ENIGMA's simple seven: Recommendations to enhance the reproducibility of resting-state fMRI in traumatic brain injury

Resting state functional magnetic resonance imaging (rsfMRI) provides researchers and clinicians with a powerful tool to examine functional connectivity across large-scale brain networks, with ever-increasing applications to the study of neurological disorders, such as traumatic brain injury (TBI). While rsfMRI holds unparalleled promise in systems neurosciences, its acquisition and analytical methodology across research groups is variable, resulting in a literature that is challenging to integrate and interpret. The focus of this narrative review is to address the primary methodological issues including investigator decision points in the application of rsfMRI to study the consequences of TBI. As part of the ENIGMA Brain Injury working group, we have collaborated to identify a minimum set of recommendations that are designed to produce results that are reliable, harmonizable, and reproducible for the TBI imaging research community. Part one of this review provides the results of a literature search of current rsfMRI studies of TBI, highlighting key design considerations and data processing pipelines. Part two outlines seven data acquisition, processing, and analysis recommendations with the goal of maximizing study reliability and between-site comparability, while preserving investigator autonomy. Part three summarizes new directions and opportunities for future rsfMRI studies in TBI patients. The goal is to galvanize the TBI community to gain consensus for a set of rigorous and reproducible methods, and to increase analytical transparency and data sharing to address the reproducibility crisis in the field.

Mechanical characterization of athletic helmet shells

Our purpose was to compare the mechanical properties of the protective outer shells of various athletic helmets in their final, fully manufactured form. Sections were taken from 3 different helmet shells (Bauer RE-AKT hockey helmet, Cascade R lacrosse helmet, and Riddell Speedflex football helmet) at 4 different locations (front, side, top, and rear) for a total of 12 test specimens. The 4 specimens from each helmet shell were potted together in epoxy resin moulds and mechanically polished. The hardness, elastic modulus and phase angle were measured using dynamic nanoindentation performed at 100 Hz with an oscillation amplitude of 1 nm (rms). Repeated ANOVA analysis was used to compare each of the dependent variables for each of the 3 helmets across the 4 different locations. The interaction between helmet type and location was significant for hardness (F6,63 = 2.84, P = 0.032, Pη2 = 0.21), elastic modulus (F6,63 = 6.412, P < 0.001, Pη2 = 0.38), and phase angle (F6,63 = 7.65, P < 0.001, Pη2 = 0.42). Polycarbonate has a higher ability to dissipate mechanical energy making it the recommended superior choice for helmet shells. In addition, the results lead us to speculate that manufacturing causes changes in the molecular weight or the distribution of fillers across locations for polyethylene but not for polycarbonate since mechanical properties are fairly uniform over the surface of football helmets, at least within a given helmet.

Preinjury Measures Do Not Predict Future Concussion Among Collegiate Student-Athletes: Findings From the CARE Consortium

ABSTRACT

This prospective cohort study aimed to determine whether preinjury characteristics and performance on baseline concussion assessments predicted future concussions among collegiate student-athletes. Participant cases (concussed = 2529; control = 30,905) completed preinjury: demographic forms (sport, concussion history, sex), Immediate Post-Concussion Assessment and Cognitive Test, Balance Error Scoring System, Sport Concussion Assessment Tool symptom checklist, Standardized Assessment of Concussion, Brief Symptom Inventory-18 item, Wechsler Test of Adult Reading, and Brief Sensation Seeking Scale. We used machine-learning logistic regressions with area under the curve, sensitivity, and positive predictive values statistics for univariable and multivariable analyses. Primary sport was determined to be the strongest univariable predictor (area under the curve = 64.3% ± 1.4, sensitivity = 1.1% ± 1.4, positive predictive value = 4.9% ± 6.5). The all-predictor multivariable model was the strongest (area under the curve = 68.3% ± 1.6, sensitivity = 20.7% ± 2.7, positive predictive value = 16.5% ± 2.0). Despite a robust sample size and novel analytical approaches, accurate concussion prediction was not achieved regardless of modeling complexity. The strongest positive predictive value (16.5%) indicated only 17 of every 100 individuals flagged would experience a concussion. These findings suggest preinjury characteristics or baseline assessments have negligible utility for predicting subsequent concussion. Researchers, healthcare providers, and sporting organizations therefore should not use preinjury characteristics or baseline assessments for future concussion risk identification at this time.

