Bidirectional Changes in Anisotropy Are Associated with Outcomes in Mild Traumatic Brain Injury

Evidence for Altered White Matter Organization After Mild Traumatic Brain Injury: A Scoping Review on the Use of Diffusion Magnetic Resonance Imaging and Blood-Based Biomarkers to Investigate Acute Pathology and Relationship to Persistent Post-Concussion Symptoms

Mild traumatic brain injury (mTBI) is the most common form of traumatic brain injury. Post-concussive symptoms typically resolve after a few weeks although up to 20% of people experience these symptoms for >3 months, termed persistent post-concussive symptoms (PPCS). Subtle white matter (WM) microstructural damage is thought to underlie neurological and cognitive deficits experienced post-mTBI. Evidence suggests that diffusion magnetic resonance imaging (dMRI) and blood-based biomarkers could be used as surrogate markers of WM organization. We conducted a scoping review according to PRISMA-ScR guidelines, aiming to collate evidence for the use of dMRI and/or blood-based biomarkers of WM organization, in mTBI and PPCS, and document relationships between WM biomarkers and symptoms. We focused specifically on biomarkers of axonal or myelin integrity post-mTBI. Biomarkers excluded from this review therefore included the following: astroglial, perivascular, endothelial, and inflammatory markers. A literature search performed across four databases, EMBASE, Scopus, Google Scholar, and ProQuest, identified 100 records: 68 analyzed dMRI, 28 assessed blood-based biomarkers, and 4 used both. Blood biomarker studies commonly assessed axonal cytoskeleton proteins (i.e., tau); dMRI studies assessed measures of WM organization (i.e., fractional anisotropy). Significant biomarker alterations were frequently associated with heightened symptom burden and prolonged recovery time post-injury. These data suggest that dMRI and blood-based biomarkers may be useful proxies of WM organization, although few studies assessed these complementary measures in parallel, and the relationship between modalities remains unclear. Further studies are warranted to assess the benefit of a combined biomarker approach in evaluating alterations to WM organization after mTBI.

Neck strength alone does not mitigate adverse associations of soccer heading with cognitive performance in adult amateur players

OBJECTIVES

Soccer heading is adversely associated with neurocognitive performance, but whether greater neck strength or anthropometrics mitigates these outcomes is controversial. Here, we examine the effect of neck strength or anthropometrics on associations of soccer heading with neurocognitive outcomes in a large cohort of adult amateur players.

METHODS

380 adult amateur league soccer players underwent standardized measurement of neck strength (forward flexion, extension, left lateral flexion, right lateral flexion) and head/neck anthropometric measures (head circumference, neck length, neck circumference and neck volume). Participants were assessed for heading (HeadCount) and cognitive performance (Cogstate) on up to 7 visits over a period of two years. Principal components analysis (PCA) was performed on 8 neck strength and anthropometric measures. We used generalized estimating equations to test the moderation effect of each of the three PCs on 8 previously identified adverse associations of 2-week and 12-month heading estimates with cognitive performance (psychomotor speed, immediate verbal recall, verbal episodic memory, attention, working memory) and of unintentional head impacts on moderate to severe central nervous system symptoms.

RESULTS

3 principal components (PC's) account for 80% of the variance in the PCA. In men, PC1 represents head/neck anthropometric measures, PC2 represents neck strength measures, and PC3 represents the flexor/extensor (F/E) ratio. In women, PC1 represents neck strength, PC2 represents anthropometrics, and PC3 represents the F/E ratio. Of the 48 moderation effects tested, only one showed statistical significance after Bonferroni correction, which was not robust to extensive sensitivity analyses.

CONCLUSION

Neither neck strength nor anthropometrics mitigate adverse associations of soccer heading with cognitive performance in adult amateur players.

