Table 5.

Summary of findings in dMRI, cognitive and behavioral evaluations, and neurological evaluations

Article	Diffusion imaging	Cognitive and behavioral evaluation	Neurological evaluation
Bahrami et al., 2016	Significant linear association between RWECP and decreased FA of left IFOF and terminal of right SLF from pre- to post-season No statistically significant association found between total RWECP and FA changes in forceps minor and major of the corpus callosum and the inferior longitudinal fasciculus	No results reported	No results reported
Bazarian et al., 2014	Significant positive correlation between percentage of voxels with FA decreasing from pre- to post-season and several helmet impact measures derived from HITS; significantly greater changes in FA and MD between pre- and post-season, and between pre- and six months post-season in contact sport athletes compared to controls; association between persistence of DTI changes between pre- and six months post-season and changes in serum ApoA1 and S100B antibodies	ImPACT; no correlations between changes in DTI between pre- and post-season; significant correlations between changes in DTI between pre- and six months post-season with both improved and worsened cognitive performance	BESS, Wii Balance Board; no correlations of balance and changes in DTI
Brett et al., 2021	Significant association between years of contact sport exposure and lower RD as well as higher FA and RK in several brain regions	No results reported	No results reported
Champagne et al., 2019	Significant decrease in FA between pre-season and post-training camp as well as pre- and one month post-season in the CC (genu and splenium) in athletes from the high exposure group; no statistically significant differences in the midsection of the CC	No results reported	No results reported
Churchill et al., 2017	Significantly higher FA and lower MD in several WM clusters in collision sport athletes, compared to contact and non-contact sport athletes at pre-season	SCAT-3; no group differences	SCAT-3; no group differences
de Souza et al., 2020	Significant association between neck strength and higher FA as well as lower RD in several WM regions at pre-season in soccer players; no significant association between MD or AD and neck strength	No results reported	No results reported
Holcomb et al., 2021	Significant positive linear relationship between percent change in FA from pre- to post-season and CMPS1 × SR in several brain regions; significant group differences in percent change in FA from pre- to post-season between high-strain football athletes and controls but not low-strain football athletes and controls	No results reported	No results reported
Kawata et al., 2020	Significant correlation between serum tau levels and elevated MD as well as lower NDI in several WM tracts; significant negative association between NfL and ODI in longitudinal fasciculus; no association between Nfl and DTI measures	No results reported	No results reported
Koerte et al., 2012a	Significantly higher RD in several WM regions, and higher AD in the CC in soccer players compared to control athletes at pre-season; no statistically significant group differences for FA and MD	No results reported	No results reported
Koerte et al., 2012b	Significant increase in trace, RD, and AD from pre- to post-season in several brain regions in contact sport athletes; no significant differences between pre- and post-season for FA	No results reported	No results reported
Kuzminski et al., 2018	Significant association between decrease of FA in the fornix-stria terminalis and cingulum-hippocampus regions (ROI analysis) from pre- to post-season and impact frequency as examined by HITS	CNS Vital Sign Assessment; neuropsychological assessment of aggression, anger and hostility, the Buss-Perry Aggression Questionnaire, anxiety, the State-Trait Anxiety Inventory, impulsivity, and the Barratt Impulsiveness Scale; significant correlation of decrease of FA in the fornix-stria terminalis region and decline in visual memory from pre- to post-season	No results reported
Lefebvre et al., 2021	Significantly higher FA in non-contact sport athletes compared to contact sport athletes in the CC and the corticospinal tract during off-season; significantly higher FA in non-contact sport athletes compared to non-athlete controls in the anterior regions of the CC and the corticospinal tracts; no group differences between contact sport and non-athlete control groups	D2 Test of Attention, Color Trails A and B, Symbol Digit Modality Test, D-KEFS' Color Word Interference Test, Rey Complex Figure Test; no group differences in cognitive performance; no correlations of cognitive performance and DTI	No results reported
Lipton et al., 2013	Significant association between number of RHI and lower FA during off-season in the temporo-occipital WM with a threshold that varied according to location (885–1550 headings per year)	Cogstate; significant association between lower FA and poorer memory scores with a threshold of 1800 headings per year; other cognitive measures were not significantly associated with headings per year	No results reported
Mayinger et al., 2018	Significant increase in trace in the brainstem and left temporal lobe as well as increase of FA in the left parietal lobe between pre- and post-season; remission to the initial status after six months of rest	ImPACT; no significant group mean declines in cognitive performance at any time point	No results reported
Saghafi et al., 2018	Based on changes in FA maps between pre- and post-season, a neural network differentiated football players with high and low RWE as derived from accelerometers with an AUROC of 85.7%	No results reported	No results reported
Slobounov et al., 2017	No longitudinal changes in DTI investigating whole brain WM divided into 48 ROIs	No results reported	No results reported
Strauss et al., 2021	Significantly greater expression of low RD, and greater expression of high FA in various brain regions in athletes with no or lower number of RHI compared to non-athlete controls	Cogstate; significantly better attention, processing speed, and memory in athletes with no or lower number of headers compared to non-athlete controls; no difference in cognitive performance between soccer players with a higher number of headers and non-athlete controls; several significant associations between volume of low and high DTI measures and cognitive performance	No results reported

AD Axial Diffusivity, AUROC Area Under the Receiver Operating Curve, BESS Balance Error Scoring System, CC Corpus Callosum, CMPS1 × SR Cumulative Maximum Principal Strain one Times Strain Rate, DKI Diffusion Kurtosis Imaging, DTI Diffusion Tensor Imaging, FA Fractional Anisotropy, HITS Head Impact Telemetry System, IFOF Inferior Fronto-occipital Fasciculus, ImPACT Immediate Post-Concussion Assessment and Cognitive Testing, MD Mean Diffusivity, NDI Neurite Density Index, NfL Neurofilament Light, ODI Orientation Dispersion Index, QSM Quantitative Susceptibility Mapping, RD Radial Diffusivity, RK Radial Kurtosis, RWE Risk of Concussion-weighted Cumulative Exposure (cumulative exposure to RHI assessed based on computed probability for a head impact based on each accelerative event), RWE_CP combined probability risk-weighted cumulative exposure (RWE based on combined probability of linear and rotational accelerations), SCAT-3 Sport Concussion Assessment Tool 3, SLF Superior Longitudinal Fasciculus, WM White Matter