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Advanced neuroimaging applied to veterans and service personnel with traumatic brain injury: state of the art and potential benefits
Abstract
Traumatic brain injury (TBI) remains one of the most prevalent forms of morbidity among Veterans and Service Members, particularly for those engaged in the conflicts in Iraq and Afghanistan. Neuroimaging has been considered a potentially useful diagnostic and prognostic tool across the spectrum of TBI generally, but may have particular importance in military populations where the diagnosis of mild TBI is particularly challenging, given the frequent lack of documentation on the nature of the injuries and mixed etiologies, and highly comorbid with other disorders such as post-traumatic stress disorder, depression, and substance misuse. Imaging has also been employed in attempts to understand better the potential late effects of trauma and to evaluate the effects of promising therapeutic interventions. This review surveys the use of structural and functional neuroimaging techniques utilized in military studies published to date, including the utilization of quantitative fluid attenuated inversion recovery (FLAIR), susceptibility weighted imaging (SWI), volumetric analysis, diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), positron emission tomography (PET), magnetoencephalography (MEG), task-based and resting state functional MRI (fMRI), arterial spin labeling (ASL), and magnetic resonance spectroscopy (MRS). The importance of quality assurance testing in current and future research is also highlighted. Current challenges and limitations of each technique are outlined, and future directions are discussed.
... To specifically study the effects of blast overpressure on CBF, arterial spin labeling (ASL) is a highly suitable MRI technique. ASL allows for the quantification of cerebral perfusion by magnetically labeling arterial blood water and has been used to detect cerebralperfusion-related pathologies such as cerebral ischemia and vasospasm [73]. ASL has been used in clinical studies investigating CBF changes associated with military-related TBI [24,26] and blast exposure [7]. ...
... Additionally, in a study by Clark et al. [26], combined ASL and DTI MRI data from Veterans with mild or moderate TBI indicated that reduced CBF is associated with poor white matter integrity and that this dynamic relationship may be responsible for adverse outcomes associated with TBI. Pseudocontinuous ASL (pCASL) is also a preferred approach for assessing CBF, as pCASL has a high labeling efficiency and signal-to-noise ratio [73,80]. It is clear that MRI techniques that monitor brain perfusion and CBF are critical to understanding the mechanisms and progression of cumulative LLB effects. ...
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.
... Brain injury leads to the rapid increase in glutamate in the interstitium [39-41], reflecting massive neuronal release of glutamate following the lesion-induced loss of ionic homeostasis [42]. In recent years, imaging techniques such as magnetic resonance spectroscopy have found that under the pathological state of TBI, the changes of neural metabolites show a complex trend involving many factors, and the changes of various neural metabolites after TBI do not follow the same or similar paths [43]. In general, N-acetylaspartate (NAA) is reduced in the acute and subacute phases of injury and recovers over time. ...
... Changes in choline, a membrane marker, elevation of which may indicate astrogliosis [49], are more variable and depend on the types and regions of TBI [46,47,50]. All these changes in metabolites may reflect altered neuronal viability, integrity, excitability, and astrogliosis [43]. Several magnetic resonance spectroscopy studies support the idea that the increase in myoinositol reflects glial hypertrophy and/ or glial proliferation, while myoinositol elevation is also associated with an increase in GFAP expression and immunoreactivity [48,51,52]. ...
Although posttraumatic stress disorder (PTSD) is on the rise, traumatic events and their consequences are often hidden or minimized by patients for reasons linked to PTSD itself. Traumatic experiences can be broadly classified into mental stress (MS) and traumatic brain injury (TBI), but the cellular mechanisms of MS-or TBI-induced PTSD remain unknown. Recent evidence has shown that the morphological remodeling of astrocytes accompanies and arguably contributes to fearful memories and stress-related disorders. In this review, we summarize the roles of astrocytes in the pathogenesis of MS-PTSD and TBI-PTSD. Astrocytes synthesize and secrete neurotrophic, pro-and anti-inflammatory factors and regulate the microenvi-ronment of the nervous tissue through metabolic pathways, ionostatic control, and homeostatic clearance of neuro-transmitters. Stress or trauma-associated impairment of these vital astrocytic functions contribute to the patho-physiological evolution of PTSD and may present therapeutic targets.
