Performance and Predictive Value of a User-Independent Platform for CT Perfusion Analysis: Threshold-Derived Automated Systems Outperform Examiner-Driven Approaches in Outcome Prediction of Acute Ischemic Stroke

Elevated cortical blood flow insufficiency volume as a predictor of adverse outcomes in aneurysmal subarachnoid hemorrhage: a large prospective quantitative computed tomography perfusion study

PURPOSE

Early hypoperfusion changes exist in patients with aneurysmal subarachnoid hemorrhage (aSAH). We aimed to investigate a readily obtainable quantitative computed tomography perfusion (CTP) parameter that could assist in quickly identifying patients at risk of delayed cerebral ischemia (DCI) and poor 90-day functional outcomes on admission.

METHODS

We prospectively collected data between 2021.04 and 2022.12. Preoperative CTP data were post-processed using RAPID software. The cortical blood flow insufficiency (CBFI) was defined as Time-to-maximum > 4.0 s. Patients were categorized into four groups according to CBFI volume distribution. To minimize differences among the groups, we employed stabilized inverse probability of treatment weighting (sIPTW). The primary outcome was DCI and poor 90-day functional outcomes (modified Rankin Scale, 3-6) was the secondary outcome. Multivariable Cox or Logistic analysis were performed to estimate the association between CBFI volume and the study outcomes, both before and after sIPTW.

RESULTS

At baseline, the mean (SD) age of the 493 participants was 55.0 (11.8) years, and 299 (60.6%) were female. One hundred and seven participants with DCI and eighty-six participants with poor 90-day functional outcomes were identified. After sIPTW, CBFI volume demonstrated a significant association with DCI (Cox regression: Group 4 versus Group 1, HR 3.69, 95% CI 1.84-7.01) and poor 90-day functional outcomes (Logistic regression: Group 4 versus Group 1, OR 4.61, 95% CI 2.01-12.50).

CONCLUSION

In this study, an elevated preoperative CBFI volume was associated with adverse outcomes in aSAH patients. More well-designed studies are needed to confirm this association.

Software with artificial intelligence-derived algorithms for analysing CT brain scans in people with a suspected acute stroke: a systematic review and cost-effectiveness analysis

Background

Artificial intelligence-derived software technologies have been developed that are intended to facilitate the review of computed tomography brain scans in patients with suspected stroke.

Objectives

To evaluate the clinical and cost-effectiveness of using artificial intelligence-derived software to support review of computed tomography brain scans in acute stroke in the National Health Service setting.

Methods

Twenty-five databases were searched to July 2021. The review process included measures to minimise error and bias. Results were summarised by research question, artificial intelligence-derived software technology and study type. The health economic analysis focused on the addition of artificial intelligence-derived software-assisted review of computed tomography angiography brain scans for guiding mechanical thrombectomy treatment decisions for people with an ischaemic stroke. The de novo model (developed in R Shiny, R Foundation for Statistical Computing, Vienna, Austria) consisted of a decision tree (short-term) and a state transition model (long-term) to calculate the mean expected costs and quality-adjusted life-years for people with ischaemic stroke and suspected large-vessel occlusion comparing artificial intelligence-derived software-assisted review to usual care.

Results

A total of 22 studies (30 publications) were included in the review; 18/22 studies concerned artificial intelligence-derived software for the interpretation of computed tomography angiography to detect large-vessel occlusion. No study evaluated an artificial intelligence-derived software technology used as specified in the inclusion criteria for this assessment. For artificial intelligence-derived software technology alone, sensitivity and specificity estimates for proximal anterior circulation large-vessel occlusion were 95.4% (95% confidence interval 92.7% to 97.1%) and 79.4% (95% confidence interval 75.8% to 82.6%) for Rapid (iSchemaView, Menlo Park, CA, USA) computed tomography angiography, 91.2% (95% confidence interval 77.0% to 97.0%) and 85.0 (95% confidence interval 64.0% to 94.8%) for Viz LVO (Viz.ai, Inc., San Fransisco, VA, USA) large-vessel occlusion, 83.8% (95% confidence interval 77.3% to 88.7%) and 95.7% (95% confidence interval 91.0% to 98.0%) for Brainomix (Brainomix Ltd, Oxford, UK) e-computed tomography angiography and 98.1% (95% confidence interval 94.5% to 99.3%) and 98.2% (95% confidence interval 95.5% to 99.3%) for Avicenna CINA (Avicenna AI, La Ciotat, France) large-vessel occlusion, based on one study each. These studies were not considered appropriate to inform cost-effectiveness modelling but formed the basis by which the accuracy of artificial intelligence plus human reader could be elicited by expert opinion. Probabilistic analyses based on the expert elicitation to inform the sensitivity of the diagnostic pathway indicated that the addition of artificial intelligence to detect large-vessel occlusion is potentially more effective (quality-adjusted life-year gain of 0.003), more costly (increased costs of £8.61) and cost-effective for willingness-to-pay thresholds of £3380 per quality-adjusted life-year and higher.

Limitations and conclusions

The available evidence is not suitable to determine the clinical effectiveness of using artificial intelligence-derived software to support the review of computed tomography brain scans in acute stroke. The economic analyses did not provide evidence to prefer the artificial intelligence-derived software strategy over current clinical practice. However, results indicated that if the addition of artificial intelligence-derived software-assisted review for guiding mechanical thrombectomy treatment decisions increased the sensitivity of the diagnostic pathway (i.e. reduced the proportion of undetected large-vessel occlusions), this may be considered cost-effective.

Future work

Large, preferably multicentre, studies are needed (for all artificial intelligence-derived software technologies) that evaluate these technologies as they would be implemented in clinical practice.

Study registration

This study is registered as PROSPERO CRD42021269609.

Funding

This award was funded by the National Institute for Health and Care Research (NIHR) Evidence Synthesis programme (NIHR award ref: NIHR133836) and is published in full in Health Technology Assessment; Vol. 28, No. 11. See the NIHR Funding and Awards website for further award information.

CT perfusion stroke lesion threshold calibration between deconvolution algorithms

CTP is an important diagnostic tool in managing patients with acute ischemic stroke, but challenges persist in the agreement of stroke lesion volumes and ischemic core-penumbra mismatch profiles determined with different CTP post-processing software. We investigated a systematic method of calibrating CTP stroke lesion thresholds between deconvolution algorithms using a digital perfusion phantom to improve inter-software agreement of mismatch profiles. Deconvolution-estimated cerebral blood flow (CBF) and Tmax was compared to the phantom ground truth via linear regression for one model-independent and two model-based deconvolution algorithms. Using the clinical standard of model-independent CBF < 30% and Tmax > 6 s as reference thresholds for ischemic core and penumbra, respectively, we determined that model-based CBF < 15% and Tmax > 6 s were the corresponding calibrated thresholds after accounting for quantitative differences revealed at linear regression. Calibrated thresholds were then validated in 63 patients with large vessel stroke by evaluating agreement (concordance and Cohen's kappa, κ) between the two model-based and model-independent deconvolution methods in determining mismatch profiles used for clinical decision-making. Both model-based deconvolution methods achieved 95% concordance with model-independent assessment and Cohen's kappa was excellent (κ = 0.87; 95% confidence interval [CI] 0.72-1.00 and κ = 0.86; 95% CI 0.70-1.00). Our systematic method of calibrating CTP stroke lesion thresholds may help harmonize mismatch profiles determined by different software.

Automated advanced imaging in acute ischemic stroke. Certainties and uncertainties

The purpose of this is study was to review pearls and pitfalls of advanced imaging, such as computed tomography perfusion and diffusion-weighed imaging and perfusion-weighted imaging in the selection of acute ischemic stroke (AIS) patients suitable for endovascular treatment (EVT) in the late time window (6-24 h from symptom onset). Advanced imaging can quantify infarct core and ischemic penumbra using specific threshold values and provides optimal selection parameters, collectively called target mismatch. More precisely, target mismatch criteria consist of core volume and/or penumbra volume and mismatch ratio (the ratio between total hypoperfusion and core volumes) with precise cut-off values. The parameters of target mismatch are automatically calculated with dedicated software packages that allow a quick and standardized interpretation of advanced imaging. However, this approach has several limitations leading to a misclassification of core and penumbra volumes. In fact, automatic software platforms are affected by technical artifacts and are not interchangeable due to a remarkable vendor-dependent variability, resulting in different estimate of target mismatch parameters. In addition, advanced imaging is not completely accurate in detecting infarct core, that can be under- or overestimated. Finally, the selection of candidates for EVT remains currently suboptimal due to the high rates of futile reperfusion and overselection caused by the use of very stringent inclusion criteria. For these reasons, some investigators recently proposed to replace advanced with conventional imaging in the selection for EVT, after the demonstration that non-contrast CT ASPECTS and computed tomography angiography collateral evaluation are not inferior to advanced images in predicting outcome in AIS patients treated with EVT. However, other authors confirmed that CTP and PWI/DWI postprocessed images are superior to conventional imaging in establishing the eligibility of patients for EVT. Therefore, the routine application of automatic assessment of advanced imaging remains a matter of debate. Recent findings suggest that the combination of conventional and advanced imaging might improving our selection criteria.

