Advanced white matter mapping in the subconcussive brain

Abstract

The topic of behavioral and structural deficits caused by concussions is an increasingly important 1 in the related research fields. With an incidence rate of 2.9 competition concussions per 1,000 athlete exposures (NCAA 2013) in collegiate football, the concussion risk to athletes is significant. However, even subconcussive blows, or blows that do not lead to a concussion diagnosis, appear to create health risks for athletes. These impacts appear to lead to significant neural changes, the severity of which may depend on the number of hits (McAllister et al., 2014). An anatomically informed, personalized-medicine tractography approach was used to determine which major white matter tracts showed the greatest degree of difference in white matter tensor measures between 17 Division I upperclassmen football players, 15 Division I upperclassman cross-country runners, and 9 socioeconomically-matched non-athlete controls. We determined the underlying microstructural white matter biomarkers, using a classic diffusion-tensor model (Pierpaoli and Basser, 1999) as well as Neurite Orientation Dispersion and Density Imaging (NODDI; Zhang et al., 2012), that predict differences across different white matter tracts in the groups of athletes. Results show widespread differences in white matter tissue properties in multiple tracts and among the 3 athletes groups, including decreased FA, increased ICVF, and OD in the football players vs the 2 control groups. These differences occurred more often in longer fiber tracts compared to shorter fiber tracts, suggesting a differential effect of head impacts based on the geometric properties of these tracts. We developed a fully automated processing pipeline for this study, available as open source code as well as open service at brainlife.io. These results support the hypothesis that multiple subconcussive blows can result in white matter structural changes, with differential effects based on the length of the fiber tract being investigated, that are detectable with diffusion MRI and tractography.