Alzheimer disease was first described in 1907 by Alois Alzheimer. From its original status as a rare disease, Alzheimer disease has become one of the most common diseases in the aging population, ranking as the fourth most common cause of death. Alzheimer disease is a progressive neurodegenerative disorder characterized by the gradual onset of dementia. The pathologic hallmarks of the disease are beta-amyloid (Aß) plaques, neurofibrillary tangles (NFTs), and reactive gliosis. Current diagnosis of Alzheimer disease is made by clinical, neuropsychological, and neuroimaging assessments. Developing new approaches for early and specific recognition of Alzheimer disease at the prodromal stages is of crucial importance. The search for therapies that can modify the course of AD to slow, delay, or prevent it is clearly the most important challenge. That search has in turn led to a search for imaging markers that can be used as outcomes in drug discovery and trials. Imaging has played a variety of roles in the study of Alzheimer disease (AD) over the past four decades. Initially, computed tomography (CT) and then magnetic resonance imaging (MRI) were used diagnostically to rule out other causes of dementia. PET scanning is a powerful imaging technique that enables in vivo examination of brain functions. It allows for noninvasive quantification of cerebral blood şow, metabolism, and receptor binding. PET scanning helps in understanding the disease’s pathogenesis, making the correct diagnosis, and monitoring the disease’s progression and response to treatment. More recently, a variety of imaging modalities including structural and functional MRI and positron emission tomography (PET) studies of cerebral metabolism with şuoro-deoxy-D-glucose (FDG) and amyloid tracers such as Pittsburgh Compound-B (PiB) , FDDNP, Florbetapir F 18 (AMYViD), şutemetamol F18 and their a combination have shown characteristic changes in the brains of patients with AD, and in prodromal and even presymptomatic states that can help rule-in the AD pathophysiological process. In the future, efforts to develop specific neuro ligands for neuropsychiatric diseases, may further enhance the sensitivity of PET scanning for early diagnosis of Alzheimer disease and may provide a biologic marker of disease progression.