... Several studies have demonstrated cortical thinning in individuals with blast-related mild TBI, primarily in the frontal cortex, 21-23 but volumetric associations are less common. 3,66 Our work suggests that there are gross alterations in brain volume remotely after blast-related mild TBI, specifically, and contributes to a growing understanding of the unique and adverse long-term effects of blast-related mild TBI on brain function. Mechanisms by which blast-related TBI may effect brain structure include tissue compression and shearing, differential tissue deformation due to varying densities and viscoelastic properties, and expansion of gas-filled spaces (including rupture of the microvasculature). ...
Importance
Blast-related mild traumatic brain injuries (TBIs), the “signature injury” of post-9/11 conflicts, are associated with clinically relevant, long-term cognitive, psychological, and behavioral dysfunction and disability; however, the underlying neural mechanisms remain unclear.
Objective
To investigate associations between a history of remote blast-related mild TBI and regional brain volume in a sample of US veterans and active duty service members.
Design, Setting, and Participants
Prospective cohort study of US veterans and active duty service members from the Long-Term Impact of Military-Relevant Brain Injury Consortium–Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC), which enrolled more than 1500 participants at 5 sites used in this analysis between 2014 and 2023. Participants were recruited from Veterans Affairs medical centers across the US; 774 veterans and active duty service members of the US military met eligibility criteria for this secondary analysis. Assessment dates were from January 6, 2015, to March 31, 2023; processing and analysis dates were from August 1, 2023, to January 15, 2024.
Exposure
All participants had combat exposure, and 82% had 1 or more lifetime mild TBIs with variable injury mechanisms.
Main Outcomes and Measures
Regional brain volume was calculated using tensor-based morphometry on 3-dimensional, T1-weighted magnetic resonance imaging scans; history of TBI, including history of blast-related mild TBI, was assessed by structured clinical interview. Cognitive performance and psychiatric symptoms were assessed with a battery of validated instruments. We hypothesized that regional volume would be smaller in the blast-related mild TBI group and that this would be associated with cognitive performance.
Results
A total of 774 veterans (670 [87%] male; mean [SD] age, 40.1 [9.8] years; 260 [34%] with blast-related TBI) were included in the sample. Individuals with a history of blast-related mild TBI had smaller brain volumes than individuals without a history of blast-related mild TBI (which includes uninjured individuals and those with non–blast-related mild TBI) in several clusters, with the largest centered bilaterally in the superior corona radiata and subcortical gray and white matter (cluster peak Cohen d range, −0.23 to −0.38; mean [SD] Cohen d , 0.28 [0.03]). Additionally, causal mediation analysis revealed that these volume differences significantly mediated the association between blast-related mild TBI and performance on measures of working memory and processing speed.
Conclusions and Relevance
In this cohort study of 774 veterans and active duty service members, robust volume differences associated with blast-related TBI were identified. Furthermore, these volume differences significantly mediated the association between blast-related mild TBI and cognitive function, indicating that this pattern of brain differences may have implications for daily functioning.
... Several studies have demonstrated cortical thinning in bTBI, primarily in the frontal cortex, 21-23 but volumetric associations are less common. 3,63 Our work suggests that there are gross alterations in brain volume remotely after bTBI specifically, and contributes to a growing acknowledgement of the unique and adverse long-term effects of blast exposure and bTBI on brain function. Many combat and training missions continue to involve high levels and prolonged exposure to blast waves. ...
Importance: Blast-related mild traumatic brain injuries (bTBI), the 'signature injury' of post-9/11 conflicts, are associated with clinically-relevant long-term cognitive, psychological, and behavioral dysfunction and disability; however, the underlying neural mechanisms remain unclear.
Objective: To investigate associations between a history of remote bTBI and regional brain volume in a sample of United States (U.S.) Veterans and Active Duty Service Members (VADSM).
Design: Prospective case-control study of U.S. VADSM of participants from the Long-term Impact of Military-relevant Brain Injury Consortium - Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC), which enrolled over 1,500 participants at five sites used in this analysis between 2014-2023.
Setting: Participants were recruited from Veterans Affairs medical centers across the U.S.
Participants: Seven hundred and seventy-four VADSM of the U.S. military met eligibility criteria for this analysis.
Exposure: All participants had combat exposure, and 82% had one or more lifetime mild TBIs with variable injury mechanisms.
Main Outcomes and Measures: Regional brain volume was calculated using tensor-based morphometry on 3D T1-weighted magnetic resonance imaging scans. TBI history, including history of blast-related injury (bTBI), was assessed by structured clinical interview. Cognitive performance and psychiatric symptoms were assessed with a battery of validated instruments. We hypothesized that regional volume would be smaller in the bTBI group, and that this would be associated with cognitive performance.
