Evidence for white matter disruption in traumatic brain injury without macroscopic lesions

White Matter Organization and Cortical Thickness Differ Among Active Duty Service Members With Chronic Mild, Moderate, and Severe Traumatic Brain Injury

Abstract This study compared findings from whole-brain diffusion tensor imaging (DTI) and volumetric magnetic resonance imaging (MRI) among 90 Active Duty Service Members with chronic mild traumatic brain injury (TBI; n = 52), chronic moderate-to-severe TBI (n = 17), and TBI-negative controls (n = 21). Data were collected on a Philips Ingenia 3T MRI with DTI in 32 directions. Results demonstrated that history of TBI was associated with differences in white matter microstructure, white matter volume, and cortical thickness in both mild TBI and moderate-to-severe TBI groups relative to controls. However, the presence, pattern, and distribution of these findings varied substantially depending on the injury severity. Spatially-defined forms of DTI fractional anisotropy (FA) analyses identified altered white matter organization within the chronic moderate-to-severe TBI group, but they did not provide clear evidence of abnormalities within the chronic mild TBI group. In contrast, DTI FA "pothole" analyses identified widely distributed areas of decreased FA throughout the white matter in both the chronic mild TBI and chronic moderate-to-severe TBI groups. Additionally, decreased white matter volume was found in several brain regions for the chronic moderate-to-severe TBI group compared with the other groups. Greater number of DTI FA potholes and reduced cortical thickness were also related to greater severity of self-reported symptoms. In sum, this study expands upon a growing body of literature using advanced imaging techniques to identify potential effects of brain injury in military Service Members. These findings may differ from work in other TBI populations due to varying mechanisms and frequency of injury, as well as a potentially higher level of functioning in the current sample related to the ability to maintain continued Active Duty status after injury. In conclusion, this study provides DTI and volumetric MRI findings across the spectrum of TBI severity. These results provide support for the use of DTI and volumetric MRI to identify differences in white matter microstructure and volume related to TBI. In particular, DTI FA pothole analysis may provide greater sensitivity for detecting subtle forms of white matter injury than conventional DTI FA analyses.

Whole Brain and Corpus Callosum Fractional Anisotropy Differences in Patients with Cognitive Impairment

Diffusion tensor imaging (DTI) is an MRI analysis method that could help assess cognitive impairment (CI) in the ageing population more accurately. In this research, we evaluated fractional anisotropy (FA) of whole brain (WB) and corpus callosum (CC) in patients with normal cognition (NC), mild cognitive impairment (MCI), and moderate/severe cognitive impairment (SCI). In total, 41 participants were included in a cross-sectional study and divided into groups based on Montreal Cognitive Assessment (MoCA) scores (NC group, nine participants, MCI group, sixteen participants, and SCI group, sixteen participants). All participants underwent an MRI examination that included a DTI sequence. FA values between the groups were assessed by analysing FA value and age normative percentile. We did not find statistically significant differences between the groups when analysing CC FA values. Both approaches showed statistically significant differences in WB FA values between the MCI-SCI and MCI-NC groups, where the MCI group participants showed the highest mean FA and highest mean FA normative percentile results in WB.

Diffusion in the corpus callosum predicts persistence of clinical symptoms after mild traumatic brain injury, a multi-scanner study

Background

Mild traumatic brain injuries (mTBIs) comprise 80% of all TBI, but conventional MRI techniques are often insensitive to the subtle changes and injuries produced in a concussion. Diffusion tensor imaging (DTI) is one of the most sensitive MRI techniques for mTBI studies with outcome and symptom associations described. The corpus callosum (CC) is one of the most studied fiber tracts in TBI and mTBI, but the comprehensive post-mTBI symptom relationship has not fully been explored.

Methods

This is a retrospective observational study of how quantitative DTI data of the CC and its sub-regions may relate to clinical presentation of symptoms and timing of resolution of symptoms in patients diagnosed with uncomplicated mTBI. DTI and clinical data were obtained retrospectively from 446 (mean age 42 years, range 13-82) civilian patients. From patient medical charts, presentation of the following common post-concussive symptoms was noted: headache, balance issues, cognitive deficits, fatigue, anxiety, depression, and emotional lability. Also recorded was the time between injury and a visit to the physician when improvement or resolution of a particular symptom was reported. FA values from the total CC and 3 subregions of the CC (genu or anterior, mid body, and splenium or posterior) were obtained from hand tracing on the Olea Sphere v3.0 SP12 free-standing workstation. DTI data was obtained from 8 different 3T MRI scanners and harmonized via ComBat harmonization. The statistical models used to explore the association between regional Fractional Anisotropy (FA) values and symptom presentation and time to symptom resolution were logistic regression and interval-censored semi-parametric Cox proportional hazard models, respectively. Subgroups related to age and timing of first scan were also analyzed.

Results

Patients with the highest FA in the total CC (p = 0.01), anterior CC (p < 0.01), and mid-body CC (p = 0.03), but not the posterior CC (p = 0.91) recovered faster from post-concussive cognitive deficits. Patients with the highest FA in the posterior CC recovered faster from depression (p = 0.04) and emotional lability (p = 0.01). There was no evidence that FA in the CC or any of its sub-regions was associated with symptom presentation or with time to resolution of headache, balance issues, fatigue, or anxiety. Patients with mTBI under 40 had higher FA in the CC and the anterior and mid-body subregions (but not the posterior subregion: p = 1.00) compared to patients 40 or over (p ≤ 0.01). There was no evidence for differences in symptom presentation based on loss of consciousness (LOC) or sex (p ≥ 0.18).

Conclusion

This study suggests that FA of the CC has diagnostic and prognostic value for clinical assessment of mTBI in a large diverse civilian population, particularly in patients with cognitive symptoms.

Neuro-psychiatric symptoms in directly and indirectly blast exposed civilian survivors of urban missile attacks

BACKGROUND

Blast-explosion may cause traumatic brain injury (TBI), leading to post-concussion syndrome (PCS). In studies on military personnel, PCS symptoms are highly similar to those occurring in post-traumatic stress disorder (PTSD), questioning the overlap between these syndromes. In the current study we assessed PCS and PTSD in civilians following exposure to rocket attacks. We hypothesized that PCS symptomatology and brain connectivity will be associated with the objective physical exposure, while PTSD symptomatology will be associated with the subjective mental experience.

METHODS

Two hundred eighty nine residents of explosion sites have participated in the current study. Participants completed self-report of PCS and PTSD. The association between objective and subjective factors of blast and clinical outcomes was assessed using multivariate analysis. White-matter (WM) alterations and cognitive abilities were assessed in a sub-group of participants (n = 46) and non-exposed controls (n = 16). Non-parametric analysis was used to compare connectivity and cognition between the groups.

RESULTS

Blast-exposed individuals reported higher PTSD and PCS symptomatology. Among exposed individuals, those who were directly exposed to blast, reported higher levels of subjective feeling of danger and presented WM hypoconnectivity. Cognitive abilities did not differ between groups. Several risk factors for the development of PCS and PTSD were identified.

CONCLUSIONS

Civilians exposed to blast present higher PCS/PTSD symptomatology as well as WM hypoconnectivity. Although symptoms are sub-clinical, they might lead to the future development of a full-blown syndrome and should be considered carefully. The similarities between PCS and PTSD suggest that despite the different etiology, namely, the physical trauma in PCS and the emotional trauma in PTSD, these are not distinct syndromes, but rather represent a combined biopsychological disorder with a wide spectrum of behavioral, emotional, cognitive and neurological symptoms.

