Effect of head impacts on diffusivity measures in a cohort of collegiate contact sport athletes

Abstract

Objective: To determine whether exposure to repetitive head impacts over a single season affects white matter diffusion measures in collegiate contact sport athletes.

Methods: A prospective cohort study at a Division I NCAA athletic program of 80 nonconcussed varsity football and ice hockey players who wore instrumented helmets that recorded the acceleration-time history of the head following impact, and 79 non-contact sport athletes. Assessment occurred preseason and shortly after the season with diffusion tensor imaging and neurocognitive measures.

Results: There was a significant (p = 0.011) athlete-group difference for mean diffusivity (MD) in the corpus callosum. Postseason fractional anisotropy (FA) differed (p = 0.001) in the amygdala (0.238 vs 0.233). Measures of head impact exposure correlated with white matter diffusivity measures in several brain regions, including the corpus callosum, amygdala, cerebellar white matter, hippocampus, and thalamus. The magnitude of change in corpus callosum MD postseason was associated with poorer performance on a measure of verbal learning and memory.

Conclusion: This study suggests a relationship between head impact exposure, white matter diffusion measures, and cognition over the course of a single season, even in the absence of diagnosed concussion, in a cohort of college athletes. Further work is needed to assess whether such effects are short term or persistent.

Figure 1. Accelerometer locations within the instrumented football and hockey helmets

Accelerometer locations (indicated by red circles) within the instrumented football and hockey helmets record acceleration at 6 locations on the head. Raw acceleration data for each recorded event are processed using an optimization algorithm to obtain linear and rotational acceleration about the head center of gravity.

Figure 2. Mean diffusivity values for the corpus callosum of noncontact and contact athletes preseason and postseason

Examination of the mean diffusivity values for the corpus callosum of noncontact and contact athletes preseason and postseason indicates a main effect of athlete group (p = 0.036).