Current and Emerging Techniques in Neuroimaging of Sport-Related Concussion

SUMMARY

Sport-related concussion (SRC) affects an estimated 1.6 to 3.8 million Americans each year. Sport-related concussion results from biomechanical forces to the head or neck that lead to a broad range of neurologic symptoms and impaired cognitive function. Although most individuals recover within weeks, some develop chronic symptoms. The heterogeneity of both the clinical presentation and the underlying brain injury profile make SRC a challenging condition. Adding to this challenge, there is also a lack of objective and reliable biomarkers to support diagnosis, to inform clinical decision making, and to monitor recovery after SRC. In this review, the authors provide an overview of advanced neuroimaging techniques that provide the sensitivity needed to capture subtle changes in brain structure, metabolism, function, and perfusion after SRC. This is followed by a discussion of emerging neuroimaging techniques, as well as current efforts of international research consortia committed to the study of SRC. Finally, the authors emphasize the need for advanced multimodal neuroimaging to develop objective biomarkers that will inform targeted treatment strategies after SRC.

School-level determinants of incidence of sports-related concussion: Findings from the CARE Consortium

OBJECTIVE

Epidemiologic research on sports-related concussion (SRC) has focused on individual risk factors, with limited research on institutional risk factors and variability in concussion rates.

METHODS

This study used data from 53,822 athletes-seasons collected at 30 United States sites (26 civilian institutions and 4 military service academies), from 2014/15 to 2018/19 academic years, by the Concussion Assessment, Research, and Education Consortium. School-level risk factors included competitive division (DI, DII, DIII), school type (military/civilian) and a Sport Risk Index (SRI; Low, Medium, High). For comparability between civilian institutions and military academies, only NCAA athletes and concussions in sports games and practices were included. Random intercepts log-binomial regression was used to estimate Risk Ratios (RRs) and model variability in SRC risk.

RESULTS

A total of 2,503 SRCs were observed during the study period, including 829 competition SRCs (33%) and 1,674 practice SRCs (67%). Most variability in SRC risk was at the level of athlete or team (within-school), rather than at the school-level. Specifically, across the three SRC outcomes (all [competition and practice combined], competition-only, and practice-only), within-school variability was 5 to 7 times greater than between-school variability. Three school-level risk factors (Division, School Type, and SRI) accounted for over one-third (36%) of between-school variability. SRI was the strongest school-level predictor of SRC risk (RR = 5.7; 95%CI: 4.2, 7.6 for High vs. Low). SRC risk was higher for Division I compared to Divisions II/III (RR = 1.6; 95%CI: 0.9, 2.9 for DI vs. DIII), and military academies had a moderately elevated risk of SRC (RR = 1.4; 95%CI: 0.7, 2.7).

CONCLUSION

A large portion of the apparent variability between schools was attributable to structural factors (sport risk and competitive level), suggesting that there were minimal systemic differences in concussion identification between schools. While most variability is within-school, understanding school-level determinants of concussion risk may still be important in providing the implementation science context for individual-level interventions.

Relationships between aggression, sensation seeking, brain stiffness, and head impact exposure: Implications for head impact prevention in ice hockey

OBJECTIVES

The objectives of this study were to (1) examine the relationship between the number of head impacts sustained in a season of men's collegiate club ice hockey and behavioral traits of aggression and sensation seeking, and (2) explore the neural correlates of these behaviors using neuroimaging.

DESIGN

Retrospective cohort study.

METHODS

Participants (n = 18) completed baseline surveys to quantify self-reported aggression and sensation-seeking tendencies. Aggression related to playing style was quantified through penalty minutes accrued during a season. Participants wore head impact sensors throughout a season to quantify the number of head impacts sustained. Participants (n = 15) also completed baseline anatomical and magnetic elastography neuroimaging scans to measure brain volumetric and viscoelastic properties. Pearson correlation analyses were performed to examine relationships between (1) impacts, aggression, and sensation seeking, and (2) impacts, aggression, and sensation seeking and brain volume, stiffness, and damping ratio, as an exploratory analysis.

