Multiple Imaging techniques were used . The diffusion tensor imaging (TDI) tests were normal as were conventional MRIs,and proton Magnetic resonance spectroscopy.
This is in contrast to two o studies in college and two studies in high school football players, none of whom experienced a concussion ,which showed decreased fractional anisotropy (FA) in certain white matter tracts and/or functional MR abnormality in the dorso-lateral frontal cortex.See here for Talavage's article regarding functional MR changes in high school players.
.Further one study (Bazarian, (see here for full text)) showed persistence of the TDI changes six months after the college football season ended. Here is the authors' summary:
" we have demonstrated that a single football season of RHIs [ repeated head impacts]without clinically evident concussion resulted in WM changes on DTI. These DTI changes correlated with multiple helmet impact measures and persisted despite 6 months of no-contact rest. This lack of WM recovery could potentially contribute to progressive, cumulative WM damage with subsequent RHI exposures. If this relationship is confirmed in longitudinal studies, efforts to limit the development of RHI-related WM changes by monitoring helmet impact measures, and further elucidation of modifiable factors that may influence WM recovery, could mitigate the long-term risk of CTE [chronic traumatic encephalopathy]."
Maugan's group did demonstrate decrease in cerebral blood flow ( CBF) in the concussed subjects which tended to return to normal over a few weeks.The authors' conclusion;
"Pediatric SRC [sports related concussion] is primarily a physiologic injury, affecting CBF significantly without evidence of measurable structural, metabolic neuronal or axonal injury."
What might account for the apparent differences in brain scan results in the college and high school players and the younger athletes studied by Maugan.
Possibly the younger players have a threshold for CNS symptoms given a head blow that is lower that the threshold for whatever tissue changes takes place that are manifest in DTI findings.
While it has been shown that some head impact levels ( as measured by accelerometers in helmets) in youth football may approach those demonstrated in high school and college they are on average lower.(see here for full text of article by Cobb, 2013 for detailed data of head impact forces ) Further the total number of impacts in a season of high school or college practice and game time may be considerably more than in a season of youth football and it may be the cumulative effects is what drives the DTI changes and whatever underlying tissue changes.Also as the years pile up, youth football and then high school and then college and then for a few professional football the total number of head impacts grows and it may be the long term cumulative effect of multiple sub-concussive plus the occasional concussive blow that leads to CTE in a minority of football participants.
Although parents may feel some reassurance from Maugan's research, there is little to be reassured about in the brain imaging studies of high school and college football players following a concussion free season as well as those studies on players with concussions.There is certainly little reassurance offered in this lengthy and detailed article from Rolling Stone.