Improving Acute Stroke Management with Computed Tomography Perfusion: A Review of Imaging Basics and Applications

Perfusion gradients promote delayed perihaematomal oedema in intracerebral haemorrhage

Perihaematomal oedema is a potential therapeutic target to improve outcome of patients with intracerebral haemorrhage, but its pathophysiology remains poorly elucidated. We investigated the longitudinal changes of cerebral perfusion and their influence on perihaematomal oedema development in 150 patients with intracerebral haemorrhage who underwent computed tomography perfusion within 6 h from onset, at 24 h and at 7 days. Perfusion parameters were measured in haemorrhagic core, perihaematomal rim, surrounding normal appearing and contralateral brain tissue. Computed tomography perfusion parameters gradually improved from the core to the periphery in each time interval with an early increase at 24 h followed by a delayed decline at 7 days compared with admission values (P < 0.001). Multivariable linear regression analysis showed that haematoma volume and cerebral blood flow gradient between normal appearing and perihaematomal rim were independently associated with absolute perihaematomal oedema volume in the different time points (within 6 h, B = 0.128, P = 0.032; at 24 h, B = 0.133, P = 0.016; at 7 days, B = 0.218, P < 0.001). In a secondary analysis with relative perihaematomal oedema as the outcome of interest, cerebral blood flow gradient between normal appearing and perihaematomal rim was an independent predictor of perihaematomal oedema only at 7 days (B = 0.239, P = 0.002). Our findings raise the intriguing hypothesis that perfusion gradients promote perihaematomal oedema development in the subacute phase after intracerebral haemorrhage.

Clinical and therapeutic variables may influence the association between infarct core predicted by CT perfusion and clinical outcome in acute stroke

OBJECTIVES

After an acute ischemic stroke, patients with a large CT perfusion (CTP) predicted infarct core (pIC) have poor clinical outcome. However, previous research suggests that this relationship may be relevant for subgroups of patients determined by pretreatment and treatment-related variables while negligible for others. We aimed to identify these variables.

METHODS

We included a cohort of 828 patients with acute proximal carotid arterial occlusions imaged with a whole-brain CTP within 8 h from stroke onset. pIC was computed on CTP Maps (cerebral blood flow < 30%), and poor clinical outcome was defined as a 90-day modified Rankin Scale score > 2. Potential mediators of the association between pIC and clinical outcome were evaluated through first-order and advanced interaction analyses in the derivation cohort (n = 654) for obtaining a prediction model. The derived model was further validated in an independent cohort (n = 174).

RESULTS

The volume of pIC was significantly associated with poor clinical outcome (OR = 2.19, 95% CI = 1.73 - 2.78, p < 0.001). The strength of this association depended on baseline National Institute of Health Stroke Scale, glucose levels, the use of thrombectomy, and the interaction of age with thrombectomy. The model combining these variables showed good discrimination for predicting clinical outcome in both the derivation cohort and validation cohorts (area under the receiver operating characteristic curve 0.780 (95% CI = 0.746-0.815) and 0.782 (95% CI = 0.715-0.850), respectively).

CONCLUSIONS

In patients imaged within 8 h from stroke onset, the association between pIC and clinical outcome is significantly modified by baseline and therapeutic variables. These variables deserve consideration when evaluating the prognostic relevance of pIC.

KEY POINTS

•The volume of CT perfusion (CTP) predicted infarct core (pIC) is associated with poor clinical outcome in acute ischemic stroke imaged within 8 h of onset. •The relationship between pIC and clinical outcome may be modified by baseline clinical severity, glucose levels, thrombectomy use, and the interaction of age with thrombectomy. •CTP pIC should be evaluated in an individual basis for predicting clinical outcome in patients imaged within 8 h from stroke onset.

Delayed perihematomal hypoperfusion is associated with poor outcome in intracerebral haemorrhage

BACKGROUND

The aim of this study was to characterize the temporal evolution and prognostic significance of perihematomal perfusion in acute intracerebral haemorrhage (ICH).

