Permutation T-statistic maps MD in the mild TBI athlete and control subject 5 (B) are superimposed on the FA map. Red voxels represent a significant preseason to postseason/injury increase, while green voxels represent a decrease. Image Source: Magnetic Resonance Imaging, published online Oct. 6, 2011

Diffusion tensor MR scans revealed subtle injuries in the brains of high school football and hockey players who took routine hits to the head—even if they did not suffer a concussion, according to a study published online Nov. 12 in Magnetic Resonance Imaging. "The study is preliminary, but raises powerful questions about the consequences of the mildest head injury among youths with developing brains," said Jeffrey Bazarian, MD, MPH, associate professor of emergency medicine at University of Rochester Medical Center in Rochester, N.Y.

The diffusion tensor imaging (DTI) scan provides detailed information of axonal injury at the cellular level. Bazarian and colleagues applied a wild bootstrap method to analyze before-and-after images of the players' brains and detected the small but noteworthy changes in the white matter of the teenagers.

In an interview with Health Imaging News, Bazarian re-iterated the value of pre- and post-injury scans. Previous studies have compared post-injury images to a normative database. The problem with that approach, Bazarian said, is the tremendous variation in how individual brains perform and look on a microstructural level. Pre- and post-injury measures provide a more accurate assessment of the impact on an individual.

For the study, Bazarian and colleagues acquired pre- and post-season DTI scans of nine athletes and six controls.

Among the athletes, one was diagnosed with a concussion and eight suffered between 26 and 399 subconcussive head blows. The researchers measured fractional anisotrophy (FA) and mean diffusivity (MD) in each white matter voxel.

The analysis showed that white matter voxels in the concussion subject had significant pre- and post- scan FA (3.2 percent) and MD (3.44 percent) changes. While control subjects had minimal changes, the eight athletes who suffered multiple subconcussive head blows also had significant changes in the percentage of white matter and were closer to the concussed brain than to the normal brains in the control group. The changes in the intermediate group were more than three times higher than controls.

The imaging changes also strongly correlated with the number of head hits (self-reported in a diary), the symptoms experienced, and independent of cognitive test results, Bazarian said.

"Although this was a very small study, if confirmed it could have broad implications for youth sports," Bazarian said. "The challenge is to determine whether a critical number of head hits exists above which this type of brain injury appears, and then to get players and coaches to agree to limit play when an athlete approached that number."

According to Bazarian, if early data are confirmed, one implication might be a recommendation for a baseline, pre-season DTI for athletes involved in contact sports. The scan could be repeated if the athlete were hurt. “The model currently exists in concussion management,” said Bazarian. Athletes are administered pre and-season brain performance tests, which are then repeated if the athlete suffers a head injury.

 If the model is extended to imaging, radiologists could see a flood of requests for DTI studies, said Bazarian.