The purpose of this study is to assess the level of neuroinflammation in Alzheimer Disease subject (mild to moderate) estimated with Binding Potential (BP) of [18F]DPA-714, and its relationship with the kinetics of cognitive decline over a 24-month follow-up period (as assessed by Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog) and Mini-Mental State Examination (MMSE) scores).