Advances in MRI-Based Detection of Cerebrovascular Changes after Experimental Traumatic Brain Injury

A Systematic Review of ASL Perfusion MRI in Mild TBI

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

Cerebral blood flow in acute concussion: preliminary ASL findings from the NCAA-DoD CARE consortium

Sport-related concussion (SRC) has become a major health problem, affecting millions of athletes each year. Despite the increasing occurrence and prevalence of SRC, its underlying mechanism and recovery course have yet to be fully elucidated. The National Collegiate Athletic Association-Department of Defense Grand Alliance: Concussion Assessment, Research and Education (CARE) Consortium is a large-scale, multisite study of the natural history of concussion across multiple sports. The Advanced Research Core (ARC) of CARE is focused on the advanced biomarker assessment of a reduced subject cohort. This paper reports findings from two ARC sites to evaluate cerebral blood flow (CBF) changes in acute SRC, as measured using advanced arterial spin labeling (ASL) magnetic resonance imaging (MRI). We compared relative CBF maps assessed in 24 concussed contact sport athletes obtained at 24-48 h after injury to those of a control group of 24 matched contact sport players. Significantly less CBF was detected in several brain regions in concussed athletes, while clinical assessments also indicated clinical symptom and performance impairments in SRC patients. Correlations were found between decreased CBF in acute SRC and clinical assessments, including Balance Error Scoring System total score and Immediate Post-Concussion Assessment and Cognitive Test memory composite and impulse control composite scores, as well as days from injury to asymptomatic. Although using different ASL MRI sequences, our preliminary results from two sites are consistent with previous reports and suggest that advanced ASL MRI methods might be useful for detecting acute neurobiological changes in acute SRC.

Characteristics of S100B and Neuron Specific Enolase in Differentiating Acute Vertigo Cases with Central Cause; a Diagnostic Accuracy Study

INTRODUCTION

Differentiating central vertigo from peripheral ones poses a challenge to specialists. The present study aimed to examine the potential screening value of S100B and neuron-specific enolase (NSE) in this regard.

METHODS

This prospective cross-sectional study recruited adult acute vertigo patients with suspected central causes visiting the emergency department (ED) in the first six hours since the onset of symptoms. The screening performance characteristics of S100B and NSE biomarkers in differentiating central vertigo cases were measured considering brain magnetic resonance imaging (MRI) as the reference test.

RESULTS

85 cases who met the criteria were enrolled to the study (82.3% female). The MRI of 21 (24.7%) cases had abnormal findings. The two groups were the same in terms of age, sex, and vital signs. Patients with abnormal brain MRI had significantly higher levels of S100B (p < 0.001) and NSE (p < 0.001). S100B and NSE had area under the receiver operating characteristic (ROC) curve of 90.3 (95% CI: 80.7 - 99.8) and 96.9 (95% CI: 93.7 - 100.0) in differentiating the central causes of acute vertigo, respectively. At the cut-off point of above 119.68 pg/l, S100b had sensitivity of 90.00% (95% CI: 78.83 -95.86) and specificity of 92.00% (95% CI: 72.49 - 98.60). The sensitivity and specificity of NSE at the cut-off point of above 18.12 ng/ml were 100.00% (95% CI: 93.14 - 100.00) and 89.47% (95% CI: 65.46 - 98.15), respectively.

CONCLUSION

The serum levels of S100B and NSE were significantly higher in patients with central vertigo, and could therefore be considered as accurate tools in screening acute vertigo cases with central causes in ED.

Cerebral Blood Flow Alterations in Acute Sport-Related Concussion

Sport-related concussion (SRC) is a major health problem, affecting millions of athletes each year. While the clinical effects of SRC (e.g., symptoms and functional impairments) typically resolve within several days, increasing evidence suggests persistent neurophysiological abnormalities beyond the point of clinical recovery after injury. This study aimed to evaluate cerebral blood flow (CBF) changes in acute SRC, as measured using advanced arterial spin labeling (ASL) magnetic resonance imaging (MRI). We compared CBF maps assessed in 18 concussed football players (age, 17.8 ± 1.5 years) obtained within 24 h and at 8 days after injury with a control group of 19 matched non-concussed football players. While the control group did not show any changes in CBF between the two time-points, concussed athletes demonstrated a significant decrease in CBF at 8 days relative to within 24 h. Scores on the clinical symptom (Sport Concussion Assessment Tool 3, SCAT3) and cognitive measures (Standardized Assessment of Concussion [SAC]) demonstrated significant impairment (vs. pre-season baseline levels) at 24 h (SCAT, p < 0.0001; SAC, p < 0.01) but returned to baseline levels at 8 days. Two additional computerized neurocognitive tests, the Automated Neuropsychological Assessment Metrics and Immediate Post-Concussion and Cognitive Testing, showed a similar pattern of changes. These data support the hypothesis that physiological changes persist beyond the point of clinical recovery after SRC. Our results also indicate that advanced ASL MRI methods might be useful for detecting and tracking the longitudinal course of underlying neurophysiological recovery from concussion.