METHODS

A single-centre prospective cohort of patients with primary spontaneous ICH receives computed tomography perfusion (CTP) within 6 h from onset (T0) and at 7 days (T7). Cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were measured in the manually outlined perihematomal low-density area. Poor functional prognosis (modified Rankin Scale 3-6) at 90 days was the outcome of interest, and predictors were explored with multivariable logistic regression.

RESULTS

A total of 150 patients were studied, of whom 52 (34.7%) had a mRS 3-6 at 90 days. Perihematomal perfusion decreased from T0 to T7 in all patients, but the magnitude of CBF and CBV reduction was larger in patients with unfavourable outcome (median CBF change -7.8 vs. -6.0 ml/100 g/min, p < .001, and median CBV change -0.5 vs. -0.4 ml/100 g, p = .010, respectively). This finding remained significant after adjustment for confounders (odds ratio [OR] for 1 ml/100 g/min CBF reduction: 1.33, 95% confidence interval [CI] (1.15-1.55), p < .001; OR for 0.1 ml/100 g CBV reduction: 1.67, 95% CI 1.18-2.35, p = .004). The presence of CBF < 20 ml/100 g/min at T7 was then demonstrated as an independent predictor of poor functional outcome (adjusted OR: 2.45, 95% CI 1.08-5-54, p = .032).

CONCLUSION

Perihaemorrhagic hypoperfusion becomes more severe in the days following acute ICH and is independently associated with poorer outcome. Understanding the underlying biological mechanisms responsible for delayed decrease in perihematomal perfusion is a necessary step towards outcome improvement in patients with ICH.

Evolution of Hypodensity on Non-Contrast CT in Correlation with Collaterals in Anterior Circulation Stroke with Successful Endovascular Reperfusion

Introduction: The aim of the study was to assess the impact of collaterals on the evolution of hypodensity on non-contrast CT (NCCT) in anterior circulation stroke with reperfusion by mechanical thrombectomy (MT). Methods: We retrospectively included stroke patients with middle cerebral artery occlusion who were reperfused by MT in early and late time window. Artificial intelligence (AI)-based software was used to calculate of hypodensity volumes at baseline NCCT (V1) and at follow-up NCCT 24 h after MT (V2), along with the difference between the two volumes (V2-V1) and the follow-up (V2)/baseline (V1) volume ratio (V2/V1). The same software was used to classify collateral status by using a 4-point scale where the score of zero indicated no collaterals and the score of three represented contrast filling of all collaterals. The volumetric values were correlated with the collateral scores. Results: Collateral scores had significant negative correlation with V1 (p = 0.035), V2, V2− V1 and V2/V1 (p < 0.001). In cases with collateral score = 3, V2 was significantly smaller or absent compared to V1; in those with collateral score 2, V2 was slightly larger than V1, and in those with scores 1 and 0 V2 was significantly larger than V1. These relationships were observed in both early and late time windows. Conclusions: The collateral status determined the evolution of the baseline hypodensity on NCCT in patients with anterior circulation stroke who had MT reperfusion. Damage can be stable or reversible in patients with good collaterals while in those with poor collaterals tissues that initially appear normal will frequently appear as necrotic after 24 h. With good collaterals, it is stable or can be reversible while with poor collaterals, normal looking tissue frequently appears as necrotic in follow-up exam. Hence, acute hypodensity represents different states of the ischemic brain parenchyma.

Endothelial SIRT6 blunts stroke size and neurological deficit by preserving blood-brain barrier integrity: a translational study

AIMS

Aging is an established risk factor for stroke; genes regulating longevity are implicated in the pathogenesis of ischaemic stroke where to date, therapeutic options remain limited. The blood-brain barrier (BBB) is crucially involved in ischaemia/reperfusion (I/R) brain injury thus representing an attractive target for developing novel therapeutic agents. Given the role of endothelial cells in the BBB, we hypothesized that the endothelial-specific expression of the recently described longevity gene SIRT6 may exhibit protective properties in stroke.