Predictive Utility of Diffusion MRI After Mild Traumatic Brain Injury in Civilian Populations: A Systematic Review

OBJECTIVE

A considerable number of people experience persisting symptoms and functional limitations after mild traumatic brain injury (mTBI). It is unclear whether subtle white matter changes contribute to this phenomenon. In this systematic review, the authors evaluated whether microstructural white matter indices on advanced MRI are related to clinical dysfunction among patients without abnormalities on standard brain computed tomography (CT) or MRI (uncomplicated mTBI).

METHODS

A search of multiple databases was performed. Studies with individuals who experienced blast-related, sports-related, or multiple mTBIs were excluded. Diffusion tensor imaging (DTI) and susceptibility-weighted imaging (SWI) metrics and cognitive, neuropsychiatric, or functional outcome measures were extracted from each study.

RESULTS

Thirteen studies were selected (participants with mTBI, N=553; healthy control group, N=438). Seven DTI studies evaluated cognitive function, with five reporting significant correlations between reduced white matter integrity and deficits in attention, processing speed, and executive function at 6-12 months after injury (three studies included only individuals with uncomplicated mTBI). Four studies found significant correlations between DTI metrics and persistent postconcussive symptoms after 3-12 months (one study included only individuals with uncomplicated mTBI). Two SWI studies reported conflicting findings regarding the relationship between the presence of microbleeds and postconcussive symptoms.

CONCLUSIONS

The results revealed that indices of microstructural white matter integrity may relate to clinical presentation 3-12 months after injury in uncomplicated mTBI. However, analysis methods and brain regions studied varied across studies. Further research is needed to identify relationships between white matter indices in specific brain regions and symptom persistence beyond 12 months.

Age of first exposure to soccer heading: Associations with cognitive, clinical, and imaging outcomes in the Einstein Soccer Study

Introduction

The objective of this study is to assess the role of age at first exposure (AFE) to soccer heading as a predictor of known adverse associations of recent and longer-term heading with brain microstructure, cognitive, and behavioral features among adult amateur soccer players.

Methods

The sample included 276 active amateur soccer players (196 male and 81 female) aged 18-53 years old. AFE to soccer heading was treated as a binary variable, dichotomized at ≤ 10 years vs. >10 years old, based on a recently promulgated US Soccer policy, which bans heading for athletes ages 10 and under.

Results

We found that soccer players who began heading at age 10 or younger performed better on tests of working memory (p = 0.03) and verbal learning (p = 0.02), while accounting for duration of heading exposure, education, sex, and verbal intelligence. No difference in brain microstructure or behavioral measures was observed between the two exposure groups.

Discussion

The findings indicate that, among adult amateur soccer players, AFE to heading before age 10 compared to later start of heading, is not associated with adverse outcomes, and may be associated with better cognitive performance in young adulthood. Cumulative heading exposure across the lifespan, rather than early life exposure, may drive risk for adverse effects and should be the focus of future longitudinal studies to inform approaches to enhance player safety.

Neuropathological Mechanisms of Mild Traumatic Brain Injury: A Perspective From Multimodal Magnetic Resonance Imaging

Mild traumatic brain injury (mTBI) accounts for more than 80% of the total number of TBI cases. The mechanism of injury for patients with mTBI has a variety of neuropathological processes. However, the underlying neurophysiological mechanism of the mTBI is unclear, which affects the early diagnosis, treatment decision-making, and prognosis evaluation. More and more multimodal magnetic resonance imaging (MRI) techniques have been applied for the diagnosis of mTBI, such as functional magnetic resonance imaging (fMRI), arterial spin labeling (ASL) perfusion imaging, susceptibility-weighted imaging (SWI), and diffusion MRI (dMRI). Various imaging techniques require to be used in combination with neuroimaging examinations for patients with mTBI. The understanding of the neuropathological mechanism of mTBI has been improved based on different angles. In this review, we have summarized the application of these aforementioned multimodal MRI techniques in mTBI and evaluated its benefits and drawbacks.