Apolipoprotein E mimetic peptide protects against diffuse brain injury

Apolipoprotein E plays a crucial role in inhibiting chronic neurodegenerative processes. However, its impact on neurological function following diffuse brain injury is still unclear. This study was designed to evaluate the therapeutic effects and mechanisms of action of apolipoprotein E mimetic peptide on diffuse brain injury. Apolipoprotein E mimetic peptide was administered into the caudal vein of rats with diffuse brain injury before and after injury. We found that apolipoprotein E mimetic peptide significantly decreased the number of apoptotic neurons, reduced extracellular signal-regulated kinase1/2 phosphorylation, down-regulated Bax and cytochrome c expression, decreased malondialdehyde content, and increased superoxide dismutase activity in a dose-dependent manner. These experimental findings demonstrate that apolipoprotein E mimetic peptide improves learning and memory function and protects against diffuse brain injury-induced apoptosis by inhibiting the extracellular signal-regulated kinase1/2-Bax mitochondrial apoptotic pathway.

Longitudinal assessment of blood-brain barrier leakage during epileptogenesis in rats. A quantitative MRI study

The blood-brain barrier (BBB) plays an important role in the homeostasis of the brain. BBB dysfunction has been implicated in the pathophysiology of various neurological disorders, including epilepsy in which it may contribute to disease progression. Precise understanding of BBB dynamics during epileptogenesis may be of importance for the assessment of future therapies, including BBB leakage blocking-agents. Longitudinal changes in BBB integrity can be studied with in vivo magnetic resonance imaging (MRI) in combination with paramagnetic contrast agents. Although this approach has shown to be suitable to detect major BBB leakage during the acute phase in experimental epilepsy models, so far no studies have provided information on dynamics of the extent of BBB leakage towards later phases. Therefore a sensitive and quantitative approach was used in the present study, involving fast T1 mapping (dynamic approach) during a steady-state infusion of gadobutrol, as well as pre- and post-contrast T1-weighted MRI (post-pre approach). This was applied in an experimental epilepsy model in which previous MRI studies failed to detect BBB leakage during epileptogenesis. Adult male Sprague-Dawley rats were injected with kainic acid to induce status epilepticus (SE). MRI experiments were performed before SE (control) and during the acute (1 day) and chronic epileptic phases (6 weeks after SE). BBB leakage was quantified by fast T1 mapping (Look-Locker gradient echo MRI) with a time resolution of 48 s from 5 min before up to 45 min after 20 min step-down infusion of 0.2M gadobutrol. In addition, T1-weighted MRI was acquired before and 45 min after infusion. MRI data were compared to post-mortem microscopic analysis using the BBB tracer fluorescein. Our MRI data showed BBB leakage, which was evident at 1 day and 6 weeks after SE in the hippocampus, entorhinal cortex, amygdala and piriform cortex. These findings were confirmed by microscopic analysis of fluorescein leakage. Furthermore, our MRI data revealed non-uniform BBB leakage throughout epileptogenesis. This study demonstrates BBB leakage in specific brain regions during epileptogenesis, which can be quantified using MRI. Therefore, MRI may be a valuable tool for experimental or clinical studies to elucidate the role of the BBB in epileptogenesis.

Sensing lanthanide metal content in biological tissues with magnetic resonance spectroscopy

The development and validation of MRI contrast agents consisting of a lanthanide chelate often requires a determination of the concentration of the agent in ex vivo tissue. We have developed a protocol that uses 70% nitric acid to completely digest tissue samples that contain Gd(III), Dy(III), Tm(III), Eu(III), or Yb(III) ions, or the MRI contrast agent gadodiamide. NMR spectroscopy of coaxial tubes containing a digested sample and a separate control solution of nitric acid was used to rapidly and easily measure the bulk magnetic susceptibility (BMS) shift caused by each lanthanide ion and gadodiamide. Each BMS shift was shown to be linearly correlated with the concentration of each lanthanide ion and gadodiamide in the 70% nitric acid solution and in digested rat kidney and liver tissues. These concentration measurements had outstanding precision, and also had good accuracy for concentrations ≥10 mM for Tm(III) Eu(III), and Yb(III), and ≥3 mM for Gd(III), gadodiamide, and Dy(III). Improved sample handling methods are needed to improve measurement accuracy for samples with lower concentrations.