Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Use of computed tomography perfusion for acute stroke in routine clinical practice: Complex scenarios, mimics, and artifacts

Background Computed tomography perfusion is becoming widely accepted and used in acute stroke treatment. Computed tomography perfusion provides pathophysiological information needed in the acute decision making. Moreover, computed tomography perfusion shows excellent correlation with diffusion-weighted imaging and perfusion-weighted sequences to evaluate core and penumbra volumes. Multimodal computed tomography perfusion has practical advantages over magnetic resonance imaging, including availability, accessibility, and speed. Nevertheless, it bears some limitations, as the limited accuracy for small ischemic lesions or brainstem ischemia. Interpretation of the computed tomography perfusion maps can sometimes be difficult. The stroke neurologist faces complex or atypical cases of cerebral ischemia and stroke mimics, and needs to decide whether the "lesions" on computed tomography perfusion are real or artifact. Aims The purpose of this review is, based on clinical cases from a comprehensive stroke center, to describe the added value that computed tomography perfusion can provide to the stroke physician in the acute phase before a treatment decision is made.

Imaging selection for acute stroke intervention

This review summarizes the current state of knowledge regarding the use of imaging to guide stroke treatment. Brain imaging plays a central role in the diagnosis of stroke and identification of the mechanism of stroke, which is relevant to acute treatment, prognosis, and secondary prevention. The chief potential modalities are computed tomography (CT) and magnetic resonance imaging (MRI). Currently, most imaging occurs in hospital but mobile stroke units have expanded CT brain imaging into the prehospital field. The proven therapies for ischemic stroke are based on achieving reperfusion and the DAWN and DEFUSE 3 trials have now firmly established a need for imaging selection based on estimated ischemic core volume to guide reperfusion decisions in patients beyond 6 h of stroke onset. However, data also indicate that estimated ischemic core volume, in conjunction with patient factors and expected time delay to reperfusion, forms one of the most useful prognostic assessments that could alter decision-making for patients within 6 h. Current trials are also investigating agents that aim to achieve neuroprotection, reduction in edema or prevention of hemorrhagic transformation. Imaging may play a role in identifying patients likely to benefit from this next generation of interventions for stroke patients.

Tissue Is More Important than Time in Stroke Patients Being Assessed for Thrombolysis

Aim

The relative prognostic importance of modern imaging profiles compared with standard clinical characteristics is uncertain in acute stroke patients. In this study, we aimed to compare baseline multimodal CT imaging measures with known clinical predictors of patient outcome at 3 months [modified Rankin scale (mRS)].

Methods

We collected baseline, 24 h, and day 90 clinical and imaging data from acute ischemic stroke patients being assessed for thrombolytic therapy between 2010 and 2015 at a single center as part of a retrospective analysis.

Results

561 patients presenting within 4.5 h of ischemic stroke onset who were eligible for thrombolysis based on standard clinical criteria were assessed. Acute infarct core volume on CTP was the strongest univariate predictor of patient outcome (mRS 0–2, R² 0.497, p < 0.001), followed by collateral grade (mRS 0–2, R² 0.281, p < 0.001). The strongest baseline clinical predictor of outcome was National Institutes of Health Stroke Scale (NIHSS) (mRS 0–2, R² = 0.203, p < 0.001). Time to treatment (mRS 0–2, R² 0.096, p = 0.01) and age (mRS 0–2, R² 0.027, p = 0.013) were relatively weak univariate baseline clinical predictors of 3-month outcome. In multivariate analysis, acute infarct core volume and collateral grade were the only significant baseline predictors of 3-month disability (both p < 0.001).

Conclusion

In patients assessed for thrombolysis by combined clinical and multimodal CT criteria within 4.5 h of onset, the size of the CTP infarct core and collateral grade on multimodal CT were highly predictive of patient outcome. Standard clinical variables, including time to treatment and NIHSS, were not as strongly predictive as multimodal CT variables.

