Accuracy and Reliability of Multiphase CTA Perfusion for Identifying Ischemic Core

Colour-coded collateral and venous outflow patterns in estimating infarct progression and predicting functional independence for stroke patients in late time window

OBJECTIVES

To investigate whether cerebral collateral and venous outflow (VO) patterns on colour-coded multi-phase computed tomography angiography (mCTA) can estimate ischaemic core growth rate (IGR) and predict 90-day functional independence for patients with late-presenting acute ischaemic stroke (AIS).

METHODS

The retrospective analysis included 127 AIS patients with a late time window. All patients underwent baseline mCTA with colour-coded reconstruction and computed tomography perfusion. Both collateral score and VO score on colour-coded mCTA maps were analysed and recorded. The IGR was calculated as ischaemic core volume divided by the time from onset to imaging. A 90-day modified Rankin Scale score of 0-2 was defined as functional independence. Kendall's Tau-b analysis was used for nonparametric correlation analysis. Propensity scores, logistic regressions, and receiver operator characteristic (ROC) curves were applied to construct the prediction model.

RESULTS

Moderate correlations were found between collateral delay and IGR (Tau-b = -0.554) and between VO and IGR (Tau-b = -0.501). High collateral score (odds ratio = 3.01) and adequate VO (odds ratio = 4.89) remained independent predictors for 90-day functional independence after adjustment. The joint predictive model, which integrated the VO score and clinical features, demonstrated an area under the ROC curve (AUC) of 0.878. The AUCs of collateral score and VO score were 0.836 and 0.883 for outcome prediction after adjustment.

CONCLUSIONS

Cerebral collateral and VO patterns based on colour-coded mCTA can effectively predict infarct progression and 90-day clinical outcomes, even for AIS patients beyond the routine time window.

ADVANCES IN KNOWLEDGE

Colour-coded mCTA is a readily understandable post-processing technique for the rapid assessment of collateral circulation and VO status in stroke imaging. A moderate correlation was observed between the characteristics of collateral delay/VO on colour-coded mCTA and IGR in patients with AIS. Both high-quality collateral circulation and "red superficial middle cerebral vein sign" can predict 90-day functional independence even for patients beyond the routine time window.

Competitive leptomeningeal flow impact on thrombectomy reperfusion grade rating

BACKGROUND

Competitive leptomeningeal flow (CLF) can be observed immediately after mechanical thrombectomy (MT) reperfusion with retrograde contrast clearing of the distal leptomeningeal branches from non-contrast opacified flow through different vascular territories. We aim to evaluate the frequency of the CLF phenomenon, to determine if it has an association with the degree of leptomeningeal collateral status, and to understand the potentia impact it may have on the final expanded Treatment in Cerebral Ischemia (eTICI) score rating.

METHODS

Retrospective analysis of a prospective MT database spanning November 2020 to December 2021. Consecutive cases of intracranial internal carotid (i-ICA) or middle cerebral artery (MCA) M1 occlusions were included. CLF was defined by the observation of retrograde clearing of distal MCA branches that were previously opacified by antegrade reperfusion. The clearance of the distal branches is presumed to occur due to CLF via non-contrast opacified posterior cerebral artery or anterior cerebral artery flow. The washout was considered CLF if it cleared abruptly with or without forward reconstitution of antegrade opacification.

RESULTS

A total of 125 patients met the inclusion criteria. The median age was 64 years (IQR 52.5-75) and 64 (51%) were men. The baseline median National Institutes of Health Stroke Scale score was 17 (IQR 12-22) and the Alberta Stroke Program Early CT Score was 9 (IQR 8-10). Median last known well time to puncture was 7 hours (IQR 4-13.1) and 30.4% received tissue plasminogen activator. Final eTICI 2c-3 was achieved in 80%. CLF was present in 32 (25.6%) patients, who had comparable baseline characteristics to patients without CLF. Twelve (37.5%) patients had regional CLF and 20 (62.5%) had focal CLF. The CLF arm had better leptomeningeal single-phase CTA collaterals than the non-CLF arm (P=0.01). The inter-rater agreement for the eTICI score was moderate when CLF was present and strong in its absence (Krippendorf's alpha=0.65 and 0.81, respectively). There was minimal agreement (Kappa=0.3) for the presence versus absence of CLF between the two operators, possibly related to reader experience.

CONCLUSION

CLF was observed in 32% of patients, was associated with better collateral flow, and impacted the reported procedural eTICI rating.

