Perfusion Imaging in Acute Traumatic Brain Injury

Post-traumatic Transient Neurological Dysfunction: A Proposal for Pathophysiology

Unexplained neurological deterioration is occasionally observed in patients with traumatic brain injuries (TBIs). We aimed to describe the clinical features of post-traumatic transient neurological dysfunction and provide new insight into its pathophysiology. We retrospectively collected data from patients with focal neurological deterioration of unknown origin during hospitalization for acute TBI for 48 consecutive months. Brain imaging, including computed tomography, diffusion-weighted imaging and perfusion-weighted imaging, and electroencephalography were conducted during the episodes. Fourteen (2.0%) patients experienced unexplained focal neurological deterioration among 713 patients who were admitted for traumatic intracranial hemorrhage during the study period. Aphasia was the predominant symptom in all patients, and hemiparesis or hemianopia was accompanied in three patients. These symptoms developed within 14 days after trauma. Structural imaging did not show any significant interval change, and electroencephalography showed persistent arrhythmic slowing in the corresponding hemisphere in most patients. Perfusion imaging revealed increased cerebral blood flow in the symptomatic hemisphere. Surgical intervention and anti-seizure medications were ineffective in abolishing the symptoms. The symptoms disappeared spontaneously after 4 h to 1 month. Transient neurological dysfunction (TND) can occur during the acute phase of TBI. Although TND may last longer than a typical transient ischemic attack or seizure, it eventually resolves regardless of treatment. Based on our observation, we postulate that this is a manifestation of spreading depolarization occurring in the injured brain, which is analogous to migraine aura.

Updates on Improving Imaging Modalities for Traumatic Brain Injury

The Center for Disease Control and Prevention reports that traumatic brain injury (TBI) was related to over 64,000 deaths in the United States in 2020, equating to more than 611 TBI-related hospitalizations and 176 TBI-related deaths per day. There are both long- and short-term sequelae involved with the pathophysiology of TBI that can range from mild to severe. Recently, more effort has been devoted to understanding the long-term consequences of TBI and how early detection of these injuries can prevent late clinical manifestations. Obtaining proper, detailed imaging is key to guiding the direction of intervention, but there is a gap in the understanding of how TBI imaging can be used to predict and prevent the long-term morbidities seen with even mild forms of TBI. There have been significant strides in the advancement of TBI imaging that allows for quicker, more affordable, and more effective imaging of intracranial bleeds, axonal injury, tissue damage, and more. Despite this, there is still room for improved standardization and more data supporting the justification of using certain imaging modalities. This review aims to outline recent advancements in TBI imaging and areas that require further investigation to improve patient outcomes and minimize the acute and chronic comorbidities associated with TBI.

Agitation after traumatic brain injury: a review of current and future concepts in diagnosis and management

OBJECTIVES

Agitation and aggression are common following traumatic brain injury. The challenges related to these disorders affect all stages of recovery, from the acute hospital to the community setting. The aim of this literature review is to provide an updated overview of the current state of post-traumatic agitation research.

METHODS

We performed a PubMed literature review which included recent confirmatory and novel research as well as classic and historical studies to integrate past and future concepts.

RESULTS

Areas explored include the personal and societal effects of post-traumatic agitation, methods for defining and diagnosing several neurobehavioral disorders, and pathophysiology and management of agitation and aggression. Target areas for future study are identified and discussed.

DISCUSSION

While much progress has been made in understanding post-traumatic agitation, there remain several key areas that require further elucidation to support the care and treatment for people with traumatic brain injury.

Cerebral perfusion changes in acute subdural hematoma

INTRODUCTION

Acute subdural hematoma (aSDH) is one of the main causes of high mortality and morbidity in traumatic brain injury. Prognosis is poor due to the rapid volume shift and mass effect. Cerebral perfusion is likely affected in this condition. This study quantifies perfusion changes in aSDH using early ER polytrauma CT with perfusion imaging (CTP).

METHODS

Data of 54 patients with traumatic aSDH were retrospectively collected. Glasgow Coma scale (GCS), perfusion parameters, therapeutic decisions and imaging data including hematoma thickness, midline shift, and hematoma localization were analyzed. The cortical perfusion parameters of each hemisphere, the area anterior to the hematoma (AAH), area below the hematoma (ABH), area posterior to the hematoma (PAH), and corresponding mirrored contralateral regions were determined.