Results: Individuals with a history of bTBI had smaller brain volumes in several clusters, with the largest centered bilaterally in the superior corona radiata and globus pallidus. Greater volume deficits were associated with a larger number of lifetime bTBIs. Additionally, causal mediation analysis revealed that these volume differences significantly mediated the association between bTBI and performance on measures of working memory and processing speed.
Conclusions and Relevance: Our results reveal robust volume differences associated with bTBI. Magnetic resonance elastography atlases reveal that the specific regions affected include the stiffest tissues in the brain, which may underlie their vulnerability to pressure waves from blast exposures. Furthermore, these volume differences significantly mediated the association between bTBI and cognitive function, indicating that this may be a helpful biomarker in tracking outcome after bTBI and suggesting potential treatment targets to prevent or limit chronic dysfunction.
... Previous studies have suggested that this is due to the neuropathological changes in these patients being functional impairment rather than structural damage (33). Significant advances in neuroimaging have recently made it possible to study functional abnormalities in mTBI using a variety of methods (34)(35)(36). The technology used in this study is based on diffusion imaging non-invasively. ...
Purpose
This study aims to investigate the glymphatic system activity changes in patients with mild traumatic brain injury (mTBI), particularly in MRI-negative patients, using analysis along the perivascular space (ALPS) technology.
Methods
A total of 161 mTBI patients (age: 15–92 years old) and 28 healthy controls (age: 15–84 years old) were included in this retrospective study. The mTBI patients were divided into MRI-negative and MRI-positive groups. ALPS index was calculated automatically using whole-brain T1-MPRAGE imaging and diffusion tensor imaging. The Student's t and chi-squared tests were performed to compare the ALPS index, age, gender, course of disease, and Glasgow Coma Scale (GCS) score between groups. Correlations among ALPS index, age, course of disease and GCS score were computed using Spearman's correlation analysis.
Results
Increased activity of the glymphatic system was suggested in mTBI patients based on ALPS index analysis, including the MRI-negative patients. There was a significant negative correlation between the ALPS index and age. In addition, a weak positive correlation between the ALPS index and course of disease was also observed. On the contrary, there was no significant correlation between the ALPS index and sex nor between the ALPS index and GCS score.
Conclusion
Our study demonstrated that the activity level of the glymphatic system was enhanced in mTBI patients, even when their brain MRI scans were negative. These findings may provide novel insights for understanding the pathophysiology of mild TBI.
... The development of various imaging techniques has enabled the notable broadening of knowledge regarding traumatic brain injury in military personnel. Of these techniques, the most effective are magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), functional MRI (fMRI), magnetic resonance spectroscopy (MRS), and susceptibilityweighted imaging (SWI) as well as positron emission tomography [4][5][6][7]. MRS, in particular its most common type-proton magnetic resonance spectroscopy ( 1 HMRS), allows for a non-invasive examination of metabolites in brain tissue in vivo, namely N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), myoinositol (mI), lipids (Lip), and lactate (Lac). The detected metabolites are markers of various cells and processes present in the brain tissue-N-acetyl aspartate is a marker of neuronal health, choline of cell membrane turnover, creatine of energy metabolism, and myoinositol of glial cells. ...
The aims of this study were to assess the common anomalies in the MRI examinations of the heads of soldiers as well as to compare the relative concentration of magnetic resonance spectroscopy (MRS) metabolites in the brains of soldiers with those of healthy age-matched controls. Overall, 54 professional male soldiers were included in the study group and 46 healthy, age-matched males were in the control group. The relative values of N-acetylaspartate (NAA), choline (Cho), and myoinositol (mI) to creatine (Cr) were assessed. The mean relative concentrations of metabolites were compared between the study and the control group, separately for the frontal and occipital lobes, as well as between the right and left hemispheres within the study group only. The most frequent findings in the head MRI of the soldiers were: asymmetric lateral ventricles and dilated perivascular spaces, enlargement of the subarachnoid spaces, and the presence of cavum septum pellucidum and cavum vergae; the high frequency of sinus disease should also be noted. In the frontal lobes, the mI/Cr ratio was significantly higher (p = 0.005), while the NAA/Cr ratio was lower (p = 0.001), in the group of soldiers (vs. the study group). In the occipital lobes, the NAA/Cr ratio was significantly lower (p = 0.005) in the military personnel and there was a tendency to a higher mI/Cr ratio in the soldiers’ occipital lobes (p = 0.056) (vs. the study group). Comparing the metabolites between the left and right hemispheres in soldiers preferring a right shooting position, a significantly higher mI/Cr (p < 0.001) ratio was observed in the right frontal lobe (vs. the left) and a markedly lower NAA/Cr (p = 0.003) in the right occipital lobe (vs. the left). These changes are associated with astrogliosis and neuronal loss, presumably secondary to repetitive mild traumatic brain injury.