RESULTS

Number of head impacts sustained was significantly related to the number of penalty minutes accrued, normalized to number of games played (r = .62, p < .01). Our secondary, exploratory analysis revealed that number of impacts, sensation seeking, and aggression were related to stiffness or damping ratio of the thalamus, amygdala, hippocampus, and frontal cortex, but not volume.

CONCLUSIONS

A more aggressive playing style was related to an increased number of head impacts sustained, which may provide evidence for future studies of head impact prevention. Further, magnetic resonance elastography may aid to monitor behavior or head impact exposure. Researchers should continue to examine this relationship and consider targeting behavioral modification programs of aggression to decrease head impact exposure in ice hockey.

Altered Brain Functional Connectivity in the Frontoparietal Network following an Ice Hockey Season

AbstractSustaining sports-related head impacts has been reported to result in neurological changes that potentially lead to later-life neurological disease. Advanced neuroimaging techniques have been used to detect subtle neurological effects resulting from head impacts, even after a single competitive season. The current study used resting-state functional magnetic resonance imaging to assess changes in functional connectivity of the frontoparietal network, a brain network responsible for executive functioning, in collegiate club ice hockey players over one season. Each player was scanned before and after the season and wore accelerometers to measure head impacts at practices and home games throughout the season. We examined pre- to post-season differences in connectivity within the frontoparietal and default mode networks, as well as the relationship between the total number of head impacts sustained and changes in connectivity. We found a significant interaction between network region of interest and time point (p = 0.016), in which connectivity between the left and right posterior parietal cortex seed regions increased over the season (p < 0.01). Number of impacts had a significant effect on frontoparietal network connectivity, such that more impacts were related to greater connectivity differences over the season (p = 0.042). Overall, functional connectivity increased in ice hockey athletes over a season between regions involved in executive functioning, and sensory integration, in particular. Furthermore, those who sustained more impacts had the greatest changes in connectivity. Consistent with prior findings in resting-state sports-related head impact literature, these findings have been suggested to represent brain injury.

Evaluating Adult Decision-Making Modifiers in Support of Youth Contact-Sport Participation

CONTEXT

Nearly 44 million youth participate in organized youth sports programs in the United States each year. However, approximately 25% of parents have considered removing their children from sports due to the fear of concussion.

OBJECTIVE

To determine which adult decision-making modifiers (eg, gender, educational attainment, career type) influenced support for youth contact-sports participation.

DESIGN

Cross-sectional study.

SETTING

Midwestern university and medical center.

PATIENTS OR OTHER PARTICIPANTS

Convenience sample of staff and faculty (N = 5761; 73.9% female) from 2017 to 2018.

MAIN OUTCOME MEASURE(S)

Support for youth contact-sports participation using multivariate binary logistic regression to calculate odds ratios and 95% CIs.

RESULTS

The sample was split between adults with children (AWCs; n = 3465, age = 45.39 ± 13.27 years, 76.72% female) and adults without children (AWOCs; n = 2296, age = 30.84 ± 9.01 years, 70.26% female). Among AWCs, those who obtained a bachelor's degree or higher were more likely to support contact-sports participation. Females were more inclined to allow all contact sports, specifically football (odds ratio [OR] = 2.22; 95% CI = 1.64, 3.01) and ice hockey (OR = 1.98; 95% CI = 1.42, 2.78). Overall, previous adult sport participation, increasing number of children, and child gender were significant modifying variables in greater support of youth contact-sports participation among AWCs (P < .001). Among AWOCs, previous sport participation in football (OR = 3.27; 95% CI = 2.14, 4.87), ice hockey (OR = 4.26; 95% CI = 2.23, 8.17), or soccer (OR = 2.29; 95% CI = 1.48, 3.54) increased the likelihood of an adult supporting contact-sports participation. Lastly, all adults were less inclined to support a daughter participating in any contact sport than a son.

CONCLUSIONS

These results reveal adult- and child-specific variables that may influence youth contact-sports participation. These decisions may be developed through the lens of certain gender role beliefs and may lead adults to perceive certain sports as more appropriate for sons than daughters.