RESULTS

We found a significant difference in Tmax in affected and unaffected whole-hemisphere data (mean 4.0 s vs. 3.3 s, p < 0.05) and a significantly different mean for Tmax in ABH and for the corresponding mirrored area (mABH) (mean 3.8 s vs. 3.1 s, p < 0.05). No significant perfusion changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) were found.

CONCLUSION

There was a significant elevation of time to maximum (Tmax) values in the underlying cortical area of aSDH. Possible pathophysiological explanations, the influence on immediate surgical decision-making and further therapeutic consequences have to be evaluated.

Cerebral Perfusion and Functional Outcome in Pediatric Head Injury Patients

OBJECTIVE

To evaluate the usefulness and degree of perfusion abnormalities in pediatric head injury patients by using computed tomography perfusion (CTP) and to assess its co-relation with neurologic outcome based on Glasgow Outcome Scale Extended Pediatric revision (GOSE-P).

METHODS

Prospective evaluation of pediatric head injury patients who were taken for CTP after admission and then on discharge. We evaluated 5 regions of interest: orbitofrontal cortex, internal capsule, thalamus, caudate nucleus, and sensorimotor cortex for cerebral blood perfusion. The patient's clinical and radiologic findings were analyzed, correlated with cerebral blood flow (CBF) and MTT (mean transient time), and the outcome assessed using the GOSE-P scale on 3-month follow-up.

RESULTS

Both CBF and MTT showed a correlation with the GOSE-P scale. In mild head injury patients, the Pearson correlation of GOSE-P with mean CBF and mean MTT was -0.11 and 0.56, respectively (P < 0.05) in the sensorimotor cortex; in moderate head injury patients the Pearson correlation of GOSE-P with mean CBF in the caudate nucleus and mean MTT in the internal capsule was -0.32 and 0.36, respectively (P < 0.05); and in severe head injury patients, the Pearson correlation of GOSE-P with mean CBF and mean MTT was -0.78 and 0.56, respectively (P < 0.05) in the caudate nucleus, which had the highest Pearson co-relation among the regions studied.

CONCLUSIONS

We conclude that CBF and MTT are 2 important radiologic parameters that can be used as prognostic indicators in pediatric head injury patients.

A Case Series of 39 United States Veterans with Mild Traumatic Brain Injury Treated with Hyperbaric Oxygen Therapy

Importance: The Defense and Veterans Brain Injury Center reported 358,088 mild traumatic brain injury (mTBI) among U.S. service members worldwide between the years 2000 and 2020. Veterans with mTBI have higher rates of Post-Traumatic Stress Disorder (PTSD), depressive disorder, substance use disorder, anxiety disorder, and suicide than their healthy counterparts. Currently, there is no effective treatment for mTBI. Objective: To assess the efficacy of hyperbaric oxygen therapy (HBOT) as a treatment option for mTBI. Design, Setting, Participants: This is a case series of 39 U.S. Veterans diagnosed with mTBI and treated with HBOT. Of these participants, 36 were men and 3 women, and their ages ranged between 28 and 69. The treatment was administered by The 22 Project (a veteran-centered nonprofit organization) using monoplace hyperbaric chambers located in Delray Beach, Florida. Neuroimaging using Single Photon Emission Computer Tomography (SPECT) brain scans performed pre- and post-HBOT were made available for secondary analysis. Nilearn Python Library was utilized to visualize the corresponding neuroimaging data. A two-sided paired t-test in R was used to compare the pre- and post-treatment results. Intervention: A full treatment of HBOT involved 40 sessions. Each session consisted of the administration of 100% oxygen at 1.5 atmospheres for 90 min, twice a day, for 20 days, Mondays to Fridays only. Main Outcome and Measure: Perfusion in the brain’s Brodmann Areas (BA) comparing pre- and post-HBOT using NeuroGam software analysis from brain SPECT scan neuroimaging and multi-symptom self-reports. Results: A comparison between the pre- and post-HBOT brain scans showed significant improvement in the brain perfusion, and the difference was statistically significant (p < 0.001). Separately, participants reported reduced pain, improved mood, and better sleep, an outcome that translated into an average of about 46.6% improvement in the measured symptoms. Conclusions and Relevance: This series demonstrated that HBOT could be a useful treatment for mTBI in U.S. veterans. The participants in the study showed marked improvement in both brain perfusion measured on SPECT scan imaging and measured mTBI symptoms. This is the first study to use brain SPECT scans with quantitative numerical measurements to demonstrate improvement in brain perfusion in veterans with mild TBI treated with HBOT and measured mTBI symptoms. Future research studies are currently being done to validate these important findings.

