18F-labeled radiopharmaceuticals for the molecular neuroimaging of amyloid plaques in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, with tremendous impact on the affected individuals and the society. Definitive diagnosis can be achieved only by post mortem examination. Clinical diagnosis criteria currently applied in clinical practice for AD often fail to accurately discriminate between AD and non-AD dementia with up to 40% of misdiagnosed patients. Several published papers demonstrated that the pre-clinical phase of AD is characterized by an early rise in beta-amyloid accumulation into inter-neuronal space, followed by a severe synaptic dysfunction. Thus, beta-amyloid protein, detected in the cerebrospinal fluid, has been considered a specific AD biomarker. Molecular imaging of beta-amyloid deposits, with positron emission tomography (PET) and 18F-labeled radiopharmaceuticals such as 18F-florbetapir, 18F-florbetaben, and 18F-flutemetamol, has emerged as potential powerful tool for aiding AD diagnosis. The aim of the present paper is to review the existing literature on the clinical use of these new amyloid tracers in order to delineate their diagnostic value and limitations.