... Neuroimaging has revealed persistent alterations in brain structure and function after extracranial injuries have healed (Wilde et al., 2015). Diffusion magnetic resonance imaging (dMRI) is particularly sensitive to axonal neuropathology of TBI, but evidence is mixed regarding alterations in white matter (WM) organization after mTBI. ...
Traumatic brain injury (TBI) in military populations can cause disruptions in brain structure and function, along with cognitive and psychological dysfunction. Diffusion magnetic resonance imaging (dMRI) can detect alterations in white matter (WM) microstructure, but few studies have examined brain asymmetry. Examining asymmetry in large samples may increase sensitivity to detect heterogeneous areas of WM alteration in mild TBI. Through the Enhancing Neuroimaging Genetics Through Meta-Analysis Military-Relevant Brain Injury working group, we conducted a mega-analysis of neuroimaging and clinical data from 16 cohorts of Active Duty Service Members and Veterans (n = 2598). dMRI data were processed together along with harmonized demographic, injury, psychiatric, and cognitive measures. Fractional anisotropy in the cingulum showed greater asymmetry in individuals with deployment-related TBI, driven by greater left lateralization in TBI. Results remained significant after accounting for potentially confounding variables including posttraumatic stress disorder, depression, and handedness, and were driven primarily by individuals whose worst TBI occurred before age 40. Alterations in the cingulum were also associated with slower processing speed and poorer set shifting. The results indicate an enhancement of the natural left laterality of the cingulum, possibly due to vulnerability of the nondominant hemisphere or compensatory mechanisms in the dominant hemisphere. The cingulum is one of the last WM tracts to mature, reaching peak FA around 42 years old. This effect was primarily detected in individuals whose worst injury occurred before age 40, suggesting that the protracted development of the cingulum may lead to increased vulnerability to insults, such as TBI.
... To date, differentiating the neural substrates of symptoms and the cognitive, behavioral, and emotional effects of PTSD and mTBI has proven challenging (Wilde et al., 2015) it is important that the two are distinguished at the level of neurobiological systems, as the treatments can differ drastically, and oftentimes establishing an effective treatment regimen can take months, if not years. Nevertheless, recent studies have shown that MEG holds promise in disentangling the neurophysiological signatures of PTSD and mTBI, with the application of machine learning routines, multivariate statistics, and classification algorithms that can reliably stratify the disorders and even identify individual cases with a high degree of accuracy (Misic et al. 2016;Rowland et al. 2017;Spadoni et al. 2018;Zhang et al. 2021). ...
Mild traumatic brain injury (mTBI) – or concussion as it is oftentimes known – is a common type of acquired brain injury that generally has a favorable prognosis. However, a significant minority of cases present with persistent postconcussive symptoms that can reduce quality of life through functional impairment. Structural brain imaging has shown to be insufficient for the scope of the problem, now labeled a “silent epidemic,” and there are increasingly concerns about the number of accumulated head knocks during sport culminating in neurodegenerative disease, such as chronic traumatic encephalopathy (CTE). The advent of powerful new approaches to understanding brain function, such as magnetoencephalography (MEG), has shown promise in revealing the electrophysiological disturbances and functional consequence that mTBI can cause. In this chapter, we review some of the literature that shows MEG can image this “invisible injury” and potentially offer a rapid diagnostic tool for evaluating “subtle” brain injuries.
... Neuroimaging has revealed persistent alterations in brain structure and function long after other extracranial injuries have healed. 9 Diffusion magnetic resonance imaging (dMRI) is particularly sensitive to the axonal neuropathology of TBI, but there is mixed evidence for alterations in white matter (WM) organization after injury, especially after mTBI. [10][11][12][13][14][15][16] Heterogeneity among patients may make effects of mTBI especially difficult to detect in group analyses, leading some researchers to take the "pothole" approach, i.e., reporting global WM disruption irrespective of location. ...