Advanced Neuroimaging Role in Traumatic Brain Injury: A Narrative Review

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

Development of a computed tomography perfusion protocol to support large animal resuscitation research

BACKGROUND

Adequate cerebral perfusion is crucial for a positive neurological outcome in trauma; however, it is difficult to characterize in the acute setting with noninvasive methods. Intra-arterial computed tomography perfusion may offer a solution. The aim of this study was to develop an intra-arterial computed tomography perfusion protocol for resuscitation research.

METHODS

The study examined intra-arterial contrast administration for computed tomography perfusion (CTP) acquisition. It consisted of three phases: intra-arterial contrast dose finding, evaluation of reproducibility, and evaluation during hypotension. Blood pressure and laser Doppler flow data were collected. In phase 1, animals underwent CTPs using several intra-arterial contrast injection protocols. In phase 2, animals underwent two CTPs 7 hours apart using the 2.5 mL/s for 3-second protocol. In phase 3, animals underwent CTPs at several pressures following a computer-controlled bleed including euvolemia and at systolic pressures of 60, 40, and 20 mm Hg. Phase 1 CTPs were evaluated for contrast-to-noise ratio. In phase 2, CTPs were compared within each animal and with laser Doppler flow using linear regression. Phase 3 CTPs were graphed against systolic pressure and fitted with a nonlinear fit.

RESULTS

The protocol using 2.5mL/s for 3 seconds was optimal, demonstrating a contrast-to-noise ratio of 40.1 and a superior arterial input function curve compared with the 1 mL/s bolus. Cerebral blood flow demonstrated high concordance between baseline and end of study CTPs (R2 = 0.82, p < 0.001). Cerebral blood flow also compared moderately well against laser Doppler flow during 8 (R2 = 0.53, p = 0.03); however, laser Doppler flow did not perform well during hypovolemia, and the favorable concordance was not maintained (R2 = 0.45, p = 0.06). Cerebral blood flow was graphed against systolic blood pressure and fitted with a nonlinear fit (R2 = 0.95, p = 0.003).

CONCLUSION

Computed tomography perfusion using intra-arterial contrast injection may offer a novel alternative to traditional CTP protocols that could prove a useful additional tool in the setting of resuscitation research.

Functional interferometric diffusing wave spectroscopy of the human brain

Cerebral blood flow (CBF) is essential for brain function, and CBF-related signals can inform us about brain activity. Yet currently, high-end medical instrumentation is needed to perform a CBF measurement in adult humans. Here, we describe functional interferometric diffusing wave spectroscopy (fiDWS), which introduces and collects near-infrared light via the scalp, using inexpensive detector arrays to rapidly monitor coherent light fluctuations that encode brain blood flow index (BFI), a surrogate for CBF. Compared to other functional optical approaches, fiDWS measures BFI faster and deeper while also providing continuous wave absorption signals. Achieving clear pulsatile BFI waveforms at source-collector separations of 3.5 cm, we confirm that optical BFI, not absorption, shows a graded hypercapnic response consistent with human cerebrovascular physiology, and that BFI has a better contrast-to-noise ratio than absorption during brain activation. By providing high-throughput measurements of optical BFI at low cost, fiDWS will expand access to CBF.

Prognostic value of CT perfusion and permeability imaging in traumatic brain injury

BACKGROUND

Currently established prognostic models in traumatic brain injury (TBI) include noncontrast computed tomography (CT) which is insensitive to early perfusion alterations associated with secondary brain injury. Perfusion CT (PCT) on the other hand offers insight into early perfusion abnormalities. We hypothesized that adding CT perfusion and permeability data to the established outcome predictors improves the performance of the prognostic model.

METHODS

A prospective cohort study of consecutive 50 adult patients with head injury and Glasgow Coma Scale score of 12 or less was performed at a single Level 1 Trauma Centre. Perfusion CT was added to routine control CT 12 hours to 24 hours after admission. Region of interest analysis was performed in six major vascular territories on perfusion and permeability parametric maps. Glasgow Outcome Scale (GOS) was used 6 months later to categorize patients' functional outcomes to favorable (GOS score > 3) or unfavorable (GOS score ≤ 3). We defined core prognostic model, consisting of age, motor Glasgow Coma Scale score, pupillary reactivity, and CT Rotterdam Score. Next, we added perfusion and permeability data as predictors and compared updated models to the core model using cross-validated areas under the receiver operator curves (cv-AUC).

