Chronic traumatic encephalopathy (CTE) is a progressive degenerative brain disease with symptoms that include memory loss, problems with impulse control, and depression that can lead to suicide. As the disease progresses, it can lead to dementia. Currently CTE can only be diagnosed postmortem where an over-accumulation of a protein called tau is observed. There is now a new experimental measure that makes it possible, for the first time, to measure tau protein in the living human brain using a novel positron emission tomography (PET) ligand, [F-18] AV-1451 (aka, [18F]-T807).