METHODS AND RESULTS

SIRT6 endothelial expression was reduced following stroke. Endothelial-specific Sirt6 knockout (eSirt6-/-) mice, as well as animals in which Sirt6 overexpression was post-ischaemically induced, underwent transient middle cerebral artery occlusion (tMCAO). eSirt6-/- animals displayed increased infarct volumes, mortality, and neurological deficit after tMCAO, as compared to control littermates. Conversely, post-ischaemic Sirt6 overexpression decreased infarct size and neurological deficit. Analysis of ischaemic brain sections revealed increased BBB damage and endothelial expression of cleaved caspase-3 in eSIRT6-/- mice as compared to controls. In primary human brain microvascular endothelial cells (HBMVECs), hypoxia/reoxygenation (H/R) reduced SIRT6 expression and SIRT6 silencing impaired the barrier function (transendothelial resistance) similar to what was observed in mice exposed to I/R. Further, SIRT6-silenced HBMVECs exposed to H/R showed reduced viability, increased cleaved caspase-3 expression and reduced activation of the survival pathway Akt. In ischaemic stroke patients, SIRT6 expression was higher in those with short-term neurological improvement as assessed by NIHSS scale and correlated with stroke outcome.

CONCLUSION

Endothelial SIRT6 exerts a protective role in ischaemic stroke by blunting I/R-mediated BBB damage and thus, it may represent an interesting novel therapeutic target to be explored in future clinical investigation.

Neurovascular Unit: Basic and Clinical Imaging with Emphasis on Advantages of Ferumoxytol

Physiological and pathological processes that increase or decrease the central nervous system's need for nutrients and oxygen via changes in local blood supply act primarily at the level of the neurovascular unit (NVU). The NVU consists of endothelial cells, associated blood-brain barrier tight junctions, basal lamina, pericytes, and parenchymal cells, including astrocytes, neurons, and interneurons. Knowledge of the NVU is essential for interpretation of central nervous system physiology and pathology as revealed by conventional and advanced imaging techniques. This article reviews current strategies for interrogating the NVU, focusing on vascular permeability, blood volume, and functional imaging, as assessed by ferumoxytol an iron oxide nanoparticle.

Vulnerability to Infarction During Cerebral Ischemia in Migraine Sufferers

BACKGROUND AND PURPOSE

Cerebral hyperexcitability in migraine experiencers might sensitize brain tissue to ischemia. We investigated whether a personal history of migraine is associated with vulnerability to brain ischemia in humans.

METHODS

Multicenter cohort study of patients with acute ischemic stroke who underwent a brain computed tomography perfusion and were scheduled to undergo reperfusion therapy. In a case-control design, we compared the proportion of subjects with no-mismatch, the volume of penumbra salvaged, as well as the final infarct size in a group of patients with migraine and a group of patients with no history of migraine.

RESULTS

We included 61 patients with migraine (34 [55.7%] men; mean age, 52.2±15.1 years; migraine without aura/migraine with aura, 44/17) and 61 patients with no history of migraine. The proportion of no-mismatch among migraineurs was significantly higher than among nonmigraineurs (17 [27.9%] versus 7 [11.5%]; P=0.039) and was more prominent among patients with migraine with aura (6 [35.3%]; P=0.030) while it was nonsignificantly increased in patients with migraine without aura (11 [25.0%]; P=0.114). Migraine, especially migraine with aura, was independently associated with a no-mismatch pattern (odds ratio, 2.65; 95% CI, 0.95-7.41 for migraine; odds ratio, 5.54; 95% CI, 1.28-23.99 for migraine with aura), and there was a linear decrease of the proportion of patients with migraine with aura with increasing quartiles of mismatch volumes. Patients with migraine with aura had also smaller volumes of salvaged penumbra (9.8±41.2 mL) compared with patients with migraine without aura (36.4±54.1 mL) and patients with no migraine (45.1±55.0 mL; P=0.056). Conversely, there was no difference in final infarct size among the 3 migraine subgroups (P=0.312).

CONCLUSIONS

Migraine is likely to increase individual vulnerability to ischemic stroke during the process of acute brain ischemia and might represent, therefore, a potential new therapeutic target against occurrence and progression of the ischemic damage.

