Table 4.
Summary of sample characteristics, study design, exposure to concussions and RHI, and dMRI pipeline for each included article
| Article |
Participants N, (Sex, Mean Age [SD]) |
Contact Sport | Control Sport | Study Design | Concussions | Assessment of RHI | Diffusion MRI Sequence | Analysis Technique |
|---|---|---|---|---|---|---|---|---|
| Bahrami et al., 2016 | 25 contact sport athletes (male, 11.72 [1.05] years) | American football | No controls | Longitudinal with 2 time points: Pre-season, post-season | Individuals with a history of concussion were excluded | Accelerometers |
3 T MRI; Voxel size: 2.2 × 2.2 × 3 mm3; 15 diffusion directions with b = 1000 s/mm2, and 15 with b = 2000 s/mm2 |
Tractography |
| Bazarian et al., 2014 | 10 contact sport athletes (male, 20.4 [1.08] years); 5 non-athlete controls (male, 20.6 [1.14] years) | American football | Non-athlete controls | Longitudinal with 3 time points: Pre-season, post-season, 6 months of no-contact sport rest | No athlete sustained a concussion during study participation; 1 athlete had sustained a concussion > 2 weeks before study participation and was included; concussion history prior to study participation not considered in analysis | Accelerometers |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 60 diffusion directions with b = 700 s/mm2 |
Voxel-wise analysis |
| Brett et al., 2021 | 75 American football players and 46 non-contact sport athletes (sex not specified, 18.52 [1.74] years) | American football | Non-contact sport (not further specified); were analyzed as one group together with the American football players | Longitudinal with 5 time points: baseline, after < 48 h, 8 days, 15 days, 45 days | Athletes were stratified into groups with 0, 1, and 2 + previous concussions that were analyzed | Self-report of years of contact sport exposure |
3 T MRI; Voxel size: 3 × 3 × 3 mm3; 30 diffusion directions with b = 1000 s/mm2, and 30 with b = 2000 s/mm2 |
TBSS |
| Champagne et al., 2019 | 33 contact sport athletes (male, 20.3 [1.4] years) | American football | No controls | Longitudinal study with 3 time points: Pre-season, post-training camp, post-season recovery after 1 month break | Individuals with concussions during the season were excluded; athletes had sustained 0–4 concussions up to 9 years before study participation; concussion history prior to study participation not considered in analysis | Accelerometers |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 30 diffusion directions with b = 1000 s/mm2 |
ROI-based analysis |
| Churchill et al., 2017 | 22 contact sport athletes (8 male, 14 female, 20.3 [1.5] years); 23 collision sport athletes (14 male, 9 female, 21.3 [1.9] years); 20 non-contact sport athletes (10 male, 10 female, 20.0 [1.7] years) |
Contact sport: Soccer, field hockey, basketball, lacrosse, water polo; Collision sport: Rugby, ice hockey, lacrosse, American football |
Volleyball | Cross-sectional at pre-season | Athletes that had sustained a concussion within 6 months prior to study participation were excluded; in athletes with a history of concussion before that, the median time since their last concussion was 2 years (range: 9 months to 8 years); athletes with previous concussions analyzed as a separate group | No quantification of RHI; exposed group |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 30 diffusion directions with b = 700 s/mm2 |
Voxel-wise analysis |
| de Souza et al., 2020 | 17 contact sport athletes (8 male, 9 female, 19.0 [1.4] years); 39 non-contact sport athletes (20 male, 19 female, 19.3 [1.0] years) | Soccer | Non-contact sport: Tennis, basketball, volleyball, running, cross country | Cross-sectional within a month of the season start | Individuals with a history of concussion were excluded | No quantification of RHI; exposed group |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 64 diffusion directions with b = 1100 s/mm2 |
TBSS |
| Holcomb et al., 2021 | 102 contact sport athletes (male, 11.7 [1.2] years); 16 non-contact sport athletes (male, 11.0 [1.8] years) | American football | Non-contact sport: Baseball, basketball, swimming, tennis, soccer | Longitudinal with pre-season and post-season assessments of up to 3 seasons | Individuals that sustained a concussion during and within 9 months prior to study participation were excluded; 6 football players had sustained a concussion 9 to 48 months before study participation; concussion history was included as a covariate | Accelerometers |
3 T MRI; Protocol 1: Voxel size: 2.2 × 2.2 × 3 mm3; Protocol 2: Voxel size: 2 × 2 × 2 mm3; Both protocols: 15 diffusion directions with b = 2000 s/mm2, and 15 with b = 1000 s/mm2 |
Voxel-wise analysis |
| Kawata et al., 2020 | 17 contact sport athletes (male, 16–17 years, no mean age or SD specified) | American football | No controls | Cross-sectional at pre-season | Individuals that had sustained a concussion within 12 months prior to study participation were excluded; number of concussions before that was included as a covariate | No quantification of RHI; exposed group |
