Application of Blood-Brain Barrier Permeability Imaging in Global Cerebral Edema

CNS Drug Delivery in Stroke: Improving Therapeutic Translation From the Bench to the Bedside

Drug development for ischemic stroke is challenging as evidenced by the paucity of therapeutics that have advanced beyond a phase III trial. There are many reasons for this lack of clinical translation including factors related to the experimental design of preclinical studies. Often overlooked in therapeutic development for ischemic stroke is the requirement of effective drug delivery to the brain, which is critical for neuroprotective efficacy of several small and large molecule drugs. Advancing central nervous system drug delivery technologies implies a need for detailed comprehension of the blood-brain barrier (BBB) and neurovascular unit. Such knowledge will permit the innate biology of the BBB/neurovascular unit to be leveraged for improved bench-to-bedside translation of novel stroke therapeutics. In this review, we will highlight key aspects of BBB/neurovascular unit pathophysiology and describe state-of-the-art approaches for optimization of central nervous system drug delivery (ie, passive diffusion, mechanical opening of the BBB, liposomes/nanoparticles, transcytosis, intranasal drug administration). Additionally, we will discuss how endogenous BBB transporters represent the next frontier of drug delivery strategies for stroke. Overall, this review will provide cutting edge perspective on how central nervous system drug delivery must be considered for the advancement of new stroke drugs toward human trials.

Microvascular dysfunction associated with unfavorable venous outflow in acute ischemic stroke patients

Unfavorable venous outflow (VO) is associated with cerebral edema, which represents microvascular dysfunction. This study estimated the relationship between VO and microvascular function in acute ischemic stroke patients. We retrospectively included 102 MCA/ICA occluded patients with anterior circulation infarction who underwent reperfusion therapy between July 2017 and April 2022. Unfavorable VO was defined as a cortical vein opacification score of 0-3 and favorable VO as that of 4-6. The clinical characteristics, collateral status, microvascular integrity, and outcomes were compared between patients with favorable and unfavorable VO. Multivariate analysis and receiver operator characteristic (ROC) analysis were used. The patients with unfavorable VO had higher extravascular-extracellular volume fraction (Ve) in the infarct core and a lower percentage of robust arterial collateral circulation. ROC analysis revealed that Ve in the infarct core predicts unfavorable VO (AUC = 0.67, sensitivity = 65.08%, specificity = 69.23%). The higher Ve in the infarct core (odds ratio = 1.011, 95% CI = 1.000-1.021, P = 0.046) and poor arterial collateral flow (odds ratio = 0.102, 95% CI = 0.032-0.327, P < 0.001) were independent predictors of unfavorable VO. This suggests that microvascular dysfunction may be one of the mechanisms underlying impaired VO.

Basis and current state of computed tomography perfusion imaging: a review

Computed tomography perfusion (CTP) is a functional imaging that allows for providing capillary-level hemodynamics information of the desired tissue in clinics. In this paper, we aim to offer insight into CTP imaging which covers the basics and current state of CTP imaging, then summarize the technical applications in the CTP imaging as well as the future technological potential. At first, we focus on the fundamentals of CTP imaging including systematically summarized CTP image acquisition and hemodynamic parameter map estimation techniques. A short assessment is presented to outline the clinical applications with CTP imaging, and then a review of radiation dose effect of the CTP imaging on the different applications is presented. We present a categorized methodology review on known and potential solvable challenges of radiation dose reduction in CTP imaging. To evaluate the quality of CTP images, we list various standardized performance metrics. Moreover, we present a review on the determination of infarct and penumbra. Finally, we reveal the popularity and future trend of CTP imaging.

Radiology- and gene-based risk stratification in small renal cell carcinoma: A preliminary study

PURPOSE

Most small renal cell carcinomas (small RCCs) will remain indolent after detection, but some stage I RCCs still metastasize. There are no risk-stratification imaging factors that could be used to identify poor-prognosis patients based on genomic profiling. Here, we evaluated the relationships between imaging parameters and RNA expressions in small RCC and attempted to identify imaging factors that could be used as effective biomarkers.