Cognitive impairment in mild traumatic brain injury: a diffusion kurtosis imaging and volumetric study

BACKGROUND

A significant number of patients with mild traumatic brain injury (mTBI) would experience cognitive deficit.

PURPOSE

To investigate the brain structural changes in sub-acute mTBI by diffusion kurtosis imaging (DKI) and volumetric analysis, and to assess the relationship between brain structural changes and cognitive functions.

MATERIAL AND METHODS

A total of 23 patients with sub-acute mTBI and 24 control participants were recruited. All the participants underwent examinations of neuropsychological tests, DKI, and magnetic resonance imaging (MRI)-based morphological scans. Images were investigated using whole brain-based analysis and further regions of interest-based analysis for subcortical nuclei. The neuropsychological tests were compared between the mTBI and the control group. Correlation analysis was performed to examine the relationship between gray matter (GM) volume, DKI parameters, and cognitive functions.

RESULTS

Compared with control participants, mTBI patients performed worse in the domains of verbal memory, attention and executive function (P < 0.05). No regional GM volume differences were observed between the mTBI and control groups (P > 0.05). Using DKI, patients with mTBI showed lower mean kurtosis (MK) in widespread white matter (WM) regions and several subcortical nuclei (P < 0.05), and higher mean diffusivity (MD) in the right pallidum (P < 0.05). Lower MK value of multiple WM regions and several subcortical nuclei correlated with cognitive impairment (P < 0.05).

CONCLUSION

DKI was sensitive in detecting brain microstructural changes in patients with sub-acute mTBI showing lower MK value in widespread WM regions and several subcortical nuclei, which were statistically associated with cognitive deficits.

A systematic review and data synthesis of longitudinal changes in white matter integrity after mild traumatic brain injury assessed by diffusion tensor imaging in adults

PURPOSE

This study aimed to review diffusion tensor imaging studies of mild traumatic brain injury (mTBI) in adults with longitudinal acquisition of data and investigate the variability of findings in association with related factors, such as the time post-injury.

METHODS

Eligible studies from PubMed and EMBASE were searched to identify relevant studies for review. Of the 540 studies, 23 observational studies without intervention and with the following characteristics were included: original research in which adults with mTBI were examined, diffusion tensor imaging was acquired at least twice, white matter integrity was investigated by estimating diffusion metrics, and mode of injury was not restricted to sport- or blast-related mTBI.

RESULTS

Baseline scans were acquired within 3 weeks post-injury, followed by longitudinal scans within 3 months and at 12 months post-injury. During the acute/subacute period, mixed results (increase, decrease, or no significant change) of fractional anisotropy (FA) were observed compared to those in controls. Some studies reported increased FA during the acute/subacute period compared to controls, followed by normalization of FA. Decreased FA was also reported during the acute/subacute period, which lasted long into the chronic phase. In the acute phase, the mean diffusivity (MD) was greater than that in the controls. Compared to the early phase of injury, MD was reduced in the follow-up phase in most studies in the mTBI group. Insignificant differences in FA and MD have been reported in several studies. Such variability limits the clinical usefulness of diffusion tensor metrics.

CONCLUSIONS

There was a high variability in reported changes in white matter integrity. Decreased FA not only in acute/subacute but also in long-term period after injury may indicate long-term neurodegenerative processes after mTBI. Nevertheless, longitudinal changes in MD towards normalization suggest possible recovery. Long-term cohort studies with research initiatives should be considered to elucidate brain changes after mTBI.