Current State of Diffusion-Weighted Imaging and Diffusion Tensor Imaging for Traumatic Brain Injury Prognostication

Advanced imaging techniques are needed to assist in providing a prognosis for patients with traumatic brain injury (TBI), particularly mild TBI (mTBI). Diffusion tensor imaging (DTI) is one promising advanced imaging technique, but has shown variable results in patients with TBI and is not without limitations, especially when considering individual patients. Efforts to resolve these limitations are being explored and include developing advanced diffusion techniques, creating a normative database, improving study design, and testing machine learning algorithms. This article will review the fundamentals of DTI, providing an overview of the current state of its utility in evaluating and providing prognosis in patients with TBI.

Sleep Quality Disturbances Are Associated with White Matter Alterations in Veterans with Post-Traumatic Stress Disorder and Mild Traumatic Brain Injury

Sleep disturbances are strongly associated with mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD). PTSD and mTBI have been linked to alterations in white matter (WM) microstructure, but whether poor sleep quality has a compounding effect on WM remains largely unknown. We evaluated sleep and diffusion magnetic resonance imaging (dMRI) data from 180 male post-9/11 veterans diagnosed with (1) PTSD (n = 38), (2) mTBI (n = 25), (3) comorbid PTSD+mTBI (n = 94), and (4) a control group with neither PTSD nor mTBI (n = 23). We compared sleep quality (Pittsburgh Sleep Quality Index, PSQI) between groups using ANCOVAs and calculated regression and mediation models to assess associations between PTSD, mTBI, sleep quality, and WM. Veterans with PTSD and comorbid PTSD+mTBI reported poorer sleep quality than those with mTBI or no history of PTSD or mTBI (p = 0.012 to <0.001). Poor sleep quality was associated with abnormal WM microstructure in veterans with comorbid PTSD+mTBI (p < 0.001). Most importantly, poor sleep quality fully mediated the association between greater PTSD symptom severity and impaired WM microstructure (p < 0.001). Our findings highlight the significant impact of sleep disturbances on brain health in veterans with PTSD+mTBI, calling for sleep-targeted interventions.

Machine learning classification of chronic traumatic brain injury using diffusion tensor imaging and NODDI: A replication and extension study

Individuals with acute and chronic traumatic brain injury (TBI) are associated with unique white matter (WM) structural abnormalities, including fractional anisotropy (FA) differences. Our research group previously used FA as a feature in a linear support vector machine (SVM) pattern classifier, observing high classification between individuals with and without acute TBI (i.e., an area under the curve [AUC] value of 75.50%). However, it is not known whether FA could similarly classify between individuals with and without history of chronic TBI. Here, we attempted to replicate our previous work with a new sample, investigating whether FA could similarly classify between incarcerated men with (n = 80) and without (n = 80) self-reported history of chronic TBI. Additionally, given limitations associated with FA, including underestimation of FA values in WM tracts containing crossing fibers, we extended upon our previous study by incorporating neurite orientation dispersion and density imaging (NODDI) metrics, including orientation dispersion (ODI) and isotropic volume (Viso). A linear SVM based classification approach, similar to our previous study, was incorporated here to classify between individuals with and without self-reported chronic TBI using FA and NODDI metrics as separate features. Overall classification rates were similar when incorporating FA and NODDI ODI metrics as features (AUC: 82.50%). Additionally, NODDI-based metrics provided the highest sensitivity (ODI: 85.00%) and specificity (Viso: 82.50%) rates. The current study serves as a replication and extension of our previous study, observing that multiple diffusion MRI metrics can reliably classify between individuals with and without self-reported history of chronic TBI.

Abcc8 (sulfonylurea receptor-1) knockout mice exhibit reduced axonal injury, cytotoxic edema and cognitive dysfunction vs. wild-type in a cecal ligation and puncture model of sepsis

Sepsis-associated brain injury (SABI) is characterized by an acute deterioration of mental status resulting in cognitive impairment and acquisition of new and persistent functional limitations in sepsis survivors. Previously, we reported that septic mice had evidence of axonal injury, robust microglial activation, and cytotoxic edema in the cerebral cortex, thalamus, and hippocampus in the absence of blood-brain barrier disruption. A key conceptual advance in the field was identification of sulfonylurea receptor 1 (SUR1), a member of the adenosine triphosphate (ATP)-binding cassette protein superfamily, that associates with the transient receptor potential melastatin 4 (TRPM4) cation channel to play a crucial role in cerebral edema development. Therefore, we hypothesized that knockout (KO) of Abcc8 (Sur1 gene) is associated with a decrease in microglial activation, cerebral edema, and improved neurobehavioral outcomes in a murine cecal ligation and puncture (CLP) model of sepsis. Sepsis was induced in 4-6-week-old Abcc8 KO and wild-type (WT) littermate control male mice by CLP. We used immunohistochemistry to define neuropathology and microglial activation along with parallel studies using magnetic resonance imaging, focusing on cerebral edema on days 1 and 4 after CLP. Abcc8 KO mice exhibited a decrease in axonal injury and cytotoxic edema vs. WT on day 1. Abcc8 KO mice also had decreased microglial activation in the cerebral cortex vs. WT. These findings were associated with improved spatial memory on days 7-8 after CLP. Our study challenges a key concept in sepsis and suggests that brain injury may not occur merely as an extension of systemic inflammation. We advance the field further and demonstrate that deletion of the SUR1 gene ameliorates CNS pathobiology in sepsis including edema, axonal injury, neuroinflammation, and behavioral deficits. Benefits conferred by Abcc8 KO in the murine CLP model warrant studies of pharmacological Abcc8 inhibition as a new potential therapeutic strategy for SABI.

Posttraumatic Stress and Traumatic Brain Injury: Cognition, Behavior, and Neuroimaging Markers in Vietnam Veterans

BACKGROUND

Posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are common in Veterans and linked to behavioral disturbances, increased risk of cognitive decline, and Alzheimer's disease.

OBJECTIVE

We studied the synergistic effects of PTSD and TBI on behavioral, cognitive, and neuroimaging measures in Vietnam war Veterans.

METHODS

Data were acquired at baseline and after about one-year from male Veterans categorized into: PTSD, TBI, PTSD+TBI, and Veteran controls without PTSD or TBI. We applied manual tractography to examine white matter microstructure of three fiber tracts: uncinate fasciculus (N = 91), cingulum (N = 87), and inferior longitudinal fasciculus (N = 95). ANCOVAs were used to compare Veterans' baseline behavioral and cognitive functioning (N = 285), white matter microstructure, amyloid-β (N = 230), and tau PET (N = 120). Additional ANCOVAs examined scores' differences from baseline to follow-up.

RESULTS

Veterans with PTSD and PTSD+TBI, but not Veterans with TBI only, exhibited poorer behavioral and cognitive functioning at baseline than controls. The groups did not differ in baseline white matter, amyloid-β, or tau, nor in behavioral and cognitive functioning, and tau accumulation change. Progression of white matter abnormalities of the uncinate fasciculus in Veterans with PTSD compared to controls was observed; analyses in TBI and PTSD+TBI were not run due to insufficient sample size.

CONCLUSIONS

PTSD and PTSD+TBI negatively affect behavioral and cognitive functioning, while TBI does not contribute independently. Whether progressive decline in uncinate fasciculus microstructure in Veterans with PTSD might account for cognitive decline should be further studied. Findings did not support an association between PTSD, TBI, and Alzheimer's disease pathology based on amyloid and tau PET.