An experimental system for detection and localization of hemorrhage using ultra-wideband microwaves with deep learning

Stroke is a leading cause of mortality and disability. Emergent diagnosis and intervention are critical, and predicated upon initial brain imaging; however, existing clinical imaging modalities are generally costly, immobile, and demand highly specialized operation and interpretation. Low-energy microwaves have been explored as low-cost, small form factor, fast, and safe probes of tissue dielectric properties, with both imaging and diagnostic potential. Nevertheless, challenges inherent to microwave reconstruction have impeded progress, hence microwave imaging (MWI) remains an elusive scientific aim. Herein, we introduce a dedicated experimental framework comprising a robotic navigation system to translate blood-mimicking phantoms within an anatomically realistic human head model. An 8-element ultra-wideband (UWB) array of modified antipodal Vivaldi antennas was developed and driven by a two-port vector network analyzer spanning 0.6-9.0 GHz at an operating power of 1 mw. Complex scattering parameters were measured, and dielectric signatures of hemorrhage were learned using a dedicated deep neural network for prediction of hemorrhage classes and localization. An overall sensitivity and specificity for detection >0.99 was observed, with Rayliegh mean localization error of 1.65 mm. The study establishes the feasibility of a robust experimental model and deep learning solution for UWB microwave stroke detection.

Continued Infarction Growth and Penumbral Consumption After Reperfusion in Vaccine-Naive Patients With COVID-19: A Case-Control Study

BACKGROUND. Neurologic sequelae of SARS-CoV-2 include potentially malignant cerebrovascular events arising from complex hemodynamic, hematologic, and inflammatory processes occurring in concert. OBJECTIVE. This study concerns the hypothesis that despite angiographic reperfusion COVID-19 promotes continued consumption of at-risk tissue volumes after acute ischemic stroke (AIS), yielding critical insights into prognostication and monitoring paradigms in vaccine-naive patients experiencing AIS. METHODS. This retrospective study compared 100 consecutive COVID-19 patients with AIS presenting between March 2020 and April 2021 with a contemporaneous cohort of 282 AIS patients without COVID-19. Reperfusion classes were dichotomized into positive (extended thrombolysis in cerebral ischemia [eTICI] score = 2c-3) and negative (eTICI score < 2c) groups. All patients underwent endovascular therapy after initial CT perfusion imaging (CTP) to document infarction core and total hypoperfusion volumes. RESULTS. Ten COVID-positive (mean age ± SD, 67 ± 12 years; seven men, three women) and 144 COVID-negative patients (mean age, 71 ± 16 years; 76 men, 68 women) undergoing endovascular reperfusion, with antecedent CTP and follow-up imaging, comprised the final dataset. Initial infarction core and total hypoperfusion volumes (mean ± SD) were 1.5 ± 18 mL and 85 ± 100 mL in COVID-negative patients and 30.5 ± 34 mL and 117 ± 80.5 mL in COVID-positive patients, respectively. Final infarction volumes were significantly larger in patients with COVID-19, with median volumes of 77.8 mL versus 18.2 mL among control patients (p = .01), as were normalized measures of infarction growth relative to baseline infarction volume (p = .05). In adjusted logistic parametric regression models, COVID positivity emerged as a significant predictor for continued infarct growth (OR, 5.10 [95% CI, 1.00-25.95]; p = .05). CONCLUSION. These findings support the potentially aggressive clinical course of cerebrovascular events in patients with COVID-19, suggesting greater infarction growth and ongoing consumption of at-risk tissues, even after angiographic reperfusion. CLINICAL IMPACT. SARS-CoV-2 infection may promote continued infarction progression despite angiographic reperfusion in vaccine-naive patients with large-vessel occlusion AIS. The findings carry potential implications for prognostication, treatment selection, and surveillance for infarction growth among revascularized patients in future waves of infection by novel viral strains.

Comparison of 3 CT Perfusion Software Packages in Estimation of Ischemic Lesions in Acute Ischemic Stroke Patients

OBJECTIVE

The aim of this study was to compare 3 computed tomography perfusion (CTP) software packages in the estimation of infarct core volumes, hypoperfusion volumes, and mismatch volumes.

METHODS

Forty-three patients with large vessel occlusion in the anterior circulation who underwent CTP imaging were postprocessed by 3 software packages: RAPID, advantage workstation (AW), and NovoStroke Kit (NSK). Infarct core volumes and hypoperfusion volumes were generated by RAPID with default settings. The AW and NSK threshold settings were the following: infarct core (cerebral blood flow [CBF] <8 mL/min/100 g, CBF <10 mL/min/100 g, CBF <12 mL/min/100 g, and cerebral blood volume [CBV] <1 mL/100 g) and hypoperfusion (Tmax >6 seconds). Mismatch volumes were then obtained for all the combinations of the settings. Bland-Altman, intraclass correlation coefficient (ICC), and Spearman ρ or Pearson correlation coefficient were applied for statistical analysis.

RESULTS

In the estimation of infarct core volumes, good agreement was observed between AW and RAPID when CBV <1 mL/100 g (ICC, 0.767; P < 0.001). For hypoperfusion volumes, good agreement (ICC, 0.811; P < 0.001) and strong correlation (r = 0.856; P < 0.001) were observed between NSK and RAPID. For mismatch volumes, the setting of CBF <10 mL/min/100 g combined with hypoperfusion with NSK resulted in moderate agreement (ICC, 0.699; P < 0.001) with RAPID, which was the best among all other settings.

CONCLUSIONS

The estimation results varied among different software packages. Advantage workstation had the best agreement with RAPID in the estimation of infarct core volumes when CBV <1 mL/100 g. NovoStroke Kit had better agreement and correlation with RAPID in the estimation of hypoperfusion volumes. NovoStroke Kit also had moderate agreement with RAPID in estimating mismatch volumes.

Cerebral perfusion imaging predicts final infarct volume after basilar artery thrombectomy

OBJECTIVES

Cerebral perfusion imaging may be used to identify the ischemic core in acute ischemic stroke (AIS) patients with a large vessel occlusion of the anterior circulation; however, perfusion parameters that predict the ischemic core in AIS patients with a basilar artery occlusion (BAO) are poorly described. We determined which cerebral perfusion parameters best predict the ischemic core after successful endovascular thrombectomy (EVT) in BAO patients.

MATERIALS AND METHODS

We performed multicenter retrospective study of BAO patients with perfusion imaging before EVT and a DWI after successful EVT. The ischemic core was defined as regions on CTP, which were co-registered to the final DWI infarct. Various time-to-maximum (Tmax) and cerebral blood flow (CBF) thresholds were compared to final infarct volume to determine the best predictor of the final infarct.

RESULTS

28 patients were included in the analysis for this study. Tmax >8s (r²: 0.56; median absolute error, 16.0 mL) and Tmax >10s (r²: 0.73; median absolute error, 11.3 mL) showed the strongest agreement between the pre-EVT CTP study and the final DWI. CBF <38% (r²: 0.76; median absolute error, 8.2 mL) and CBF <34% (r²: 0.76; median absolute error, 9.1 mL) also correlated well with final infarct volume on DWI.

CONCLUSIONS

Pre-EVT CT perfusion imaging is useful to predict the final ischemic infarct volume in BAO patients. Tmax >8s and Tmax >10s were the strongest predictors of the post-EVT final infarct volume.

Regional computed tomography perfusion deficits in patients with hypoglycemia: two case reports

Background

Hypoglycemia in patients with diabetes mellitus, particularly type 1 can mimic acute ischemic stroke by causing focal neurological deficits. In acute ischemic stroke, the interpretation of emergency imaging including computed tomography with angiography and perfusion is crucial to guide revascularizing therapy including intravenous thrombolysis. However, different metabolic abnormalities and stroke mimics can cause focal hypoperfusion.

Methods

We describe two type 1 diabetes patients presenting with acute focal neurological deficits and hypoglycemia, who underwent multimodal computed tomography and follow-up imaging.

Case presentation

Patient 1, a 20-year-old man presented with aphasia and interstitial glucose level of 54 mg/dl. Patient 2, a 77-year-old man presented with aphasia, mild right-sided brachiofacial paresis and interstitial glucose level of 83 mg/dl. On brain imaging, no acute infarct signs were noted. Yet, both had focal left hemispheric cerebral hypoperfusion without large-vessel occlusion or stenosis. Due to persistent symptoms after normalization of blood glucose and despite a perfusion imaging pattern that was interpretated as non-typical for ischemia, both patients underwent thrombolysis without any complications.

Conclusion

Computed tomography perfusion might help to discriminate hypoglycemia with focal neurological signs from acute stroke, but further evidence is needed.

Diagnostic Performance of Computed Tomography Angiography and Computed Tomography Perfusion Tissue Time-to-Maximum in Vasospasm Following Aneurysmal Subarachnoid Hemorrhage

Background

Vasospasm is a treatable cause of deterioration following aneurysmal subarachnoid hemorrhage. Cerebral computed tomography perfusion mean transit times have been proposed as a predictor of vasospasm but suffer from well‐known technical limitations. We evaluated fully automated, thresholded time‐to‐maxima of the tissue residue function (T_max) for determination of vasospasm following aneurysmal subarachnoid hemorrhage.

