The accumulation of ?-Amyloid and tau proteins in the brain is hallmark pathology for Alzheimer disease. Recently developed positron emission tomography (PET) tracers, including [18F]-AV-1451, bind to tau in neurofibrillary tangles in the brain. So, could tau imaging become a diagnostic marker for Alzheimer disease and provide insights into the pathophysiology of the neurodegenerative disorder that destroys brain cells?