Rationale: improving the early detection of AD at prodromal pre-dementia stages has become a major matter of concern. There is now an important body of literature stating that early isolated cognitive deficits (Mild Cognitive Impairment-MCI-) predict the risk of developing AD. Several biomarkers are now available : specific and sensitive neuropsychological assessments, morphometric evaluation of hippocampal volume and white matter changes by MRI, cerebrospinal fluid or plasma dosage of Ab fragments and tau proteins, assessment of brain glucose hypometabolism in temporo-parietal regions with PET [F18]FDG. However, PET imaging using labelled compounds specifically binding to APs has been suggested to improve the diagnostic reliability and to potentially help in shortening the delay until formal clinical diagnosis of AD. F18 AV45 is a new radiotracer which kinetics characteristics allows 10 to 15 minutes acquisition 50 to 60 minutes post injection.

Objectives: The primary objective of the study is to compare F18 AV45 cortical uptake in AD, MCI patients and Healthy Controls.

Secondary objectives will be to compare cortical uptake of F18 AV45 in MCI subject who will have convert toward dementia versus those who will not, at two year follow-up period, to compare level of 18F-AV45 cortical uptake with neuropsychological testing, PET FDG hypometabolism, ApoE genotype.

Method: Prospective multicentric study. 65 patients expected to enter the study.

Primary outcome measure: Standard Uptake Volume ratios.

Inclusion Criteria:

• Patients suffering from Alzheimer's Disease (NINCDS-ADRDA) or from amnesic MCI
• 18 < MMS <= 28 for patients
• 28 <= MMS for healthy volunteers
• study period > 7 years
• native language : french
• signed informed consent
• affiliated to a social security system

Exclusion Criteria:

• alcoholism in medical history
• diabetes
• arterial hypertension (180/100 and more)
• chronical pulmonary disease with hypoxis
• cranial traumatism with loss of consciousness > 15 minutes
• severe depressive syndrome or anxiety
• psychiatric disease in medical history (excepted simple episodes of depression)