METHODS

We acquired biopsy specimens of 18 clear cell carcinomas that had undergone perfusion CT (pCT) and MRI between April 2018 and March 2019. We performed RNA sequencing, assessed RNA expressions, and calculated each tumor's cell-cycle progression (CCP) score, which has prognostic value in predicting metastatic progression. We classified the tumors into two groups: clear cell type A (ccA) and type B (ccB). CcA has better survival compared to ccB. We evaluated the following characteristics of each tumor: tumor size, presence of pseudocapsule, and fat. We used the pCT and MRI to measure each tumor's volume transfer constant (Ktrans), rate constant (Kep), extracellular extravascular volume fraction (VE), fractional plasma volume (VP), and apparent diffusion coefficient (ADC). The correlations between these small RCC imaging parameters and the tumor size and RNA expressions were determined.

RESULTS

The tumor size was significantly correlated with Kep and inversely correlated with VE, VP, ADC, and hallmark angiogenesis. The CCP score was significantly inversely correlated with Ktrans and Kep. The ccA tumors tended to show a pseudocapsule on MRI.

CONCLUSION

Tumor size was correlated with low perfusion, but not with prognostic factors based on genomic profiling. Imaging parameters (e.g., Ktrans and Kep) and tumor characteristics (e.g., pseudocapsule) may enable gene-based risk stratification in small RCC.

Vasospasm: Role of Imaging in Detection and Monitoring Treatment

Cerebral vasospasm (VS) and delayed cerebral ischemia (DCI) are important complications of aneurysmal subarachnoid hemorrhage (ASAH). Imaging approaches to VS monitoring include noninvasive bedside assessment with transcranial Doppler ultrasonography, angiographic evaluation with digital subtraction angiography, and computed tomography (CT) angiography. DCI is a clinical diagnosis and is not fully explained by the presence of angiographic VS. CT perfusion has shown clinical utility and implications for future research in the evaluation of DCI in patients with ASAH. This review article discusses the common approaches to diagnosis and monitoring of VS and DCI, current treatment strategies, and future research directions.

Blood-brain barrier permeability imaging as a predictor for delayed cerebral ischaemia following subarachnoid haemorrhage. A narrative review

BACKGROUND

Aneurysmal subarachnoid haemorrhage is associated with significant morbidity and mortality due to the myriad of complications contributing to early brain injury and delayed cerebral ischaemia. There is increasing interest in the exploration of the association between blood-brain barrier integrity and risks of delayed cerebral ischaemia and poor outcomes. Despite recent advances in cerebral imaging, radiographic imaging of blood-brain barrier disruption, as a biomarker for outcome prediction, has not been adopted in clinical practice.

METHODS

We performed a narrative review by searching for articles describing molecular changes or radiological identification of changes in BBB permeability following subarachnoid haemorrhage (SAH) on MEDLINE. Preclinical studies were analysed if reported structural changes and clinical studies were included if they investigated for radiological markers of BBB disruption and its correlation with delayed cerebral ischaemia.

RESULTS

There is ample preclinical evidence to suggest that there are structural changes in BBB permeability following SAH. The available clinical literature has demonstrated correlations between permeability imaging and outcomes following aneurysmal subarachnoid haemorrhage (aSAH).

CONCLUSION

Radiological biomarkers offer a potential non-invasive prognostication tool and may also allow early identifications of patients who may be at risk of DCI.

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.

The Updated Role of the Blood Brain Barrier in Subarachnoid Hemorrhage: From Basic and Clinical Studies

Subarachnoid hemorrhage (SAH) is a type of hemorrhagic stroke associated with high mortality and morbidity. The blood-brain-barrier (BBB) is a structure consisting primarily of cerebral microvascular endothelial cells, end feet of astrocytes, extracellular matrix, and pericytes. Post-SAH pathophysiology included early brain injury and delayed cerebral ischemia. BBB disruption was a critical mechanism of early brain injury and was associated with other pathophysiological events. These pathophysiological events may propel the development of secondary brain injury, known as delayed cerebral ischemia. Imaging advancements to measure BBB after SAH primarily focused on exploring innovative methods to predict clinical outcome, delayed cerebral ischemia, and delayed infarction related to delayed cerebral ischemia in acute periods. These predictions are based on detecting abnormal changes in BBB permeability. The parameters of BBB permeability are described by changes in computed tomography (CT) perfusion and magnetic resonance imaging (MRI). K_ep seems to be a stable and sensitive indicator in CT perfusion, whereas K^trans is a reliable parameter for dynamic contrast-enhanced MRI. Future prediction models that utilize both the volume of BBB disruption and stable parameters of BBB may be a promising direction to develop practical clinical tools. These tools could provide greater accuracy in predicting clinical outcome and risk of deterioration. Therapeutic interventional exploration targeting BBB disruption is also promising, considering the extended duration of post-SAH BBB disruption.