Decreased Interhemispheric Functional Connectivity and Its Associations with Clinical Correlates following Traumatic Brain Injury

Objective

To explore the interhemispheric functional coordination following traumatic brain injury (TBI) and its association with posttraumatic anxiety and depressive symptoms.

Methods

This was a combination of a retrospective cohort study and a cross-sectional observational study. We investigated the functional coordination between hemispheres by voxel-mirrored homotopic connectivity (VMHC). Grey matter volumes were examined by voxel-based morphometry (VBM), and microstructural integrity of the corpus callosum (CC) was assessed by diffusion tension imaging (DTI). The anxiety and depressive symptoms were evaluated with the Hospital Anxiety and Depression Scale.

Results

The VMHC values of the bilateral middle temporal gyrus (MTG) and orbital middle frontal gyrus (MFG) were significantly decreased in TBI patients versus the healthy controls. Weakened homotopic functional connectivity (FC) in the bilateral orbital MFG is moderate positively correlated with anxiety and depressive symptoms. The white matter integrity in the CC was extensively reduced in TBI patients. In the receiver operating characteristic analysis, the VMHC value of the orbital MFG could distinguish TBI from HC with an area under the curve of 0.939 (sensitivity of 1 and specificity of 0.867).

Conclusion

TBI disrupts the interhemispheric functional and structural connection, which is correlated with posttraumatic mood disorders. These findings may serve as a clinical indicator for diagnosis.

Combining Multiple Indices of Diffusion Tensor Imaging Can Better Differentiate Patients with Traumatic Brain Injury from Healthy Subjects

AIM

Diffuse axonal injury (DAI) is one of the most common pathological features of traumatic brain injury (TBI). Diffusion tensor imaging (DTI) indices can be used to identify and quantify white matter microstructural changes following DAI. Recently, many studies have used DTI with various machine learning approaches to predict white matter microstructural changes following TBI. The current study sought to examine whether our classification approach using multiple DTI indices in conjunction with machine learning is a useful tool for diagnosing/classifying TBI patients and healthy controls.

METHODS

Participants were adult patients with chronic TBI (n = 26) with DAI pathology, and age- and sex-matched healthy controls (n = 26). DTI images were obtained from all participants. Tract-based spatial statistics analyses were applied to DTI images. Classification models were built using principal component analysis and support vector machines. Receiver operator characteristic curve analysis and area under the curve were used to assess the classification performance of the different classifiers.

RESULTS

Tract-based spatial statistics revealed significantly decreased fractional anisotropy, as well as increased mean diffusivity, axial diffusivity, and radial diffusivity in patients with TBI compared with healthy controls (all p-values < 0.01). The principal component analysis and support vector machine-based machine learning classification using combined DTI indices classified patients with TBI and healthy controls with an accuracy of 90.5% with an area under the curve of 93 ± 0.09.

CONCLUSION

These results highlight the potential of our approach combining multiple DTI measures to identify patients with TBI.

Evaluation of the Effectiveness of Newer Helmet Designs with Emergent Shell and Padding Technologies Versus Older Helmet Models for Preserving White Matter Following a Season of High School Football

We aimed to objectively compare the effects of wearing newer, higher-ranked football helmets (HRank) vs. wearing older, lower-ranked helmets (LRank) on pre- to post-season alterations to neuroimaging-derived metrics of athletes' white matter. Fifty-four high-school athletes wore an HRank helmet, and 62 athletes wore an LRank helmet during their competitive football season and completed pre- and post-season diffusion tensor imaging (DTI). Longitudinal within- and between-group DTI metrics [fractional anisotropy (FA) and mean/axial/radial diffusivity (MD, AD, RD)] were analyzed using tract-based spatial statistics. The LRank helmet group exhibited significant pre- to post-season reductions in MD, AD, and RD, the HRank helmet group displayed significant pre- to post-season increases in FA, and both groups showed significant pre- to post-season increases in AD (p's < .05 [corrected]). Between-group analyses revealed the pre- to post-season increase in AD was significantly less for athletes wearing HRank compared to LRank (p < .05 [corrected]). These data provide in vivo evidence that wearing an HRank helmet may be efficacious for preserving white matter from head impact exposure during high school football. Future prospective longitudinal investigations with complimentary imaging and behavioral outcomes are warranted to corroborate these initial in vivo findings.

Early Axonal Injury and Delayed Cytotoxic Cerebral Edema are Associated with Microglial Activation in a Mouse Model of Sepsis

Sepsis-induced brain injury is associated with an acute deterioration of mental status resulting in cognitive impairment and acquisition of new functional limitations in sepsis survivors. However, the exact nature of brain injury in this setting is often subtle and remains to be fully characterized both in preclinical studies and at the bedside. Given the translation potential for the use of magnetic resonance imaging (MRI) to define sepsis-induced brain injury, we sought to determine and correlate the cellular changes with neuroradiographic presentations in a classic murine model of sepsis induced by cecal ligation and puncture (CLP). Sepsis was induced in 6-10-week-old male C57/BL6 mice by CLP. We used immunohistochemistry (IHC) to define neuropathology in a mouse model of sepsis along with parallel studies using MRI, focusing on cerebral edema, blood-brain barrier (BBB) disruption, and microglial activation on days 1 and 4 days after CLP. We demonstrate that septic mice had evidence of early axonal injury, inflammation, and robust microglial activation on day 1 followed by cytotoxic edema on day 4 in the cortex, thalamus, and hippocampus in the absence of BBB disruption. We note the superiority of the MRI to detect subtle brain injury and cytotoxic cerebral edema in comparison with the traditional gold standard assessment, i.e., percent brain water (wet-dry weight method). We conclude that inflammatory changes in the septic brain can be detected in real time, and further studies are needed to understand axonal injury and the impact of inhibition of microglial activation on the development of cerebral edema.

Traumatic axonal injury: is the prognostic information produced by conventional MRI and DTI complementary or supplementary?

OBJECTIVE

A traumatic axonal injury (TAI) diagnosis has traditionally been based on conventional MRI, especially on those sequences with a higher sensitivity to edema and blood degradation products. A more recent technique, diffusion tensor imaging (DTI), can infer the microstructure of white matter (WM) due to the restricted diffusion of water in organized tissues. However, there is little information regarding the correlation of the findings obtained by both methods and their use for outcome prognosis. The main objectives of this study were threefold: 1) study the correlation between DTI metrics and conventional MRI findings; 2) evaluate whether the prognostic information provided by the two techniques is supplementary or complementary; and 3) determine the incremental value of the addition of these variables compared to a traditional prognostic model.

METHODS

The authors studied 185 patients with moderate to severe traumatic brain injury (TBI) who underwent MRI with DTI study during the subacute stage. The number and volume of lesions in hemispheric subcortical WM, corpus callosum (CC), basal ganglia, thalamus, and brainstem in at least four conventional MRI sequences (T1-weighted, T2-weighted, FLAIR, T2* gradient recalled echo, susceptibility-weighted imaging, and diffusion-weighted imaging) were determined. Fractional anisotropy (FA) was measured in 28 WM bundles using the region of interest method. Nonparametric tests were used to evaluate the colocalization of macroscopic lesions and FA. A multivariate logistic regression analysis was performed to assess the independent prognostic value of each neuroimaging modality after adjustment for relevant clinical covariates, and the internal validation of the model was evaluated in a contemporary cohort of 92 patients.