Thrombectomy with and without computed tomography perfusion imaging for large-vessel occlusion stroke in the extended time window: a meta-analysis of randomized clinical trials

Objective

In recent years, several studies have used computed tomography perfusion (CTP) to assess whether mechanical thrombectomy can be performed in patients with large-vessel occlusion (LVO) stroke in an extended time window. However, it has the disadvantage of being time-consuming and expensive. This study aimed to compare the impact of the CTP group with the non-CTP group [non-contrast CT (NCCT) ± CT angiography (CTA)] on the prognosis of this patient population.

Methods

A search of PubMed, EMBASE, and the Cochrane Library databases was conducted to collect randomized controlled trials (RCTs) comparing the two strategies. Outcome indicators and factors influencing prognosis were summarized by standardized mean differences, ratios, and relative risks with 95% confidence intervals using a random-effects model.

Results

A total of two RCTs were included in the combined analysis. There were no significant differences in the main outcome indicators (modified Rankin Scale score at 90 days, successful postoperative reperfusion rate) or the incidence of adverse events (90-day mortality and symptomatic intracranial hemorrhage) between the NCCT ± CTA and CTP groups. The time from the last puncture appeared to be significantly shorter in the NCCT ± CTA group than in the CTP group (SMD: -0.14; 95% CI: -0.24, -0.04). Among them, age (OR: 0.96; 95% CI: 0.94, 0.98), ASPECTS (OR: 1.18; 95% CI: 1.12, 1.24), NIHSS score (OR: 0.90; 95% CI: 0.89, 0.91), and diabetes (OR: 0.69; 95% CI: 0.54, 0.88) were associated with a 90-day independent functional outcome.

Conclusion

These findings suggest that the choice of NCCT ± CTA (without CTP) for the assessment of mechanical thrombectomy within 6-24 h after LVO in the anterior circulation is not significantly different from CTP; instead, the choice of NCCT ± CTA significantly reduces the time from onset to arterial puncture.

Comparison of Computed Tomography Perfusion and Multiphase Computed Tomography Angiogram in Predicting Clinical Outcomes in Endovascular Thrombectomy

BACKGROUND

In patients with acute stroke who undergo endovascular thrombectomy, the relative prognostic power of computed tomography perfusion (CTP) parameters compared with multiphase CT angiogram (mCTA) is unknown. We aimed to compare the predictive accuracy of mCTA and CTP parameters on clinical outcomes.

METHODS

We included patients with acute ischemic stroke who had anterior circulation large vessel occlusion within 24 hours of onset in Melbourne Brain Centre at the Royal Melbourne Hospital. All patients underwent CTP for endovascular thrombectomy, and the mCTA collateral score was determined using CTP-reconstructed mCTA images. The primary outcome was 90-day functional outcomes defined by modified Rankin Scale. Multivariable logistic regression models analyzed associations between mCTA and CTP parameters and 90-day functional outcomes. The ability to discriminate 90 days-functional outcomes was compared between mCTA collateral score and CTP parameters using receiver operating curve analysis and C statistics.

RESULTS

One hundred and twenty patients were included. The median age was 69 years (interquartile range, 60-79), the median baseline National Institutes of Health Stroke Scale score was 14 (interquartile range, 9-19). The baseline ischemic core volume, defined by CTP-based relative cerebral blood flow <30%, was associated with excellent functional outcome (modified Rankin Scale score 0-1; odds ratio, 0.942 [-0.897 to -0.989]; P=0.015) and poor functional outcome (modified Rankin Scale score 5-6; odds ratio, 1.032 [1.007-1.056]; P=0.010) at 90 days in the analysis of multivariable regression. There was no significant association between the mCTA score and excellent functional outcome (P=0.58) or poor functional outcome (P=0.155). The relative cerebral blood flow <30%-based regression model best fit the data for the 90-day poor functional outcome (C statistic, 0.834).

CONCLUSIONS

The CTP-based ischemic core volume may provide better discrimination for 90-day functional outcomes for patients with acute stroke undergoing endovascular thrombectomy than the mCTA collateral score.

Comparison of time consumption and success rate between CT angiography- and CT perfusion- based imaging assessment strategy for the patients with acute ischemic stroke

BACKGROUND

Our study aimed to compare the time consumption and success rate between CTA- and CTP- based assessment strategy, and to clarify the risk factors associated with the CTP scan failure.

METHODS

Clinical and radiological data of 437 consecutive AIS patients who underwent multiphase CTA or CTP for pre-treatment evaluation were retrospectively enrolled (CTA group, n = 302; CTP group, n = 135). Time consumption and success rate of CTA- and CTP- based assessment strategy were compared using Mann-Whitney U test and Chi-Squared Test. Univariate analysis and receiver operating curve analysis were used to clarify the risk factors, and their performance in predicting the CTP scan failure.