Sex differences in acute and long-term brain recovery after concussion

Concussion is associated with acute disturbances in brain function and behavior, with potential long‐term effects on brain health. However, it is presently unclear whether there are sex differences in acute and long‐term brain recovery. In this study, magnetic resonance imaging (MRI) was used to scan 61 participants with sport‐related concussion (30 male, 31 female) longitudinally at acute injury, medical clearance to return to play (RTP), and 1‐year post‐RTP. A large cohort of 167 controls (80 male, 87 female) was also imaged. Each MRI session assessed cerebral blood flow (CBF), along with white matter fractional anisotropy (FA) and mean diffusivity (MD). For concussed athletes, the parameters were converted to difference scores relative to matched control subgroups, and partial least squares modeled the main and sex‐specific effects of concussion. Although male and female athletes did not differ in acute symptoms or time to RTP , all MRI measures showed significant sex differences during recovery. Males had greater reductions in occipital‐parietal CBF (mean difference and 95%CI: 9.97 ml/100 g/min, [4.84, 15.12] ml/100 g/min, z = 3.73) and increases in callosal MD (9.07 × 10⁻⁵, [−14.14, −3.60] × 10⁻⁵, z = −3.46), with greatest effects at 1‐year post‐RTP. In contrast, females had greater reductions in FA of the corona radiata (16.50 × 10⁻³, [−22.38, −11.08] × 10⁻³, z = −5.60), with greatest effects at RTP. These findings provide new insights into how the brain recovers after a concussion, showing sex differences in both the acute and chronic phases of injury.

Acute Diffusion Tensor and Kurtosis Imaging and Outcome following Mild Traumatic Brain Injury

In this prospective cohort study, we investigated associations between acute diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI) metrics and persistent post-concussion symptoms (PPCS) 3 months after mild traumatic brain injury (mTBI). Adult patients with mTBI (n = 176) and community controls (n = 78) underwent 3 Tesla magnetic resonance imaging (MRI) within 72 h post-injury, estimation of cognitive reserve at 2 weeks, and PPCS assessment at 3 months. Eight DTI and DKI metrics were examined with Tract-Based Spatial Statistics. Analyses were performed in the total sample in uncomplicated mTBI only (i.e., without lesions on clinical MRI), and with cognitive reserve both controlled for and not. Patients with PPCS (n = 35) had lower fractional anisotropy (in 2.7% of all voxels) and kurtosis fractional anisotropy (in 6.9% of all voxels), and higher radial diffusivity (in 0.3% of all voxels), than patients without PPCS (n = 141). In uncomplicated mTBI, only fractional anisotropy was significantly lower in patients with PPCS. Compared with controls, patients with PPCS had widespread deviations in all diffusion metrics. When including cognitive reserve as a covariate, no significant differences in diffusion metrics between patients with and without PPCS were present, but patients with PPCS still had significantly higher mean, radial, and axial diffusivity than controls. In conclusion, patients who developed PPCS had poorer white matter microstructural integrity acutely after the injury, compared with patients who recovered and healthy controls. Differences became less pronounced when cognitive reserve was controlled for, suggesting that pre-existing individual differences in axonal integrity accounted for some of the observed differences.

ACR Appropriateness Criteria® Head Trauma: 2021 Update

Head trauma (ie, head injury) is a significant public health concern and is a leading cause of morbidity and mortality in children and young adults. Neuroimaging plays an important role in the management of head and brain injury, which can be separated into acute (0-7 days), subacute (<3 months), then chronic (>3 months) phases. Over 75% of acute head trauma is classified as mild, of which over 75% have a normal Glasgow Coma Scale score of 15, therefore clinical practice guidelines universally recommend selective CT scanning in this patient population, which is often based on clinical decision rules. While CT is considered the first-line imaging modality for suspected intracranial injury, MRI is useful when there are persistent neurologic deficits that remain unexplained after CT, especially in the subacute or chronic phase. Regardless of time frame, head trauma with suspected vascular injury or suspected cerebrospinal fluid leak should also be evaluated with CT angiography or thin-section CT imaging of the skull base, respectively. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Diffusion tensor imaging findings and neuropsychological performance in adults with TBI across the spectrum of severity in the chronic-phase

PRIMARY OBJECTIVE

To examine associations between neuroimaging indicators of cerebral tract integrity and neurocognitive functioning in traumatic brain injury (TBI).