RESULTS

Differences in the lesion load between patients according to their severity and outcome were found. Colocalization of macroscopic nonhemorrhagic TAI lesions (not microbleeds) and lower FA was limited to the internal and external capsule, corona radiata, inferior frontooccipital fasciculus, CC, and brainstem. However, a significant association between the FA value and the identification of macroscopic lesions in distant brain regions was also detected. Specifically, lower values of FA of some hemispheric WM bundles and the splenium of the CC were related to a higher number and volume of hyperintensities in the brainstem. The regression analysis revealed that age, motor score, hypoxia, FA of the genu of the CC, characterization of TAI lesions in the CC, and the presence of thalamic/basal ganglia lesions were independent prognostic factors. The performance of the proposed model was higher than that of the IMPACT (International Mission on Prognosis and Analysis of Clinical Trials in TBI) model in the validation cohort.

CONCLUSIONS

Very limited colocalization of hyperintensities (none for microbleeds) with FA values was discovered. DTI and conventional MRI provide complementary prognostic information, and their combination can improve the performance of traditional prognostic models.

White Matter Alterations Are Associated With Cognitive Dysfunction Decades After Moderate-to-Severe Traumatic Brain Injury and/or Posttraumatic Stress Disorder

BACKGROUND

Possible white matter (WM) alterations following moderate-to-severe traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) and their relationship to clinical outcome have yet to be investigated decades after trauma. We utilized structural magnetic resonance imaging and diffusion tensor images to investigate brain volume and WM alterations in Vietnam War veterans with moderate-to-severe TBI and/or PTSD examined 5 decades after trauma.

METHODS

Data from 160 veterans-history of moderate-to-severe TBI (n = 23), history of TBI+PTSD (n = 36), history of PTSD (n = 53), and control veterans (n = 48)-were obtained from the Department of Defense Alzheimer's Disease Neuroimaging Initiative database. Voxel-based morphometry and tract-based spatial statistics were used to investigate ongoing brain morphometry and WM abnormalities. The fractional anisotropy (FA) and mean diffusivity were then correlated with neuropsychological scores and amyloid deposition in the trauma groups.

RESULTS

Compared with control subjects, the three trauma groups showed gray matter atrophy, lower FA, and distinctly higher diffusivity in the major WM tracts, including the corpus callosum, external and internal capsules, cingulum, and inferior and superior longitudinal fasciculi. The FA and mean diffusivity correlated with cognitive deficits in the trauma groups. Furthermore, the FA in the cingulum correlated negatively with amyloid deposition in the posterior cingulate cortex of all three trauma groups.

CONCLUSIONS

Diffusion tensor imaging detected WM abnormalities that correlated with the severity of present cognitive dysfunction and the degree of cortical amyloid deposition decades after moderate-to-severe TBI and/or PTSD. These results may hint that PTSD secondary to TBI may incur late cognitive sequalae and persistence of brain microstructure alterations.

Evaluation of White Matter Integrity Utilizing the DELPHI (TMS-EEG) System

Objective

The aim of this study was to evaluate brain white matter (WM) fibers connectivity damage in stroke and traumatic brain injury (TBI) subjects by direct electrophysiological imaging (DELPHI) that analyzes transcranial magnetic stimulation (TMS)-evoked potentials (TEPs).

Methods

The study included 123 participants, out of which 53 subjects with WM-related pathologies (39 stroke, 14 TBI) and 70 healthy age-related controls. All subjects underwent DELPHI brain network evaluations of TMS-electroencephalogram (EEG)-evoked potentials and diffusion tensor imaging (DTI) scans for quantification of WM microstructure fractional anisotropy (FA).

Results

DELPHI output measures show a significant difference between the healthy and stroke/TBI groups. A multidimensional approach was able to classify healthy from unhealthy with a balanced accuracy of 0.81 ± 0.02 and area under the curve (AUC) of 0.88 ± 0.01. Moreover, a multivariant regression model of DELPHI output measures achieved prediction of WM microstructure changes measured by FA with the highest correlations observed for fibers proximal to the stimulation area, such as frontal corpus callosum (r = 0.7 ± 0.02), anterior internal capsule (r = 0.7 ± 0.02), and fronto-occipital fasciculus (r = 0.65 ± 0.03).

Conclusion

These results indicate that features of TMS-evoked response are correlated to WM microstructure changes observed in pathological conditions, such as stroke and TBI, and that a multidimensional approach combining these features in supervised learning methods serves as a strong indicator for abnormalities and changes in WM integrity.

The effects of internal jugular vein compression for modulating and preserving white matter following a season of American tackle football: A prospective longitudinal evaluation of differential head impact exposure

The purpose of this clinical trial was to examine whether internal jugular vein compression (JVC)-using an externally worn neck collar-modulated the relationships between differential head impact exposure levels and pre- to postseason changes in diffusion tensor imaging (DTI)-derived diffusivity and anisotropy metrics of white matter following a season of American tackle football. Male high-school athletes (n = 284) were prospectively assigned to a non-collar group or a collar group. Magnetic resonance imaging data were collected from participants pre- and postseason and head impact exposure was monitored by accelerometers during every practice and game throughout the competitive season. Athletes' accumulated head impact exposure was systematically thresholded based on the frequency of impacts of progressively higher magnitudes (10 g intervals between 20 to 150 g) and modeled with pre- to postseason changes in DTI measures of white matter as a function of JVC neck collar wear. The findings revealed that the JVC neck collar modulated the relationships between greater high-magnitude head impact exposure (110 to 140 g) and longitudinal changes to white matter, with each group showing associations that varied in directionality. Results also revealed that the JVC neck collar group partially preserved longitudinal changes in DTI metrics. Collectively, these data indicate that a JVC neck collar can provide a mechanistic response to the diffusion and anisotropic properties of brain white matter following the highly diverse exposure to repetitive head impacts in American tackle football. Clinicaltrials.gov: NCT# 04068883.

Investigation of dynamic deformation of the midbrain in rear-end collision using human brain FE model

Mild traumatic brain injury (TBI), including concussions, can cause symptoms affecting physical or cognitive domains in the acute and chronic phases. In this study, we investigated the dynamic deformation of the brain stem, which might be important for these symptoms, using a human brain finite element model through reconstruction simulations of rear-end collisions in three different velocities. In all simulations, high maximum principal strain values were observed at the midbrain that were higher than those in the corpus callosum. These findings could provide some mechanical insights into brain disorders associated with mild TBI.

Comprehensive rehabilitation in a patient with corpus callosum syndrome after traumatic brain injury: Case report

RATIONALE

Corpus callosum syndrome is a rare consequence of traumatic brain injuries. We provide a case of a patient with typical corpus callosum syndrome following a traumatic brain injury, and demonstrate neural reorganization and significant neural regeneration after comprehensive rehabilitation, using diffusion tensor imaging fiber bundle tracking.

PATIENT CONCERNS

We found typical clinical manifestations of damage to the corpus callosum.

DIAGNOSES, INTERVENTIONS, AND OUTCOMES

We diagnosed a Traumatic Brain Injury (diffuse axonal injury and rupture of corpus callosum). The patient underwent a comprehensive multifaceted rehabilitation program including drug therapy, integrated physical therapy, occupational therapy, acupuncture, music therapy, computer-aided cognitive rehabilitation training, transcranial magnetic stimulation, and hyperbaric oxygen therapy. This rehabilitation program resulted in greatly improved physical and communication ability.

