Assessment of thalamic perfusion in patients with mild traumatic brain injury by true FISP arterial spin labelling MR imaging at 3T

Neutralization of Interleukin 1-beta is associated with preservation of thalamic capillaries after experimental traumatic brain injury

Introduction

Traumatic brain injury to thalamo-cortical pathways is associated with posttraumatic morbidity. Diffuse mechanical forces to white matter tracts and deep grey matter regions induce an inflammatory response and vascular damage resulting in progressive neurodegeneration. Pro-inflammatory cytokines, including interleukin-1β (IL-1β), may contribute to the link between inflammation and the injured capillary network after TBI. This study investigates whether IL-1β is a key contributor to capillary alterations and changes in pericyte coverage in the thalamus and cortex after TBI.

Methods

Animals were subjected to central fluid percussion injury (cFPI), a model of TBI causing widespread axonal and vascular pathology, or sham injury and randomized to receive a neutralizing anti-IL-1β or a control, anti-cyclosporin A antibody, at 30 min post-injury. Capillary length and pericyte coverage of cortex and thalamus were analyzed by immunohistochemistry at 2- and 7-days post-injury.

Results and Conclusion

Our results show that early post-injury attenuation of IL-1β dependent inflammatory signaling prevents capillary damage by increasing pericyte coverage in the thalamus.

Temporal Alterations in Cerebrovascular Glycocalyx and Cerebral Blood Flow after Exposure to a High-Intensity Blast in Rats

The glycocalyx is a proteoglycan-glycoprotein structure lining the luminal surface of the vascular endothelium and is susceptible to damage due to blast overpressure (BOP) exposure. The glycocalyx is essential in maintaining the structural and functional integrity of the vasculature and regulation of cerebral blood flow (CBF). Assessment of alterations in the density of the glycocalyx; its components (heparan sulphate proteoglycan (HSPG/syndecan-2), heparan sulphate (HS), and chondroitin sulphate (CS)); CBF; and the effect of hypercapnia on CBF was conducted at 2-3 h, 1, 3, 14, and 28 days after a high-intensity (18.9 PSI/131 kPa peak pressure, 10.95 ms duration, and 70.26 PSI·ms/484.42 kPa·ms impulse) BOP exposure in rats. A significant reduction in the density of the glycocalyx was observed 2-3 h, 1-, and 3 days after the blast exposure. The glycocalyx recovered by 28 days after exposure and was associated with an increase in HS (14 and 28 days) and in HSPG/syndecan-2 and CS (28 days) in the frontal cortex. In separate experiments, we observed significant decreases in CBF and a diminished response to hypercapnia at all time points with some recovery at 3 days. Given the role of the glycocalyx in regulating physiological function of the cerebral vasculature, damage to the glycocalyx after BOP exposure may result in the onset of pathogenesis and progression of cerebrovascular dysfunction leading to neuropathology.

Effects of Low-Level Blast on Neurovascular Health and Cerebral Blood Flow: Current Findings and Future Opportunities in Neuroimaging

Low-level blast (LLB) exposure can lead to alterations in neurological health, cerebral vasculature, and cerebral blood flow (CBF). The development of cognitive issues and behavioral abnormalities after LLB, or subconcussive blast exposure, is insidious due to the lack of acute symptoms. One major hallmark of LLB exposure is the initiation of neurovascular damage followed by the development of neurovascular dysfunction. Preclinical studies of LLB exposure demonstrate impairment to cerebral vasculature and the blood-brain barrier (BBB) at both early and long-term stages following LLB. Neuroimaging techniques, such as arterial spin labeling (ASL) using magnetic resonance imaging (MRI), have been utilized in clinical investigations to understand brain perfusion and CBF changes in response to cumulative LLB exposure. In this review, we summarize neuroimaging techniques that can further our understanding of the underlying mechanisms of blast-related neurotrauma, specifically after LLB. Neuroimaging related to cerebrovascular function can contribute to improved diagnostic and therapeutic strategies for LLB. As these same imaging modalities can capture the effects of LLB exposure in animal models, neuroimaging can serve as a gap-bridging diagnostic tool that permits a more extensive exploration of potential relationships between blast-induced changes in CBF and neurovascular health. Future research directions are suggested, including investigating chronic LLB effects on cerebral perfusion, exploring mechanisms of dysautoregulation after LLB, and measuring cerebrovascular reactivity (CVR) in preclinical LLB models.

Imaging Approach to Concussion

The acute and long-term neurobiological sequelae of concussion (mild traumatic brain injury [mTBI]) and sub-concussive head trauma have become increasingly apparent in recent decades in part due to neuroimaging research. Although imaging has an established role in the clinical management of mTBI for the identification of intracranial lesions warranting urgent interventions, MR imaging is increasingly employed for the detection of post-traumatic sequelae which carry important prognostic significance. As neuroimaging research continues to elucidate the pathophysiology of TBI underlying prolonged recovery and the development of persistent post-concussive symptoms, there is a strong motivation to translate these techniques into clinical use for improved diagnosis and therapeutic monitoring.

Perfusion Imaging of Traumatic Brain Injury

The mechanisms for regulating cerebral blood flow (CBF) are highly sensitive to traumatic brain injury (TBI). The perfusion imaging technique may be used to assess CBF and identify perfusion abnormalities following a TBI. Studies have identified CBF disturbances across the injury severity spectrum and correlations with both acute and long-term indices of clinical outcome. Although not yet widely used in the clinical context, this is an important area of ongoing research.

Assessment of vibration modulated regional cerebral blood flow with MRI

Human brain experiences vibration of certain magnitude and frequency during various physical activities such as vehicle transportation and machine operation, which may cause traumatic brain injury or other brain diseases. However, the mechanisms of brain pathogenesis due to vibration are not fully elucidated due to the lack of techniques to study brain functions while applying vibration to the brain at a specific magnitude and frequency. Here, this study reported a custom-built head-worn electromagnetic actuator that applied vibration to the brain in vivo at an accurate frequency inside a magnetic resonance imaging scanner while cerebral blood flow (CBF) was acquired. Using this technique, CBF values from 45 healthy volunteers were quantitatively measured immediately following vibration at 20, 30, 40 Hz, respectively. Results showed increasingly reduced CBF with increasing frequency at multiple regions of the brain, while the size of the regions expanded. Importantly, the vibration-induced CBF reduction regions largely fell inside the brain's default mode network (DMN), with about 58 or 46% overlap at 30 or 40 Hz, respectively. These findings demonstrate that vibration as a mechanical stimulus can change strain conditions, which may induce CBF reduction in the brain with regional differences in a frequency-dependent manner. Furthermore, the overlap between vibration-induced CBF reduction regions and DMN suggested a potential relationship between external mechanical stimuli and cognitive functions.

A Systematic Review of ASL Perfusion MRI in Mild TBI

Mild traumatic brain injury (mTBI) is a major public health concern. Cerebrovascular alterations play a significant role in the evolution of injury sequelae and in the process of post-traumatic brain repair. Arterial spin labeling (ASL) is an advanced perfusion magnetic resonance imaging technique that permits noninvasive quantification of cerebral blood flow (CBF). This is the first systematic review of ASL research findings in patients with mTBI. Our approach followed the American Academy of Neurology (AAN) and PRISMA guidelines. We searched Ovid/MEDLINE, Web of Science, Scopus, and the Cochrane Index for relevant articles published as of February 20, 2020. Full-text results were combined into Rayyan software for further evaluation. Data extraction, including risk of bias ratings, was performed using American Academy of Neurology's four-tiered classification scheme. Twenty-three articles met inclusion criteria comprising data on up to 566 mTBI patients and 654 control subjects. Of the 23 studies, 18 reported some type of regional CBF abnormality in mTBI patients at rest or during a cognitive task, with more findings of decreased than increased CBF. The evidence supports the conclusion that mTBI likely causes ASL-derived CBF anomalies. However, synthesis of findings was challenging due to substantial methodological variations across studies and few studies with low risk of bias. Thus, larger-scale prospective cohort studies are needed to more definitively chart the course of CBF changes in humans after mTBI and to understand how individual difference factors contribute to post-injury CBF changes.

