omalu tells us he already knew fred mcneil had cte before he died. how? >> using a p.e.t. scan technology that he develop and partly owns. >> can you see the red areas is identifying the tao in his brain. >> if it is true, fred mcneil would be the first person in the world to have his cte diagnosed while still alive and then confirmed with an autopsy after his death. >> it explains a lot. because i am seeing a lot of that. the tao protein. >> but it is early. too early. just 14 nfl players, including hall of famer tony dorset have been examined using this technology. only mcneil's diagnosis has been confirmed. the question is, will the test be able to distinguish cte from other dementias? like alzheimer's? >> fred played in the first ten years of the league this is what, super bowl 50 is coming. i know there's a huge number of players and families. between that point and now. when fred first started playing that are going to be experiencing this. and it's important to have information for them to get help and support. >> even if none of it can erase the damage done to fred

sanjay gupta brings us the story of former minnesota vikings linebacker fred mcneil. >> the night before he passed he was watching monday night football with his ucla slippers under his bed. he was proud of the game and what he did. >> reporter: even until the end of his life, former minnesota vikings linebacker fred mcneil loved football. >> he was a monster. he was a monster, indeed, like all over the field. first one to the ball. >> reporter: despite how much of his life football later took from him. >> fred did everything he was -- you know, he played ball, went to law school, prepared for life after football. you know, we had the kids. you know, it was a good life. >> reporter: he played in two super bowls. was no ordinary player. his sons say no ordinary man. >> he was the best friend of ours. our first best friend. he was superman. >> and then it changed. >> reporter: it changed. cte, chronic traumatic encephalopathy entered their lives. at the time they had no idea what was happening. >> i remember we were playing basketball, me and him. we kind of got into an argument while play