Methods and Results

Retrospective analysis of 540 arterial segments from 36 encounters in 31 consecutive patients with aneurysmal subarachnoid hemorrhage undergoing computed tomography angiography (CTA), computed tomography perfusion, and digital subtraction angiography (DSA) within 24 hours. T_max at 4, 6, 8, and 10 s was generated using RAPID (iSchemaView Inc., Menlo Park, CA). Dual‐reader CTA and computed tomography perfusion interpretations were compared for patients with and without vasospasm on DSA (DSA+ and DSA−). Logistic regression models were developed using CTA and T_max as input predictors and DSA vasospasm as outcome in adjusted and unadjusted models. Imaging studies from all 31 subjects (mean age 47.3±11.1, 77% female, 65% with single aneurysm with mean size of 6.0±2.9 mm) were included. Vasospasm was identified in 42 segments on DSA and 59 segments on CTA, with significant associations across individual vessel segments (P<0.001). In adjusted analyses, DSA vasospasm was associated with CTA (odds ratio [OR], 2.43; 95% CI, 0.94–6.32; P=0.068) as well as territory‐specific T_max>6 seconds delays (OR, 3.57; 95% CI, 1.36–9.35; P=0.009). Sensitivity/specificity for DSA vasospasm was 31%/91% for CTA, 26%/89% for T_max>6 seconds, and 12%/99% for CTA+T_max>6 seconds.

Conclusions

CTA and T_max offer high specificity for presence of vasospasm; their utility, even in combination, as screening tests is, however, limited by poor sensitivity.

Automated Brain Perfusion Imaging in Acute Ischemic Stroke: Interpretation Pearls and Pitfalls

Recent advancements in computed tomography technology, including improved brain coverage and automated processing of the perfusion data, have reinforced the use of perfusion computed tomography imaging in the routine evaluation of patients with acute ischemic stroke. The DAWN (Diffusion Weighted Imaging or Computerized Tomography Perfusion Assessment With Clinical Mismatch in the Triage of Wake Up and Late Presenting Strokes Undergoing Neurointervention) and DEFUSE 3 (Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke 3) trials have established the benefit of endovascular thrombectomy in patients with acute ischemic stroke with anterior circulation large vessel occlusion up to 24 hours of last seen normal, using perfusion imaging-based patient selection. The compelling data has prompted stroke centers to increasingly introduce automated perfusion computed tomography imaging in the routine evaluation of patients with acute ischemic stroke. We present a comprehensive overview of the acquisition and interpretation of automated perfusion imaging in patients with acute ischemic stroke with a special emphasis on the interpretation pearls, pitfalls, and stroke mimicking conditions.

Automated Detection of Ischemic Stroke and Subsequent Patient Triage in Routinely Acquired Head CT

Purpose

Advanced machine-learning (ML) techniques can potentially detect the entire spectrum of pathology through deviations from a learned norm.

We investigated the utility of a weakly supervised ML tool to detect characteristic findings related to ischemic stroke in head CT and provide subsequent patient triage.

Methods

Patients having undergone non-enhanced head CT at a tertiary care hospital in April 2020 with either no anomalies, subacute or chronic ischemia, lacunar infarcts of the deep white matter or hyperdense vessel signs were retrospectively analyzed. Anomaly detection was performed using a weakly supervised ML classifier. Findings were displayed on a voxel-level (heatmap) and pooled to an anomaly score. Thresholds for this score classified patients into i) normal, ii) inconclusive, iii) pathological. Expert-validated radiological reports were considered as ground truth. Test assessment was performed with ROC analysis; inconclusive results were pooled to pathological predictions for accuracy measurements.

Results

During the investigation period 208 patients were referred for head CT of which 111 could be included. Definite ratings into normal/pathological were feasible in 77 (69.4%) patients. Based on anomaly scores, the AUC to differentiate normal from pathological scans was 0.98 (95% CI 0.97–1.00). The sensitivity, specificity, positive and negative predictive values were 100%, 40.6%, 80.6% and 100%, respectively.

Conclusion

Our study demonstrates the potential of a weakly supervised anomaly-detection tool to detect stroke findings in head CT. Definite classification into normal/pathological was made with high accuracy in > 2/3 of patients. Anomaly heatmaps further provide guidance towards pathologies, also in cases with inconclusive ratings.

Normative distribution of posterior circulation tissue time-to-maximum: Effects of anatomic variation, tracer kinetics, and implications for patient selection in posterior circulation ischemic stroke

The generalization of perfusion-based, anterior circulation large vessel occlusion selection criteria to posterior circulation stroke is not straightforward due to physiologic delay, which we posit produces physiologic prolongation of the posterior circulation perfusion time-to-maximum (Tmax). To assess normative Tmax distributions, patients undergoing CTA/CTP for suspected ischemic stroke between 1/2018-3/2019 were retrospectively identified. Subjects with any cerebrovascular stenoses, or with follow-up MRI or final clinical diagnosis of stroke were excluded. Posterior circulation anatomic variations were identified. CTP were processed in RAPID and segmented in a custom pipeline permitting manually-enforced arterial input function (AIF) and perfusion estimations constrained to pre-specified vascular territories. Seventy-one subjects (mean 64 ± 19 years) met inclusion. Median Tmax was significantly greater in the cerebellar hemispheres (right: 3.0 s, left: 2.9 s) and PCA territories (right: 2.9 s; left: 3.3 s) than in the anterior circulation (right: 2.4 s; left: 2.3 s, p < 0.001). Fetal PCA disposition eliminated ipsilateral PCA Tmax delays (p = 0.012). Median territorial Tmax was significantly lower with basilar versus any anterior circulation AIF for all vascular territories (p < 0.001). Significant baseline delays in posterior circulation Tmax are observed even without steno-occlusive disease and vary with anatomic variation and AIF selection. The potential for overestimation of at-risk volumes in the posterior circulation merits caution in future trials.

Emerging role of artificial intelligence in stroke imaging

Introduction: The recognition and therapy of patients with stroke is becoming progressively intricate as additional treatment choices become accessible and new associations between disease characteristics and treatment response are incessantly uncovered. Therefore, clinicians must regularly learn new skill, stay up to date with the literature and integrate advances into daily practice. The application of artificial intelligence (AI) to assist clinical decision making could diminish inter-rater variation in routine clinical practice and accelerate the mining of vital data that could expand recognition of patients with stroke, forecast of treatment responses and patient outcomes.Areas covered: In this review, the authors provide an up-to-date review of AI in stroke, analyzing the latest papers on this subject. These have been divided in two main groups: stroke diagnosis and outcome prediction.Expert opinion: The highest value of AI is its capability to merge, select and condense a large amount of clinical and imaging features of a single patient and to associate these with fitted models that have gone through robust assessment and optimization with large cohorts of data to support clinical decision making.

Effect of different thresholds for CT perfusion volumetric analysis on estimated ischemic core and penumbral volumes

Purpose

This single-center study compared three threshold settings for automated analysis of the ischemic core (IC) and penumbral volumes using computed tomographic perfusion, and their accuracy for predicting final infarct volume (FIV) in patients with anterior circulation acute ischemic stroke (AIS).

Methods

Fifty-two consecutive AIS patients undergoing mechanical thrombectomy (November 2015–March 2018) were included. Perfusion images were retrospectively analyzed using a single CT Neuro perfusion application (syngo.via 4.1, Siemens Healthcare GmbH). Three threshold values (S1–S3) were derived from another commercial package (RAPID; iSchema View) (S1), up-to-date syngo.via default values (S2), and adapted values for syngo.via from a reference study (S3). The results were compared with FIV determined by non-contrast CT.

Results

The median IC volume (mL) was 24.6 (interquartile range: 13.7–58.1) with S1 and 30.1 (20.1–53.1) with S2/S3. After removing the contralateral hemisphere from the analysis, the median IC volume decreased by 1.33(0–3.14) with S1 versus 9.13 (6.24–14.82) with S2/S3. The median penumbral volume (mL) was 74.52 (49.64–131.91), 77.86 (46.56–99.23), and 173.23 (125.86–200.64) for S1, S2, and S3, respectively. Limiting analysis to the affected hemisphere, the penumbral volume decreased by 1.6 (0.13–9.02), 19.29 (12.59–26.52), and 58.33 mL (45.53–74.84) for S1, S2, and S3, respectively. The correlation between IC and FIV was highest in patients with successful recanalization (n = 34, r = 0.784 for S1; r = 0.797 for S2/S3).

Conclusion

Optimizing thresholds significantly improves the accuracy of estimated IC and penumbral volumes. Current recommended values produce diversified results. International guidelines based on larger multicenter studies should be established to support the standardization of volumetric analysis in clinical decision-making.

Safety of Ticagrelor in Moderate and Severe Acute Ischemic Stroke: A Single-Center Retrospective Review

OBJECTIVES

Ticagrelor may be superior to aspirin after minor ischemic stroke or TIA, particularly in patients with symptomatic atherosclerotic disease. However, there may be an increased risk of intracerebral hemorrhage in patients with moderate to severe ischemic stroke, and ticagrelor has not been studied in this patient population. Therefore, we sought to evaluate the safety of ticagrelor after moderate or severe ischemic stroke.

MATERIALS AND METHODS

Retrospective chart review of all patients admitted with acute ischemic stroke and NIHSS 6 or greater who were discharged on ticagrelor between January 2016 and December 2019. Patients who underwent angioplasty, stenting or carotid revascularization during the hospitalization were excluded.