Replicability of proton MR spectroscopic imaging findings in mild traumatic brain injury: Implications for clinical applications

PURPOSE

Proton magnetic resonance spectroscopy (1H MRS) offers biomarkers of metabolic damage after mild traumatic brain injury (mTBI), but a lack of replicability studies hampers clinical translation. In a conceptual replication study design, the results reported in four previous publications were used as the hypotheses (H1-H7), specifically: abnormalities in patients are diffuse (H1), confined to white matter (WM) (H2), comprise low N-acetyl-aspartate (NAA) levels and normal choline (Cho), creatine (Cr) and myo-inositol (mI) (H3), and correlate with clinical outcome (H4); additionally, a lack of findings in regional subcortical WM (H5) and deep gray matter (GM) structures (H6), except for higher mI in patients' putamen (H7).

METHODS

26 mTBI patients (20 female, age 36.5 ± 12.5 [mean ± standard deviation] years), within two months from injury and 21 age-, sex-, and education-matched healthy controls were scanned at 3 Tesla with 3D echo-planar spectroscopic imaging. To test H1-H3, global analysis using linear regression was used to obtain metabolite levels of GM and WM in each brain lobe. For H4, patients were stratified into non-recovered and recovered subgroups using the Glasgow Outcome Scale Extended. To test H5-H7, regional analysis using spectral averaging estimated metabolite levels in four GM and six WM structures segmented from T1-weighted MRI. The Mann-Whitney U test and weighted least squares analysis of covariance were used to examine mean group differences in metabolite levels between all patients and all controls (H1-H3, H5-H7), and between recovered and non-recovered patients and their respectively matched controls (H4). Replicability was defined as the support or failure to support the null hypotheses in accordance with the content of H1-H7, and was further evaluated using percent differences, coefficients of variation, and effect size (Cohen's d).

RESULTS

Patients' occipital lobe WM Cho and Cr levels were 6.0% and 4.6% higher than controls', respectively (Cho, d = 0.37, p = 0.04; Cr, d = 0.63, p = 0.03). The same findings, i.e., higher patients' occipital lobe WM Cho and Cr (both p = 0.01), but with larger percent differences (Cho, 8.6%; Cr, 6.3%) and effect sizes (Cho, d = 0.52; Cr, d = 0.88) were found in the comparison of non-recovered patients to their matched controls. For the lobar WM Cho and Cr comparisons without statistical significance (frontal, parietal, temporal), unidirectional effect sizes were observed (Cho, d = 0.07 - 0.37; Cr, d = 0.27 - 0.63). No differences were found in any metabolite in any lobe in the comparison between recovered patients and their matched controls. In the regional analyses, no differences in metabolite levels were found in any GM or WM region, but all WM regions (posterior, frontal, corona radiata, and the genu, body, and splenium of the corpus callosum) exhibited unidirectional effect sizes for Cho and Cr (Cho, d = 0.03 - 0.34; Cr, d = 0.16 - 0.51).

CONCLUSIONS

We replicated findings of diffuse WM injury, which correlated with clinical outcome (supporting H1-H2, H4). These findings, however, were among the glial markers Cho and Cr, not the neuronal marker NAA (not supporting H3). No differences were found in regional GM and WM metabolite levels (supporting H5-H6), nor in putaminal mI (not supporting H7). Unidirectional effect sizes of higher patients' Cho and Cr within all WM analyses suggest widespread injury, and are in line with the conclusion from the previous publications, i.e., that detection of WM injury may be more dependent upon sensitivity of the 1H MRS technique than on the selection of specific regions. The findings lend further support to the corollary that clinic-ready 1H MRS biomarkers for mTBI may best be achieved by using high signal-to-noise-ratio single-voxels placed anywhere within WM. The biochemical signature of the injury, however, may differ and therefore absolute levels, rather than ratios may be preferred. Future replication efforts should further test the generalizability of these findings.

Impaired neuronal integrity in traumatic brain injury detected by 123I-iomazenil single photon emission computed tomography and MRI

This study was aiming at investigating the extent of neuronal damage in cases of traumatic brain injury (TBI) with diffuse axonal injury (DAI) using ¹²³I-iomazenil(IMZ) SPECT and MRI. We compared the findings in 31 patients with TBI without any major focal brain lesions and 25 age-matched normal controls. Subjects underwent ¹²³I-IMZ SPECT and MRI, and also assessment by cognitive function tests. The partial volume effect of ¹²³I-IMZ SPECT was corrected using MRI. In the patients with TBI, decreased spatial concentration of ¹²³I-IMZ binding was detected in the medial frontal/orbitofrontal cortex, posterior cingulate gyrus, cuneus, precuneus, and superior region of the cerebellum. ROC analysis of ¹²³I-IMZ SPECT for the detection of neuronal injury showed a high diagnostic ability of ¹²³I-IMZ binding density for TBI in these areas. The decreased ¹²³I-IMZ uptake density in the cuneus and precuneus was associated with cognitive decline after the injury. In the patients with TBI, brain atrophy was detected in the frontal lobe, anterior temporal and parietal cortex, corpus callosum, and posterior part of the cerebellum. Evaluation of the neuronal integrity by ¹²³I-IMZ SPECT and MRI provides important information for the diagnosis and pathological interpretation in cases of TBI with DAI.

Incipient chronic traumatic encephalopathy in active American football players: neuropsychological assessment and brain perfusion measures

Background and aims

Chronic traumatic encephalopathy (CTE) is a degenerative disease caused by repetitive traumatic brain injury (TBI). Because CTE can be definitely diagnosed only post-mortem, it would be important to explore clinical and radiological correlates of CTE and TBI. The aims of this study were to assess (1) the relationship between the neuropsychological profile of active American football players and the traumatic load; (2) whether traumatic brain injury associated with American football activity has a specific cerebral perfusion pattern; and (3) whether this perfusion pattern correlates with neuropsychological performances.

Methods

In 20 American football players [median age [25th–75th percentile] 25.0 [21.6–31.2] years, all males], we evaluated history, traumatic load and symptoms using the TraQ (Trauma Questionnaire), and cognitive performances on neuropsychological tests. Brain perfusion was estimated using arterial spin labeling MRI and compared to a group of 19 male age-matched (28.0 [24.8–32.3] years) healthy subjects.

Results

We found different cognitive performances between American football players stratified according to field position and career length. Linemen had poorer executive, verbal, and visual performances; a career > 7 years was associated with poorer verbal fluency performances. American football players had statistically significant reduced cerebral blood flow values in sensory-motor areas in comparison with healthy controls. Poorer neuropsychological performances correlated with lower perfusion in specific brain areas.

Conclusions

Our study seems to confirm that CTE in American football players is influenced by the field position and the career length, and correlates with lower cognitive performances linked to lower perfusion in specific brain areas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10072-022-06212-7.

Chronic cerebral blood flow alterations in traumatic brain injury and sports-related concussions

PRIMARY OBJECTIVE

Traumatic brain injury (TBI) and sports-related concussion (SRC) may result in chronic functional and neuroanatomical changes. We tested the hypothesis that neuroimaging findings (cerebral blood flow (CBF), cortical thickness, and ¹H-magnetic resonance (MR) spectroscopy (MRS)) were associated to cognitive function, TBI severity, and sex.

RESEARCH DESIGN

Eleven controls, 12 athletes symptomatic following ≥3SRCs and 6 patients with moderate-severe TBI underwent MR scanning for evaluation of cortical thickness, brain metabolites (MRS), and CBF using pseudo-continuous arterial spin labeling (ASL). Cognitive screening was performed using the RBANS cognitive test battery.

MAIN OUTCOMES AND RESULTS

RBANS-index was impaired in both injury groups and correlated with the injury severity, although not with any neuroimaging parameter. Cortical thickness correlated with injury severity (p = 0.02), while neuronal density, using the MRS marker ((NAA+NAAG)/Cr, did not. On multivariate analysis, injury severity (p = 0.0003) and sex (p = 0.002) were associated with CBF. Patients with TBI had decreased gray (p = 0.02) and white matter (p = 0.02) CBF compared to controls. CBF was significantly lower in total gray, white matter and in 16 of the 20 gray matter brain regions in female but not male athletes when compared to female and male controls, respectively.

