Ken Belson / New York Times News Service

Until now, chronic traumatic encephalopathy — a degenerative condition found among athletes and others who have suffered repeated concussions — could only be diagnosed post-mortem. But new research suggests that PET scans could be used to identify and treat CTE in living patients.

For years, researchers have had to use tissue obtained posthumously to diagnose chronic traumatic encephalopathy, or CTE, the degenerative brain disease that has bedeviled athletes, soldiers and others who have suffered repeated head hits and concussions.

But a study published in The American Journal of Geriatric Psychiatry this week suggests that PET scans could one day be used to diagnose the disease in living patients.

Last year, five retired NFL players who were 45 and older and suffered from mood swings, depression and cognitive problems were given PET, or positron emission tomography, scans. The authors of the study said those scans revealed tau protein deposits in their brains, a signature of CTE. While not definitive, the distribution of tau in the retired players was consistent with those found in the autopsies of players who had CTE.

But the size of the group was tiny; far larger and more in-depth studies will be needed before PET scans can be used to identify the tau pathology in patients who are not already experiencing cognitive problems.

It may take years and perhaps decades for doctors to determine how much of a role head hits and brain trauma have in patients with CTE, as opposed to one’s genetic predisposition and other health maladies like heart disease.

But the study is a first step toward the possibility of using PET scans to develop strategies to prevent the onset of the disease and provide treatment for those suffering from it.

“For the first time, it opens the possibility we can intervene and stop the inexorable decline” of those with CTE, said Dr. Julian Bailes, the co-director of the NorthShore Neurological Institute in Evanston, Ill., and originator of the research. “We are connecting more dots. This was the holy grail of CTE.”

The players in the study received intravenous injections of FDDNP, a chemical marker designed to bind to deposits of amyloid beta plaques and neurofibrillary tau tangles that are signs of Alzheimer’s disease. The FDDNP was then viewed on the PET scans, which were compared to those of healthy men of similar age, body mass, education and family history of dementia.

The tests were done at Semel Institute for Neuroscience and Human Behavior at UCLA. The five players had all suffered at least one concussion. The players consisted of a linebacker, a guard, a center, a defensive lineman and a quarterback.

“Early detection of tau proteins may help us to understand what is happening sooner in the brains of these injured athletes,” said Dr. Gary Small, a professor of psychiatry and biobehavioral sciences at the Semel Institute and the lead author of the study. “Our findings may also guide us in developing strategies and interventions to protect those with early symptoms, rather than try to repair damage once it becomes extensive.”

Neuroscientists have been encouraged by the growing number of researchers who have added to the knowledge of concussions and head trauma, which they claim has traditionally been underfinanced. And while they are encouraged by the possibility that PET scans may be used to diagnose CTE in living patients, they would need to see larger studies to be convinced of its efficacy.

Researchers, too, have been limited to studying patients who have effectively been self-selected: football players, other athletes and soldiers, all of whom have shown significant symptoms of CTE. Larger studies tracking patients over many years need to be done to determine how prevalent the disease is in the general population and whether certain people are predisposed to getting the disease.