RESULTS

Of 183 patients discharged on ticagrelor, 61 patients were included. Median age was 61 (IQR 52-68); 33 (54%) patients were men. Median NIHSS was 11 (IQR 8-15). Fourteen (23%) patients received IV alteplase and 35 (57%) patients received mechanical thrombectomy. Stroke mechanism was large artery atherosclerosis in 53 (87%) of patients, of which 40 (71%) were deemed intracranial atherosclerosis. Final infarct volume was greater than 10 mL in 32 (52%) patients. Follow-up information was available for 53 (87%) patients; median length of follow-up was 3 (IQR 2-6) months. Six (10%) patients experienced recurrent ischemic stroke. No patients experienced symptomatic intracerebral hemorrhage after initiation of ticagrelor. One (2%) patient experienced major bleeding.

CONCLUSIONS

This study provides preliminary evidence supporting the potential safety of ticagrelor following moderate or severe acute ischemic stroke. These findings support the need for future prospective studies.

Automated CT Perfusion Imaging to Aid in the Selection of Patients With Acute Ischemic Stroke for Mechanical Thrombectomy: A Health Technology Assessment

BACKGROUND

Stroke is a sudden interruption in the blood supply to a part of the brain, causing loss of neurological function. It is the third leading cause of death in Canada and affects mainly older people. In the acute setting, neuroimaging is integral to stroke evaluation and decision-making. The neuroimaging results guide patient selection for mechanical thrombectomy. Using automated image processing techniques facilitates efficient review of this information and communication between centres. We conducted a health technology assessment of automated CT perfusion imaging as a tool for selecting stroke patients with anterior circulation occlusion for mechanical thrombectomy. This assessment included an evaluation of clinical effectiveness, cost-effectiveness, and the budget impact of publicly funding automated CT perfusion imaging.

METHODS

We performed a systematic literature search of the clinical evidence. We assessed the risk of bias of each study using QUADAS-2 or the Cochrane risk-of-bias tool, and the quality of the body of evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. We performed a systematic economic literature search and approximated cost-effectiveness based on previous analyses. We also analyzed the budget impact of publicly funding automated CT perfusion imaging to evaluate people with acute ischemic stroke in Ontario.

RESULTS

Automated CT perfusion imaging had a sensitivity of 84% for identifying the infarct core (dead tissue that does not recover despite restoring blood flow with mechanical thrombectomy), compared with diffusion-weighted MRI imaging at 24 hours. One study reported that 7% of patients were misclassified with respect to eligibility for mechanical thrombectomy (either erroneously classified as eligible or erroneously classified non-eligible). Two randomized controlled trials (DEFUSE 3 and DAWN) demonstrated the efficacy of mechanical thrombectomy up to 24 hours after stroke onset, with patient selection guided by automated CT perfusion imaging. These data showed that a significantly higher proportion of patients in the mechanical thrombectomy group achieved functional independence compared with the standard care group (DEFUSE 3: risk ratio: 2.67 [95% confidence interval 1.60-4.48]; DAWN: adjusted rate difference: 33% [95% credible interval 21%-44%]; GRADE: Moderate).A previous health technology assessment in stroke patients presenting at 0 to 6 hours after stroke symptom onset and the results from recent randomized controlled trials for patients presenting at 6 to 24 hours informed the evaluation of cost-effectiveness. Mechanical thrombectomy informed by automated CT perfusion imaging to assess eligibility is likely to be cost-effective for patients presenting at 6 to 24 hours after stroke symptom onset. The annual budget impact of publicly funding automated CT perfusion imaging in Ontario over the next 5 years would be $1.3 million in year 1 and $0.9 million each year thereafter. Some of the costs of automated CT perfusion imaging could be offset by avoiding unnecessary patient transfers between hospitals.

CONCLUSIONS

Automated CT perfusion imaging has an acceptable sensitivity and specificity for detecting brain areas that have been affected by stroke. In patients selected for mechanical thrombectomy using automated CT perfusion imaging, there was significant improvement in functional independence. Mechanical thrombectomy informed by automated CT perfusion imaging is likely to be cost-effective. We estimate that publicly funding automated CT perfusion imaging in Ontario would result in additional costs of $1.3 million in year 1 and $0.9 million per year thereafter.

Comparing the outcomes of two independent computed tomography perfusion softwares and their impact on therapeutic decisions in acute ischemic stroke

BACKGROUND

To compare the computed tomography perfusion (CTP) outcomes derived from two commercial CTP processing software and evaluate their concordance in terms of eligibility for mechanical thrombectomy (MT) in acute ischemic stroke (AIS), based on DEFUSE III criteria.

METHODS

A total of 118 patients (62 patients in the MT group and 56 patients in the non-MT (NMT) group) were included. Volumetric perfusion outputs were compared between Syngo.via (package A) and RAPID (package B). Influence on proceeding or not-proceeding with MT was based on DEFUSE III imaging eligibility criteria.

RESULTS

Median core infarct/hypoperfusion volumes were 12.3/126 mL in the MT group and 7.7/29.3 ml in the NMT group with package A and 10.5/138 mL and 1.9/24.5 mL with package B, respectively. In the MT group (n=62), concordant perfusion results in terms of patient triage were noted in all but two cases. Of these, one patient would not have qualified (low ASPECTS), while the other qualified based on package A results. For the NMT group (n=56), there was discordance in terms of MT eligibility in seven cases. However, none of these patients qualified for MT based on DEFUSE III criteria.

CONCLUSIONS

Both perfusion softwares showed high concordance in correctly triaging patients in the MT versus NMT groups (110/118, 93.2%), which further improved when all DEFUSE III imaging criteria were considered (117/118, 99.1%). The core/hypoperfusion volumes in the NMT group and core infarct volumes in the MT groups were comparable. The hypoperfusion volumes in the MT group varied slightly but did not affect triage between groups.

Assessment of Ischemic Volumes by Using Relative Filling Time Delay on CTP Source Image in Patients with Acute Stroke with Anterior Circulation Large Vessel Occlusions

BACKGROUND AND PURPOSE

Thrombectomy up to 24 hours after stroke onset in patients with specific ischemic brain volumes remains a challenge, because many stroke centers do not apply specialized software to calculate ischemic volumes at advanced imaging. We aimed to establish the association between relative filling time delay on CTP source imaging and ischemic volume parameters and the infarct penumbra to core volume mismatch in patients with acute ischemic stroke.

MATERIALS AND METHODS

Consecutive patients with acute ischemic stroke and with M1 segment MCA with or without terminal ICA occlusions on baseline CTA and CTP within 24 hours of stroke symptom onset were included. Ischemic volumes were analyzed with software based on CTP maps. Relative filling time delay was classified into 4 grades-grade 0: relative filling time delay = 0 seconds; grade 1: relative filling time delay >0 to ≤4 seconds; grade 2: relative filling time delay >4 to ≤8 seconds; and grade 3: relative filling time delay > 8 seconds. Differences in ischemic volume parameters among relative filling time delay grades were tested.

RESULTS

We recruited 138 patients (median age, 69 years; 62.3% male). Different median volumes of the infarct core (grade 0, 7.3 mL; grade 1, 23.3 mL; grade 2, 45.7 mL; grade 3, 135 mL [P < .001]) and the penumbra (grade 0, 47.6 mL; grade 1, 90 mL; grade 2, 110 mL; grade 3, 92 mL [P = .043]) were observed among relative filling time delay grades. Target mismatch (defined by the criteria of the DEFUSE 3 trial) was identified in 71.7% of the patients (99/138). A relative filling time delay grade ≤ 1 independently predicted target mismatch, with a sensitivity of 0.79 (95% CI, 0.7-0.87) and a specificity of 0.66 (95% CI, 0.49-0.8).

CONCLUSIONS

Relative filling time delay grade based on CTP source imaging is a simple and effective parameter for evaluating ischemic volumes and target mismatch in patients with acute ischemic stroke. Further studies that compare relative filling time delay grade with clinical functional outcomes are necessary.

Qualitative versus automatic evaluation of CT perfusion parameters in acute posterior circulation ischaemic stroke

Purpose

To compare the diagnostic accuracy (ACC) in the detection of acute posterior circulation strokes between qualitative evaluation of software-generated colour maps and automatic assessment of CT perfusion (CTP) parameters.

Methods

Were retrospectively collected 50 patients suspected of acute posterior circulation stroke who underwent to CTP (GE “Lightspeed”, 64 slices) within 24 h after symptom onset between January 2016 and December 2018. The Posterior circulation-Acute Stroke Prognosis Early CT Score (pc-ASPECTS) was used for quantifying the extent of ischaemic areas on non-contrast (NC)CT and colour-coded maps generated by CTP4 (GE) and RAPID (iSchemia View) software. Final pc-ASPECTS was calculated on follow-up NCCT and/or MRI (Philips Intera 3.0 T or Philips Achieva Ingenia 1.5 T). RAPID software also elaborated automatic quantitative mismatch maps.

Results

By qualitative evaluation of colour-coded maps, MTT-CTP4D and Tmax-RAPID showed the highest sensitivity (SE) (88.6% and 90.9%, respectively) and ACC (84% and 88%, respectively) compared with the other perfusion parameters (CBV, CBF). Baseline NCCT and CBF provided by RAPID quantitative perfusion mismatch maps had the lowest SE (29.6% and 6.8%, respectively) and ACC (38% and 18%, respectively). CBF and Tmax assessment provided by quantitative RAPID perfusion mismatch maps showed significant lower SE and ACC than qualitative evaluation. No significant differences were found between the pc-ASPECTSs assessed on colour-coded MTT and Tmax maps neither between the scores assessed on colour-coded CBV-CTP4D and CBF-RAPID maps.

Conclusion

Qualitative analysis of colour-coded maps resulted more sensitive and accurate in the detection of ischaemic changes than automatic quantitative analysis.