CONCLUSIONS

Injury severity correlated with CBF, cognitive function, and cortical thickness. CBF also correlated with sex and was reduced in female, not male, athletes. Chronic CBF changes may contribute to the persistent injury mechanisms in TBI and rSRC.

Cerebral blood flow network differences correlated with cognitive impairment in mild traumatic brain injury

Purpose

To examine whether the cerebral blood flow (CBF) and CBF connectivity differences are sex-specific and whether these differences are correlated with cognitive impairment in mTBI.

Methods

Resting-state perfusion magnetic resonance imaging was performed in 40 patients with acute mTBI and 40 healthy controls by using pseudocontinuous arterial spin labeling within 14 days following injury. The differences in normalized CBF were first compared and CBF connectivity of the brain regions with significant CBF differences were compared next. The association between the normalized CBF and CBF connectivity differences and cognitive function were further investigated.

Results

Men patients had lower normalized CBF in the frontal gyrus, temporal gyrus and hippocampus and decreased negative CBF connectivity between brain regions including the hippocampus, temporal gyrus, postcentral gyrus and lenticular nucleus, putamen, compared with men controls. Women patients had lower normalized CBF in the frontal gyrus, however had higher normalized CBF in the temporal gyrus and hippocampus, compared with women controls. Additionally, women patients showed increased positive CBF connectivity between the seed region of interest (ROI) of the right inferior temporal gyrus and temporal gyrus and frontal gyrus, and had increased positive CBF connectivity between the seed ROI of the right hippocampus and the temporal gyrus. Furthermore, men patients had higher CBF in the right middle temporal gyrus and left precentral gyrus than women patients.

Conclusion

This study provides evidence of sex differences in both decreased and increased CBF and CBF connectivity and association with cognitive outcome in the acute stage after mTBI.

Advanced Neuroimaging Role in Traumatic Brain Injury: A Narrative Review

Traumatic brain injury (TBI) is a common source of morbidity and mortality among civilians and military personnel. Initial routine neuroimaging plays an essential role in rapidly assessing intracranial injury that may require intervention. However, in the context of TBI, limitations of routine neuroimaging include poor visualization of more subtle changes of brain parenchymal after injury, poor prognostic ability and inability to analyze cerebral perfusion, metabolite and mechanical properties. With the development of modern neuroimaging techniques, advanced neuroimaging techniques have greatly boosted the studies in the diagnosis, prognostication, and eventually impacting treatment of TBI. Advances in neuroimaging techniques have shown potential, including (1) Ultrasound (US) based techniques (contrast-enhanced US, intravascular US, and US elastography), (2) Magnetic resonance imaging (MRI) based techniques (diffusion tensor imaging, magnetic resonance spectroscopy, perfusion weighted imaging, magnetic resonance elastography and functional MRI), and (3) molecular imaging based techniques (positron emission tomography and single photon emission computed tomography). Therefore, in this review, we aim to summarize the role of these advanced neuroimaging techniques in the evaluation and management of TBI. This review is the first to combine the role of the US, MRI and molecular imaging based techniques in TBI. Advanced neuroimaging techniques have great potential; still, there is much to improve. With more clinical validation and larger studies, these techniques will be likely applied for routine clinical use from the initial research.

Association of Traumatic Brain Injury With and Without Loss of Consciousness With Neuropathologic Outcomes in Community-Dwelling Older Persons

Importance

A history of traumatic brain injury (TBI) has been considered a risk factor for Alzheimer dementia. However, the specific association of TBI, even without loss of consciousness (LOC), with pathologic findings that underlie Alzheimer dementia, including Alzheimer disease (AD), non-AD neurodegenerative, and vascular pathologic findings, remains unclear.

Objective

To examine the association between TBI with and without LOC and neuropathologic findings in community-based cohorts.

Design, Setting, and Participants

This cross-sectional analysis used neuropathologic data from 1689 participants from the Religious Orders Study, the Rush Memory and Aging Project, and the Minority Aging Research Study. These studies began enrollment in 1994, 1997, and 2004, respectively. The current study's data set was frozen on April 3, 2021, when the mean (SD) length of follow-up for the participants was 8.7 (5.5) years.

Exposure

Traumatic brain injury exposure was assessed using a standardized, self-reported questionnaire at baseline and annual follow-up visits. Participants were categorized into those (1) without TBI exposure (n = 1024), (2) with TBI with LOC (n = 161), or (3) with TBI without LOC (n = 504).

Main Outcomes and Measures

Neuropathologic measures of amyloid-β, paired helical filament tangles, neocortical Lewy bodies, transactive response DNA-binding protein 43, hippocampal sclerosis, gross infarcts, and microinfarcts were assessed. Multiple linear regression and logistic regression models were used to determine whether TBI with or without LOC (compared with no TBI exposure as the reference group) was associated with neuropathologic outcomes after adjusting for age at death, sex, and educational level. Whether the apolipoprotein E (APOE) ε4 allele and sex differences modified associations was also examined.

Results

A total of 1689 participants (1138 [67%] women and 551 [33%] men; mean [SD] age at death, 89.2 [6.7] years; 80 [5%] Black, 46 [3%] Latino, 1639 [97%] non-Latino, and 1601 [95%] White) participated in the study. Compared with participants without TBI, participants with TBI with LOC had a greater amyloid-β load (estimate, 0.25; 95% CI, 0.06-0.43; P = .008) and higher odds of having 1 or more gross infarcts (odds ratio [OR], 1.45; 95% CI, 1.04-2.02; P = .02) and 1 or more microinfarcts (OR, 1.70; 95% CI, 1.21-2.38; P = .002), particularly subcortical microinfarcts (OR, 1.85; 95% CI, 1.23-2.79; P = .002). Those with TBI without LOC had higher odds of neocortical Lewy bodies (OR, 1.37; 95% CI, 1.01-1.87; P = .04) and 1 or more cortical microinfarcts (OR, 1.43; 95% CI, 1.09-1.87; P = .008). The association of TBI with and without LOC with vascular pathologic outcomes persisted after controlling for vascular risk factors and vascular disease burden. Traumatic brain injury with or without LOC was not associated with paired helical filament tangles, transactive response DNA-binding protein 43, or hippocampal sclerosis. No interactions occurred with APOE ε4 or sex.

Conclusions and Relevance

This cross-sectional analysis suggests that a history of TBI, even without LOC, is associated with age-related neuropathologic outcomes, both neurodegenerative and vascular. The variation in the neuropathologic outcomes in individuals with and without LOC may provide clues to potential mechanisms, diagnoses, and management in persons with TBI.

Hippocampal and rostral anterior cingulate blood flow is associated with affective symptoms in chronic traumatic brain injury

OBJECTIVE

The purpose of this study was to assess cerebral blood flow (CBF) and its association with self-reported symptoms in chronic traumatic brain injury (TBI).

PARTICIPANTS

Sixteen participants with mild to severe TBI and persistent self-reported neurological symptoms, 6 to 72 months post-injury were included. For comparison, 16 age- and gender-matched healthy normal control participants were also included.

MAIN MEASURES

Regional CBF and brain volume were assessed using pseudo-continuous Arterial Spin Labeling (PCASL) and T₁-weighted data respectively. Cognitive function and self-reported symptoms were assessed in TBI participants using the national institutes of health (NIH) Toolbox Cognition Battery and Patient-Reported Outcome Measurement Information System respectively. Associations between CBF and cognitive function, symptoms were assessed.

RESULTS

Global CBF and regional brain volumes were similar between groups, but region of interest (ROI) analysis revealed lower CBF bilaterally in the thalamus, hippocampus, left caudate, and left amygdala in the TBI group. Voxel-wise analysis revealed that CBF in the hippocampus, parahippocampus, rostral anterior cingulate, inferior frontal gyrus, and other temporal regions were negatively associated with self-reported anger, anxiety, and depression symptoms. Furthermore, region of interest (ROI) analysis revealed that hippocampal and rostral anterior cingulate CBF were negatively associated with symptoms of fatigue, anxiety, depression, and sleep issues.

