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Repetitive subconcussive head impacts (RSHI) are believed to induce sub‐clinical brain injuries, potentially resulting in cumulative, long‐term brain alterations. This study explores patterns of longitudinal brain white matter changes across sports with RSHI‐exposure. A systematic literature search identified 22 datasets with longitudinal diffusion magnetic resonance imaging data. Four datasets were centrally pooled to perform uniform quality control and data preprocessing. A total of 131 non‐concussed active athletes (American football, rugby, ice hockey; mean age: 20.06 ± 2.06 years) with baseline and post‐season data were included. Nonparametric permutation inference (one‐sample t tests, one‐sided) was applied to analyze the difference maps of multiple diffusion parameters. The analyses revealed widespread lateralized patterns of sports‐season‐related increases and decreases in mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) across spatially distinct white matter regions. Increases were shown across one MD‐cluster (3195 voxels; mean change: 2.34%), one AD‐cluster (5740 voxels; mean change: 1.75%), and three RD‐clusters (817 total voxels; mean change: 3.11 to 4.70%). Decreases were shown across two MD‐clusters (1637 total voxels; mean change: −1.43 to −1.48%), two RD‐clusters (1240 total voxels; mean change: −1.92 to −1.93%), and one AD‐cluster (724 voxels; mean change: −1.28%). The resulting pattern implies the presence of strain‐induced injuries in central and brainstem regions, with comparatively milder physical exercise‐induced effects across frontal and superior regions of the left hemisphere, which need further investigation. This article highlights key considerations that need to be addressed in future work to enhance our understanding of the nature of observed white matter changes, improve the comparability of findings across studies, and promote data pooling initiatives to allow more detailed investigations (e.g., exploring sex‐ and sport‐specific effects). [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to use non‐invasive proton magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) to monitor changes in prefrontal white matter metabolite levels and tissue microstructure in female rugby players with and without concussion (ages 18–23, n = 64). Evaluations including clinical tests and 3 T MRI were performed at the beginning of a season (in‐season) and followed up at the end of the season (off‐season). Concussed athletes were additionally evaluated 24–72 hr (n = 14), three months (n = 11), and six months (n = 8) post‐concussion. Reduced glutamine at 24–72 hr and three months post‐concussion, and reduced glutamine/creatine at three months post‐concussion were observed. In non‐concussed athletes (n = 46) both glutamine and glutamine/creatine were lower in the off‐season compared to in‐season. Within the MRS voxel, an increase in fractional anisotropy (FA) and decrease in radial diffusivity (RD) were also observed in the non‐concussed athletes, and correlated with changes in glutamine and glutamine/creatine. Decreases in glutamine and glutamine/creatine suggest reduced oxidative metabolism. Changes in FA and RD may indicate neuroinflammation or re‐myelination. The observed changes did not correlate with clinical test scores suggesting these imaging metrics may be more sensitive to brain injury and could aid in assessing recovery of brain injury from concussion. [ABSTRACT FROM AUTHOR]