RESEARCH DESIGN

Between-Groups design with two TBI groups and controls.

METHOD AND PROCEDURES

Forty-four participants with TBI and 27 matched controls completed diffusion tensor imaging and neuropsychological measures of processing speed, attention, memory, and executive function. Multivariate analyses were conducted to examine group differences in white matter integrity (fractional anisotropy) for 11 regions of interest and cognitive performance among adult males with chronic phase, mild, moderate, or severe TBI. Correlational analyses investigated associations between white matter integrity, brain injury severity, and cognitive status.

MAIN OUTCOMES AND RESULTS

Participants with moderate or severe TBI exhibited reduced white matter integrity in 8 of 11 ROIs and worse performance on most cognitive measures, relative to control participants. Persons with mild TBI did not differ from controls on white matter integrity values and differed on one measure of processing speed. Significant correlations were found between injury severity ratings and 10 ROIs, most notably between ROIs and measures of processing speed or memory.

CONCLUSIONS

These findings provide nuanced information regarding white matter connectivity as it relates to neurocognitive abilities across the TBI severity spectrum.

Evaluation of diffusion measurements reveals radial diffusivity indicative of microstructural damage following acute, mild traumatic brain injury

PURPOSE

Mild TBI, characterized by microstructural damage, often undetectable on conventional imaging techniques, is a pervasive condition that disturbs brain function and can potentially result in long-term deficits. Deciphering the underlying microstructural damage in mild TBI is crucial for establishing a reliable diagnosis and enabling effective therapeutics. Efforts to capture this damage have been extensive, but results have been inconsistent and incomplete.

METHODS

To that effect, we set out to examine the shape of the diffusion tensor in mild TBI during the acute phase of injury. We inspected diffusivity and geometric measurements describing the diffusion tensor's shape and compared mild TBI (N = 34, 20.4-66.6 yo) measurements with those from healthy control (N = 42, 20.7-67.2 yo) participants using voxelwise tract-based spatial statistics. Subsequently, to explore associations between the diffusion measurements in mild TBI, we performed nonparametric statistics and machine learning techniques.

RESULTS

Overall, mild TBI displayed a diffuse increase in D_λ2, D_λ3, D_radial, D_mean, and C_spherical, with a diffuse decrease in A_fractional, A_mode, and C_linear, in addition to no change in D_axial or C_planar. Most notably, our results provide evidence for D_radial as a potential biomarker for microstructural damage, specifically its main component D_λ2, based on their performance in discriminating between mild TBI and control groups. A_fractional was also found to be important for discriminating between groups.

CONCLUSION

Our results revealed the importance of a diffusion measurement often overlooked, D_radial, in assessing TBI and suggest differentiating diffusion measurements has the potential utility to detect variations in the underlying pathophysiology after injury.

Joint analysis of frontal theta synchrony and white matter following mild traumatic brain injury

Some of the most disabling aspects of mild traumatic brain injury (mTBI) include lingering deficits in executive functioning. It is known that mTBI can damage white matter tracts, but it remains unknown how this structural brain damage translates into cognitive deficits. This experiment utilized theta band phase synchrony to identify the dysfunctional neural operations that contribute to cognitive problems following mTBI. Sub-acute stage (< 2 weeks) mTBI patients (N = 52) and healthy matched controls (N = 32) completed a control-demanding task with concurrent EEG. Structural MRI was also collected. While there were no performance-specific behavioral differences between groups in the dot probe expectancy task, the degree of theta band phase synchrony immediately following injury predicted the degree of symptom recovery two months later. Although there were no differences in fractional anisotropy (FA) between groups, joint independent components analysis revealed that a smaller network of lower FA-valued voxels contributed to a diminished frontal theta phase synchrony network in the mTBI group. This finding suggests that frontal theta band markers of cognitive control are sensitive to sub-threshold structural aberrations following mTBI.