CONCLUSION

Regional CBF deficit was observed in the group with chronic TBI compared to the normal control (NC) group despite similar volume of cerebral structures. The observed negative correlation between regional CBF and affective symptoms suggests that CBF-targeted intervention may potentially improve affective symptoms and quality of life after TBI, which needs to be assessed in future studies.

Noninvasive magnetic resonance imaging techniques in mild traumatic brain injury research and diagnosis

Mild traumatic brain injury (mTBI), frequently referred to as concussion, is one of the most common neurological disorders. The underlying neural mechanisms of functional disturbances in the brains of concussed individuals remain elusive. Novel forms of brain imaging have been developed to assess patients postconcussion, including functional magnetic resonance imaging (fMRI), susceptibility-weighted imaging (SWI), diffusion MRI (dMRI), and perfusion MRI [arterial spin labeling (ASL)], but results have been mixed with a more common utilization in the research environment and a slower integration into the clinical setting. In this review, the benefits and drawbacks of the methods are described: fMRI is an effective method in the diagnosis of concussion but it is expensive and time-consuming making it difficult for regular use in everyday practice; SWI allows detection of microhemorrhages in acute and chronic phases of concussion; dMRI is primarily used for the detection of white matter abnormalities, especially axonal injury, specific for mTBI; and ASL is an alternative to the BOLD method with its ability to track cerebral blood flow alterations. Thus, the absence of a universal diagnostic neuroimaging method suggests a need for the adoption of a multimodal approach to the neuroimaging of mTBI. Taken together, these methods, with their underlying functional and structural features, can contribute from different angles to a deeper understanding of mTBI mechanisms such that a comprehensive diagnosis of mTBI becomes feasible for the clinician.

Cerebral Blood Flow Predicts Recovery in Children with Persistent Post-Concussion Symptoms after Mild Traumatic Brain Injury

Persistent post-concussion symptoms (PPCS) following pediatric mild traumatic brain injury (mTBI) are associated with differential changes in cerebral blood flow (CBF). Given its potential as a therapeutic target, we examined CBF changes during recovery in children with PPCS. We hypothesized that CBF would decrease and that such decreases would mirror clinical recovery. In a prospective cohort study, 61 children and adolescents (mean age 14 [standard deviation = 2.6] years; 41% male) with PPCS were imaged with three-dimensional (3D) pseudo-continuous arterial spin-labelled (pCASL) magnetic resonance imaging (MRI) at 4-6 and 8-10 weeks post-injury. Exclusion criteria included any significant past medical history and/or previous concussion within the past 3 months. Twenty-three participants had clinically recovered at the time of the second scan. We found that relative and mean absolute CBF were higher in participants with poor recovery, 44.0 (95% confidence interval [CI]: 43.32, 44.67) than in those with good recovery, 42.19 (95% CI: 41.77, 42.60) mL/min/100 g gray tissue and decreased over time (β = -1.75; p < 0.001). The decrease was greater in those with good recovery (β = 2.29; p < 0.001) and predicted outcome in 77% of children with PPCS (odds ratio [OR] 0.54, 95% CI: 0.36, 0.80; p = 0.002). Future studies are warranted to validate the utility of CBF as a useful predictive biomarker of outcome in PPCS.

Attenuation of tonic inhibition prevents chronic neurovascular impairments in a Thy1-ChR2 mouse model of repeated, mild traumatic brain injury

Rationale: Mild traumatic brain injury (mTBI), the most common type of brain trauma, frequently leads to chronic cognitive and neurobehavioral deficits. Intervening effectively is impeded by our poor understanding of its pathophysiological sequelae.

Methods: To elucidate the long-term neurovascular sequelae of mTBI, we combined optogenetics, two-photon fluorescence microscopy, and intracortical electrophysiological recordings in mice to selectively stimulate peri-contusional neurons weeks following repeated closed-head injury and probe individual vessel's function and local neuronal reactivity.

Results: Compared to sham-operated animals, mTBI mice showed doubled cortical venular speeds (115 ± 25%) and strongly elevated cortical venular reactivity (53 ± 17%). Concomitantly, the pericontusional neurons exhibited attenuated spontaneous activity (-57 ± 79%) and decreased reactivity (-47 ± 28%). Post-mortem immunofluorescence revealed signs of peri-contusional senescence and DNA damage, in the absence of neuronal loss or gliosis. Alteration of neuronal and vascular functioning was largely prevented by chronic, low dose, systemic administration of a GABA-A receptor inverse agonist (L-655,708), commencing 3 days following the third impact.

Conclusions: Our findings indicate that repeated mTBI leads to dramatic changes in the neurovascular unit function and that attenuation of tonic inhibition can prevent these alterations. The sustained disruption of the neurovascular function may underlie the concussed brain's long-term susceptibility to injury, and calls for development of better functional assays as well as of neurovascularly targeted interventions.

Cerebral perfusion is associated with blast exposure in military personnel without moderate or severe TBI

Due to the use of improvised explosive devices, blast exposure and mild traumatic brain injury (mTBI) have become hallmark injuries of the Iraq and Afghanistan wars. Although the mechanisms of the effects of blast on human neurobiology remain active areas of investigation, research suggests that the cerebrovasculature may be particularly vulnerable to blast via molecular processes that impact cerebral blood flow. Given that recent work suggests that blast exposure, even without a subsequent TBI, may have negative consequences on brain structure and function, the current study sought to further understand the effects of blast exposure on perfusion. One hundred and eighty military personnel underwent pseudo-continuous arterial spin labeling (pCASL) imaging and completed diagnostic and clinical interviews. Whole-brain analyses revealed that with an increasing number of total blast exposures, there was significantly increased perfusion in the right middle/superior frontal gyri, supramarginal gyrus, lateral occipital cortex, and posterior cingulate cortex as well as bilateral anterior cingulate cortex, insulae, middle/superior temporal gyri and occipital poles. Examination of other neurotrauma and clinical variables such as close-range blast exposures, mTBI, and PTSD yielded no significant effects. These results raise the possibility that perfusion may be an important neural marker of brain health in blast exposure.

Emerging Utility of Applied Magnetic Resonance Imaging in the Management of Traumatic Brain Injury

Traumatic brain injury (TBI) is a widespread and expensive problem globally. The standard diagnostic workup for new TBI includes obtaining a noncontrast computed tomography image of the head, which provides quick information on operative pathologies. However, given the limited sensitivity of computed tomography for identifying subtle but meaningful changes in the brain, magnetic resonance imaging (MRI) has shown better utility for ongoing management and prognostication after TBI. In recent years, advanced applications of MRI have been further studied and are being implemented as clinical tools to help guide care. These include functional MRI, diffusion tensor imaging, MR perfusion, and MR spectroscopy. In this review, we discuss the scientific basis of each of the above techniques, the literature supporting their use in TBI, and how they may be clinically implemented to improve the care of TBI patients.

Cerebral Perfusion Effects of Cognitive Training and Transcranial Direct Current Stimulation in Mild-Moderate TBI

Background: Persistent post-traumatic symptoms (PPS) after traumatic brain injury (TBI) can lead to significant chronic functional impairment. Pseudocontinuous arterial spin labeling (pCASL) has been used in multiple studies to explore changes in cerebral blood flow (CBF) that may result in acute and chronic TBI, and is a promising neuroimaging modality for assessing response to therapies. Methods: Twenty-four subjects with chronic mild-moderate TBI (mmTBI) were enrolled in a pilot study of 10 days of computerized executive function training combined with active or sham anodal transcranial direct current stimulation (tDCS) for treatment of cognitive PPS. Behavioral surveys, neuropsychological testing, and magnetic resonance imaging (MRI) with pCASL sequences to assess global and regional CBF were obtained before and after the training protocol. Results: Robust improvements in depression, anxiety, complex attention, and executive function were seen in both active and sham groups between the baseline and post-treatment visits. Global CBF decreased over time, with differences in regional CBF noted in the right inferior frontal gyrus (IFG). Active stimulation was associated with static or increased CBF in the right IFG, whereas sham was associated with reduced CBF. Neuropsychological performance and behavioral symptoms were not associated with changes in CBF. Discussion: The current study suggests a complex picture between mmTBI, cerebral perfusion, and recovery. Changes in CBF may result from physiologic effect of the intervention, compensatory neural mechanisms, or confounding factors. Limitations include a small sample size and heterogenous injury sample, but these findings suggest promising directions for future studies of cognitive training paradigms in mmTBI.

