Dr. Johnson is a Professor of Radiology and Neurology at the Harvard Medical School. He is also an Associate Radiologist and the Director of Molecular Neuroimaging in the Division of Nuclear Medicine and Molecular Imaging (Department of Radiology) at the Massachusetts General Hospital (MGH). Dr. Johnson also serves as an associate physician and staff neurologist in the Memory Disorders Unit at the Brigham and Women's Hospital as well as a Clinical Associate in Neurology at the MGH. Dr. Johnson is co-director of the Neuroimaging Program of the Massachusetts Alzheimer's Disease Research Center and its Dominantly Inherited Alzheimer Network (DIAN) research initiatives. He oversees the Clinical Brain Positron Emission Tomography (PET) Service at the MGH and also practices as a neurologist that specializes in neurodegenerative disorders. Dr. Johnson maintains an Internet teaching atlas of neuroimaging known as the Whole Brain Atlas.