Repeated subconcussive head impacts compromise white matter integrity: A longitudinal DTI and NODDI study in collegiate football players

Repetitive subconcussive impacts are a growing concern in contact sports due to their potential cumulative effects on brain structure, despite the absence of overt clinical symptoms. In this study, we investigated the effect of repeated subconcussive impact (RSCI) exposure on white matter (WM) microstructure in collegiate football players using advanced neuroimaging techniques. Twenty-two male athletes (ages 18-22) from the Queen’s University Varsity Football Team were prospectively monitored over a single season. Participants were stratified into high-exposure (HE) and low-exposure (LE) groups based on impact frequency quantified with helmet-mounted accelerometers. MRI assessments, performed at pre-season, post-training camp, and post-season, included diffusion tensor imaging (DTI) metrics, including fractional anisotropy (FA) and mean diffusivity (MD), and neurite orientation dispersion and density imaging (NODDI) metrics, such as neurite density index (V _in ), orientation dispersion index (ODI), and isotropic volume fraction (V _iso ). Between-group comparisons revealed that HE athletes exhibited significantly lower FA and higher MD in the corticospinal tracts at pre-season, along with increased V _iso and reduced V _in and ODI in key association pathways compared to LE athletes. Longitudinal analyses demonstrated dynamic changes over the season, with significant alterations in diffusion metrics suggesting both acute injury responses and potential compensatory remodelling. These findings indicate that even in the absence of clinically diagnosed concussion, repetitive subconcussive impacts are associated with quantifiable changes in WM integrity. Our results underscore the need for improved monitoring and intervention strategies in contact sports to mitigate the risk of cumulative neural injury and to safeguard long-term brain health in athletes.