Evaluation of Musculoskeletal Re-Injury Occurrence in Previously Concussed National Football League Athletes

Introduction

Increased risk of musculoskeletal (MSK) injury post-concussion has been reported in collegiate athletes, yet it is unknown if professional football athletes are at the same risk of secondary injury. The objective of this study was to determine if the risk of MSK injury in National Football League (NFL) athletes increases after concussion.

Methods

NFL injury reports from 2013 to 2017 were collected from public websites. Concussed athletes (n=91) were equally matched to a non-injured control and an athlete with an incident of musculoskeletal (MSK) injury.

Results

Following their return to sport, concussed athletes were 2.35 times more likely to have a subsequent MSK injury relative to non-injured controls (95% CI: 2.35 [1.25, 4.44], P = 0.01), but were no more likely than athletes with an incident MSK injury (P = 0.55). Likewise, athletes with an incident MSK injury were no more likely to have a subsequent MSK injury than controls (P = 0.08).

Discussion

Increased odds of MSK injury in the 12-week period following a concussion in professional football athletes warrants future research on the acute effects of concussion and the relationship to MSK injury risk.

Sex differences in mechanisms of head impacts in collegiate soccer athletes

BACKGROUND

There has been growing interest in head impacts related to sports participation due to potential long- and short-term consequences of head injuries. Our purpose was to compare head impact magnitude and frequency between men's and women's intercollegiate soccer players based on head impact mechanism.

METHODS

28 collegiate soccer players (16 women: age = 19.94 (1.06) years, height = 163.75 (5.15) cm, mass = 61.21 (5.09) kg; 12 men: age = 20.25 (1.14) years, height = 180.34 (6.03) cm, mass = 74.09 (9.32) kg) wore xPatch (X2 Biosystems, Seattle, WA) head impact sensors. Each practice and game was video recorded in order to confirm head impacts. The independent variable was impact mechanism (head to head, head to body (other than head), head to ground, ball to head, goal to head, and combination). Sensors collected linear and rotational accelerations and frequency of head impacts per 1000 athlete exposures.

FINDINGS

Men were more likely to sustain head impacts than women (IRR = 1.74, CI₉₅ = 1.59-1.92). The highest head impact incidence rate for men was head to body (IR = 611.68, CI₉₅ = 553.11-670.25) while the highest impact incidence rate for women was ball to head (IR = 302.29, CI₉₅ = 270.93-333.64). The interaction between sex and mechanism was significant for rotational accelerations (F_{4, 1720} = 3.757, P = .005, ω² = 0.013) but not for linear accelerations (F_4,1720 = 0.680, P = .606, ω² < 0.001, 1 - β = 0.223).

INTERPRETATION

To reduce the frequency of head impacts in men, perhaps rules governing player to player contact should be more strictly enforced as these data confirm frequent player-to-head contact during soccer practices and games. Prevention efforts for women should be focused on limiting the amount of purposeful heading (planned contact between the head and ball) occurring during play especially since these impacts had higher magnitudes compared to men.

Impact Mitigation Properties of Women's Lacrosse Headgear

Recently, protective headgear has been released for women's lacrosse despite the fact that contact to the head is illegal. The purposes of this study were to (1) compare the linear and rotational impact attenuation properties of 2 brands of lacrosse headgear at 4 different locations during laboratory pendulum impacts and (2) determine impact dissipation of new and used lacrosse headgear. We measured peak rotational acceleration (PRA; rad/s²) and linear acceleration (PLA; g) at 4 impact locations (side, rear boss non-centric (NC), front boss, and front) in two headgear brands (Cascade LX, Hummingbird). Two headgear service lives (new headgear, used headgear) were included for the second analysis. During the slower speed, there was a significant interaction between impact location and helmet brand (p = 0.002) for PLA. No other findings were significant. While the Hummingbird headgear reduced linear and rotational accelerations of the headform better than the Cascade headgear during slow velocity impacts to the front and front boss locations, it did so due to extreme motion of the helmet upon impact that we believe may compromise protection of the head and face from lacerations and other injuries.