Customizing TMS Applications in Traumatic Brain Injury Using Neuroimaging

Optimizing transcranial magnetic stimulation (TMS) treatments in traumatic brain injury (TBI) and co-occurring conditions may benefit from neuroimaging-based customization.

PARTICIPANTS

Our total sample (N = 97) included 58 individuals with TBI (49 mild, 8 moderate, and 1 severe in a state of disordered consciousness), of which 24 had co-occurring conditions (depression in 14 and alcohol use disorder in 10). Of those without TBI, 6 individuals had alcohol use disorder and 33 were healthy controls. Of our total sample, 54 were veterans and 43 were civilians.

DESIGN

Proof-of-concept study incorporating data from 5 analyses/studies that used multimodal approaches to integrate neuroimaging with TMS.

MAIN MEASURES

Multimodal neuroimaging methods including structural magnetic resonance imaging (MRI), MRI-guided TMS navigation, functional MRI, diffusion MRI, and TMS-induced electric fields. Outcomes included symptom scales, neuropsychological tests, and physiological measures.

RESULTS

It is feasible to use multimodal neuroimaging data to customize TMS targets and understand brain-based changes in targeted networks among people with TBI.

CONCLUSIONS

TBI is an anatomically heterogeneous disorder. Preliminary evidence from the 5 studies suggests that using multimodal neuroimaging approaches to customize TMS treatment is feasible. To test whether this will lead to increased clinical efficacy, studies that integrate neuroimaging and TMS targeting data with outcomes are needed.

BDNF Val66Met Positive Players Demonstrate Diffusion Tensor Imaging Consistent With Impaired Myelination Associated With High Levels of Soccer Heading: Indication of a Potential Gene-Environment Interaction Mechanism

The purpose of this study was to examine the potential effect modifying role of the BDNF Val66Met polymorphism on the association of soccer heading with white matter microstructure. We studied 312 players enrolled in the ongoing Einstein Soccer Study, a longitudinal study of amateur soccer player in New York City and surrounding areas. At enrollment and 2 years later, total heading in the prior 12 months (12-mo.) was estimated using an established self-report instrument and diffusion tensor imaging (DTI) was performed. Generalized Estimating Equations (GEE) logistic regression models were employed to test effect modification by the BDNF Val66Met polymorphism on the association between 12-mo. heading exposure and DTI. We identified a significant interaction of 12-mo heading*BDNF Val66Met genotype on the presence of low Radial Diffusivity, a DTI marker associated with myelination. Only Met (+) players demonstrated significantly reduced odds of low RD [OR (95 % CI): -2.36 (-3.53, -1.19)] associated with the highest vs. lowest quartile of 12-mo heading exposure. BDNF Val66Met (+) soccer players with long-term exposure to high levels of heading exhibit less low Radial Diffusivity, suggesting impaired re-myelination may be a substrate of the previously reported association between heading and poor functional outcomes in soccer players.

Preliminary evidence from a prospective DTI study suggests a posterior-to-anterior pattern of recovery in college athletes with sports-related concussion

OBJECTIVES

We compared the integrity of white matter (WM) microstructure to the course of recovery in athletes who sustained one sports-related concussion (SRC), assessing individual longitudinal changes in WM fiber tracts following SRC using pre- and post-injury measurements.

MATERIALS AND METHODS

Baseline diffusion tensor imaging (DTI) scans and neuropsychological tests were collected on 53 varsity contact-sport college athletes. Participants (n = 13) who subsequently sustained an SRC underwent DTI scans and neuropsychological testing at 2 days, 2 weeks, and 2 months following injury.