LESSONS

Comprehensive rehabilitation can significantly improve the function of patients with corpus callosum syndrome and may cause neural remodeling, as seen on diffusion tensor imaging.

Altered Functional Brain Networks in Patients with Traumatic Anosmia: Resting-State Functional MRI Based on Graph Theoretical Analysis

OBJECTIVE

Traumatic anosmia is a common disorder following head injury; however, little is known regarding its neural basis and influence on the functional networks. Therefore, we aimed to investigate the functional connectivity changes in patients with traumatic anosmia compared to healthy controls using resting-state functional magnetic resonance imaging (rs-fMRI).

MATERIALS AND METHODS

Sixteen patients with traumatic anosmia and 12 healthy controls underwent rs-fMRI. Differences in the connectivity of the olfactory and whole brain networks were compared between the two groups. Graph theoretical parameters, such as modularity and global efficiency of the whole brain or olfactory networks, were calculated and compared. Correlation analyses were performed between the parameters and disease severity.

RESULTS

Patients with traumatic anosmia showed decreased intra-network connectivity in the olfactory network (false discovery rate [FDR]-corrected p < 0.05) compared with that in healthy controls. Furthermore, the inter-network connectivity was increased in both the olfactory (FDR-corrected p < 0.05) and whole brain networks (degree-based statistic-corrected p < 0.05) in the anosmia group. The whole brain networks showed decreased modularity (p < 0.001) and increased global efficiency (p = 0.019) in patients with traumatic anosmia. The modularity and global efficiency were correlated with disease severity in patients with anosmia (p < 0.001 and p = 0.002, respectively).

CONCLUSION

Traumatic anosmia increased the inter-network connectivity observed with rs-fMRI in the olfactory and global brain functional networks. rs-fMRI parameters may serve as potential biomarkers for traumatic anosmia by revealing a more widespread functional damage than previously expected.

Assessment of Auditory Pathways Using Diffusion Tensor Imaging in Patients with Neurofibromatosis Type 1

Aim:

The aim of our study was to determine whether the diffusion properties of the auditory pathways alter between patients with Neurofibromatosis type 1 (NF1) and the healthy subjects. DTI can well demonstrate FA and ADC changes in auditory tracts and it may be a guide to identify the candidates for hearing loss among NF1 children.

Methods:

The study population consisted of 43 patients with NF1 and 21 healthy controls. Diffusion tensor imaging (DTI) was used to measure apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values from lemniscus lateralis, colliculus inferior, corpus geniculatum mediale and Heschl's gyrus. The results were compared with those of the control group.

Results:

The ADC values of lateral lemniscus, colliculus inferior and corpus geniculatum mediale were significantly higher in NF1 compared to those of the control group. On the other hand, decreased FA values were observed in lateral lemniscus and colliculus inferior in patients with NF1.

Conclusion:

The increase in ADC and reduction in FA in the auditory pathways of patients with NF1 may suggest microstructural alterations, such as a decrease in the number of axons, edema or inflammation in the auditory tracts.

Cognitive and spectral coherence of EEG alterations in resting state in children with chronic TBI

Introduction. TBI is associated with alterations in cortico-subcortical connectivity. However, little attention has been paid to its clinical characteristics and functional connectivity in pediatric patients with chronic TBI. Objective. To evaluate the cognitive performance and spectral coherence of a group of children with TBI in non-acute phase. Method. Cross-sectional study of 15 children with chronic TBI and 17 healthy children. The Neuropsychological Assessment of Children (Evaluación Neuropsicológica Infantil, ENI) was used and the resting activity of the EEG with eyes-closed was recorded. Offline, two-second epochs of the EEG of each participant were chosen and the spectral coherence was estimated in a range of 1.6 to 30 Hz. The cognitive performance between groups was compared with T-test/Mann-Whitney U Test and MANOVA for the coherence values. Results. The TBI group showed a lower performance (p ≤ 0.05) in metalinguistic, visuospatial skills, attention, memory, non-verbal flexibility, planning, and organization. Differences (p ≤ 0.000) were found both inter and intrahemispherically in the spectral coherence between the groups, particularly on F1-F3 (95% CI: 0.543 - 0.557) over the whole frequency range and F3-C3 (95% CI: 0.503 - 0.515) in delta, theta, alpha2, and beta frequencies. Discussion and conclusión. Our findings suggest alterations of hypo and hyper functional connectivity, particularly on the frontal and parietal lobes of both hemispheres, even after several years of a TBI. It is possible that a subtle difference in the degree of connectivity is crucial in the genesis or successful development of attentional, mnesic, executive, and visuospatial processes.

MRS and DTI evidence of progressive posterior cingulate cortex and corpus callosum injury in the hyper-acute phase after Traumatic Brain Injury

The posterior cingulate cortex (PCC) and corpus callosum (CC) are susceptible to trauma, but injury often evades detection. PCC Metabolic disruption may predict CC white matter tract injury and the secondary cascade responsible for progression. While the time frame for the secondary cascade remains unclear in humans, the first 24 h (hyper-acute phase) are crucial for life-saving interventions.

Objectives: To test whether Magnetic Resonance Imaging (MRI) markers are detectable in the hyper-acute phase and progress after traumatic brain injury (TBI) and whether alterations in these parameters reflect injury severity.

Methods: Spectroscopic and diffusion-weighted MRI data were collected in 18 patients with TBI (within 24 h and repeated 7–15 days following injury) and 18 healthy controls (scanned once).

Results: Within 24 h of TBI N-acetylaspartate was reduced (F = 11.43, p = 0.002) and choline increased (F = 10.67, p = 0.003), the latter driven by moderate-severe injury (F = 5.54, p = 0.03). Alterations in fractional anisotropy (FA) and axial diffusivity (AD) progressed between the two time-points in the splenium of the CC (p = 0.029 and p = 0.013). Gradual reductions in FA correlated with progressive increases in choline (p = 0.029).

Conclusions: Metabolic disruption and structural injury can be detected within hours of trauma. Metabolic and diffusion parameters allow identification of severity and provide evidence of injury progression.

White matter during concussion recovery: Comparing diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI)

Concussion pathophysiology in humans remains incompletely understood. Diffusion tensor imaging (DTI) has identified microstructural abnormalities in otherwise normal appearing brain tissue, using measures of fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD). The results of prior DTI studies suggest that acute alterations in microstructure persist beyond medical clearance to return to play (RTP), but these measures lack specificity. To better understand the observed effects, this study combined DTI with neurite orientation dispersion and density imaging (NODDI), which employs a more sophisticated description of water diffusion in the brain. A total of 66 athletes were recruited, including 33 concussed athletes, scanned within 7 days after concussion and at RTP, along with 33 matched controls. Both univariate and multivariate methods identified DTI and NODDI parameters showing effects of concussion on white matter. Spatially extensive decreases in FA and increases in AD and RD were associated with reduced intra-neurite water volume, at both the symptomatic phase of injury and RTP, indicating that effects persist beyond medical clearance. Subsequent analyses also demonstrated that concussed athletes with higher symptom burden and a longer recovery time had greater reductions in FA and increased AD, RD, along with increased neurite dispersion. This study provides the first longitudinal evaluation of concussion from acute injury to RTP using combined DTI and NODDI, significantly enhancing our understanding of the effects of concussion on white matter microstructure.