A Cerebrovascular Hypothesis of Neurodegeneration in mTBI

OBJECTIVES

Mild traumatic brain injury (mTBI) is a major public health concern that has generated considerable scientific interest as a complex brain disorder that is associated with long-term neural consequences. This article reviews the literature on cerebrovascular dysfunction in chronic mTBI, with a focus on the long-term neural implications of such dysfunction.

METHODS AND RESULTS

Evidence is presented from human neuroimaging studies to support cerebrovascular involvement in long-term mTBI pathology. In addition, a pathway between mTBI and neurodegeneration via cerebrovascular dysfunction is explored.

CONCLUSIONS

Future work focused on identifying the neurobiological mechanisms underlying the neural consequences of mTBI will be important to guide therapeutic interventions and long-term care for patients with mTBI.

Neuroimaging and Psychometric Assessment of Mild Cognitive Impairment After Traumatic Brain Injury

Traumatic brain injury (TBI) can be serious partly due to the challenges of assessing and treating its neurocognitive and affective sequelae. The effects of a single TBI may persist for years and can limit patients’ activities due to somatic complaints (headaches, vertigo, sleep disturbances, nausea, light or sound sensitivity), affective sequelae (post-traumatic depressive symptoms, anxiety, irritability, emotional instability) and mild cognitive impairment (MCI, including social cognition disturbances, attention deficits, information processing speed decreases, memory degradation and executive dysfunction). Despite a growing amount of research, study comparison and knowledge synthesis in this field are problematic due to TBI heterogeneity and factors like injury mechanism, age at or time since injury. The relative lack of standardization in neuropsychological assessment strategies for quantifying sequelae adds to these challenges, and the proper administration of neuropsychological testing relative to the relationship between TBI, MCI and neuroimaging has not been reviewed satisfactorily. Social cognition impairments after TBI (e.g., disturbed emotion recognition, theory of mind impairment, altered self-awareness) and their neuroimaging correlates have not been explored thoroughly. This review consolidates recent findings on the cognitive and affective consequences of TBI in relation to neuropsychological testing strategies, to neurobiological and neuroimaging correlates, and to patient age at and assessment time after injury. All cognitive domains recognized by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) are reviewed, including social cognition, complex attention, learning and memory, executive function, language and perceptual-motor function. Affect and effort are additionally discussed owing to their relationships to cognition and to their potentially confounding effects. Our findings highlight non-negligible cognitive and affective impairments following TBI, their gravity often increasing with injury severity. Future research should study (A) language, executive and perceptual-motor function (whose evolution post-TBI remains under-explored), (B) the effects of age at and time since injury, and (C) cognitive impairment severity as a function of injury severity. Such efforts should aim to develop and standardize batteries for cognitive subdomains—rather than only domains—with high ecological validity. Additionally, they should utilize multivariate techniques like factor analysis and related methods to clarify which cognitive subdomains or components are indeed measured by standardized tests.

Cerebral Blood Flow and Its Connectivity Deficits in Mild Traumatic Brain Injury at the Acute Stage

Objective

The influence of cognitive impairment after mild traumatic brain injury (mTBI) on cerebral vascular perfusion has been widely concerned, yet the resting-state cerebral blood flow (CBF) connectivity alterations based on arterial spin labeling (ASL) in mild traumatic brain injury (mTBI) remain unclear. This study investigated region CBF and CBF connectivity features in acute mTBI patients, as well as the associations between CBF changes and cognitive impairment.

Materials and Methods

Forty-five acute mTBI patients and 42 health controls underwent pseudocontinuous arterial spin labeling (pCASL) perfusion magnetic resonance imaging (MRI). The alterations in regional CBF and relationship between the CBF changes and cognitive impairment were detected. The ASL-CBF connectivity of the brain regions with regional CBF significant differences was also compared between two groups. Neuropsychological tests covered seven cognitive domains. Associations between the CBF changes and cognitive impairment were further investigated.

Results

Compared with the healthy controls, the acute mTBI patients exhibited increased CBF in the bilateral inferior temporal gyrus (ITG) and decreased CBF in the right middle frontal gyrus (MFG), the bilateral superior frontal gyrus (SFG), and the right cerebellum posterior lobe (CPL). In the mTBI patients, significant correlations were identified between the CBF changes and cognitive impairment. Importantly, the acute mTBI patients exhibited CBF disconnections between the right CPL and right fusiform gyrus (FG) as well as bilateral ITG, between the left SFG and left middle occipital gyrus (MOG), and between the right SFG and right FG as well as right parahippocampal gyrus.

Conclusion

Our results suggest that acute mTBI patients exhibit both regional CBF abnormalities and CBF connectivity deficits, which may underlie the cognitive impairment of the acute mTBI patients.

Dynamic Functional Network Analysis in Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is one of the most common neurological disorders for which a subset of patients develops persistent postconcussive symptoms. Previous studies discovered abnormalities and disruptions in the brain functional networks of mTBI patients principally using static functional connectivity measures which assume that neural communication across the brain is static during resting state conditions. In this study, we examine the differences in dynamic neural communication between mTBI and control participants through the application of a combination of dynamic functional analysis and graph theoretic algorithms. Resting state functional magnetic resonance imaging data was obtained on 47 mTBI patients at the acute stage of injury and 30 demographically matched healthy control participants. Results show unique alterations in both the static and dynamic functional connectivity at the acute stage in mTBI patients who suffer persistent symptoms (≥6 months after injury). In addition, mTBI patients with postconcussion syndrome demonstrated a unique allocation of time in various brain states compared to both control participants and mTBI patients with favorable outcomes. These findings suggest that global damage to the overall communication across the brain in the acute stage may contribute to chronic mTBI symptoms. Dynamic functional analysis is a powerful tool that provides insights into the brain states and the innovative analysis methodology utilized may hold the potential to delineate patients predisposed to poor outcomes upon early presentation following injury.

Structural abnormalities in thalamo-prefrontal tracks revealed by high angular resolution diffusion imaging predict working memory scores in concussed children

Because of their high prevalence, heterogeneous clinical presentation, and wide-ranging sequelae, concussions are a challenging neurological condition, especially in children. Shearing forces transmitted across the brain during concussions often result in white matter damage. The neuropathological impact of concussions has been discerned from animal studies and includes inflammation, demyelination, and axonal loss. These pathologies can overlap during the sub-acute stage of recovery. However, due to the challenges of accurately modeling complex white matter structure, these neuropathologies have not yet been differentiated in children in vivo. In the present study, we leveraged recent advances in diffusion imaging modeling, tractography, and tractometry to better understand the neuropathology underlying working memory problems in concussion. Studying a sample of 16 concussed and 46 healthy youths, we used novel tractography methods to isolate 11 working memory tracks. Along these tracks, we measured fractional anisotropy, diffusivities, track volume, apparent fiber density, and free water fraction. In three tracks connecting the right thalamus to the right dorsolateral prefrontal cortex (DLPFC), we found microstructural differences suggestive of myelin alterations. In another track connecting the left anterior-cingulate cortex with the left DLPFC, we found microstructural changes suggestive of axonal loss. Structural differences and tractography reconstructions were reproduced using test-retest analyses. White matter structure in the three thalamo-prefrontal tracks, but not the cingulo-prefrontal track, appeared to play a key role in working memory function. The present results improve understanding of working memory neuropathology in concussions, which constitutes an important step toward developing neuropathologically informed biomarkers of concussion in children.

Relationships Between Subcortical Shape Measures and Subjective Symptom Reporting in US Service Members With Mild Traumatic Brain Injury

OBJECTIVE

To assess interactions of subcortical structure with subjective symptom reporting associated with mild traumatic brain injury (mTBI), using advanced shape analysis derived from volumetric MRI.