RESULTS

Relying on tract-based spatial statistics (TBSS) analyses, we found that radial diffusivity (RD) and mean diffusivity (MD) were significantly increased at 2 days post-injury compared to the same-subject baseline (corrected p < 0.02). These alterations were visible in anterior/posterior WM regions spanning both hemispheres, demonstrating a diffuse pattern of injury after concussion. Implicated WM fiber tracts at 2 days include the following: right superior/inferior longitudinal fasciculus; right/left inferior fronto-occipital fasciculus; right corticospinal tract; right acoustic radiation; right/left anterior thalamic radiations; right/left uncinate fasciculus; and forceps major/minor. At 2 weeks post-injury, persistently elevated RD and MD were observed solely in prefrontal portions of WM fiber tracts (using same-subject contrasts). No significant differences were found for FA in any of the post-injury comparisons to baseline. Plots of individual subject RD and MD in prefrontal WM demonstrated homogenous increases from baseline to just after SRC; thereafter, trajectories became more variable. Most subjects' diffusivity values remained elevated at 2 months post-injury relative to their own baseline. Over the 2-month period after SRC, recovery of WM fiber tracts appeared to follow a posterior-to-anterior trend, paralleling the posterior-anterior pattern of WM maturation previously identified in the normal population.

CONCLUSION

These results suggest greater vulnerability of prefrontal regions to SRC, underline the importance of an individualized approach to concussion management, and show promise for using RD and MD for imaging-based diagnosis of SRC.

MRI-defined White Matter Microstructural Alteration Associated with Soccer Heading Is More Extensive in Women than Men

Purpose To examine the role of sex in abnormal white matter microstructure after soccer heading as identified by using the diffusion-tensor imaging (DTI) metric fractional anisotropy (FA). Materials and Methods In this prospective cross-sectional study, 98 individuals who were enrolled in a larger prospective study of amateur soccer players (from 2013 to 2016) were matched 1:1 for age and history of soccer heading in the prior 12 months. Among the subjects, 49 men (mean age, 25.7 years; range, 18-50 years) and 49 women (mean age, 25.8 years; range, 18-50 years) with median total soccer headings per year of 487 and 469, respectively, underwent 3.0-T DTI. Images were registered to the Johns Hopkins University template. A voxelwise linear regression was fitted for FA with terms for the number of headings during the previous 12 months and its interaction with sex after controlling for the following potential confounders: age, years of education, number of lifetime concussions, and handedness. In the resulting statistical maps, P < .01 indicated a statistically significant difference, with a threshold cluster size larger than 100 mm3. Results Among men, three regions were identified in which greater heading exposure was associated with lower FA; eight such regions were identified among women (>100 contiguous voxels, P < .01). In seven of the eight regions identified in women, the association between heading and FA was stronger in women than in men. There was no significant difference of heading with FA between the sexes for any region in which heading was associated with FA among men (P > .01, <100 contiguous voxels). Conclusion With similar exposure to heading, women exhibit more widespread evidence of microstructural white matter alteration than do men, suggesting preliminary support for a biologic divergence of brain response to repetitive trauma. © RSNA, 2018 Online supplemental material is available for this article.

Understanding individual variability in symptoms and recovery following mTBI: A role for TMS-EEG?

The pathophysiology associated with mild traumatic brain injury (mTBI) includes neurometabolic and cytoskeletal changes that have been shown to impair structural and functional connectivity. Evidence that persistent neuropsychological impairments post injury are linked to structural and functional connectivity changes is increasing. However, to date the relationship between connectivity changes, heterogeneity of persistent symptoms and recovery post mTBI has been poorly characterised. Recent innovations in neuroimaging provide new ways of exploring connectivity changes post mTBI. Namely, combined transcranial magnetic stimulation and electroencephalography (TMS-EEG) offers several advantages over traditional approaches for studying connectivity changes post TBI. Its ability to perturb neural function in a controlled manner allows for measurement of causal interactions or effective connectivity between brain regions. We review the current literature assessing structural and functional connectivity following mTBI and outline the rationale for the use of TMS-EEG as an ideal tool for investigating the neural substrates of connectivity dysfunction and reorganisation post mTBI. The diagnostic, prognostic and potential therapeutic implications will also be explored.