RESULTS

Significant advantage over core model was shown by the model, containing both mean cerebral extravascular-extracellular volume per unit of tissue volume and cerebral blood volume of the least perfused arterial territory in addition to core predictors (cv-AUC, 0.75; 95% confidence interval, 0.51-0.84 vs. 0.6; 95% confidence interval, 0.37-0.74).

CONCLUSION

The development of cerebral ischemia and traumatic cerebral edema constitutes the secondary brain injury and represents the target for therapeutic interventions. Our results suggest that adding CT perfusion and permeability data to the established outcome predictors improves the performance of the prognostic model in the setting of moderate and severe TBI.

LEVEL OF EVIDENCE

Prognostic study, level III.

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

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

Advanced neuroimaging in traumatic brain injury: an overview

Traumatic brain injury (TBI) is a common condition with many potential acute and chronic neurological consequences. Standard initial radiographic evaluation includes noncontrast head CT scanning to rapidly evaluate for pathology that might require intervention. The availability of fast, relatively inexpensive CT imaging has fundamentally changed the clinician's ability to noninvasively visualize neuroanatomy. However, in the context of TBI, limitations of head CT without contrast include poor prognostic ability, inability to analyze cerebral perfusion status, and poor visualization of underlying posttraumatic changes to brain parenchyma. Here, the authors review emerging advanced imaging for evaluation of both acute and chronic TBI and include QuickBrain MRI as an initial imaging modality. Dynamic susceptibility-weighted contrast-enhanced perfusion MRI, MR arterial spin labeling, and perfusion CT are reviewed as methods for examining cerebral blood flow following TBI. The authors evaluate MR-based diffusion tensor imaging and functional MRI for prognostication of recovery post-TBI. Finally, MR elastography, MR spectroscopy, and convolutional neural networks are examined as future tools in TBI management. Many imaging technologies are being developed and studied in TBI, and some of these may hold promise in improving the understanding and management of TBI. ABBREVIATIONS ASL = arterial spin labeling; CNN = convolutional neural network; CTP = perfusion CT; DAI = diffuse axonal injury; DMN = default mode network; DOC = disorders of consciousness; DTI = diffusion tensor imaging; FA = fractional anisotropy; fMRI = functional MRI; GCS = Glasgow Coma Scale; MD = mean diffusivity; MRE = MR elastography; MRS = MR spectroscopy; mTBI = mild TBI; NAA = N-acetylaspartate; SWI = susceptibility-weighted imaging; TBI = traumatic brain injury; UHF = ultra-high field.

Using computerized tomography perfusion to measure cerebral hemodynamics following treatment of traumatic brain injury in rabbits

The present study aimed to investigate the use of computerized tomography (CT) perfusion for evaluating cerebral hemodynamics following traumatic brain injury (TBI) in rabbits. The animals were randomly assigned into four groups (n=10 animals/group): i) Control, ii) TBI, iii) TBI + common decompression and iv) TBI + controlled decompression groups. A TBI model was established in rabbits using epidural balloon inflation. In the groups receiving intervention, animals were provided common decompression or controlled decompression treatments. Conventional CT and CT perfusion scanning were performed, with cerebral hemodynamic indices, including regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV) and mean transit time (MTT) being measured. Blood-brain barrier (BBB) permeability was evaluated using Evans blue staining. Compared with those in the control group, rCBF and rCBV values of the bilateral temporal lobes and basal ganglion in the TBI, TBI + common decompression and TBI + controlled decompression groups were significantly lower, whereas the MTT values were markedly prolonged and Evans blue dye content was greatly increased (P<0.01). Controlled decompression was demonstrated to be more potent than common decompression for preventing TBI-induced decline in rCBF and rCBV values in the bilateral temporal lobes and basal ganglion, as well as reversing TBI-induced extension of MTT in the bilateral temporal lobes (P<0.01 vs. TBI group). However, neither common nor controlled decompression could reduce TBI-induced increase in BBB permeability. In conclusion, these findings indicate that CT perfusion may be used to monitor cerebral hemodynamics following TBI in rabbits. Controlled decompression was deduced to be more potent than common decompression for preventing abnormalities in cerebral hemodynamics after TBI.

Neuroimaging of Traumatic Brain Injury

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