King-Devick Test Reliability in National Collegiate Athletic Association Athletes: A National Collegiate Athletic Association-Department of Defense Concussion Assessment, Research and Education Report

CONTEXT

The King-Devick (KD) test has received considerable attention in the literature as an emerging concussion assessment. However, important test psychometric properties remain to be addressed in large-scale independent studies.

OBJECTIVE

To assess (1) test-retest reliability between trials, (2) test-retest reliability between years 1 and 2, and (3) reliability of the 2 administration modes.

DESIGN

Cross-sectional study.

SETTING

Collegiate athletic training facilities.

PATIENTS OR OTHER PARTICIPANTS

A total of 3248 intercollegiate student-athletes participated in year 1 (male = 55.3%, age = 20.2 ± 2.3 years, height = 1.78 ± 0.11 m, weight = 80.7 ± 21.0 kg) and 833 participated in both years.

MAIN OUTCOME MEASURE(S)

Time, in seconds, to complete the KD error free. The KD test reliability was assessed between trials and between annual tests over 2 years and stratified by test modality (spiral-bound cards [n = 566] and tablet [n = 264]).

RESULTS

The KD test was reliable between trials (trial 1 = 43.2 ± 8.3 seconds, trial 2 = 40.8 ± 7.8 seconds; intraclass correlation coefficient [ICC] (2,1) = 0.888, P < .001), between years (year 1 = 40.8 ± 7.4 seconds, year 2 = 38.7 ± 7.7 seconds; ICC [2,1] = 0.827, P < .001), and for both spiral-bound cards (ICC [2,1] = 0.834, P < .001) and tablets (ICC [2,1] = 0.827, P < .001). The mean change between trials for a single test was -2.4 ± 3.8 seconds. Although most athletes improved from year 1 to year 2, 27.1% (226 of 883) of participants demonstrated worse (slower) KD times (3.2 ± 3.9 seconds) in year 2.

CONCLUSIONS

The KD test was reliable between trials and years and when stratified by modality. A small improvement of 2 seconds was identified with annual retesting, likely due to a practice effect; however, 27% of athletes displayed slowed performance from year 1 to year 2. These results suggest that the KD assessment was a reliable test with modest learning effects over time and that the assessment modality did not adversely affect baseline reliability.

Differences in the Mechanism of Head Impacts Measured Between Men's and Women's Intercollegiate Lacrosse Athletes

Background

Lacrosse is a rapidly growing sport in the United States. Comparing the magnitude and frequency of head impact mechanisms between sexes will provide data for injury prevention techniques and risk reduction of head injuries.

Purpose

To compare sex-specific differences in the magnitude and frequency of head impact mechanisms in National Collegiate Athletic Association (NCAA) Division III intercollegiate lacrosse athletes.

Study Design

Cohort study; Level of evidence, 2.

Methods

A total of 31 NCAA Division III intercollegiate lacrosse athletes (16 men [mean age, 21 ± 1 years; mean height, 179.70 ± 5.82 cm; mean weight, 80.71 ± 6.33 kg] and 15 women [mean age, 20 ± 1 years; mean height, 165.43 ± 5.25 cm; mean weight, 64.08 ± 7.59 kg]) voluntarily participated in this study. Participants wore xPatch sensors at every event during the 2015 spring season. Sensors recorded the magnitude, frequency, and location of head impacts over 10g. Linear (g) and rotational (deg/s²) acceleration determined impact magnitudes. We calculated incidence rates (IRs; per 1000 athlete-exposures [AEs]) and incidence rate ratios (IRRs) with 95% CIs to determine frequency differences. Film footage from each event was synchronized with the time of each head impact for verification and mechanism coding. Sex and impact mechanism served as the independent variables.

Results

A significant interaction was found between impact mechanism and sex (P < .001) and main effects for impact mechanism (P < .001) and sex (P < .001). The most common mechanism in men's lacrosse was head to body (IR, 970.55/1000 AEs [95% CI, 266.14-331.98]), and in women's lacrosse, stick to head (IR, 289.87/1000 AEs [95% CI, 124.32-184.55]) was most common. Only 9 of 419 impermissible head impacts in men's lacrosse games were classed as penalties (2%); 7 of 25 impermissible head impacts in women's lacrosse games were called as penalties (28%).