Neuroimaging of brain trauma in sports

Computed tomography (CT) and magnetic resonance imaging (MRI) have revolutionized the assessment of traumatic brain injury (TBI) by permitting rapid detection and localization of acute intracranial injuries. In concussion, the most common presentation of sports-related head trauma, CT and MRI are unrevealing. This normal appearance of the brain on standard neuroimaging, however, belies the structural and functional pathology that underpins concussion-related symptoms and dysfunction. Advances in neuroimaging have expanded our ability to gain insight into this microstructural and functional brain pathology. This chapter will present both conventional and more advanced imaging approaches (e.g., diffusion tensor imaging, magnetization transfer imaging, magnetic resonance spectroscopy, functional MRI, arterial spin labeling, magnetoencephalography) to the assessment of TBI in sports and discuss some of the current and potential future roles of brain imaging in the assessment of injured athletes.

Differences in Brain Architecture in Remote Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is brain trauma from an external impact with a loss of consciousness less than 30 min. Mild TBI results in several biopsychosocial impairments, with pronounced cognitive deficits thought to resolve within 3 months of injury. Previous research suggests that these impairments are due to a temporary inability to appropriately allocate neural resources in response to cognitive demands. Our study questioned this assumption and instead hypothesized that mTBI was associated with long-term neural disruptions and compromised brain structure integrity. By extension, we investigated the likelihood that functional restitution and cognitive resolution following mTBI may be due to some form of neurofunctional reorganization. To this end, we examined abnormalities in resting state functional connectivity and structure (volume, thickness, and fractional anisotropy) in two groups of mTBI-those with 1-10 years time post-injury (mTBI1-10), and those with 20-65 years time post-injury, relative to age-, sex-, and education-matched controls. We observed abnormalities in brain architecture only in the mTBI1-10 group, characterized by functional hypo-activation in the right frontal pole, smaller frontal pole volume, and lesser fractional anisotropy in the genu of the corpus callosum that extended near the right frontal pole. This frontal region is laterally specialized to regulate function specific to socio-emotional processes. Collectively, neural disruptions and structural insult in mTBI may persist up to 10 years following injury, but injury-related pathology may resolve with longer recovery time. Disruption to frontal-dependent function that supports socio-emotional processes also may interfere with cognitive functioning, as in the case of chronic mTBI.

Inter-Subject Variability of Axonal Injury in Diffuse Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of cognitive morbidity worldwide for which reliable biomarkers are needed. Diffusion tensor imaging (DTI) is a promising biomarker of traumatic axonal injury (TAI); however, existing studies have been limited by a primary reliance on group-level analytic methods not well suited to account for inter-subject variability. In this study, 42 adults with TBI of at least moderate severity were examined 3 months following injury and compared with 35 healthy controls. DTI data were used for both traditional group-level comparison and subject-specific analysis using the distribution-corrected Z-score (DisCo-Z) approach. Inter-subject variation in TAI was assessed in a threshold-invariant manner using a threshold-weighted overlap map derived from subject-specific analysis. Receiver operator curve analysis was used to examine the ability of subject-specific DTI analysis to identify TBI subjects with significantly impaired processing speed in comparison with region of interest-based fractional anisotropy (FA) measurements and clinical characteristics. Traditional group-wise analysis demonstrated widespread reductions of white matter FA within the TBI group (voxel-wise p < 0.05, corrected), despite relatively low consistency of subject-level effects secondary to widespread variation in the spatial distribution of TAI. Subject-specific mapping of TAI with the DisCo-Z approach was the best predictor of impaired processing speed, achieving high classification accuracy (area under the curve [AUC] = 0.94). In moderate-to-severe TBI, there is substantial inter-subject variation in TAI, with extent strongly correlated to post-traumatic deficits in processing speed. Significant group-level effects do not necessarily represent consistent effects at the individual level. Better accounting for inter-subject variability in neurobiological manifestations of TBI may substantially improve the ability to detect and classify patterns of injury.