Traumatic brain injury (TBI), a significant concern in military populations, is associated with alterations in brain structure and function, cognition, as well as physical and psychological dysfunction. Diffusion magnetic resonance imaging (dMRI) is particularly sensitive to changes in brain structure following TBI, as alterations in white matter (WM) microstructure are common. However, dMRI studies in mild TBI (mTBI) are conflicting, likely due to relatively small samples, sample heterogeneity (demographics, pre- and comorbidities) and injury characteristics (mechanism; chronicity). Furthermore, few studies account for brain asymmetry, which may impact cognitive functions subserved by WM tracts. Examining brain asymmetry in large samples may increase sensitivity to detect heterogeneous areas of subtle WM alteration in mTBI.
Through the Enhancing Neuroimaging and Genetics through Meta-analysis (ENIGMA) Military-Relevant Brain Injury working group, we conducted a mega-analysis of neuroimaging and clinical data from 16 cohorts of Active Duty Service Members and Veterans ( n= 2,598; 2,321 males/277 females; age 19-85 years). 1,080 reported a deployment-related TBI, 480 had a history of only non-military-related TBI, 823 reported no history of TBI, and 215 did not differentiate between military and non-military TBI. dMRI data were processed in a harmonized manner along with harmonized demographic, injury, psychiatric, and cognitive measures. Hemispheric asymmetry of fractional anisotropy (FA, a common proxy for myelin organization) was calculated for 19 WM tracts and compared between those with and without TBI history.
FA in the cingulum showed greater asymmetry in individuals with a history of deployment-related TBI; this effect was driven by greater left lateralization in the group with TBI. There was a trend towards lower FA of the right cingulum in the TBI group. These results remained significant after accounting for potentially confounding variables including posttraumatic stress disorder, depression, and handedness and were driven primarily by individuals who had sustained their worst TBI before age 40. We further found that alterations in the cingulum were associated with slower processing speed and poorer set shifting.
The results indicate an enhancement of the previously reported natural left laterality, possibly due to vulnerability of the non-dominant hemisphere or compensatory mechanisms in the dominant hemisphere. The cingulum is one of the last WM tracts to mature, reaching peak FA around 42 years old. This effect was primarily detected in individuals whose worst injury occurred before age 40, suggesting that the protracted development of the cingulum may lead to increased vulnerability to insults, such as TBI.
Mild to moderate traumatic brain injury (TBI) due to blast exposure is frequently diagnosed in veterans returning from the wars in Iraq and Afghanistan. However, it is unclear whether neural damage resulting from blast TBI differs from that found in TBI due to blunt-force trauma (e.g., falls and motor vehicle crashes). Little is also known about the effects of blast TBI on neural networks, particularly over the long term. Because impairment in working memory has been linked to blunt-force TBI, the present functional magnetic resonance imaging (fMRI) study sought to investigate whether brain activation in response to a working memory task would discriminate blunt-force from blast TBI. Twenty-five veterans (mean age = 29.8 years, standard deviation = 6.01 years, 1 female) who incurred TBI due to blast an average of 4.2 years prior to enrollment and 25 civilians (mean age = 27.4 years, standard deviation = 6.68 years, 4 females) with TBI due to blunt-force trauma performed the Sternberg Item Recognition Task while undergoing fMRI. The task involved encoding 1, 3, or 5 items in working memory. A group of 25 veterans (mean age = 29.9 years, standard deviation = 5.53 years, 0 females) and a group of 25 civilians (mean age = 27.3 years, standard deviation = 5.81 years, 0 females) without history of TBI underwent identical imaging procedures and served as controls. Results indicated that the civilian TBI group and both control groups demonstrated a monotonic relationship between working memory set size and activation in the right caudate during encoding, whereas the blast TBI group did not (p
Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease confirmed at postmortem. Those at highest risk are professional athletes who participate in contact sports and military personnel who are exposed to repetitive blast events. All neuropathologically confirmed CTE cases, to date, have had a history of repetitive head impacts. This suggests that repetitive head impacts may be necessary for the initiation of the pathogenetic cascade that, in some cases, leads to CTE. Importantly, while all CTE appears to result from repetitive brain trauma, not all repetitive brain trauma results in CTE. Magnetic resonance imaging has great potential for understanding better the underlying mechanisms of repetitive brain trauma. In this review, we provide an overview of advanced imaging techniques currently used to investigate brain anomalies. We also provide an overview of neuroimaging findings in those exposed to repetitive head impacts in the acute/subacute and chronic phase of injury and in more neurodegenerative phases of injury, as well as in military personnel exposed to repetitive head impacts. Finally, we discuss future directions for research that will likely lead to a better understanding of the underlying mechanisms separating those who recover from repetitive brain trauma vs. those who go on to develop CTE.