Limited Colocalization of Microbleeds and Microstructural Changes after Severe Traumatic Brain Injury

Severe traumatic brain injury (TBI) produces shearing forces on long-range axons and brain vessels, causing axonal and vascular injury. To examine whether microbleeds and axonal injury colocalize after TBI, we performed whole-brain susceptibility-weighted imaging (SWI) and diffusion tensor imaging (DTI) in 14 patients during the subacute phase after severe TBI. SWI was used to determine the number and volumes of microbleeds in five brain regions: the frontotemporal lobe; parieto-occipital lobe; midsagittal region (cingular cortex, parasagittal white matter, and corpus callosum); deep nuclei (basal ganglia and thalamus); and brainstem. Averaged fractional anisotropy (FA) and mean diffusivity (MD) were measured to assess microstructural changes in the normal appearing white matter attributed to axonal injury in the same five regions. Regional expressions of microbleeds and microstructure were used in a partial least-squares model to predict the impairment of consciousness in the subacute stage after TBI as measured with the Coma Recovery Scale-Revised (CRS-R). Only in the midsagittal region, the expression of microbleeds was correlated with regional changes in microstructure as revealed by DTI. Microbleeds and microstructural DTI-based metrics of deep, but not superficial, brain regions were able to predict individual CRS-R. Our results suggest that microbleeds are not strictly related to axonal pathology in other than the midsagittal region. While each measure alone was predictive, the combination of both metrics scaled best with individual CRS-R. Structural alterations in deep brain structures are relevant in terms of determining the severity of impaired consciousness in the acute stage after TBI.

Alterations in Blood-Brain Barrier Permeability in Patients with Systemic Lupus Erythematosus

BACKGROUND AND PURPOSE

Neuropsychiatric systemic lupus erythematosus refers to central and peripheral nervous system involvement, which may occur secondary to antineuronal antibodies crossing the blood-brain barrier that preferentially target cells in the hippocampus leading to abnormal hypermetabolism and atrophy. Thus, we hypothesized that alterations in BBB permeability, detected on dynamic contrast-enhanced MR imaging, occur in the hippocampus in patients with systemic lupus erythematosus before development of neuropsychiatric systemic lupus erythematosus.

MATERIALS AND METHODS

Six patients with systemic lupus erythematosus without neuropsychiatric systemic lupus erythematosus and 5 healthy controls underwent dynamic contrast-enhanced MR imaging with postprocessing into BBB permeability parameters (K ^trans and Ve) and CBF. Standardized methods selected ROI sampling of the abnormal brain regions detected on FDG-PET. The mean and SD of K ^trans, Ve, and CBF were calculated. Linear regression and nonparametric Spearman rank correlation analyses of K ^trans and Ve with CBF were performed. Dynamic contrast-enhanced curves and the area under the curve were generated for each brain region. Student t test comparisons were performed.

RESULTS

Quantitative data revealed that patients with systemic lupus erythematosus have statistically increased K ^trans (P < .001) and Ve (P < .001) compared with controls. In patients with systemic lupus erythematosus, statistically significant positive correlations were seen between K ^trans (P < .001) and Ve (P < .001) with CBF. Furthermore, the mean area under the curve revealed statistically increased BBB permeability in the hippocampus (P = .02) compared with other brain regions in patients with systemic lupus erythematosus compared with controls.

CONCLUSIONS

These initial findings are proof-of-concept to support the hypothesis that patients with systemic lupus erythematosus have increased BBB permeability, specifically in the hippocampus, compared with other brain regions. These findings may advance our understanding of the underlying pathophysiology affecting the brain in autoimmune diseases.

Early focal brain injury after subarachnoid hemorrhage correlates with spreading depolarizations

OBJECTIVE

To investigate whether spreading depolarization (SD)-related variables at 2 different time windows (days 1-4 and 5-8) after aneurysmal subarachnoid hemorrhage (aSAH) correlate with the stereologically determined volume of early focal brain injury on the preinterventional CT scan.