RESULTS

Time consumption of CTP scan and reconstruction was significantly longer than that of CTA [775 s vs 263.5 s, P < 0.001]. CTP scan showed significantly higher failure rate than CTA (11% vs 1%, P < 0.001). Severe motion was the most common cause of CTP failure (n = 12, 80%). Baseline National Institute of Health Stroke Scale (NIHSS) score in CTP failure group was significantly higher than that in CTP success group [17 vs 13, P = 0.007]. Baseline NIHSS score of 11 was the optimal threshold value to predict CTP failure with an area under the curve of 0.715, a sensitivity of 86.7%, and a specificity of 45.0%.

CONCLUSIONS

CTP- based strategy showed longer time consumption and higher failure rate than CTA- based strategy. High baseline NIHSS score was significantly associated with CTP scan failure in AIS patients.

Acute stroke imaging selection for mechanical thrombectomy in the extended time window: is it time to go back to basics? A review of current evidence

Treatment with endovascular therapy in the extended time window for acute ischaemic stroke with large vessel occlusion involves stringent selection criteria based on the two landmark studies DAWN and DEFUSE3. Current protocols typically include the requirement of advanced perfusion imaging which may exclude a substantial proportion of patients from receiving a potentially effective therapy. Efforts to offer endovascular reperfusion therapies to all appropriate candidates may be facilitated by the use of simplified imaging selection paradigms with widely available basic imaging techniques, such as non-contrast CT and CT angiography. Currently available evidence from our literature review suggests that patients meeting simplified imaging selection criteria may benefit as much as those patients selected using advanced imaging techniques (CT perfusion or MRI) from endovascular therapy in the extended time window. A comprehensive understanding of the role of imaging in patient selection is critical to optimising access to endovascular therapy in the extended time window and improving outcomes in acute stroke. This article provides an overview on current developments and future directions in this emerging area.

Deep learning-based identification of acute ischemic core and deficit from non-contrast CT and CTA

The accurate identification of irreversible infarction and salvageable tissue is important in planning the treatments for acute ischemic stroke (AIS) patients. Computed tomographic perfusion (CTP) can be used to evaluate the ischemic core and deficit, covering most of the territories of anterior circulation, but many community hospitals and primary stroke centers do not have the capability to perform CTP scan in emergency situation. This study aimed to identify AIS lesions from widely available non-contrast computed tomography (NCCT) and CT angiography (CTA) using deep learning. A total of 345AIS patients from our emergency department were included. A multi-scale 3D convolutional neural network (CNN) was used as the predictive model with inputs of NCCT, CTA, and CTA+ (8 s delay after CTA) images. An external cohort with 108 patients was included to further validate the generalization performance of the proposed model. Strong correlations with CTP-RAPID segmentations (r = 0.84 for core, r = 0.83 for deficit) were observed when NCCT, CTA, and CTA+ images were all used in the model. The diagnostic decisions according to DEFUSE3 showed high accuracy when using NCCT, CTA, and CTA+ (0.90±0.04), followed by the combination of NCCT and CTA (0.87±0.04), CTA-alone (0.76±0.06), and NCCT-alone (0.53±0.09).

Detection of Perfusion Deficits in Multiphase Computed Tomography Angiography-A Stroke Imaging Technique Based on Iodine Mapping on Spectral Computed Tomography: Initial Findings

OBJECTIVE

The purpose of this study was to explore a novel method for brain tissue differentiation using quantitative analysis of multiphase computed tomography (CT) angiography (MP-CTA) on spectral CT, to assess whether it can distinguish underperfused from normal tissue, using CT perfusion (CTP) as reference.

METHODS

Noncontrast CT and MP-CTA images from 10 patients were analyzed in vascular regions through measurements of Hounsfield unit (HU) at 120 kV, HU at 40 keV, and iodine density. Regions were categorized as normal or ischemic according to CTP. Hounsfield unit and iodine density were compared regarding ability to separate normal and ischemic tissue, the difference in maximum time derivative of the right over left hemisphere ratio.

RESULTS

Iodine density had the highest maximum time derivatives and generated the largest mean separation between normal and ischemic tissue.

CONCLUSIONS

The method can be used to categorize tissue as normal or underperfused. Using iodine quantification seems to give a more distinct differentiation of perfusion defects compared with conventional HU.