Mild fever as a catalyst for consumption of the ischaemic penumbra despite endovascular reperfusion

Cerebrovascular ischaemia is potentiated by hyperthermia, and even mild temperature elevation has proved detrimental to ischaemic brain. Infarction progression following endovascular reperfusion relates to multiple patient-specific and procedural variables; however, the potential influence of mild systemic temperature fluctuations is not fully understood. This study aims to assess the relationship between systemic temperatures in the early aftermath of acute ischaemic stroke and the loss of at-risk penumbral tissues, hypothesizing consumption of the ischaemic penumbra as a function of systemic temperatures, irrespective of reperfusion status. A cross-sectional, retrospective evaluation of a single-institution, prospectively collected endovascular therapy registry was conducted. Patients with anterior circulation, large vessel occlusion acute ischaemic stroke who underwent initial CT perfusion, and in whom at least four-hourly systemic temperatures were recorded beginning from presentation and until the time of final imaging outcome were included. Initial CT perfusion core and penumbra volumes and final MRI infarction volumes were computed. Systemic temperature indices including temperature maxima were recorded, and pre-defined temperature thresholds varying between 37°C and 38°C were examined in unadjusted and adjusted regression models which included glucose, collateral status, reperfusion status, CT perfusion-to-reperfusion delay, general anaesthesia and antipyretic exposure. The primary outcome was the relative consumption of the penumbra, reflecting normalized growth of the at-risk tissue volume ≥10%. The final study population comprised 126 acute ischaemic stroke subjects (mean 63 ± 14.5 years, 63% women). The primary outcome of penumbra consumption ≥10% occurred in 51 (40.1%) subjects. No significant differences in baseline characteristics were present between groups, with the exception of presentation glucose (118 ± 26.6 without versus 143.1 ± 61.6 with penumbra consumption, P = 0.009). Significant differences in the likelihood of penumbra consumption relating to systemic temperature maxima were observed [37°C (interquartile range 36.5 − 37.5°C) without versus 37.5°C (interquartile range 36.8 − 38.2°C) with penumbra consumption, P = 0.001]. An increased likelihood of penumbra consumption was observed for temperature maxima in unadjusted (odds ratio 3.57, 95% confidence interval 1.65 − 7.75; P = 0.001) and adjusted (odds ratio 3.06, 95% confidence interval 1.33 − 7.06; P = 0.009) regression models. Significant differences in median penumbra consumption were present at a pre-defined temperature maxima threshold of 37.5°C [4.8 ml (interquartile range 0 − 11.5 ml) versus 21.1 ml (0 − 44.7 ml) for subjects not reaching or reaching the threshold, respectively, P = 0.007]. Mild fever may promote loss of the ischaemic penumbra irrespective of reperfusion, potentially influencing successful salvage of at-risk tissue volumes following acute ischaemic stroke.

Penumbra volume predicts unfavorable outcome in patients with acute minor stroke or transient ischemic attack

BACKGROUND

A subgroup of patients with acute minor stroke (AMS) or transient ischemic attack (TIA) become disabled due to disease progression (DP) or recurrent stroke within 3 months. The aim of this article is to identify the risk factors for DP in AMS/TIA patients. In the literature, no studies focused on computed tomography perfusion (CTP) in AMS/TIA patients at the acute stage.

METHODS

This retrospective study included patients with AMS or TIA (onset of symptoms ≤4.5 hours, baseline National Institutes of Health Stroke Scale [NIHSS] score of 0-4). DP was defined as a deterioration of NIHSS score of ≥2 points during hospitalization or modified Ranking Scale ≥2 at 3-month follow-up. Clinical data and imaging results were retrieved and measured for statistical analysis.

RESULTS

From 2011 to 2017, total 135 patients were eligible for further analysis: 28 patients (20.7%, DP group) and 107 patients (79.3%, non-DP group). The DP group had significantly higher larger penumbra volumes (p = 0.028). In univariate model of the logistic regression, patients with the following risk factors tended to have unfavorable outcome: female gender, higher HbA1c, chronic kidney disease stage ≥3b, intracranial atherosclerosis, and penumbra volume were associated unfavorable outcome, but larger deadcore volume was not. In further multivariate analysis, only penumbra volume >5 cm (p = 0.049, odds ratio [OR] = 3.21, 95% CI: 1.00-10.27) had the statistical significance. The cut-point value of the penumbra volume for unfavorable outcome in AMS/TIA patients was 4.73 cm.

CONCLUSION

One fifth of the AMS/TIA patients had unfavorable outcome at 90 days. In CTP performed within 4.5 hours after the onset of AMS/TIA, the penumbra volume (>5 cm) was a significant risk factor for DP, and the cut-point value was 4.73 cm. Further studies could be designed to involve this subgroup of patients for more aggressive treatment.

Flat-panel detector CT assessment in stroke to reduce times to intra-arterial treatment: A study of multiphase computed tomography angiography in the angiography suite to bypass conventional imaging

BACKGROUND

Bypassing the emergency department and the computed tomography suite by directly transporting to the neuroangiography suite for imaging assessment and treatment may shorten reperfusion times while maintaining proper patient selection.

OBJECTIVE

To determine whether flat-panel detector multiphase computed tomography angiography protocol is associated with reduced treatment times and a similar safety profile as the standard imaging protocol.

METHODS

Single-center prospective study of consecutive patients with anterior circulation large vessel occlusion strokes transferred to our facility for consideration of endovascular therapy from May 2016 to December 2017. Those with basilar strokes and/or presenting to the emergency department were excluded. Patients were categorized into two groups: (1) flat-panel detector CT assessment in stroke to reduce times to intra-arterial treatment group, with patients transferred directly to the suite for multiphase computed tomography angiography; and (2) patients undergoing standard protocol including computed tomography ± computed tomography angiography/CT perfusion. The groups were matched for age, baseline National Institute of Health Stroke Scale, and pretreatment glucose. Baseline characteristics, time metrics, and outcomes were compared.

RESULTS

Out of 419 patients who underwent endovascular therapy over the study period, 210 patients fit inclusion criteria, with 54 (25.7%) in the flat-panel detector CT assessment in stroke to reduce times to intra-arterial treatment group. After matching, 49 flat-panel detector CT assessment in stroke to reduce times to intra-arterial treatment/control pairs were generated and analyzed. Baseline characteristics were well balanced. Flat-panel detector CT assessment in stroke to reduce times to intra-arterial treatment patients had significantly shorter median door-to-puncture (33 [26.5-47] vs. 55 [44.5-66] min, p < 0.001), door-to-reperfusion (85 [57.5-115.5] vs. 110 [80-153], p = 0.005) and picture-to-puncture (18 [13.5-22.5] vs. 42 [32-47.5] min, p < 0.001) times. There were no differences in rates of successful reperfusion (modified thrombolysis in cerebral infarction 2b-3, 95.9% vs. 100%, p = 0.5), parenchymal hematomas type-2 (4.1% vs. 2%, p = 1.00), good outcome (90-day modified Rankin Scale 0-2, 44.9% vs. 40.8%, p = 0.68), and 90-day mortality (14.3% vs. 22.4%, p = 0.30).

CONCLUSION

Directly transferring patients to angiography and using multiphase computed tomography angiography to determine the eligibility for endovascular therapy is safe and may result in a significant reduction in treatment times. Future larger studies are warranted.

Microstructural Integrity of Salvaged Penumbra after Mechanical Thrombectomy

BACKGROUND AND PURPOSE

There are sparse data on the microstructural integrity of salvaged penumbral tissue after mechanical thrombectomy of large-vessel occlusions. The aim of the study was to analyze possible microstructural alteration in the penumbra and their association with clinical symptoms as well as angiographic reperfusion success in patients undergoing mechanical thrombectomy.

MATERIALS AND METHODS

All patients who underwent mechanical thrombectomy for large-vessel occlusions in the anterior circulation and who received an admission CT perfusion together with postinterventional DTIs were included (n = 65). Angiographic reperfusion success by means of modified Thrombolysis in Cerebral Infarction (mTICI) scale and clinical outcome were recorded. Microstructural integrity was assessed by DTI evaluating the mean diffusivity index within the salvaged gray matter of the former penumbra.

RESULTS

The mean diffusivity index was higher in completely recanalized patients (mTICI 3: -0.001 ± 0.034 versus mTICI <3: -0.030 ± 0.055, P = .03). There was a positive correlation between the mean diffusivity index and NIHSS score improvement (r = 0.49, P = .003) and the mean diffusivity index was associated with midterm functional outcome (r = -0.37, P = .04) after adjustment for confounders. In mediation analysis, the mean diffusivity index and infarction growth mediated the association between reperfusion success and clinical outcomes.

CONCLUSIONS

The macroscopic salvaged penumbra included areas of microstructural integrity changes, most likely related to the initial hypoperfusion. These abnormalities were found early after mechanical thrombectomy, were dependent on angiographic results, and correlated with the clinical outcome. When confirmed, these findings prompt the evaluation of therapies for protection of the penumbral tissue integrity.