© 2015 International Society of Neuropathology.
Soccer is played by more than 250 million people worldwide. Repeatedly heading the ball may place soccer players at high risk for repetitive subconcussive head impacts (RSHI). This study evaluates the long-term effects of RSHI on neurochemistry in athletes without a history of clinically diagnosed concussion, but with a high exposure to RSHI. Eleven former professional soccer players (mean age 52.0 ± 6.8 years) and a comparison cohort of fourteen age- and gender-matched former non-contact sport athletes (mean age 46.9 ± 7.9 years) underwent 3T magnetic resonance spectroscopy (MRS) and neurocognitive evaluation. In the soccer players a significant increase was observed in both, choline, a membrane marker, and myo-inositol, a marker of glial activation, compared to control athletes. Additionally, myo-inositol and glutathione were significantly correlated with lifetime estimate of RSHI within the soccer group. There was no significant difference in neurocognitive tests between groups. Results of this study suggest an association between RSHI in soccer players and MRS markers of neuroinflammation, suggesting that even subconcussive head impacts affect the neurochemistry of the brain and may precede neurocognitive changes. Future studies will need to determine the role of neuroinflammation in RSHI and the effect on neurocognitive function.
Imaging plays a key role in the diagnosis and longitudinal follow up of traumatic brain injury (TBI). Among injury pathologies, vascular injury is associated with diffuse axonal injury (DAI) and traumatic axonal injury (TAI). The vascular network is ubiquitous and is an integral part of the tissue structure. In this chapter, we focus on angiographic and venographic-related imaging methods and their role in assessing mild, moderate, and severe TBI. We begin with an introduction to susceptibility weighted imaging (SWI) and magnetic resonance angiography (MRA) and then provide evidence of different types of vascular damage. Examples of TBI-induced microbleeds are presented along with the concept of low-impact medullary vein damage (MVD). This MVD has been seen even for so-called mild TBI cases. Vascular damage can also manifest as a reduction in local perfusion even when no clear macroscopic vessel damage is seen. To further understand the role of vascular abnormalities, we then introduce the different perfusion weighted imaging (PWI) techniques available and their application in TBI. The combination of SWI and PWI should make it possible to differentiate the role of local thrombus versus changes in oxygen saturation in MVD, for example. Since MRA and SWI are able to provide a full description of the brain's vasculature in 3D, we briefly discuss the presence of finite element modeling in understanding vascular injury. We conclude with recommendations related to the use of perfusion with MRA, SWI, and oxygen saturation measurements to obtain a complete picture of the hemodynamics of the brain. © Springer Science+Business Media New York 2013. All rights are reserved.
Children with attention deficit disorder (ADHD) appear to have trouble controlling attention. The difficulties they have are readily apparent in their everyday behavior, particularly in the classroom, but it has been hard for researchers to pinpoint the source of the problem. Many aspects of attention appear to be intact in experimental studies of these children. Recently, the research focus has shifted from attention itself to the executive processes that control attention. This chapter reviews research on the stop signal paradigm, which requires subjects to inhibit an ongoing response. It has been particularly successful in distinguishing children with ADHD from children with related syndromes and from children with no psychiatric diagnoses. The deficit in response inhibition may be the key deficit underlying ADHD.
Traumatic brain injury (TBI), and particularly concussion, is a major concern for the U.S. Military because of the associated short term disability, long term cognitive and pain symptoms suffered by some, and risk of prolonged or permanent neurologic injury if the Service member incurs a second TBI before full recovery from the first. Concussions were seen more often during the recent conflicts in Afghanistan and Iraq than in prior conflicts, such as the Vietnam War, because of the use of improvised explosive devices that typically caused non-penetrating closed head injury. Since 2000 more than 300,000 Service members were diagnosed with TBI, of which more than 80 % were concussions. Improved TBI screening tools also have identified a higher than expected incidence of concussions occurring in garrison. In this review we summarize current epidemiologic data for TBI in the Military, and describe contemporary Military procedures and strategies for TBI prevention, identification, evaluation, and acute and chronic care. Key TBI clinical research priorities and programs are described, and innovative organizational plans to address future TBI needs are summarized.