Former Chicago Bear Caesar Renti wonders if his health has yet to pay the price for his time on the football field.

"I'm always watching and seeing if there are some change. Yearly I see a doctor and do all the things I do to take care of myself. It is something that I worry about," said Renti.

The now vice president of Pastoral Services at Methodist Healthcare played college ball in the 80's and then went pro.

"You get a dinger, and you feel dazed. You don't really think about it. You just shake it off and go to the next play," said Renti.

But his old helmet gives an even better picture of how times have changed. Gashes and scratches on the tough plastic surface tell part of the story. Unfortunately, the rest of the story about chronic traumatic encephalopathy (CTE) can only be diagnosed after death.

But researchers are hoping a new study on former NFL players could help diagnose CTE while a person is still alive.

It's underway in three U.S. cities including Phoenix, home to former Minnesota Vikings tight end Steve Jordan; he signed up for the trial

"If we do nothing, then nothing gets done. That's kind of the basics of it," said Jordan.

Researchers will focus on the tau protein, which stabilizes nerve cells in the brain.

In CTE, the tau protein forms clumps that slowly spread through the brain, killing brain cells.

The tau protein plays a role in other neurodegenerative diseases, like Alzheimer’s, but is the hallmark of CTE and has a distinct pattern inside the brain.

Dr. Kendall Van Jensen, a brain disorder researcher in Phoenix, will lead the study.

"Currently there are no treatments for CTE, but there are drugs and things that people are using for Alzheimer's disease that may diminish the amount of tau, and so maybe those things could be used in CTE," says Dr. Van Jensen.

If she and her team can validate the tau protein as a biomarker and if the protein can be isolated in a blood sample, they say it might be possible to develop a simple blood test for diagnosing CTE.

Dallas isn't a test site, so Rentie has to watch from the sidelines. But he will use the power of prayer to keep his mind at its best for as long as possible.