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UNITED STATES  —  Several studies have established a link between concussions often sustained while playing football and chronic traumatic encephalopathy, or CTE.

Right now, though, doctors can only make that diagnosis after the sufferer is deceased. As NBC’s Bianca Castro reports, scientists are looking for a way to change this.

Caesar Rentie, a former Chicago Bear, wonders if his health has yet to pay the price for his time on the gridiron.

“I’m always watching and seeing if there are some changes,” he said. “Yearly I see a doctor and do all the things I do to take care of myself, but it is something that I worry about.”

The now-VP of Pastoral Services at Methodist Healthcare played college ball in the 80s before going pro.

“You get a dinger and you feel a little dazed. You don’t really think about it, you just shake it off and go to the next play,” he said.

But his old helmet gives an even better picture of how times have changes.

“Talking about, you know, the collisions and the injuries or if you just look at the gash, and this is pretty hard plastic.”

But now, a new study on former NFL players could help diagnose CTE while a person is still alive. It’s about to get underway in three U.S. cities, including Phoenix, home to former Minnesota Vikings tight end Steve Jordan, who signed up for the trial.

“If we do nothing, then nothing gets done. That’s kind of the basics of it,” he said.

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.

“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.”

Doctor Kendall Van Keuren-Jensen, a brain disorder researcher in Phoenix, will lead the study. If she and her team can validate the tau protein as a bio-marker 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.

CTE has been identified in people as young as 17 years old. Athletes with longer careers in contact sports like football and boxing are at higher risk of developing CTE.