3 T MRI; 6 diffusion directions with b = 500 s/mm2, 15 with b = 1000 s/mm2, 15 with b = 2000s/mm2, and 60 with b = 3000 s/mm2 |
TBSS |
| Koerte et al., 2012a | 12 contact sport athletes (male, 19.7 [1.6] years); 11 non-contact sport athletes (male, 21.4 [2.8] years) | Soccer | Swimming | Cross-sectional at pre-season | Individuals with a history of concussion were excluded | No quantification of RHI; exposed group |
3 T MRI; 64 directions |
TBSS |
| Koerte et al., 2012b | 25 contact sport athletes (male, 22.24 [1.59] years) | Ice hockey | No controls | Longitudinal with 2 time points: Pre-season, post-season | 14 athletes had sustained at least 1 concussion before study participation; 5 athletes sustained a concussion during the season and were analyzed as a separate group | No quantification of RHI; exposed group |
3 T MRI; Voxel size: 2.2 × 2.2 × 2.2mm3; 60 diffusion directions with 700 s/mm2 |
TBSS |
| Kuzminski et al., 2018 | 17 contact sport athletes (male, 16 [0.73] years) | American football | No controls | Longitudinal with 2 time points: Pre-season, post-season | 1 athlete sustained a concussion during the study and was analyzed separately; 6 athletes reported at least one concussion prior to study participation; concussion history prior to study participation not considered in analysis | Accelerometers |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 31 diffusion directions with b = 1000 s/mm2 |
TBSS |
| Lefebvre et al., 2021 | 23 contact sport athletes (11 male, 12 female, 22.7 years, no SD specified); 24 non-contact sport athletes (12 male, 12 female, 22.7 years, no SD specified); 24 non-athlete controls (12 male, 12 female, 22.7 years, no SD specified) | Rugby, soccer | Athlete controls (swimming); Non-athlete controls | Cross-sectional during off-season | Individuals with a history of concussion were excluded | No quantification of RHI; exposed group |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 64 diffusion directions with b = 1000 s/mm2 |
Tractography |
| Lipton et al., 2013 | 37 contact sport athletes (28 males, 9 females, 30.9 years, no SD specified, range 21–44 years) | Soccer | No controls | Cross-sectional around off season | Lifetime number of concussions was included as a covariate | Self-report questionnaire on prior heading exposure |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 32 diffusion directions with b = 800 s/mm2 |
Voxel-wise analysis |
| Mayinger et al., 2018 | 15 contact sport athletes (male, 20.0 [1.0] years); 5 non-athlete controls (male, 20.93 [1.1] years) | American football | Non-athlete controls | Longitudinal with 3 time points: Pre-season, post-season, 6 months of no-contact sport rest | No athlete sustained a concussion during study participation; 3 athletes had sustained a concussion > 1 year prior to study participation; concussion history not considered in statistical analysis | No quantification of RHI; exposed group |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 60 diffusion directions with b = 1200 s/mm2 |
TBSS |
| Saghafi et al., 2018 | 122 contact sport athletes (sex not specified, 9–18 years) | American football | No controls | Longitudinal with 2 time points: Pre-season, post-season | Individuals with a history of concussion were excluded | Accelerometers |
3 T MRI; Voxel size: 2.2 × 2.2 × 2.2 mm3; 15 diffusion directions with b = 1000 s/mm2 |
FA maps, deep learning |
| Slobounov et al., 2017 | 18 contact sport athletes (male, 21.6 [1.28] years) | American football | No controls | Longitudinal with 2 time points: Pre-season, post-season | No athlete sustained a concussion during or within 9 months prior study participation; 6 athletes had sustained one previous concussion, 2 had two previous concussions; concussion history not considered in statistical analysis | Accelerometers |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 30 diffusion directions with b = 1000 s/mm2, and 30 with b = 2000s/mm2 |
TBSS |
| Strauss et al., 2021 | 246 contact sport athletes (174 male, 72 female, 25.48 [7.2] years); 72 non-collision sport athletes (30 male, 42 female, 22.76 [5.2] years): 116 non-athlete controls (63 male, 53 female, 28.96 [11.1] years) | Soccer | Non-contact sport: Baseball, swimming, tennis, running/track, gymnastics, rowing/crew, cycling, dancing, figure skating; non-athlete controls | Longitudinal with 2 time points: Baseline, and after 2 years | Lifetime number of concussions was quantified, and previous concussion history (yes/no) included as a covariate | Self-report questionnaire on prior heading exposure |
3 T MRI; Voxel size: 2 × 2 × 2 mm3; 32 diffusion directions with b = 800 s/mm2 |
Voxel-wise analysis |
3T 3Tesla, MRI Magnetic Resonance Imaging, RHI Repetitive Head Impacts, ROI Region of Interest, SD Standard Deviation, TBSS Tract-Based Spatial Statistics