METHODS

In this observational multicenter study of 54 patients, volumes of unaffected brain tissue, ventricles, cerebellum, aSAH, intracerebral hemorrhage, and focal parenchymal hypodensity were stereologically estimated. Patients were electrocorticographically monitored using subdural electrodes for 81.8 hours (median) (interquartile range: 70.6-90.5) during days 1-4 (n = 54) and for 75.9 (59.5-88.7) hours during days 5-8 (n = 51). Peak total SD-induced depression duration of a recording day (PTDDD) and peak numbers of (1) SDs, (2) isoelectric SDs, and (3) spreading depressions of a recording day were determined following the recommendations of the Co-Operative Studies on Brain Injury Depolarizations.

RESULTS

Thirty-three of 37 patients with early focal brain injury (intracerebral hemorrhage and/or hypodensity) in contrast to 7 of 17 without displayed SDs during days 1-4 (sensitivity: 89% [95% confidence interval, CI: 75%-97%], specificity: 59% [CI: 33%-82%], positive predictive value: 83% [CI: 67%-93%], negative predictive value: 71% [CI: 42%-92%], Fisher exact test, p < 0.001). All 4 SD-related variables during days 1-4 significantly correlated with the volume of early focal brain injury (Spearman rank order correlations). A multiple ordinal regression analysis identified the PTDDD as the most important predictor.

CONCLUSIONS

Our findings suggest that early focal brain injury after aSAH is associated with early SDs and further support the notion that SDs are a biomarker of focal brain lesions.

Mechanisms of Global Cerebral Edema Formation in Aneurysmal Subarachnoid Hemorrhage

A growing body of clinical literature emphasizes the impact of cerebral edema in early brain injury following aneurysmal subarachnoid hemorrhage (aSAH). Aneurysm rupture itself initiates global cerebral edema in up to two thirds of cases. Although cerebral edema is not a universal feature of aSAH, it portends a poor clinical course, with quantitative analysis revealing a direct correlation between cerebral edema and poor outcome, including mortality and cognitive deficits. Mechanistically, global cerebral edema has been linked to global ischemia at the time of aneurysm rupture, dysfunction of autoregulation, blood breakdown products, neuroinflammation, and hyponatremia/endocrine abnormalities. At a molecular level, several culprits have been identified, including aquaporin-4, matrix metalloproteinase-9, SUR1-TRPM4 cation channels, vascular endothelial growth factor, bradykinin, and others. Here, we review these cellular and molecular mechanisms of global cerebral edema formation in aSAH. Given the importance of edema to the outcome of patients with aSAH and its status as a highly modifiable pathological process, a better understanding of cerebral edema in aSAH promises to hasten the development of medical therapies to improve outcomes in this frequently devastating disease.

Effects of Radiation Exposure on the Cost-Effectiveness of CT Angiography and Perfusion Imaging in Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

CT angiography and perfusion imaging is an important prognostic tool in the management of patients with aneurysmal subarachnoid hemorrhage. The purpose of this study was to perform a cost-effectiveness analysis of advanced imaging in patients with SAH, incorporating the risks of radiation exposure from CT angiography and CT perfusion imaging.

MATERIALS AND METHODS

The risks of radiation-induced brain cancer and cataracts were incorporated into our established decision model comparing the cost-effectiveness of CT angiography and CT perfusion imaging and transcranial Doppler sonography in SAH. Cancer risk was calculated by using National Cancer Institute methodology. The remaining input probabilities were based on literature data and a cohort at our institution. Outcomes were expected quality-adjusted life years gained, costs, and incremental cost-effectiveness ratios. One-way, 2-way, and probabilistic sensitivity analyses were performed.

RESULTS

CT angiography and CT perfusion imaging were the dominant strategies, resulting in both better health outcomes and lower costs, even when incorporating brain cancer and cataract risks. Our results remained robust in 2-way sensitivity analyses varying the prolonged latency period up to 30 years, with either brain cancer risk up to 50 times higher than the upper 95% CI limit or the probability of cataracts from 0 to 1. Results were consistent for scenarios that considered either symptomatic or asymptomatic patients with SAH. Probabilistic sensitivity analysis confirmed our findings over a broad range of selected input parameters.

CONCLUSIONS

While risks of radiation exposure represent an important consideration, CT angiography and CT perfusion imaging remained the preferred imaging compared with transcranial Doppler sonography in both asymptomatic and symptomatic patients with SAH, with improved health outcomes and lower health care costs, even when modeling a significantly higher risk and shorter latency period for both cataract and brain cancer than that currently known.