of the following:

     • cardiac surgery or myocardial infarction within the last 6 months;
     • unstable angina
     • coronary artery disease that required a change in medication within the last 3 months
     • decompensated congestive heart failure
     • significant cardiac arrhythmia or conduction disturbance, particularly those resulting in atrial or ventricular fibrillation, or causing syncope, near syncope, or other alterations in mental status
     • severe mitral or aortic valvular disease
     • uncontrolled high blood pressure
     • congenital heart disease
     • clinically significant abnormal result on ECG, including but not limited to QTc>450 msec iii. Clinically significant infectious disease, including AIDS or HIV infection or active hepatitis B, active hepatitis C, HIV-1, or HIV-2

4. History of drug or alcohol abuse within the last year, or prior prolonged history of abuse.

5. Patients who have the evidence of neurodegenerative disorders other than AD, cognitive impairment resulting from trauma or brain damage, brain infarction, clinically significant psychiatric disease, epilepsy, are excluded.