PARTICIPANTS

Seventy-six cognitively symptomatic individuals with mTBI and 59 service members sustaining only orthopedic injury.

DESIGN

Descriptive cross-sectional study.

MAIN MEASURES

Self-report symptom measures included the PTSD Checklist-Military, Neurobehavioral Symptom Inventory, and Symptom Checklist-90-Revised. High-dimensional measures of shape characteristics were generated from volumetric MRI for 7 subcortical structures in addition to standard volume measures.

RESULTS

Several significant interactions between group status and symptom measures were observed across the various shape measures. These interactions were revealed in the right thalamus and globus pallidus for each of the shape measures, indicating differences in structure thickness and expansion/contraction for these regions. No relationships with volume were observed.

CONCLUSION

Results provide evidence for the sensitivity of shape measures in differentiating symptomatic mTBI individuals from controls, while volumetric measures did not exhibit this same sensitivity. Disruptions to thalamic nuclei identified here highlight the role of the thalamus in the spectrum of symptoms associated with mTBI. Additional work is needed to prospectively, and longitudinally, assess these measures along with cognitive performance and advanced multimodal imaging methods to extend the utility of shape analysis in relation to functional outcomes in this population.

A semi-quantitative sport-specific assessment of recurrent traumatic brain injury: the TraQ questionnaire and its application in American football

Chronic traumatic encephalopathy (CTE) is very frequent and studied among contact sport players, above all American Football. Now, the defined diagnosis is only post-mortem and, consequently, more detailed diagnostic in-vivo instruments are needed to facilitate diagnosis and to allow a follow up. This clinical questionnaire (Trauma Questionnaire-TraQ) has been designed to investigate in parallel the traumatic load and clinical and cognitive subjective symptoms. It evaluates 4 anamnestic fields (specific sport activity, all previous pathological events, clinical manifestations compatible with TBI (traumatic brain injury) or CTE and subjective perception of personal memory efficacy with PRMQ questionnaire). The aim of TraQ questionnaire is to allow a standardized follow-up of active players and to identify subclinical disturbances that may become warnings. A pilot comparative study with TraQ on 105 subjects (75 AF players and 30 comparable people without a history of contact-sports activity) revealed that AF players have an increased amount of severe head trauma, an amplified level of subjective aggressiveness, more olfactory deficits but also more speech subjective problems, previously never related with CTE. In view of the obtained results, the TraQ seems to be useful (1) to obtain a better quantification of the traumatic load; (2) to differentiate the risk of long-term neurological consequences, allowing better management of different athletes right from the pre-symptomatic phases; (3) to manage prevention strategies if regularly applied to periodic visits to sports fitness; and (4) to identify the predisposing factors for the development of CTE and other neurological consequences of TBI with follow-up studies.

Determinants of social behavior deficits and recovery after pediatric traumatic brain injury

Traumatic brain injury (TBI) during early childhood is associated with a particularly high risk of developing social behavior impairments, including deficits in social cognition that manifest as reduced social interactions, with profound consequences for the individuals' quality of life. A number of pre-injury, post-injury, and injury-related factors have been identified or hypothesized to determine the extent of social behavior problems after childhood TBI. These include variables associated with the individual themselves (e.g. age, genetics, the injury severity, and extent of white matter damage), proximal environmental factors (e.g. family functioning, parental mental health), and more distal environmental factors (e.g. socioeconomic status, access to resources). In this review, we synthesize the available evidence demonstrating which of these determinants influence risk versus resilience to social behavior deficits after pediatric TBI, drawing upon the available clinical and preclinical literature. Injury-related pathology in neuroanatomical regions associated with social cognition and behaviors will also be described, with a focus on findings from magnetic resonance imaging and diffusion tensor imaging. Finally, study limitations and suggested future directions are highlighted. In summary, while no single variable can alone accurately predict the manifestation of social behavior problems after TBI during early childhood, an increased understanding of how both injury and environmental factors can influence social outcomes provides a useful framework for the development of more effective rehabilitation strategies aiming to optimize recovery for young brain-injured patients.

Neuroimaging of Traumatic Brain Injury

The purpose of this article is to review conventional and advanced neuroimaging techniques performed in the setting of traumatic brain injury (TBI). The primary goal for the treatment of patients with suspected TBI is to prevent secondary injury. In the setting of a moderate to severe TBI, the most appropriate initial neuroimaging examination is a noncontrast head computed tomography (CT), which can reveal life-threatening injuries and direct emergent neurosurgical intervention. We will focus much of the article on advanced neuroimaging techniques including perfusion imaging and diffusion tensor imaging and discuss their potentials and challenges. We believe that advanced neuroimaging techniques may improve the accuracy of diagnosis of TBI and improve management of TBI.

Chronic Upregulation of Cleaved-Caspase-3 Associated with Chronic Myelin Pathology and Microvascular Reorganization in the Thalamus after Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) is associated with long-term disabilities and devastating chronic neurological complications including problems with cognition, motor function, sensory processing, as well as behavioral deficits and mental health problems such as anxiety, depression, personality change and social unsuitability. Clinical data suggest that disruption of the thalamo-cortical system including anatomical and metabolic changes in the thalamus following TBI might be responsible for some chronic neurological deficits following brain trauma. Detailed mechanisms of these pathological processes are not completely understood. The goal of this study was to evaluate changes in the thalamus following TBI focusing on cleaved-caspase-3, a specific effector of caspase pathway activation and myelin and microvascular pathologies using immuno- and histochemistry at different time points from 24 h to 3 months after controlled cortical impact (CCI) in adult Sprague-Dawley rats. Significant increases in cleaved-caspase-3 immunoreactivity in the thalamus were observed starting one month and persisting for at least three months following experimental TBI. Further, the study demonstrated an association of cleaved-caspase-3 with the demyelination of neuronal processes and tissue degeneration in the gray matter in the thalamus, as reflected in alterations of myelinated fiber integrity (luxol fast blue) and decreases in myelin basic protein (MBP) immunoreactivity. The immunofluorescent counterstaining of cleaved-caspase-3 with endothelial barrier antigen (EBA), a marker of blood-brain barrier, revealed limited direct and indirect associations of cleaved caspase-3 with blood-brain barrier damage. These results demonstrate for the first time a significant chronic upregulation of cleaved-caspase-3 in selected thalamic regions associated with cortical regions directly affected by CCI injury. Further, our study is also the first to report that significant upregulation of cleaved-caspase-3 in selected ipsilateral thalamic regions is associated with microvascular reorganization reflected in the significant increases in the number of microvessels with blood-brain barrier alterations detected by EBA staining. These findings provide new insights into potential mechanisms of TBI cell death involving chronic activation of caspase-3 associated with disrupted cortico-thalamic and thalamo-cortical connectivity. Moreover, this study offers the initial evidence that this upregulation of activated caspase-3, delayed degeneration of myelinated nerve fibers and microvascular reorganization with impaired blood-brain barrier integrity in the thalamus might represent reciprocal pathological processes affecting neuronal networks and brain function at the chronic stages of TBI.

Imaging of Concussion in Young Athletes

Conventional neuroimaging examinations are typically normal in concussed young athletes. A current focus of research is the characterization of subtle abnormalities after concussion using advanced neuroimaging techniques. These techniques have the potential to identify biomarkers of concussion. In the future, such biomarkers will likely provide important clinical information regarding the appropriate time interval before return to play, as well as the risk for prolonged postconcussive symptoms and long-term cognitive impairment. This article discusses results from advanced imaging techniques and emphasizes imaging modalities that will likely become available in the near future for the clinical evaluation of concussed young athletes.