CT-based Techniques for Brain Perfusion

Recent rapid advances in endovascular treatment for acute ischemic stroke highlight the crucial role of neuroimaging especially multimodal computed tomography (CT) including CT perfusion in stroke triage and management decisions. With an increasing focus on changes in cerebral physiology along with time-based matrices in clinical decisions for acute ischemic stroke, CT perfusion provides a rapid and practical modality for assessment and identification of salvageable tissue at risk and infarct core and provides a better understanding of the changes in cerebral physiology. Although there are challenges with the lack of standardization and accuracy of quantitative assessment, CT perfusion is evolving as a cornerstone for imaging-based strategies in the rapid management of acute ischemic stroke.

The diagnosis and clinical management of the neuropsychiatric manifestations of lupus

Neuropsychiatric (NP) involvement in Systemic Lupus Erythematosus (SLE), can be a severe and troubling manifestation of the disease that heavily impacts patient's health, quality of life and disease outcome. It is one of the most complex expressions of SLE which can affect central, peripheral and autonomous nervous system. Complex interrelated pathogenetic mechanisms, including genetic factors, vasculopathy, vascular occlusion, neuroendocrine-immune imbalance, tissue and neuronal damage mediated by autoantibodies, inflammatory mediators, blood brain barrier dysfunction and direct neuronal cell death can be all involved. About NPSLE a number of issues are still matter of debate: from classification and burden of NPSLE to attribution and diagnosis. The role of neuroimaging and new methods of investigation still remain pivotal and rapidly evolving as well as is the increasing knowledge in the pathogenesis. Overall, two main pathogenetic pathways have been recognized yielding different clinical phenotypes: a predominant ischemic-vascular one involving large and small blood vessels, mediated by aPL, immune complexes and leuko-agglutination which it is manifested with more frequent focal NP clinical pictures and a predominantly inflammatory-neurotoxic one mediated by complement activation, increased permeability of the BBB, intrathecal migration of autoantibodies, local production of immune complexes and pro-inflammatory cytokines and other inflammatory mediators usually appearing as diffuse NP manifestations. In the attempt to depict a journey throughout NPSLE from diagnosis to a reasoned therapeutic approach, classification, epidemiology, attribution, risk factors, diagnostic challenges, neuroimaging techniques and pathogenesis will be considered in this narrative review based on the most relevant and recent published data.

Arterial input function placement effect on computed tomography lung perfusion maps

BACKGROUND

A critical source of variability in dynamic perfusion computed tomography (DPCT) is the arterial input function (AIF). However, the impact of the AIF location in lung DPCT has not been investigated yet. The purpose of this study is to determine whether the location of the AIF within the central pulmonary arteries influences the accuracy of lung DPCT maps.

METHODS

A total of 54 lung DPCT scans were performed in three pigs using different rates and volumes of iodinated contrast media. Pulmonary blood flow (PBF) perfusion maps were generated using first-pass kinetics in three different AIF locations: the main pulmonary trunk (PT), the right main (RM) and the left main (LM) pulmonary arteries. A total of 162 time density curves (TDCs) and corresponding PBF perfusion maps were generated. Linear regression and Spearman's rank correlation coefficient were used to compare the TDCs. PBF perfusion maps were compared quantitatively by taking twenty six regions of interest throughout the lung parenchyma. Analysis of variance (ANOVA) was used to compare the mean PBF values among the three AIF locations. Two chest radiologists performed qualitative assessment of the perfusion maps using a 3-point scale to determine regions of perfusion mismatch.

RESULTS

The linear regression of the TDCs from the RM and LM compared to the PT had a median (range) of 1.01 (0.98-1.03). The Spearman rank correlation between the TDCs was 0.88 (P<0.05). ANOVA analysis of the perfusion maps demonstrated no statistical difference (P>0.05). Qualitative comparison of the perfusion maps resulted in scores of 1 and 2, demonstrating either identical or comparable maps with no significant difference in perfusion defects between the different AIF locations.

CONCLUSIONS

Accurate PBF perfusion maps can be generated with the AIF located either at the PT, RM or LM pulmonary arteries.

