Keith Johnson, M.D., leads the ACTC PET Imaging Unit, and is a Professor of Radiology at Harvard Medical School and Director of Molecular Neuroimaging in the Department of Radiology at Massachusetts General Hospital. Dr. Johnson has extensive experience in imaging research in neurodegenerative diseases, is a PI of the Harvard Aging Brain Study, and oversees the brain PET imaging program at MGH, which includes active research programs in imaging of amyloid-beta and PHF tau. Dr. Johnson leads the PET component of the A4 Study, as well as several other AD clinical trials. In addition, Dr. Johnson is a practicing Neurologist, Associate Physician in Neurology at Massachusetts General Hospital, and Associate Neurologist in the Division of Cognitive and Behavioral Neurology at Brigham and Women’s Hospital. He oversees the Clinical Brain PET Service at the MGH.