Transient Ischemic Attack Results in Delayed Brain Atrophy and Cognitive Decline

BACKGROUND AND PURPOSE

Transient ischemic attack (TIA) initiates an ischemic cascade without resulting in frank infarction and, as such, represents a novel model to study the effects of this ischemic cascade and secondary neurodegeneration in humans.

METHODS

Patients with suspected TIA underwent acute brain perfusion imaging, and those with acute ischemia were enrolled into a prospective observational study. We collected baseline and 90-day magnetic resonance imaging, including MP-RAGE (high-resolution T1 sequence) and cognitive assessment with the Montreal Cognitive Assessment. Brain morphometry and within patient statistical analysis were performed to identify changes between baseline and 90-day imaging and clinical assessments.

RESULTS

Fifty patients with TIA with acute perfusion lesions were studied. All patients experienced a decrease in global cortical gray matter (P=0.005). Patients with anterior circulation TIA (n=31) also had a significant reduction in the volume of the pons (P<0.001), ipsilesional parietal lobe (P<0.001), occipital lobe (P=0.002), frontal lobe (P<0.001), temporal lobe (P=0.003), and thalamus (P=0.016). Patients with an anterior perfusion lesion on acute imaging also had a significant decrease in Montreal Cognitive Assessment between baseline and day 90 (P=0.027), which may be related to the volume of thalamic atrophy (R²=0.28; P=0.009).

CONCLUSIONS

In a prospective observational study, patients with TIA confirmed by acute perfusion imaging experienced a significant reduction in global gray matter and focal structural atrophy related to the area of acute ischemia. The atrophy also resulted in a proportional decreased cognitive performance on the Montreal Cognitive Assessment. Further studies are required to identify the mechanisms of this atrophy.

Ischemic core thresholds change with time to reperfusion: A case control study

Introduction

We aimed to identify whether acute ischemic stroke patients with known complete reperfusion after thrombectomy had the same baseline computed tomography perfusion (CTP) ischemic core threshold to predict infarction as thrombolysis patients with complete reperfusion.

Methods

Patients who underwent thrombectomy were matched by age, clinical severity, occlusion location, and baseline perfusion lesion volume to patients who were treated with intravenous alteplase alone from the International Stroke Perfusion Imaging Registry. A pixel‐based analysis of coregistered pretreatment CTP and 24‐hour diffusion‐weighted imaging (DWI) was then undertaken to define the optimum CTP thresholds for the ischemic core.

Results

There were 132 eligible thrombectomy patients and 132 matched controls treated with alteplase alone. Baseline National Institutes of Health Stroke Scale (median, 15; interquartile range [IQR], 11–19), age (median, 65; IQR, 59–80), and time to intravenous treatment (median, 153 minutes; IQR, 82–315) were well matched (all p > 0.05). Despite similar baseline CTP ischemic core volumes using the previously validated measure (relative cerebral blood flow [rCBF], <30%), thrombectomy patients had a smaller median 24‐hour infarct core of 17.3ml (IQR, 11.3–32.8) versus 24.3ml (IQR, 16.7–42.2; p = 0.011) in alteplase‐treated controls. As a result, the optimal threshold to define the ischemic core in thrombectomy patients was rCBF <20% (area under the curve [AUC], 0.89; 95% CI, 0.84, 0.94), whereas in alteplase controls the optimal ischemic core threshold remained rCBF <30% (AUC, 0.83; 95% CI, 0.77, 0.85).