Neuroradiology of the Brain

A variety of imaging modalities are currently used to evaluate the brain. Prior to the 1970s, neurologic imaging involved radiographs, invasive procedures for spinal and carotid artery air and contrast injection, and painful patient manipulation. The brain was considered inaccessible to imaging and referred to as "the dark continent." Since then, advances in neuroradiology have moved the brain from being a dark continent to evaluation techniques that illuminate brain contents and pathology. These advances enable quick acquisition of images for prompt diagnosis and treatment. This article reviews anatomy, diagnostic principles, and clinical application of brain imaging beyond plain radiographs.

CT perfusion and angiographic assessment of pial collateral reperfusion in acute ischemic stroke: the CAPRI study

BACKGROUND

The purpose of this study was to evaluate the correlation between a novel angiographic score for collaterals and CT perfusion (CTP) parameters in patients undergoing endovascular treatment for acute ischemic stroke (AIS).

METHODS

103 patients (mean age 66.7±12.7; 48.5% men) with AIS in the anterior circulation territory, imaged with non-contrast CT, CT angiography, and CTP, admitted within 8 h from symptom onset and treated with any endovascular approach, were retrospectively included in the study. Clinical, neuroradiological data, and all time intervals were collected. Careggi Collateral Score (CCS) was used for angiographic assessment of collaterals and the Alberta Stroke Program Early CT Score (ASPECTS) for semiquantitative analysis of CTP maps. Two centralized core laboratories separately reviewed angiographic data, whereas CT findings were evaluated by an expert neuroradiologist. Univariate and multivariate analysis were performed considering CCS both as an ordinal and a dichotomous variable.

RESULTS

37/103 patients (35.9%) received intravenous tissue plasminogen activator. Median (IQR) ASPECTS was 9 (6-10) for admission CT, 9 (5-10) for cerebral blood volume (CBV) maps, 3 (2-3) for mean transit time maps, 3 (2-4), for cerebral blood flow maps, and 5 (3-7) for CTP mismatch. Univariate analysis showed a significant correlation between CCS and ASPECTS for all CTP parameters. Multivariate analysis confirmed an independent association only between CCS and CBV (p=0.020 when CCS was considered as a dichotomous variable, p=0.026 with ordinal CCS).

CONCLUSIONS

A correlation between angiographic assessment of the collateral circulation and CTP seems to be present, suggesting that CCS may provide an indirect evaluation of the infarct core volume to consider for patient selection in AIS.

Temporal changes in blood-brain barrier permeability and cerebral perfusion in lacunar/subcortical ischemic stroke

Background

Cerebral microvascular abnormality is frequently associated with lacunar and subcortical ischemic lesions. We performed acute and follow-up CT perfusion scans over the first 3 months after ischemic stroke to investigate disturbances of the blood–brain barrier (BBB) and cerebral perfusion in patients with lacunar/subcortical lesions compared to those with cortical lesions alone.

Methods

Thirty-one patients with lacunar/subcortical infarct (n = 14) or with cortical large vessel infarct (n = 17) were recruited and underwent a CT perfusion study at admission, 24 h, 7 days and 3 months after stroke using a two-phase imaging protocol. Functional maps of BBB permeability surface area product (BBB-PS), cerebral blood flow (CBF) and blood volume (CBV) at follow-up were co-registered with those at admission, and the measurements in non-infarcted ipsilateral basal ganglia and thalamus were compared within each group and between the two groups.

Results

For the lacunar/subcortical group, BBB-PS within non-infarcted ipsilateral basal ganglia and thalamus peaked at day 7 compared to all other time points, and was significantly higher than the cortical group at day 7 and month 3. The CBF and CBV in the same region were significantly lower at admission and transient hyperemia was seen at day 7 in the lacunar/subcortical group.

Conclusion

Disturbed BBB-PS and compromised cerebral perfusion over the first 3 months post stroke were shown in the non-infarcted basal ganglia and thalamus of lacunar/subcortical stroke using CT perfusion. Future studies are required to elucidate the relationship of post-stroke BBB disturbances to chronic cognitive impairment.