Neuroimaging Studies Illustrate the Commonalities Between Ageing and Brain Diseases

The lack of specificity in neuroimaging studies of neurological and psychiatric diseases suggests that these different diseases have more in common than is generally considered. Potentially, features that are secondary effects of different pathological processes may share common neurobiological underpinnings. Intriguingly, many of these mechanisms are also observed in studies of normal (i.e., non-pathological) brain ageing. Different brain diseases may be causing premature or accelerated ageing to the brain, an idea that is supported by a line of "brain ageing" research that combines neuroimaging data with machine learning analysis. In reviewing this field, I conclude that such observations could have important implications, suggesting that we should shift experimental paradigm: away from characterizing the average case-control brain differences resulting from a disease toward methods that place individuals in their age-appropriate context. This will also lead naturally to clinical applications, whereby neuroimaging can contribute to a personalized-medicine approach to improve brain health.

Could Arterial Spin Labeling Distinguish Patients in Minimally Conscious State from Patients in Vegetative State?

Purpose

Diagnostic error is common among patients with vegetative state (VS) and minimally conscious state (MCS). The purpose of this article is to use three-dimensional pseudo-continuous arterial spin labeling (pcASL) to compare cerebral blood flow (CBF) patterns in patients in MCS with those in VS.

Methods

Patients meeting MCS and VS criteria were identified. Two post-labeling delay (PLD) time pcASL on 3.0-Tesla magnetic resonance imaging scanner system were performed with patients in the resting awake state. After registration to T1WI structure imaging, multiple brain regions of interest of ASL CBF map were automatically separated. The average CBF value of every brain region was calculated and compared between the MCS and VS groups with t-tests.

Results

Fifteen patients with VS were identified, with ages ranging from 33 to 71 years. Eight patients who met the MCS criteria ranged in age from 23 to 61 years. Compared with VS, the regional CBF for MCS had a pattern of significantly increased CBF in the regions including the putamen, anterior cingulate gyrus, and medial frontal cortex. A left-lateralized pattern was observed to differentiate MCS from VS. CBF with PLD 2.5 s could find more regions of pattern differentiating MCS from VS than with PLD 1.5 s, except for the pallidum.

Conclusion

MCS might be differentiated from VS by different ranges of regional CBF as measured by ASL. Multi-PLD ASL may serve as an adjunct method to separate MCS from VS and assess functional reserve in patients recovering from severe brain injuries.

Blood biomarkers are associated with brain function and blood flow following sport concussion

BACKGROUND

Secondary injury pathophysiology after sport-related concussion (SRC) is poorly understood. Blood biomarkers may be a useful tool for characterizing these processes, yet there are limitations in their application as a single modality. Combining blood biomarker analysis with advanced neuroimaging may help validate their continued utility in brain injury research by elucidating important secondary injury mechanisms. Hence, the purpose of this study was to evaluate co-modulation between peripheral blood biomarkers and advanced functional brain imaging after SRC.

METHODS

Forty-three university level athletes from 7 sports were recruited (16 recently concussed athletes; 15 healthy athletes with no prior history of concussion; 12 healthy athletes with a history of concussion). Seven blood biomarkers were evaluated: s100B, total tau (T-tau), von Willebrand factor (vWF), brain derived neurotrophic factor (BDNF), peroxiredoxin (PRDX)-6, monocyte chemoattractant protein (MCP)-1 and -4. Resting-state functional MRI was employed to assess global neural connectivity (Gconn), and arterial spin labelling was used to evaluate cerebral blood flow (CBF). We tested for concurrent alterations in blood biomarkers and MRI measures of brain function between athlete groups using a non-parametric, bootstrapped resampling framework.

RESULTS

Compared to healthy athletes, recently concussed athletes showed greater concurrent alterations in several peripheral blood biomarker and MRI measures: a decrease in T-Tau and Gconn, a decrease in T-Tau and CBF, a decrease in Gconn with elevated PRDX-6, a decrease in CBF with elevated PRDX-6, and a decrease in Gconn with elevated MCP-4. In addition, compared to healthy athletes with no concussion history, healthy athletes with a history of concussion displayed greater concurrent alterations in blood biomarkers and Gconn; lower GConn covaried with higher blood levels of s100B and MCP-4.

CONCLUSION

We identified robust relationships between peripheral blood biomarkers and MRI measures in both recently concussed athletes and healthy athletes with a history of concussion. The results from this combinatorial approach further support that human concussion is associated with inflammation, oxidative stress, and cellular damage, and that physiological perturbations may extend chronically beyond recovery. Finally, our results support the continued implementation of blood biomarkers as a tool to investigate brain injury, particularly in a multimodal framework.

Perfusion Imaging in Acute Traumatic Brain Injury

Traumatic brain injury (TBI) is a significant problem worldwide and neuroimaging plays a critical role in diagnosis and management. Recently, perfusion neuroimaging techniques have been explored in TBI to determine and characterize potential perfusion neuroimaging biomarkers to aid in diagnosis, treatment, and prognosis. In this article, computed tomography (CT) bolus perfusion, MR imaging bolus perfusion, MR imaging arterial spin labeling perfusion, and xenon CT are reviewed with a focus on their applications in acute TBI. Future research directions are also discussed.

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.

Investigating structural and perfusion deficits due to repeated head trauma in active professional fighters

Repeated head trauma experienced by active professional fighters results in various structural, functional and perfusion damage. However, whether there are common regions of structural and perfusion damage due to fighting and whether these structural and perfusion differences are associated with neuropsychological measurements in active professional fighters is still unknown. To that end, T1-weighted and pseudocontinuous arterial spin labeling MRI on a group of healthy controls and active professional fighters were acquired. Voxelwise group comparisons, in a univariate and multivariate sense, were performed to investigate differences in gray and white matter density (GMD, WMD) and cerebral blood flow (CBF) between the two groups. A significantly positive association between global GMD and WMD was obtained with psychomotor speed and reaction time, respectively, in our cohort of active professional fighters. In addition, regional WMD deficit was observed in a cluster encompassing bilateral pons, hippocampus, and thalamus in fighters (0.49 ± 0.04 arbitrary units (a.u.)) as compared to controls (0.51 ± 0.05a.u.). WMD in the cluster of active fighters was also significantly associated with reaction time. Significantly lower CBF was observed in right inferior temporal lobe with both partial volume corrected (46.9 ± 14.93 ml/100 g/min) and non-partial volume corrected CBF maps (25.91 ± 7.99 ml/100 g/min) in professional fighters, as compared to controls (65.45 ± 22.24 ml/100 g/min and 35.22 ± 12.18 ml/100 g/min respectively). A paradoxical increase in CBF accompanying right cerebellum and fusiform gyrus in the active professional fighters (29.52 ± 13.03 ml/100 g/min) as compared to controls (19.43 ± 12.56 ml/100 g/min) was observed with non-partial volume corrected CBF maps. Multivariate analysis with both structural and perfusion measurements found the same clusters as univariate analysis in addition to a cluster in right precuneus. Both partial volume corrected and non-partial volume corrected CBF of the cluster in the thalamus had a significantly positive association with the number of fights. In addition, GMD of the cluster in right precuneus was significantly associated with psychomotor speed in our cohort of active professional fighters. Our results suggest a heterogeneous pattern of structural and CBF deficits due to repeated head trauma in active professional fighters. This finding indicates that investigating both structural and CBF changes in the same set of participants may help to understand the pathophysiology and progression of cognitive decline due to repeated head trauma.

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Repetitive head trauma revealed no global structural or global perfusion deficits.

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Cluster of significantly lower WMD was associated with reaction time in fighters.

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Fighters had lower CBF in right inferior temporal lobe.

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Multivariate analysis revealed a cluster associated with number of fights.

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Combined analysis of structural and perfusion measurements is recommended.