"Code-Stroke" CT Perfusion; Challenges and Pitfalls

RATIONALE AND OBJECTIVES

Regarding the most recent ischemic stroke treatment guideline, perfusion imaging has been recommended up to 24 hours after initial symptoms of brain infarction. Patients with a significant amount of salvageable peri-infarct ischemia and no contraindications benefit from delayed thrombolysis and intra-arterial thrombectomy. This approach causes increasingly more CT perfusion to be done in the subacute phase of ischemic stroke. CT perfusion findings in this "subacute phase" are slightly different from "hyper-acute" ischemic stroke. The interpreting radiologist must be confident in reporting the CT perfusion study in an urgent setting since these studies are under the umbrella of "code-stroke" and should be read in minutes. In addition, results of the CT perfusion have a critical effect on the patient's outcome and misinterpretation can be fatal in that underestimation of the salvageable ischemia excludes the patient from potential effective treatment. Underestimation of infarct volume may cause unnecessary thrombolysis/thrombectomy and potentially fatal intracranial hemorrhage.

MATERIALS AND METHODS

In this review, we are trying to explain the basic concept of "code-stroke" CT perfusion, typical findings, and pitfalls in a practical way.

Computer-aided imaging analysis in acute ischemic stroke - background and clinical applications

Tools for medical image analysis have been developed to reduce the time needed to detect abnormalities and to provide more accurate results. Particularly, tools based on artificial intelligence and machine learning techniques have led to significant improvements in medical imaging interpretation in the last decade. Automatic evaluation of acute ischemic stroke in medical imaging is one of the fields that witnessed a major development. Commercially available products so far aim to identify (and quantify) the ischemic core, the ischemic penumbra, the site of arterial occlusion and the collateral flow but they are not (yet) intended as standalone diagnostic tools. Their use can be complementary; they are intended to support physicians' interpretation of medical images and hence standardise selection of patients for acute treatment. This review provides an introduction into the field of computer-aided diagnosis and focuses on the automatic analysis of non-contrast-enhanced computed tomography, computed tomography angiography and perfusion imaging. Future studies are necessary that allow the evaluation and comparison of different imaging strategies and post-processing algorithms during the diagnosis process in patients with suspected acute ischemic stroke; which may further facilitate the standardisation of treatment and stroke management.

Computed tomography perfusion in stroke mimics

OBJECTIVE

To describe the prevalence and patterns of abnormal findings on automated computed tomography perfusion in patients with stroke mimic.

METHODS

We reviewed a retrospective multi-site cohort of consecutive patients undergoing computed tomography perfusion for suspected acute ischemic stroke within 24 h from last normal (June 2017 to December 2017). The primary outcome was the diagnosis of stroke mimic. Hypoperfusion abnormalities on iSchemaView RAPID automated computed tomography perfusion were compared between patients with stroke/transient ischemic attack and stroke mimic using mixed-effects multivariable logistic regression, focusing on absence of perfusion abnormalities and discordance with clinical symptoms and computed tomography angiography findings.

RESULTS

Of 410 consecutive patients who underwent computed tomography perfusion, 348 met inclusion criteria (178 (51%) stroke, 19 (6%) transient ischemic attack, and 151 (43%) mimic). Time-to-maximum of the tissue residue function (T_max>6s) abnormalities were seen in 42 (28%) patients with stroke mimic and 122 (62%) patients with stroke/transient ischemic attack (p < 0.001). Patients with stroke mimic were more likely to have a normal T_max pattern (volume = 0mL; adjusted OR: 2.2, 95% CI: 1.1-4.3, p = 0.02). When the T_max pattern was abnormal, a higher proportion of patients with stroke mimic had T_max patterns fully discordant with clinical symptoms than patients with stroke/transient ischemic attack (28/39 (71%) vs. 10/115 (9%), p < 0.001). Fully discordant T_max abnormalities were strongly associated with stroke mimic (adjusted OR: 48.6, 95% CI: 7.0-336, p < 0.001), with a negative predictive value for identifying mimic of 91% (95% CI: 85-94%).

CONCLUSION

While one-quarter of patients with stroke mimic show T_max abnormalities on automated RAPID computed tomography perfusion imaging, the majority of patterns were discordant with symptoms and vessel status. Normal or fully discordant T_max abnormalities are were more common with stroke mimic and may inform stroke treatment decision making.

Endovascular Therapy and Ethnic Disparities in Stroke Outcomes

BACKGROUND AND PURPOSE

Ethnic disparities in stroke are well described, with a higher incidence of disability and increased mortality in Blacks versus Whites. We sought to compare the clinical outcomes between those ethnic groups after stroke endovascular therapy (ET).

METHODS

We performed a retrospective review of the prospectively acquired Grady Endovascular Stroke Outcomes Registry between September 1, 2010 and September 30, 2015. Patients were dichotomized into two groups - Caucasians and African-Americans - and matched for age, pretreatment glucose level, and baseline National Institutes of Health Stroke Scale (NIHSS) score. Baseline characteristics as well as procedural and outcome parameters were compared.

RESULTS

Out of the 830 patients treated with ET, 308 pairs of patients (n = 616) underwent primary analysis. African-Americans were younger (p < 0.01), had a higher prevalence of hypertension (p < 0.01) and diabetes (p = 0.04), and had higher Alberta Stroke Program Early CT Score values (p = 0.03) and shorter times to treatment (p = 0.01). Blacks more frequently had Medicaid coverage and less private insurance (29.6 vs. 11.4% and 41.5 vs. 60.3%, respectively, p < 0.01). The remaining baseline characteristics, including baseline NIHSS score and CT perfusion-derived ischemic core volumes, were well balanced. There were no differences in the overall distribution of 90-day modified Rankin scale scores (p = 0.28), rates of successful reperfusion (84.7 vs. 85.7%, p = 0.91), good outcomes (49.1 vs. 44%, p = 0.24), or parenchymal hematomas (6.5 vs. 6.8%, p = 1.00). Blacks had lower 90-day mortality rates (18 vs. 24.6%, p = 0.04) in univariate analysis, which persisted as a nonsignificant trend after adjustment for potential confounders (OR 0.52, 95% CI 0.26-1.03, p = 0.06).

CONCLUSIONS

Despite unique baseline characteristics, African-Americans treated with ET for large vessel occlusion strokes have similar outcomes as Caucasians. Greater availability of ET may diminish the ethnic/racial disparities in stroke outcomes.

Automated CT Perfusion Prediction of Large Vessel Acute Stroke from Intracranial Atherosclerotic Disease

Background and Purpose

We have observed that large vessel occlusion acute strokes (LVOS) due to intracranial atherosclerotic disease (ICAD) present with more benign CT perfusion (CTP) profiles, which we presume to potentially represent enhanced collateralization compared to embolic LVOS. We aim to determine if CTP profiles can predict ICAD in LVOS.

Methods

Retrospective review of a prospectively collected interventional stroke database from September 2010 to March 2015. Patients with intracranial ICA/MCA-M1/M2 occlusions and CTP were dichotomized into ICAD versus non-ICAD etiologies. Ischemic core (relative cerebral blood flow < 30%) and hypoperfusion volumes were estimated by automated CTP.

Results

A total of 250 patients met the inclusion criteria, comprised of 21 (8%) ICAD and 229 non-ICAD etiologies. Baseline characteristics were similar between groups, except for higher HbA1c levels (p < 0.01), LDL cholesterol (p < 0.01), systolic blood pressure (p < 0.01), and lower rate of atrial fibrillation (p < 0.01) in ICAD patients. There were no significant differences in volumes of baseline ischemic core (p = 0.54) among groups. ICAD patients had smaller Tmax > 4 s, Tmax > 6 s, and Tmax > 10 s absolute lesions, and a higher ratio of Tmax > 4 s/Tmax > 6 s volumes (median 2 [1.6-2.3] vs. 1.6 [1.4-2.0]; p = 0.02). A Tmax > 4 s/Tmax > 6 s ratio ≥2 showed specificity = 73%/sensitivity = 52% for ICAD and was observed in 47.6% of ICAD versus 26.1% of non-ICAD patients (p = 0.07). Clinical outcomes were comparable amongst groups. Multivariate logistic regression revealed that Tmax > 4 s/Tmax > 6 s ratio ≥2 (OR 3.75, 95% CI 1.05-13.14, p = 0.04), higher LDL cholesterol (OR 1.1, 95% CI 1.01-1.03, p = 0.01), and higher systolic pressure (OR 1.03, 95% CI 1.01-1.04, p = 0.01) were independently associated with ICAD.

Conclusion

An automated CTP Tmax > 4 s/Tmax > 6 s ratio ≥2 profile was found independently associated with underlying ICAD LVOS.

Clinical and Imaging Outcomes of Endovascular Therapy in Patients with Acute Large Vessel Occlusion Stroke and Mild Clinical Symptoms

Background

The minimal stroke severity justifying endovascular intervention remains elusive. However, a significant proportion of patients presenting with large vessel occlusion stroke (LVOS) and mild symptoms go untreated and face poor outcomes. We aimed to evaluate the clinical outcomes of patients presenting with LVOS and low symptom scores (National Institutes of Health Stroke Scale [NIHSS] score ≤8) undergoing endovascular therapy (ET).

Methods

We performed a retrospective analysis of a prospectively collected ET database between September 2010 and March 2016. Endovascularly treated patients with LVOS and a baseline NIHSS score ≤8 were included. Baseline patient characteristics, procedural details, and outcome parameters were collected. Efficacy outcomes were the rate of good outcome (90-day modified Rankin Scale score 0-2) and of successful reperfusion (modified Treatment in Cerebral Infarction [mTICI] score 2b-3). Safety was assessed by the rate of parenchymal hematoma (parenchymal hematoma type 1 [PH-1] and parenchymal hematoma type 2 [PH-2]) and 90-day mortality. Logistic regression was used to identify predictors of good clinical outcomes.