Conclusion

The impact mechanisms of head to body in men's lacrosse and stick to head in women's lacrosse are penalties but occur frequently, suggesting that a focus on stressing rule enforcement is warranted. Because mechanism and sex affect the magnitude of head impacts, proper offensive and defensive techniques against opponents should be encouraged to reduce head impacts.

The Ability of an Aftermarket Helmet Add-On Device to Reduce Impact-Force Accelerations During Drop Tests

CONTEXT

  The Guardian Cap provides a soft covering intended to mitigate energy transfer to the head during football contact. Yet how well it attenuates impacts remains unknown.

OBJECTIVE

  To evaluate the changes in the Gadd Severity Index (GSI) and linear acceleration during drop tests on helmeted headforms with or without Guardian Caps.

DESIGN

  Crossover study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Nine new football helmets sent directly from the manufacturer.

INTERVENTION(S)

  We dropped the helmets at 3 velocities on 6 helmet locations (front, side, right front boss, top, rear right boss, and rear) as prescribed by the National Operating Committee on Standards for Athletic Equipment. Helmets were tested with facemasks in place but no Guardian Cap and then retested with the facemasks in place and the Guardian Cap affixed.

MAIN OUTCOME MEASURE(S)

  The GSI scores and linear accelerations measured in g forces.

RESULTS

  For the GSI, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F_10,50 = 3.01, P = .005) but not at the low (F_3.23,16.15 = 0.84, P = .50) or medium (F_10,50 = 1.29, P = .26) velocities. Similarly for linear accelerations, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F_10,50 = 3.01, P = .002, ω² = 0.05) but not at the low (F_10,50 = 0.49, P = .89, ω² < 0.01, 1-β = 0.16) or medium (F_5.20,26.01 = 2.43, P = .06, ω² < 0.01, 1-β = 0.68) velocities.

CONCLUSIONS

  The Guardian Cap failed to significantly improve the helmets' ability to mitigate impact forces at most locations. Limited evidence indicates how a reduction in GSI would provide clinically relevant benefits beyond reducing the risk of skull fracture or a similar catastrophic event.

Comparison of head impact location during games and practices in Division III men's lacrosse players

BACKGROUND

Head impacts have been studied extensively in football, but little similar research has been conducted in men's lacrosse. It is important to understand the location and magnitude of head impacts during men's lacrosse to recognize the risk of head injury.

METHODS

Descriptive epidemiology study set on collegiate lacrosse fields. Eleven men's lacrosse players (age=20.9±1.13years, mass=83.91±9.04kg, height=179.88±5.99cm) volunteered to participate. We applied X2 sensors behind the right ear of participants for games and practices. Sensors recorded data on linear and rotational accelerations and the location of head impacts. We calculated incidence rates per 1000 exposures with 95% confidence intervals for impact locations and compared the effect of impact location on linear and rotational accelerations with Kruskal-Wallis tests.

FINDINGS

We verified 167 head impacts (games=112; practices=55). During games, the incidence rate was 651.16 (95% confidence interval=530.57-771.76). The high and low incidence rates for head impact locations during games were: side=410.7 (95% confidence interval=292.02-529.41) and top=26.79 (95% confidence interval=3.53-57.10). For games and practices combined, the impact locations did not significantly affect linear (χ²₃=6.69, P=0.08) or rotational acceleration (χ²₃=6.34, P=0.10).

INTERPRETATION

We suggest further research into the location of head impacts during games and practices. We also suggest player and coach education on head impacts as well as behavior modification in men's lacrosse athletes to reduce the incidence of impacts to the side of the head in an effort to reduce potential injury.

Post-Season Neurophysiological Deficits Assessed by ImPACT and fMRI in Athletes Competing in American Football

Neurocognitive assessment, functional magnetic resonance imaging, and head impact monitoring were used to evaluate neurological changes in high school football players throughout competitive seasons. A substantial number of asymptomatic athletes exhibited neurophysiological changes that persisted post-season, with abnormal measures significantly more common in athletes receiving 50 or more hits per week during the season.