Alterations in default-mode network connectivity may be influenced by cerebrovascular changes within 1 week of sports related concussion in college varsity athletes: a pilot study

The goal of this pilot study is to use complementary MRI strategies to quantify and relate cerebrovascular reactivity, resting cerebral blood flow and functional connectivity alterations in the first week following sports concussion in college varsity athletes. Seven college athletes (3F/4M, age = 19.7 ± 1.2 years) were imaged 3-6 days following a diagnosed sports related concussion and compared to eleven healthy controls with no history of concussion (5M/6F, 18-23 years, 7 athletes). Cerebrovascular reactivity and functional connectivity were measured using functional MRI during a hypercapnia challenge and via resting-state regional partial correlations, respectively. Resting cerebral blood flow was quantified using arterial spin labeling MRI methods. Group comparisons were made within and between 18 regions of interest. Cerebrovascular reactivity was increased after concussion when averaged across all regions of interest (p = 0.04), and within some default-mode network regions, the anterior cingulate and the right thalamus (p < 0.05) independently. The FC was increased in the concussed athletes within the default-mode network including the left and right hippocampus, precuneus and ventromedial prefrontal cortex (p < 0.01), with measures being linearly related to cerebrovascular reactivity in the hippocampus in the concussed athletes. Significant resting cerebral blood flow changes were not detected between the two groups. This study provides evidence for increased cerebrovascular reactivity and functional connectivity in the medial regions of the default-mode network within days of a single sports related concussion in college athletes. Our findings emphasize the utility of complementary cerebrovascular measures in the interpretation of alterations in functional connectivity following concussion.

Symptom correlates of cerebral blood flow following acute concussion

Concussion is associated with significant symptoms within hours to days post-injury, including disturbances in physical function, cognition, sleep and emotion. However, little is known about how subjective impairments correlate with objective measures of cerebrovascular function following brain injury. This study examined the relationship between symptoms and cerebral blood flow (CBF) in individuals following sport-related concussion. Seventy university level athletes had CBF measured using Arterial Spin Labelling (ASL), including 35 with acute concussion and 35 matched controls and their symptoms were assessed using the Sport Concussion Assessment Tool 3 (SCAT3). For concussed athletes, greater total symptom severity was associated with elevated posterior cortical CBF, although mean CBF was not significantly different from matched controls (p = 0.46). Examining symptom clusters, athletes reporting greater cognitive symptoms also had lower frontal and subcortical CBF, relative to athletes with greater somatic symptoms. The "cognitive" and "somatic" subgroups also exhibited significant differences in CBF relative to controls (p ≤ 0.026). This study demonstrates objective CBF correlates of symptoms in recently concussed athletes and shows that specific symptom clusters may have distinct patterns of altered CBF, significantly extending our understanding of the neurobiology of concussion and traumatic brain injury.

Arterial Spin Labeling Perfusion of the Brain: Emerging Clinical Applications

Arterial spin labeling (ASL) is a magnetic resonance (MR) imaging technique used to assess cerebral blood flow noninvasively by magnetically labeling inflowing blood. In this article, the main labeling techniques, notably pulsed and pseudocontinuous ASL, as well as emerging clinical applications will be reviewed. In dementia, the pattern of hypoperfusion on ASL images closely matches the established patterns of hypometabolism on fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) images due to the close coupling of perfusion and metabolism in the brain. This suggests that ASL might be considered as an alternative for FDG, reserving PET to be used for the molecular disease-specific amyloid and tau tracers. In stroke, ASL can be used to assess perfusion alterations both in the acute and the chronic phase. In arteriovenous malformations and dural arteriovenous fistulas, ASL is very sensitive to detect even small degrees of shunting. In epilepsy, ASL can be used to assess the epileptogenic focus, both in peri- and interictal period. In neoplasms, ASL is of particular interest in cases in which gadolinium-based perfusion is contraindicated (eg, allergy, renal impairment) and holds promise in differentiating tumor progression from benign causes of enhancement. Finally, various neurologic and psychiatric diseases including mild traumatic brain injury or posttraumatic stress disorder display alterations on ASL images in the absence of visualized structural changes. In the final part, current limitations and future developments of ASL techniques to improve clinical applicability, such as multiple inversion time ASL sequences to assess alterations of transit time, reproducibility and quantification of cerebral blood flow, and to measure cerebrovascular reserve, will be reviewed. ^© RSNA, 2016 Online supplemental material is available for this article.

The Pathophysiology of Concussion

Concussion is a significant issue in medicine and the media today. With growing interest on the long-term effects of sports participation, it is important to understand what occurs in the brain after an impact of any degree. While some of the basic pathophysiology has been elucidated, much is still unknown about what happens in the brain after traumatic brain injury, particularly with milder injuries where no damage can be seen at the structural level on standard neuroimaging. Understanding the chain of events from a cellular level using studies investigating more severe injuries can help to drive research efforts in understanding the symptomatology that is seen in the acute phase after concussion, as well as point to mechanisms that may underlie persistent post-concussive symptoms. This review discusses the basic neuropathology that occurs after traumatic brain injury at the cellular level. We also present the pathology of chronic traumatic encephalopathy and its similarities to other neurodegenerative diseases. We conclude with recent imaging and biomarker findings looking at changes that may occur after repeated subconcussive blows, which may help to guide efforts in understanding if cumulative subconcussive mechanical forces upon the brain are detrimental in the long term or if concussive symptoms mark the threshold for brain injury.

Cerebral Perfusion Changes in Post-Concussion Syndrome: A Prospective Controlled Cohort Study

The biology of post-concussive symptoms is unclear. Symptoms are often increased during activities, and have been linked to decreased cerebrovascular reactivity and perfusion. The aim of this study was to examine cerebral blood flow (CBF) in children with different clinical recovery patterns following mild traumatic brain injury (mTBI). This was a prospective controlled cohort study of children with mTBI (ages 8 to 18 years) who were symptomatic with post-concussive symptoms at one month post-injury (symptomatic, n = 27) and children who had recovered quickly (asymptomatic, n = 24). Pseudo continuous arterial spin labeling magnetic resonance imaging (MRI) was used to quantify CBF. The mTBI groups were imaged at 40 days post-injury. Global and regional CBF were compared with healthy controls of similar age and sex but without a history of mTBI (n = 21). Seventy-two participants (mean age: 14.1 years) underwent neuroimaging. Significant differences in CBF were found: global CBF was higher in the symptomatic group and lower in the asymptomatic group compared with controls, (F(2,69) 9.734; p < 0.001). Post-injury symptom score could be predicted by pre-injury symptoms and CBF in presence of mTBI (adjusted R2 = 0.424; p < 0.001). Altered patterns of cerebral perfusion are seen following mTBI and are associated with the recovery trajectory. Symptomatic children have higher CBF. Children who "recovered" quickly, have decreased CBF suggesting that clinical recovery precedes the cerebral recovery. Further longitudinal studies are required to determine if these perfusion patterns continue to change over time.

Dynamic association between perfusion and white matter integrity across time since injury in Veterans with history of TBI

OBJECTIVE

Cerebral blood flow (CBF) plays a critical role in the maintenance of neuronal integrity, and CBF alterations have been linked to deleterious white matter changes. Although both CBF and white matter microstructural alterations have been observed within the context of traumatic brain injury (TBI), the degree to which these pathological changes relate to one another and whether this association is altered by time since injury have not been examined. The current study therefore sought to clarify associations between resting CBF and white matter microstructure post-TBI.

METHODS

37 veterans with history of mild or moderate TBI (mmTBI) underwent neuroimaging and completed health and psychiatric symptom questionnaires. Resting CBF was measured with multiphase pseudocontinuous arterial spin labeling (MPPCASL), and white matter microstructural integrity was measured with diffusion tensor imaging (DTI). The cingulate cortex and cingulum bundle were selected as a priori regions of interest for the ASL and DTI data, respectively, given the known vulnerability of these regions to TBI.

RESULTS

Regression analyses controlling for age, sex, and posttraumatic stress disorder (PTSD) symptoms revealed a significant time since injury × resting CBF interaction for the left cingulum (p < 0.005). Decreased CBF was significantly associated with reduced cingulum fractional anisotropy (FA) in the chronic phase; however, no such association was observed for participants with less remote TBI.

CONCLUSIONS

Our results showed that reduced CBF was associated with poorer white matter integrity in those who were further removed from their brain injury. Findings provide preliminary evidence of a possible dynamic association between CBF and white matter microstructure that warrants additional consideration within the context of the negative long-term clinical outcomes frequently observed in those with history of TBI. Additional cross-disciplinary studies integrating multiple imaging modalities (e.g., DTI, ASL) and refined neuropsychiatric assessment are needed to better understand the nature, temporal course, and dynamic association between brain changes and clinical outcomes post-injury.