Making Soccer Safer for the Brain: DTI-defined Exposure Thresholds for White Matter Injury Due to Soccer Heading
Authors: Molly Zimmerman PhD., Richard Lipton, Walter Stewart PhD., Edwin Gulko MD., Michael Lipton MD, PhD., Craig Branch PhD
PURPOSE: Heading the soccer ball may represent a form of repetitive mild trauma and may be associated with cognitive impairment. Because abnormally low white matter FA has been associated with cognitive impairment in patients with TBI, we hypothesized that a threshold level exists for heading exposure above which evidence of white matter injury is detectable.
METHOD AND MATERIALS: 32 amateur soccer players were recruited. Heading exposure was assessed with a standardized questionnaire and DTI was performed. Regions of Interest (ROI) were determined using a voxelwise t-test comparing FA between subjects with heading frequency ≥1,320/year with those <1,320/year. Based on our threshold hypothesis, we assumed an S or inverse S shape, nonlinear regression model based on Inverse Logit functions with four parameters: (1) associational direction and scale factor (β1), (2) baseline (β2) in FA measures for players with low frequency of headings, (3) departure position (β3) in heading-exposure scales from baseline and (4) slope (β4) of the curve. These parameters were estimated utilizing a stochastic search algorithm, simulated annealing (Kirkpatrick et al., 1983).
RESULTS: 5 ROIs were identified in temporooccipital white matter and one frontal white matter. Nonlinear regression reduced mean square error by 14% to 93% across all ROIs when compared to linear regression fits. All curve fitting detected an inverse S shape, indicating that FA decreases as exposure to heading increases. Estimates of departure position (β3) in heading-exposure scales were around 1500 in 4 temporooccipital ROIs 1000 in the 5th ROI. β3 was 1300 in the frontal ROI.
CONCLUSION: Greater heading frequency is associated with low FA. Exceeding a threshold for heading frequency (1000-1500) may result in brain abnormalities similar to those seen in TBI. Investigation of the relationship of the imaging abnormalities to cognitive performance is needed.
CLINICAL RELEVANCE/APPLICATION: Soccer heading is associated with DTI findings similar to TBI. The exposure threshold we identify suggests public health interventions to minimize excess exposure and, thereby, the adverse outcomes.
Presenation at 97th scientific assembly and annual meeting of radiological society 2011 11.27-12.02