Diffusion MRI abnormalities in adolescent rats given repeated mild traumatic brain injury

Objective

Mild traumatic brain injury (mTBI) is a serious health concern in the adolescent population. Repeated mTBI may result in more pronounced deficits, and has been associated with long‐term neurological consequences including neurodegeneration. As such, there is a critical need for the development of objective mTBI biomarkers to help guide medical management. Diffusion‐weighted imaging (DWI) is an advanced magnetic resonance imaging (MRI) technique that may detect brain abnormalities after mTBI. Diffusion tensor imaging (DTI) is the most commonly applied DWI method, and initial studies have reported DTI changes in mTBI patients. Furthermore, new DWI methods (e.g., track‐weighted imaging; TWI) are being developed that may also be sensitive to mTBIs, but remain to be comprehensively studied.

Methods

This study utilized the Awake Closed Head Injury (ACHI) model of mTBI to investigate changes in DTI and TWI following repeated mTBI in adolescent male and female rats. A total of four ACHI impacts, two/day over two consecutive days, were delivered beginning on postnatal day 25. At 1 day and 7 days postinjury, rats were euthanized and brains were collected for DWI analyses.

Results

Rats given repeated mTBI displayed changes in fractional anisotropy and radial diffusivity (i.e., DTI measures), as well as track density (i.e., TWI).

Interpretation

These findings are consistent with initial DTI findings in mTBI patients, suggest that TWI may complement DTI, support the utility of DWI measures as biomarkers in mTBI, and further validate the ACHI rat model of mTBI.

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

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

Profiling biomarkers of traumatic axonal injury: From mouse to man

Traumatic brain injury (TBI) poses a major public health problem on a global scale. Its burden results from high mortality and significant morbidity in survivors. This stems, in part, from an ongoing inadequacy in diagnostic and prognostic indicators despite significant technological advances. Traumatic axonal injury (TAI) is a key driver of the ongoing pathological process following TBI, causing chronic neurological deficits and disability. The science underpinning biomarkers of TAI has been a subject of many reviews in recent literature. However, in this review we provide a comprehensive account of biomarkers from animal models to clinical studies, bridging the gap between experimental science and clinical medicine. We have discussed pathogenesis, temporal kinetics, relationships to neuro-imaging, and, most importantly, clinical applicability in order to provide a holistic perspective of how this could improve TBI diagnosis and predict clinical outcome in a real-life setting. We conclude that early and reliable identification of axonal injury post-TBI with the help of body fluid biomarkers could enhance current care of TBI patients by (i) increasing speed and accuracy of diagnosis, (ii) providing invaluable prognostic information, (iii) allow efficient allocation of rehabilitation services, and (iv) provide potential therapeutic targets. The optimal model for assessing TAI is likely to involve multiple components, including several blood biomarkers and neuro-imaging modalities, at different time points.

Common Patterns of Regional Brain Injury Detectable by Diffusion Tensor Imaging in Otherwise Normal-Appearing White Matter in Patients with Early Moderate to Severe Traumatic Brain Injury

Traumatic brain injury (TBI) alters the lives of millions of people every year. Although mortality rates have improved, attributed to better pre-hospital care and reduction of secondary injury in the critical care setting, improvements in functional outcomes post-TBI have been difficult to achieve. Diffusion-tensor imaging (DTI) allows detailed measurement of microstructural damage in regional brain tissue post-TBI, thus improving our understanding of the extent and severity of TBI. Twenty subjects were recruited from a neurological intensive care unit and compared to 18 healthy control subjects. Magnetic resonance imaging (MRI) scanning was performed on a 3.0-Tesla Siemens TIM Trio Scanner (Siemens Medical Solutions, Erlangen, Germany) including T1- and T2-weighted sequences and DTI. Images were processed using DTIStudio software. SAS (SAS Institute Inc., Cary, NC) was used for statistical analysis of group differences in 14 brain regions (25 regions of interests [ROIs]). Seventeen TBI subjects completed scanning. TBI and control subjects did not differ in age or sex. All TBI subjects had visible lesions on structural MRI. TBI subjects had seven brain regions (nine ROIs) that showed significant group differences on DTI metrics (fractional anisotropy, radial diffusion, or mean diffusion) compared to noninjured subjects, including the corpus callosum (genu and splenium), superior longitudinal fasciculus, internal capsule, right retrolenticular internal capsule, posterior corona radiata, and thalamus. However, 16 ROIs showed relatively normal DTI measures. Quantitative DTI demonstrates multiple areas of microstructual injury in specific normal-appearing white matter brain regions. DTI may be useful for assessing the extent of brain injury in patients with early moderate to severe TBI.

Injury of the Precommissural Fornix in a Patient with Subarachnoid Hemorrhage: A Case Report

OBJECTIVES

We investigated injury of the pre- or postcommissural fornix in a patient with subarachnoid hemorrhage (SAH) using diffusion tensor imaging.

CASE DESCRIPTION

A 48-year-old male patient was diagnosed as SAH due to rupture of the right middle cerebral artery bifurcation aneurysm. After 9 weeks from onset, he was transferred to the rehabilitation department and he showed memory impairment. The whole fornix was reconstructed using single-tract fornix model based on a fiber assignment by continuous tracking, and separated fornices (pre- and postcommissural fornices) were reconstructed using 2-tract fornix model based on a probabilistic tractography method. The fractional anisotropy (FA), mean diffusivity, and fiber volume were measured in the patient and 6 normal control subjects. The integrities of both reconstructed whole fornices that were reconstructed using probabilistic tractography method were preserved. By contrast, in the results of 2-tract fornix model, the precommissural fornices showed discontinuations in both fornical cruses. In addition, the FA and fiber volume of both precommissural fornices in the patient were decreased by more than 2 standard deviations of those of normal control subjects.

CONCLUSIONS

Separate evaluations of the pre- and postcommissural fornices using 2-tract fornix model would be useful for diagnosis in patients with memory impairment following SAH.

Human Brain Modeling with Its Anatomical Structure and Realistic Material Properties for Brain Injury Prediction

Impairments of executive brain function after traumatic brain injury (TBI) due to head impacts in traffic accidents need to be obviated. Finite element (FE) analyses with a human brain model facilitate understanding of the TBI mechanisms. However, conventional brain FE models do not suitably describe the anatomical structure in the deep brain, which is a critical region for executive brain function, and the material properties of brain parenchyma. In this study, for better TBI prediction, a novel brain FE model with anatomical structure in the deep brain was developed. The developed model comprises a constitutive model of brain parenchyma considering anisotropy and strain rate dependency. Validation was performed against postmortem human subject test data associated with brain deformation during head impact. Brain injury analyses were performed using head acceleration curves obtained from reconstruction analysis of rear-end collision with a human whole-body FE model. The difference in structure was found to affect the regions of strain concentration, while the difference in material model contributed to the peak strain value. The injury prediction result by the proposed model was consistent with the characteristics in the neuroimaging data of TBI patients due to traffic accidents.

Abundant unusual neural branches from the fornix in patients with mild traumatic brain injury: A diffusion tensor tractography study

OBJECTIVES

Since the introduction of diffusion tensor tractography (DTT), several studies have been reported on the mechanisms for the recovery of an injured fornix in patients with traumatic brain injury (TBI). We report on patients who showed abundant unusual neural branches from the fornix following mild TBI using DTT.

METHODS

Five patients with mild TBI who complained of memory impairment and showed preserved integrity of the fornix with abundant unusual neural branches on DTT, and eight normal subjects were recruited. DTT parameters (fractional anisotropy [FA] and fibre number) of the fornix were measured.