Results

A total of 935 patients were considered; 72 patients with an NIHSS score ≤8 were included. Median [IQR] age was 61.5 years [56.2-73.0]; 39 patients (54%) were men. Mean (SD) baseline NIHSS score, computed tomography perfusion core volume, and ASPECTS were 6.3 (1.5), 7.5 mL (16.1), and 8.5 (1.3), respectively. Twenty-eight patients (39%) received intravenous tissue plasminogen activator. Occlusions locations were as follows: 29 (40%) proximal MCA-M1, 20 (28%) MCA-M2, 6 (8%) ICA terminus, and 9 (13%) vertebrobasilar. Tandem occlusion was documented in 7 patients (10%). Sixty-seven patients (93%) achieved successful reperfusion (mTICI score 2b-3); 52 (72%) had good 90-day outcomes. Mean final infarct volume was 32.2 ± 59.9 mL. Parenchymal hematoma occurred in 4 patients (6%). Ninety-day mortality was 10% (n = 7). Logistic regression showed that only successful reperfusion (OR 27.7, 95% CI 1.1-655.5, p = 0.04) was an independent predictor of good outcomes.

Conclusion

Our findings demonstrate that ET is safe and feasible for LVOS patients presenting with mild clinical syndromes. Future controlled studies are warranted.

Correlation of Tmax volumes with clinical outcome in anterior circulation stroke

BACKGROUND AND PURPOSE

The recent thrombectomy trials have shown that perfusion imaging is helpful in proper patient selection in thromboembolic stroke. In this study, we analyzed the correlation of pretreatment T_max volumes in MR and CT perfusion with clinical outcome after thrombectomy.

METHODS

Forty-one consecutive patients with middle cerebral artery occlusion (MCA) or carotid T occlusion treated with thrombectomy were included. T_max volumes at delays of >4, 6, 8, and 10 s as well as infarct core and mismatch ratio were automatically estimated in preinterventional MRI or CT perfusion using RAPID software. These perfusion parameters were correlated with clinical outcome. Outcome was assessed using modified Rankin scale at 90 days.

RESULTS

In patients with successful recanalization of MCA occlusion, T_max > 8 and 10 s showed the best linear correlation with clinical outcome (r = 0.75; p = .0139 and r = 0.73; p = .0139), better than infarct core (r = 0.43; p = .2592). In terminal internal carotid artery occlusions, none of the perfusion parameters showed a significant correlation with clinical outcome.

CONCLUSIONS

T_max at delays of >8 and 10 s is a good predictor for clinical outcome in MCA occlusions. In carotid T occlusion, however, T_max volumes do not correlate with outcome.

Computed Tomographic Perfusion Selection and Clinical Outcomes After Endovascular Therapy in Large Vessel Occlusion Stroke

Background and Purpose—

Different imaging paradigms have been used to select patients for endovascular therapy in stroke. We sought to determine whether computed tomographic perfusion (CTP) selection improves endovascular therapy outcomes compared with noncontrast computed tomography alone.

Methods—

Review of a prospectively collected registry of anterior circulation stroke patients undergoing stent-retriever thrombectomy at a tertiary care center between September 2010 and March 2016. Patients undergoing CTP were compared with those with noncontrast computed tomography alone. The primary outcome was the shift in the 90-day modified Rankin scale (mRS).

Results—

A total of 602 patients were included. CTP-selected patients (n=365, 61%) were younger ( P =0.02) and had fewer comorbidities. CTP selection (n=365, 61%) was associated with a favorable 90-day mRS shift (adjusted odds ratio [aOR]=1.49; 95% confidence interval [CI], 1.06–2.09; P =0.02), higher rates of good outcomes (90-day mRS score 0–2: 52.9% versus 40.4%; P =0.005), modified Thrombolysis in Cerebral Infarction-3 reperfusion (54.8% versus 40.1%; P <0.001), smaller final infarct volumes (24.7 mL [9.8–63.1 mL] versus 34.6 mL [13.1–88 mL]; P =0.017), and lower mortality (16.6% versus 26.8%; P =0.005). When matched on age, National Institutes of Health Stroke Scale (NIHSS) score, and glucose (n=424), CTP remained associated with a favorable 90-day mRS shift ( P =0.016), lower mortality ( P =0.02), and higher rates of reperfusion ( P <0.001). CTP better predicted functional outcomes in patients presenting after 6 hours (as assessed by comparison of logistic regression models: Akaike information criterion: 199.35 versus 287.49 and Bayesian information criterion: 196.71 versus 283.27) and those with an Alberta Stroke Program Early Computed Tomography Score ≤7 (Akaike information criterion: 216.69 versus 334.96 and Bayesian information criterion: 213.6 versus 329.94).

Conclusions—

CTP selection is associated with a favorable mRS shift in patients undergoing stent-retriever thrombectomy. Future prospective studies are warranted.

4D-CTA improves diagnostic certainty and accuracy in the detection of proximal intracranial anterior circulation occlusion in acute ischemic stroke

INTRODUCTION

In acute ischemic stroke, imaging of the cranio-cervical vessels is essential for intra-arterial treatment selection. Fast, reliable and easy accessible imaging is necessary 24 hours a day, 7 days a week. Radiologists in training and non-expert readers often perform initial reviewing. In this pilot study, the potential benefit of adding 4Dimensional-CT Angiography (4D-CTA) to the patient selection protocol for intra-arterial therapy is investigated.

MATERIALS AND METHODS

Twenty-five datasets of prospectively recruited patients, eligible for intra-arterial treatment, were enrolled. Four radiologists-in-training consecutively reviewed CTA, CT-Perfusion and 4D-CTA (post-processed from CTP datasets) and scored: occlusion-presence and diagnostic certainty (scale 1-10). Time-to-diagnosis was registered.

RESULTS

Arterial occlusion was present in 8 patients. Accuracy improved from 88-92% after CTA and CTP assessment to 96-100% after 4D-CTA assessment (P-values >0,05). Mean diagnostic certainty improved from 7,2-8,6 to 8,8-9,3 (P-values all < 0,05). Mean time to diagnosis increased from 3, 5, 5 and 4 minutes after CTA to 9, 14, 12, and 10 minutes after 4D-CTA.

CONCLUSION

4D-CTA as an additive to regular CTA and CT-Perfusion in patients with acute ischemic stroke eligible for intra-arterial treatment shows a tendency to increase diagnostic accuracy and improves diagnostic certainty, when reviewed by radiologist in training, while only mildly prolonging time to diagnosis.

Body Temperature Modulates Infarction Growth following Endovascular Reperfusion

BACKGROUND AND PURPOSE

The neuronal substrate is highly sensitive to temperature elevation; however, its impact on the fate of the ischemic penumbra has not been established. We analyzed interactions between temperature and penumbral expansion among successfully reperfused patients with acute ischemic stroke, hypothesizing infarction growth and worse outcomes among patients with fever who achieve full reperfusion.

MATERIALS AND METHODS

Data from 129 successfully reperfused (modified TICI 2b/3) patients (mean age, 65 ± 15 years) presenting within 12 hours of onset were examined from a prospectively collected acute ischemic stroke registry. CT perfusion was analyzed to produce infarct core, hypoperfusion, and penumbral mismatch volumes. Final DWI infarction volumes were measured, and relative infarction growth was computed. Systemic temperatures were recorded throughout hospitalization. Correlational and logistic regression analyses assessed the associations between fever (>37.5°C) and both relative infarction growth and favorable clinical outcome (90-day mRS of ≤2), corrected for NIHSS score, reperfusion times, and age. An optimized model for outcome prediction was computed by using the Akaike Information Criterion.

RESULTS

The median presentation NIHSS score was 18 (interquartile range, 14-22). Median (interquartile range) CTP-derived volumes were: core = 9.6 mL (1.5-25.3 mL); hypoperfusion = 133 mL (84.2-204 mL); and final infarct volume = 9.6 mL (8.3-45.2 mL). Highly significant correlations were observed between temperature of >37.5°C and relative infarction growth (Kendall τ correlation coefficient = 0.24, P = .002). Odds ratios for favorable clinical outcome suggested a trend toward significance for fever in predicting a 90-day mRS of ≤2 (OR = 0.31, P = .05). The optimized predictive model for favorable outcomes included age, NIHSS score, procedure time to reperfusion, and fever. Likelihood ratios confirmed the superiority of fever inclusion (P < .05). Baseline temperature, range, and maximum temperature did not meet statistical significance.

CONCLUSIONS

These findings suggest that imaging and clinical outcomes may be affected by systemic temperature elevations, promoting infarction growth despite reperfusion.

Automated CT Perfusion for Ischemic Core Volume Prediction in Tandem Anterior Circulation Occlusions

BACKGROUND/AIM

CT perfusion (CTP) predicts ischemic core volumes in acute ischemic stroke (AIS); however, assumptions made within the pharmacokinetic model may engender errors by the presence of tracer delay or dispersion. We aimed to evaluate the impact of hemodynamic disturbance due to extracranial anterior circulation occlusions upon the accuracy of ischemic core volume estimation with an automated perfusion analysis tool (RAPID) among AIS patients with large-vessel occlusions.

METHODS

A prospectively collected, interventional database was retrospectively reviewed for all cases of endovascular treatment of AIS between September 2010 and March 2015 for patients with anterior circulation occlusions with baseline CTP and full reperfusion (mTICI3).

