Brain imaging using radioactive dye can detect early evidence of Alzheimer's disease that may predict future cognitive decline among adults with mild or no cognitive impairment, according to a 36-month follow-up study. Alzheimer's disease -- which currently has no cure -- afflicts an estimated five million U.S. adults, and is the sixth-leading cause of death among adults, according to the Centers for Disease Control and Prevention. Prior studies have found that changes in the brain begin years, and possibly decades, before cognitive symptoms emerge. A biomarker that could accurately identify those at greatest risk for cognitive decline could help clinicians better evaluate and treat patients, while also accelerating the testing of drugs to treat the disease.