RESULTS

All five patients showed memory impairment on only one subscale of the Memory Assessment Scale (MAS), although the global MAS was within the normal range. The FN of the fornix was increased by more than two standard deviations in all five patients compared with that of normal subjects, while the FA value was within two standard deviations of that of normal subjects. On the DTT for the fornix of the patients, three types of unusual neural tracts from the fornix not observed in normal subjects were observed in patients.

CONCLUSION

The abundant unusual neural branches from the fornix might be a recovery phenomenon of a mildly injured fornix, although the integrity of the fornix was preserved in these patients.

Structural, Functional, and Metabolic Brain Markers Differentiate Collision versus Contact and Non-Contact Athletes

There is growing concern about how participation in contact sports affects the brain. Retrospective evidence suggests that contact sports are associated with long-term negative health outcomes. However, much of the research to date has focused on former athletes with significant health problems. Less is known about the health of current athletes in contact and collision sports who have not reported significant medical issues. In this cross-sectional study, advanced magnetic resonance imaging (MRI) was used to evaluate multiple aspects of brain physiology in three groups of athletes participating in non-contact sports (N = 20), contact sports (N = 22), and collision sports (N = 23). Diffusion tensor imaging was used to assess white matter microstructure based on measures of fractional anisotropy (FA) and mean diffusivity (MD); resting-state functional MRI was used to evaluate global functional connectivity; single-voxel spectroscopy was used to compare ratios of neural metabolites, including N-acetyl aspartate (NAA), creatine (Cr), choline, and myo-inositol. Multivariate analysis revealed structural, functional, and metabolic measures that reliably differentiated between sport groups. The collision group had significantly elevated FA and reduced MD in white matter, compared to both contact and non-contact groups. In contrast, the collision group showed significant reductions in functional connectivity and the NAA/Cr metabolite ratio, relative to only the non-contact group, while the contact group overlapped with both non-contact and collision groups. For brain regions associated with contact sport participation, athletes with a history of concussion also showed greater alterations in FA and functional connectivity, indicating a potential cumulative effect of both contact exposure and concussion history on brain physiology. These findings indicate persistent differences in brain physiology for athletes participating in contact and collision sports, which should be considered in future studies of concussion and subconcussive impacts.

White matter microstructure in athletes with a history of concussion: Comparing diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI)

Sport concussion is associated with disturbances in brain function in the absence of gross anatomical lesions, and may have long-term health consequences. Diffusion-weighted magnetic resonance imaging (MRI) methods provide a powerful tool for investigating alterations in white matter microstructure reflecting the long-term effects of concussion. In a previous study, diffusion tensor imaging (DTI) showed that athletes with a history of concussion had elevated fractional anisotropy (FA) and reduced mean diffusivity (MD) parameters. To better understand these effects, this study compared DTI results to neurite orientation dispersion and density imaging (NODDI), which was used to estimate the intracellular volume fraction (V_IC ) and orientation dispersion index (ODI). Sixty-eight (68) varsity athletes were recruited, including 37 without a history of concussion and 31 with concussion >6 months prior to imaging. Univariate analyses showed elevated FA and decreased MD for concussed athletes, along with increased V_IC and reduced ODI, indicating greater neurite density and coherence of neurite orientation within white matter. Multivariate analyses also showed that for athletes with a history of concussion, white matter regions with increased FA had increased V_IC and decreased ODI, with greater effects among athletes who were imaged a longer time since their last concussion. These findings enhance our understanding of the relationship between the biophysics of water diffusion and concussion neurobiology for young, healthy adults. Hum Brain Mapp 38:4201-4211, 2017. © 2017 Wiley Periodicals, Inc.

Disorder of Executive Function of the Brain after Head Injury and Mild Traumatic Brain Injury - Neuroimaging and Diagnostic Criteria for Implementation of Administrative Support in Japan

The diagnotic criteria for disorder of the executive function of the brain (DEFB) as a syndrome of sequela were administratively established (ad-DEFB) in Japan in 2006 to support disabled patients whose impairment, limited to cognition (memory, attention, execution, and behavior), emerges after organic brain injuries regardless of physical deficits. However, some patients suffering from traumatic brain injury (TBI) have been excluded from receiving medico-social services. In particular, this tendency is more prominent in patients with mild TBI because no lesions are apparent on conventional computed tomography (CT) or magnetic resonance imaging (MRI) in the chronic phase. Recent development of new MRI neuroimaging modalities and positron emission tomography (PET) imaging makes it possible to detect regions of minute organic lesions and metabolic dysfunction in the brain where organic lesions may be absent or cannot be detected on conventional CT or MRI. In this review, we discuss diagnostic criteria for mild TBI and ad-DEFB, the relationship between the two disorders, characteristic neuroimaging [(MRI and 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET)] of diffuse brain injury including cerebral concussion, which is the principal cause of mild TBI, and suggested pathological mechanisms of ad-DEFB in DBI.

Investigating Microstructural Abnormalities and Neurocognition in Sub-Acute and Chronic Traumatic Brain Injury Patients with Normal-Appearing White Matter: A Preliminary Diffusion Tensor Imaging Study

For a significant percentage of subjects, with chronic traumatic brain injury (TBI), who report persisting cognitive impairment and functional loss, the diagnosis is often impeded by the fact that routine neuroimaging often does not reveal any abnormalities. In this paper, we used diffusion tensor imaging (DTI) to investigate the apparently normal white matter (as assessed by routine magnetic resonance imaging) in the brains of 19 subjects with sub-acute (9) and chronic (10) TBI. We also assessed memory, executive function, and visual-motor coordination in these subjects. Using a voxel-wise approach, we investigated if parameters of diffusion were significantly different between TBI subjects and 17 healthy controls (HC), who were demographically matched to the TBI group. We also investigated if changes in DTI parameters were associated with neuropsychological performance in either group. Our results indicate significantly increased mean and axial diffusivity (MD and AD, respectively) values in widespread brain locations in TBI subjects, while controlling for age, sex, and time since injury. HC performed significantly better than the TBI subjects on tests of memory and executive function, indicating the persisting functional loss in chronic TBI. We found no correlation between diffusion parameters and performance on test of executive function in either group. We found negative correlation between FA and composite memory scores, and positive correlation between RD and visuomotor coordination test scores, in various tracts in both groups. Our study suggests that changes in MD and AD can indicate persisting micro-structure abnormalities in normal-appearing white matter in the brains of subjects with chronic TBI. Our results also suggest that FA in major white matter tracts is correlated with memory in health and in disease, alike; larger and longitudinal studies are needed to discern potential differences in these correlations in the two groups.

The differences of the precommissural and postcommissural fornix in the hippocampal location: a diffusion tensor tractography study

PURPOSE

The precommissural fornix and postcommissural fornix have different connections to the basal forebrain and septal region, and mammillary body, respectively. However, little is known about the differences of the precommissural fornix and postcommissural fornix in the hippocampal location. In this study, using diffusion tensor tractography, we investigated the differences of the precommissural fornix and postcommissural fornix in the hippocampal location.

METHODS

We recruited 25 healthy volunteers for this study. For reconstruction of the precommissural fornix and postcommissural fornix, we placed the seed region of interest on the septal nucleus, and the mammillary body, respectively. The target regions of interest (ROI) was given on the crus of the fornix on the coronal image. Evaluations of the anatomical location of the precommissural fornix and postcommissural fornix were performed using the highest probabilistic location in the hippocampal formation.