RESULTS

Out of 685 treated patients, 114 fit the inclusion criteria. Comparison between tandem (n = 21) and nontandem groups (n = 93) revealed similar baseline ischemic core (20 ± 19 vs. 19 ± 25 cm(3); p = 0.8), Tmax >6 s (175 ± 109 vs. 162 ± 118 cm(3); p = 0.6), Tmax >10 s (90 ± 84 vs. 90 ± 91 cm(3); p = 0.9), and final infarct volumes (45 ± 47 vs. 37 ± 45 cm(3); p = 0.5). Baseline core volumes were found to correlate with final infarct volumes for the tandem (r = 0.49; p = 0.02) and nontandem (r = 0.44; p < 0.01) groups. The mean absolute difference between estimated core and final infarct volume was similar between patients with and those without (24 ± 41 vs. 17 ± 41 cm(3); p = 0.5) tandem lesions.

CONCLUSIONS

The prediction of baseline ischemic core volumes through an optimized CTP analysis employing rigorous normalization, thresholding, and voxel-wise analysis is not significantly influenced by the presence of underlying extracranial carotid steno-occlusive disease in large-vessel AIS.

Automated CT Perfusion Ischemic Core Volume and Noncontrast CT ASPECTS (Alberta Stroke Program Early CT Score)

Background and Purpose—

The semiquantitative noncontrast CT Alberta Stroke Program Early CT Score (ASPECTS) and RAPID automated computed tomography (CT) perfusion (CTP) ischemic core volumetric measurements have been used to quantify infarct extent. We aim to determine the correlation between ASPECTS and CTP ischemic core, evaluate the variability of core volumes within ASPECTS strata, and assess the strength of their association with clinical outcomes.

Methods—

Review of a prospective, single-center database of consecutive thrombectomies of middle cerebral or intracranial internal carotid artery occlusions with pretreatment CTP between September 2010 and September 2015. CTP was processed with RAPID software to identify ischemic core (relative cerebral blood flow<30% of normal tissue).

Results—

Three hundred and thirty-two patients fulfilled inclusion criteria. Median age was 66 years (55–75), median ASPECTS was 8 (7–9), whereas median CTP ischemic core was 11 cc (2–27). Median time from last normal to groin puncture was 5.8 hours (3.9–8.8), and 90-day modified Rankin scale score 0 to 2 was observed in 54%. The correlation between CTP ischemic core and ASPECTS was fair ( R =−0.36; P <0.01). Twenty-six patients (8%) had ASPECTS <6 and CTP core ≤50 cc (37% had modified Rankin scale score 0–2, whereas 29% were deceased at 90 days). Conversely, 27 patients (8%) had CTP core >50 cc and ASPECTS ≥6 (29% had modified Rankin scale 0–2, whereas 21% were deceased at 90 days). Moderate correlations between ASPECTS and final infarct volume ( R =−0.42; P <0.01) and between CTP ischemic core and final infarct volume ( R =0.50; P <0.01) were observed; coefficients were not significantly influenced by the time from stroke onset to presentation. Multivariable regression indicated ASPECTS ≥6 (odds ratio 4.10; 95% confidence interval, 1.47–11.46; P =0.01) and CTP core ≤50 cc (odds ratio 3.86; 95% confidence interval, 1.22–12.15; P =0.02) independently and comparably predictive of good outcome.

Conclusions—

There is wide variability of CTP-derived core volumes within ASPECTS strata. Patient selection may be affected by the imaging selection method.

Comparison of Perfusion CT Software to Predict the Final Infarct Volume After Thrombectomy

Background and Purpose—

Computed tomographic perfusion represents an interesting physiological imaging modality to select patients for reperfusion therapy in acute ischemic stroke. The purpose of our study was to determine the accuracy of different commercial perfusion CT software packages (Philips (A), Siemens (B), and RAPID (C)) to predict the final infarct volume (FIV) after mechanical thrombectomy.

Methods—

Single-institutional computed tomographic perfusion data from 147 mechanically recanalized acute ischemic stroke patients were postprocessed. Ischemic core and FIV were compared about thrombolysis in cerebral infarction (TICI) score and time interval to reperfusion. FIV was measured at follow-up imaging between days 1 and 8 after stroke.

Results—

In 118 successfully recanalized patients (TICI 2b/3), a moderately to strongly positive correlation was observed between ischemic core and FIV. The highest accuracy and best correlation are shown in early and fully recanalized patients (Pearson r for A=0.42, B=0.64, and C=0.83; P <0.001). Bland–Altman plots and boxplots demonstrate smaller ranges in package C than in A and B. Significant differences were found between the packages about over- and underestimation of the ischemic core. Package A, compared with B and C, estimated more than twice as many patients with a malignant stroke profile ( P <0.001). Package C best predicted hypoperfusion volume in nonsuccessfully recanalized patients.

Conclusions—

Our study demonstrates best accuracy and approximation between the results of a fully automated software (RAPID) and FIV, especially in early and fully recanalized patients. Furthermore, this software package overestimated the FIV to a significantly lower degree and estimated a malignant mismatch profile less often than other software.

Performance of CT ASPECTS and Collateral Score in Risk Stratification: Can Target Perfusion Profiles Be Predicted without Perfusion Imaging?

BACKGROUND AND PURPOSE

Endovascular trials suggest that revascularization benefits a subset of acute ischemic stroke patients with large-artery occlusion and small-core infarct volumes. The objective of our study was to identify thresholds of noncontrast CT-ASPECTS and collateral scores on CT angiography that best predict ischemic core volume thresholds quantified by CT perfusion among patients with acute ischemic stroke.

MATERIALS AND METHODS

Fifty-four patients with acute ischemic stroke (<12 hours) and MCA/intracranial ICA occlusion underwent NCCT/CTP during their initial evaluation. CTP analysis was performed on a user-independent platform (RApid processing of PerfusIon and Diffusion), computing core infarct (defined as CBF of <30% normal). A target mismatch profile consisting of infarction core of ≤50 mL was selected to define candidates with acute ischemic stroke likely to benefit from revascularization.

RESULTS

NCCT-ASPECTS of ≥9 with a CTA collateral score of 3 had 100% specificity for identifying patients with a CBF core volume of ≤50 mL. NCCT-ASPECTS of ≤6 had 100% specificity for identifying patients with a CBF core volume of >50 mL. In our cohort, 44 (81%) patients had an NCCT-ASPECTS of ≥9, a CTA collateral score of 3, or an NCCT-ASPECTS of ≤6.

CONCLUSIONS

Using an NCCT-ASPECTS of ≥9 or a CTA collateral score of 3 best predicts CBF core volume infarct of ≤50 mL, while an NCCT-ASPECTS of ≤6 best predicts a CBF core volume infarct of >50 mL. Together these thresholds suggest that a specific population of patients with acute ischemic stroke not meeting such profiles may benefit most from CTP imaging to determine candidacy for revascularization.

Large Volumes of Critically Hypoperfused Penumbral Tissue Do Not Preclude Good Outcomes After Complete Endovascular Reperfusion

Background and Purpose—

Acute ischemic stroke patients with large volumes of severe hypoperfusion ( T max >10 s>100 mL) on magnetic resonance imaging have a higher likelihood of intracranial hemorrhage and poor outcomes after reperfusion. We aim to evaluate the impact of the extent of T max >10 s CTP lesions in patients undergoing successful treatment.

Methods—

Retrospective database review of endovascular acute ischemic stroke treatment between September 2010 and March 2015 for patients with anterior circulation occlusions with baseline RAPID CTP and full reperfusion (mTICI 3). The primary outcome was the impact of the T max >10 s lesion spectrum on infarct growth. Secondary safety and efficacy outcomes included parenchymal hematomas and good clinical outcomes (90-day modified Rankin Scale score, 0–2).

Results—

Of 684 treated patients, 113 patients fit the inclusion criteria. T max >10 s>100 mL patients (n=37) had significantly higher baseline National Institutes of Health Stroke Scale (20.7±3.8 versus 17.0±5.9; P <0.01), more internal carotid artery terminus occlusions (29% versus 9%; P =0.02), and larger baseline (38.6±29.6 versus 11.7±15.8 mL; P <0.01) and final (60.7±60.0 versus 29.4±33.9 mL; P <0.01) infarct volumes when compared with patients without T max >10 s>100 mL (n=76); however, the 2 groups were otherwise well balanced. There were no significant differences in infarct growth (22.1±51.6 versus 17.8±32.4 mL; P =0.78), severe intracranial hemorrhage (PH2: 2% versus 4%; P =0.73), good outcomes (90-day mRS score, 0–2: 56% versus 59%; P =0.83), or 90-day mortality (16% versus 7%; P =0.28). On multivariate analysis, only baseline National Institutes of Health Stroke Scale (odds ratio, 1.19; 95% confidence interval, 1.06–1.34; P <0.01) and baseline infarct core volume (odds ratio, 1.05; 95% confidence interval, 1.02–1.08; P <0.01) were independently associated with T max >10 s>100 mL. There was no association between T max >10 s>100 mL with any PH, good outcome, or infarct growth.

Conclusions—

In the setting of limited baseline ischemic cores, large T max >10 s lesions on computed tomographic perfusion do not seem to be associated with a higher risk of parenchymal hematomas and do not preclude good outcomes in patients undergoing endovascular reperfusion with contemporary technology.