How to Improve the Management of Acute Ischemic Stroke by Modern Technologies, Artificial Intelligence, and New Treatment Methods

Stroke remains one of the leading causes of death and disability in Europe. The European Stroke Action Plan (ESAP) defines four main targets for the years 2018 to 2030. The COVID-19 pandemic forced the use of innovative technologies and created pressure to improve internet networks. Moreover, 5G internet network will be helpful for the transfer and collecting of extremely big databases. Nowadays, the speed of internet connection is a limiting factor for robotic systems, which can be controlled and commanded potentially from various places in the world. Innovative technologies can be implemented for acute stroke patient management soon. Artificial intelligence (AI) and robotics are used increasingly often without the exception of medicine. Their implementation can be achieved in every level of stroke care. In this article, all steps of stroke health care processes are discussed in terms of how to improve them (including prehospital diagnosis, consultation, transfer of the patient, diagnosis, techniques of the treatment as well as rehabilitation and usage of AI). New ethical problems have also been discovered. Everything must be aligned to the concept of “time is brain”.

Multiphase CT Angiography: A Useful Technique in Acute Stroke Imaging-Collaterals and Beyond

Multiphase CTA offers several important advantages over the traditional single-phase CTA technique in acute ischemic stroke, including improved detection of large-vessel occlusion, improved characterization of collateral status, improved tolerance of patient motion and poor hemodynamics, and higher interrater reliability. These benefits are gleaned at little additional cost in terms of time, risk to the patient, and capital expense. Existing data suggest that there are important benefits to using multiphase CTA in lieu of single-phase CTA in the initial vessel assessment of patients with acute stroke.

Dynamic CTA-Derived Perfusion Maps Predict Final Infarct Volume: The Simple Perfusion Reconstruction Algorithm

BACKGROUND AND PURPOSE

Infarct core volume measurement using CTP (CT perfusion) is a mainstay paradigm for stroke treatment decision-making. Yet, there are several downfalls with cine CTP technology that can be overcome by adopting the simple perfusion reconstruction algorithm (SPIRAL) derived from multiphase CTA. We compare SPIRAL with CTP parameters for the prediction of 24-hour infarction.

MATERIALS AND METHODS

Seventy-two patients had admission NCCT, multiphase CTA, CTP, and 24-hour DWI. All patients had successful/quality reperfusion. Patient-level and cohort-level receiver operator characteristic curves were generated to determine accuracy. A 10-fold cross-validation was performed on the cohort-level data. Infarct core volume was compared for SPIRAL, CTP-time-to-maximum, and final DWI by Bland-Altman analysis.

RESULTS

When we compared the accuracy in patients with early and late reperfusion for cortical GM and WM, there was no significant difference at the patient level (0.83 versus 0.84, respectively), cohort level (0.82 versus 0.81, respectively), or the cross-validation (0.77 versus 0.74, respectively). In the patient-level receiver operating characteristic analysis, the SPIRAL map had a slightly higher, though nonsignificant (P < .05), average receiver operating characteristic area under the curve (cortical GM/WM, r = 0.82; basal ganglia  = 0.79, respectively) than both the CTP-time-to-maximum (cortical GM/WM = 0.82; basal ganglia = 0.78, respectively) and CTP-CBF (cortical GM/WM = 0.74; basal ganglia = 0.78, respectively) parameter maps. The same relationship was observed at the cohort level. The Bland-Altman plot limits of agreement for SPIRAL and time-to-maximum infarct volume were similar compared with 24-hour DWI.

CONCLUSIONS

We have shown that perfusion maps generated from a temporally sampled helical CTA are an accurate surrogate for infarct core.

Multimodal CT in Acute Stroke

PURPOSE OF REVIEW

Multimodal CT imaging (non-contrast CT, NCCT; CT angiography, CTA; and CT Perfusion, CTP) is central to acute ischemic stroke diagnosis and treatment. We reviewed the purpose and interpretation of each component of multimodal CT, as well as the evidence for use in routine care.

RECENT FINDINGS

Acute stroke thrombolysis can be administered immediately following NCCT in acute ischemic stroke patients assessed within 4.5 h of symptom onset. Definitive identification of a large vessel occlusion (LVO) requires vascular imaging, which is easily achieved with CTA. This is critical, as the standard of care for LVO within 6 h of onset is now endovascular thrombectomy (EVT). CTA source images can also be used to estimate the efficacy of collateral flow in LVO patients. The final component (CTP) permits a more accurate assessment of the extent of the ischemic penumbra. Complete multimodal CT, including objective penumbral measurement with CTP, has been used to extend the EVT window to 24 h. There is also randomized controlled trial evidence for extension of the IV thrombolysis window to 9 h with multimodal CT. Although there have been attempts to assess for responders to reperfusion strategies beyond 6 h ("late window") using collateral grades, the only evidence for treatment of this group of patients is based on selection using multimodal CT including CTP. The development of fully automated software providing quantitative ischemic penumbral and core volumes has facilitated the adoption of CTP and complete multimodal CT into routine clinical use. Multimodal CT is a powerful imaging algorithm that is central to current ischemic stroke patient care.