RESULTS

The precommissural fornix and postcommissural fornix were located at an average of 83.9 and 87.5% between the lateral margin of the red nucleus and collateral sulcus on the axial plane, and 77.2 and 81.4% between the lateral margin of the midbrain and the inferior longitudinal fasciculus on the coronal plane. Significant differences of location in the medio-lateral direction were observed in the axial and coronal plane (p < 0.05). However, no significant differences of location in the antero-posterior direction were observed between precommissrual and postcommissural fornix (p > 0.05).

CONCLUSIONS

The reconstructed precommissural fornix and postcommissural fornix were connected to the cornu ammonis 1(CA1) of the hippocampus, and the precommissural fornix was located more laterally to the postcommissural fornix in the CA1.

Diagnostic Challenge of Diffusion Tensor Imaging in a Patient With Hemiplegia After Traumatic Brain Injury

A 51-year-old man showed hemiplegia on his right side after a traumatic brain injury (TBI). On initial brain computed tomography (CT) scan, an acute subdural hemorrhage in the right cerebral convexity and severe degrees of midline shifting and subfalcine herniation to the left side were evident. On follow-up brain magnetic resonance imaging (MRI), there were multiple microhemorrhages in the left parietal and occipital subcortical regions. To explain the occurrence of right hemiplegia after brain damage which dominantly on the right side of brain, we used diffusion tensor imaging (DTI) to reconstruct the corticospinal tract (CST), which showed nearly complete injury on the left CST. We also performed motor-evoked potentials, and stimulation of left motor cortex evoked no response on both sides of upper extremity. We report a case of patient with hemiplegia after TBI and elucidation of the case by DTI rather than CT and MRI.

Both hemorrhagic and non-hemorrhagic traumatic MRI lesions are associated with the microstructural damage of the normal appearing white matter

Traumatic microbleeds (TMBs) and non-hemorrhagic lesions (NHLs) on MRI are regarded as surrogate markers of diffuse axonal injury. However, the actual relation between lesional and diffuse pathology remained unclear, since lesions were related to clinical parameters, largely influenced by extracranial factors. The aim of this study is to directly compare TMBs, NHLs and their regional features with the co-existing diffuse injury of the normal appearing white matter (NAWM) as measured by diffusion tensor imaging (DTI). Thirty-eight adults with a closed traumatic brain injury (12 mild, 4 moderate and 22 severe) who underwent susceptibility weighted imaging (SWI), T1-, T2 weighted and FLAIR MRI and routine CT were included in the study. TMB (on SWI) and NHL (on T1-, T2 weighted and FLAIR images) features and Rotterdam scores were evaluated. DTI metrics such as fractional anisotropy (FA) and mean diffusivity (MD) were measured over different NAWM regions. Clinical parameters including age; Glasgow Coma Scale; Rotterdam score; TMB and NHL features were correlated to regional NAWM diffusivity using multiple regression. Overall NHL presence and basal ganglia area TMB load were significantly, negatively correlated with the subcortical NAWM FA values (partial r=-0.37 and -0.36; p=0.006 and 0.025, respectively). The presence of any NHL, or TMBs located in the basal ganglia area indicates diffuse NAWM damage even after adjusting for clinical and CT parameters. To estimate DAI, a conventional lesional MRI pathology evaluation might at least in part substitute the use of quantitative DTI, which is yet not widely feasible in a clinical setting.

Current Clinical Applications and Future Potential of Diffusion Tensor Imaging in Traumatic Brain Injury

In the setting of acute central nervous system (CNS) emergencies, computed tomography (CT) and conventional magnetic resonance imaging (MRI) play an important role in the identification of life-threatening intracranial injury. However, the full extent or even presence of brain damage frequently escapes detection by conventional CT and MRI. Advanced MRI techniques such as diffusion tensor imaging (DTI) are emerging as important adjuncts in the diagnosis of microstructural white matter injury in the acute and postacute brain-injured patient. Although DTI aids in detection of brain injury pathology, which has been repeatedly associated with typical adverse clinical outcomes, the evolution of acute changes and their long-term prognostic implications are less clear and the subject of much active research. A major aim of current research is to identify imaging-based biomarkers that can identify the subset of TBI patients who are at risk for adverse outcome and can therefore most benefit from ongoing care and rehabilitation as well as future therapeutic interventions.The aim of this study is to introduce the current methods used to obtain DTI in the clinical setting, describe a set of common interpretation strategies with their associated advantages and pitfalls, as well as illustrate the clinical utility of DTI through a set of specific patient scenarios. We conclude with a discussion of future potential for the management of TBI.

Differences in Brain Metabolic Impairment between Chronic Mild/Moderate TBI Patients with and without Visible Brain Lesions Based on MRI

Introduction. Many patients with mild/moderate traumatic brain injury (m/mTBI) in the chronic stage suffer from executive brain function impairment. Analyzing brain metabolism is important for elucidating the pathological mechanisms associated with their symptoms. This study aimed to determine the differences in brain glucose metabolism between m/mTBI patients with and without visible traumatic brain lesions based on MRI. Methods. Ninety patients with chronic m/mTBI due to traffic accidents were enrolled and divided into two groups based on their MRI findings. Group A comprised 50 patients with visible lesions. Group B comprised 40 patients without visible lesions. Patients underwent FDG-PET scans following cognitive tests. FDG-PET images were analyzed using voxel-by-voxel univariate statistical tests. Results. There were no significant differences in the cognitive tests between Group A and Group B. Based on FDG-PET findings, brain metabolism significantly decreased in the orbital gyrus, cingulate gyrus, and medial thalamus but increased in the parietal and occipital convexity in Group A compared with that in the control. Compared with the control, patients in Group B exhibited no significant changes. Conclusions. These results suggest that different pathological mechanisms may underlie cognitive impairment in m/mTBI patients with and without organic brain damage.

Detection of Functional Homotopy in Traumatic Axonal Injury

OBJECTIVE

This study aimed to explore the interhemispheric intrinsic connectivity in traumatic axonal injury (TAI) patients.

METHODS

Twenty-one patients with TAI (14 males, seven females; mean age, 38.71 ± 15.25 years) and 22 well-matched healthy controls (16 males, six females; mean age, 38.50 ± 13.82 years) were recruited, and from them we obtained resting-state fMRI data. Interhemispheric coordination was examined using voxel-mirrored homotopic connectivity (VMHC) and seed-based functional connectivity analysis was performed.

RESULTS

We observed significantly decreased VMHC in a number of regions in TAI patients, including the prefrontal, temporal, occipital, parietal, and posterior cingulate cortices, thalami and cerebellar posterior lobes. Subsequent seed-based functional connectivity analysis revealed widely disrupted functional connectivity between the regions of local homotopic connectivity deficits and other areas of the brain, particularly the areas subserving the default, salience, integrative, and executive systems. The lower VMHC of the inferior frontal gyrus and basal ganglia, thalamus, and caudate were significant correlated with the Beck Depression Inventory score, Clinical Dementia Rating score, and Mini-Mental State Examination score, respectively.

CONCLUSION

TAI is associated with regionally decreased interhemispheric interactions and extensively disrupted seed-based functional connectivity, generating further evidence of diffuse disconnection being associated with clinical symptoms in TAI patients.

KEY POINTS

• Traumatic axonal injury is associated with decreased interhemispheric connectivity • Traumatic axonal injury couples with widely disrupted functional connectivity • These alterations support the default, salience, integrative, and executive functions.