The imaging found suspicious chemical changes in the former athletes' brains. They'd suffered multiple hits to the head during play and showed behavior symptoms indicating possible brain damage. The chemical changes were not found in five healthy study participants.
The results from this noninvasive "virtual biopsy" technique suggest that the athletes had chronic traumatic encephalopathy, the study authors said.
The disease is a suspected cause of "punch-drunk" symptoms, memory lapses and behavior changes in NFL players and others who have had repeated concussions.
The issue has gained scrutiny since autopsies found brain degeneration in a handful of former NFL players who died young. Concerns about the dangers of repeated concussions have led to congressional hearings, policy recommendations from doctor groups and restrictions on how soon professional and student athletes can return to play after being hit in the head.
The study is being presented Wednesday at the Radiological Society of North America's annual meeting in Chicago.
Researchers used a specialized type of MRI scan that measures chemicals. Altered levels of certain chemicals in brain tissue signify damage, said lead author Alexander Lin of Harvard University's Brigham and Women's Hospital.
"It tells us that these guys with repetitive head injury do have something that is biochemically abnormal," Lin said.
There were no "before and after" images of the athletes' brains, and the research doesn't prove that repeated head blows caused the damage. But it provides intriguing evidence that needs to be confirmed in additional research, said Dr. Jeffrey Kutcher, chief director of a neurological sports injury program at the University of Michigan.
"It's an important step," said Kutcher, who was not involved in the study.
Currently, chronic traumatic encephalopathy or CTE is diagnosed by pathologists inspecting brain tissue during autopsies.
There is no treatment for the condition. But if it turns out that chemical changes in the brain are a true symptom, then scientists could test drugs that would affect those chemicals to see if that slows or prevents symptoms.
"The only way we can get to the point of studying potential treatments is to be able to diagnose it during life," said Robert Stern, a study co-author and a director of the Boston University center studying CTE. Several former NFL players have agreed to donate their brains after death for the research.
If the new imaging proves to be an accurate detection method, then the technique could potentially help determine whether athletes with head injuries can return to sports or should stop playing for good, said Dr. Stefan Bluml, director of an imaging technology lab at Childrens Hospital Los Angeles.