CT perfusion cerebral blood volume does not always predict infarct core in acute ischemic stroke

We investigated the practical clinical utility of the CT perfusion (CTP) cerebral blood volume (CBV) parameter for differentiating salvageable from non-salvageable tissue in acute ischemic stroke (AIS). Fifty-five patients with AIS were imaged within 6 h from onset using CTP. Admission CBV defect (CBVD) volume was outlined using previously established gray and white matter CBV thresholds for infarct core. Admission cerebral blood flow (CBF) hypoperfusion and CBF/CBV mismatch were visually evaluated. Truncation of the ischemic time-density curve (ITDC) and hypervolemia status at admission, recanalization at 24-h CT angiography, hemorrhagic transformation (HT) at 24 h and/or 7-day non-contrast CT (NCCT), final infarct volume as indicated by 3-month NCCT defect (NCCTD) and 3-month modified Rankin Score were determined. Patients with recanalization and no truncation had the highest correlation (R = 0.81) and regression slope (0.80) between CBVD and NCCTD. Regression slopes were close to zero for patients with admission hypervolemia with/without recanalization. Hypervolemia underestimated (p = 0.02), while recanalization and ITDC truncation overestimated (p = 0.03) the NCCTD. Among patients with confirmed recanalization at 24 h, 38 % patients had an admission CBF/CBV mismatch within normal appearing areas on respective NCCT. 83 % of these patients developed infarction in admission hypervolemic CBF/CBV mismatch tissue. A reduction in CBV is a valuable predictor of infarct core when the acquisition of ITDC data is complete and hypervolemia is absent within the tissue destined to infarct. Raised or normal CBV is not always indicative of salvageable tissue, contrary to the current definition of penumbra.

Hemodynamic effects of combined focal cerebral ischemia and amyloid protein toxicity in a rat model: a functional CT study

Background/Objective

Clinical evidence indicates that cerebral ischemia (CI) and a pathological factor of Alzheimer's disease, the β-amyloid (Aβ) protein, can increase the rate of cognitive impairment in the ageing population. Using the CT Perfusion (CTP) functional imaging, we sought to investigate the interaction between CI and the Aβ protein on cerebral hemodynamics.

Methods

A previously established rat model of CI and Aβ was used for the CTP study. Iodinated contrast was given intravenously, while serial CT images of sixteen axial slices were acquired. Cerebral blood flow (CBF) and blood volume (CBV) parametric maps were co-registered to a rat brain atlas and regions of interest were drawn on the maps. Microvascular alteration was investigated with histopathology.

Results

CTP results revealed that ipsilateral striatum of Aβ+CI and CI groups showed significantly lower CBF and CBV than control at the acute phase. Striatal CBF and CBV increased significantly at week 1 in the CI and Aβ+CI groups, but not in the Aβ alone or control group. Histopathology showed that average density of dilated microvessels in the ipsilateral striatum in CI and Aβ+CI groups was significantly higher than control at week 1, indicating this could be associated with hyperperfusion and hypervolemia observed from CTP results.

Conclusion

These results demonstrate that CTP can quantitatively measure the hemodynamic disturbance on CBF and CBV functional maps in a rat model of CI interacting with Aβ.

Temporal changes in CT perfusion values before and after cranioplasty in patients without symptoms related to external decompression: a pilot study

INTRODUCTION

Little is known about hemodynamic disturbances affecting cerebral hemispheres in traumatic brain injury (TBI) after cranioplasty.

METHODS

We prospectively investigated six stable TBI patients who underwent cranioplasty more than 90 days after effective decompressive craniectomy. Computerized tomography perfusion (CTP) studies and evaluation of clinical outcome were performed for each patient before cranioplasty and at 7 days and 3 months after surgery. Cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were measured in multiple cortical circular regions positioned in cranioplasty-treated and contralateral hemispheres.

RESULTS

Neither complications associated with cranioplasty nor changes in outcome were observed. On the treated side, CBF and CBV values were higher before and 7 days after cranioplasty than at 3 months after surgery, whereas MTT values were lower at 7 days than at 3 months after surgical treatment.

CONCLUSIONS

Our results indicate that cortical perfusion progressively declines in the cranioplasty treated hemisphere but remains stable in the contralateral hemisphere after surgery and suggest that CTP can represent a promising tool for a longitudinal analysis of hemodynamic abnormalities occurring in TBI patients after cranioplasty. In addition, these data imply a possible role of cranioplasty in restoring flow to meet the prevailing metabolic demand.