PurposeTo quantify the effects of an externally worn collar device for mitigating the influence of repetitive head impacts on alterations to diffusion tensor imaging (DTI) metrics of white matter.MethodsFifteen female high-school soccer athletes (age: 14.00–16.98 yrs) completed pre- and post-season DTI over two consecutive years, including measures of diffusivity, changes in which may be associated with brain dysfunction. The collar was worn during year 1 (Yr1) but not during year 2 (Yr2). Athlete exposures (AEs) and head impact exposure were recorded over the competitive seasons.ResultsThere were no significant differences in AEs or head impact exposures between Yr1 and Yr2 (P > 0.05). In Yr2, there was significant pre- to post-season mean diffusivity and/or axial diffusivity reduction in multiple WM regions (corrected P < 0.05). Pre- to post-season mean diffusivity, axial diffusivity, and radial diffusivity decreases were 3.04% ± 2.53%, 2.97% ± 2.19%, and 3.37% ± 3.34%, respectively, significantly greater than pre- to post-season changes in Yr1 (mean diffusivity: − 0.31% ± 1.78%, P = 0.0014; axial diffusivity: − 0.02% ± 2.25%, P = 0.0014; radial diffusivity: − 0.63% ± 2.10%, P = 0.0030).ConclusionsMild bilateral compression to athletes’ internal jugular vein through collar application may have increased intracranial blood volume and spatially redistributed head-impact-derived brain energy absorption. However, future research is needed to elucidate the potential clinical significance of WM changes of various degrees.Clinical trails registrationNCT03014492.