Interpretation

Thrombectomy salvaged tissue with lower CBF, likely attributed to earlier reperfusion. For patients who achieve rapid reperfusion, a stricter rCBF threshold to estimate the ischemic core should be considered. Ann Neurol 2017;82:995–1003

Current evidence for endovascular therapy in stroke and remaining uncertainties

Class 1 level A evidence now supports endovascular thrombectomy as best practice in the management of large vessel occlusion acute ischaemic stroke. However, significant questions pertaining to initial imaging, radiological assessment, patient selection and therapeutic limits remain unanswered. A specific cohort of patients who benefit from endovascular thrombectomy has been established, although current uncertainties regarding selection of those not meeting top-tier evidence criteria may potentially deny certain patients the benefit of intervention. This is of particular relevance in patients presenting in a delayed manner. Whilst superior outcomes are achieved with reduced time to endovascular reperfusion, denying patients intervention based on symptom duration alone may not be appropriate. Advanced understanding of ischaemic stroke pathophysiology supports an individualized approach to patient evaluation, given variance in the rate of ischaemic core progression and the extent of salvageable penumbra. Physiological imaging techniques may therefore be utilized to better inform patient selection for endovascular thrombectomy and evidence suggests that a transition from time-based to tissue-based therapeutic thresholds may be of greater value. Multiple ongoing randomized controlled trials aim to further define the benefit of endovascular thrombectomy and it is hoped that these results will advance, and possibly broaden, patient selection criteria to ensure that maximum benefit from the intervention may be achieved.

Collateral response modulates the time–penumbra relationship in proximal arterial occlusions

Objective

While clinical benefit from thrombolysis decreases with increase in time from stroke onset, the relationship of acute physiologic tissue compartments and collateral response to stroke onset time remains unclear.

Methods

We studied consecutive patients with proximal arterial occlusions (n = 355) with whole-brain perfusion CT with CT angiography within 6 hours of stroke onset. Penumbra and core were defined using voxel-based thresholds. Tissue mismatch was defined as the ratio of penumbra to core. Collateral scores were assessed using a previously validated visual score.

Results

Mean (SD) age was 72.1 (12.4) years, median (interquartile range) NIH Stroke Scale score 16 (4), mean (SD) time to imaging 152.5 (69.7) minutes. Penumbra volume (Spearman ρ = 0.119,p= 0.026) and mismatch increased (Spearman ρ = 0.115,p= 0.030) with time from onset. Core volume decreased (Spearman ρ = −0.112,p= 0.035) while collateral scores increased with time (Spearman ρ = 0.117,p= 0.028). On multivariable regression, good collateral scores predicted longer time since onset (β = 0.101,p= 0.039) while mismatch was not a predictor (β = 0.001,p= 0.351). Good collateral score was the strongest independent predictor of final infarct volume and improvement in clinical deficit.

Conclusions

In our large patient cohort study of proximal arterial occlusions, we found an incremental collateral response and preserved penumbral volume with time. Thus, tissue viability can be maintained in this time window (0–6 hours) after stroke if leptomeningeal collaterals are able to sustain the penumbra. Our findings suggest that a longer therapeutic window may exist for intra-arterial intervention and that multimodal imaging may have a role in strokes of unknown onset time.

Contribution of Neuro-Imaging for Prediction of Functional Recovery after Ischemic Stroke

Prediction measures of recovery and outcome after stroke perform with only modest levels of accuracy if based only on clinical data. Prediction scores can be improved by including morphologic imaging data, where size, location, and development of the ischemic lesion is best documented by magnetic resonance imaging. In addition to the primary lesion, the involvement of fiber tracts contributes to prognosis, and consequently the use of diffusion tensor imaging (DTI) to assess primary and secondary pathways improves the prediction of outcome and of therapeutic effects. The recovery of ischemic tissue and the progression of damage are dependent on the quality of blood supply. Therefore, the status of the supplying arteries and of the collateral flow is not only crucial for determining eligibility for acute interventions, but also has an impact on the potential to integrate areas surrounding the lesion that are not typically part of a functional network into the recovery process. The changes in these functional networks after a localized lesion are assessed by functional imaging methods, which additionally show altered pathways and activated secondary centers related to residual functions and demonstrate changes in activation patterns within these networks with improved performance. These strategies in some instances record activation in secondary centers of a network, for example, also in homolog contralateral areas, which might be inhibitory to the recovery of primary centers. Such findings might have therapeutic consequences, for example, image-guided inhibitory stimulation of these areas. In the future, a combination of morphological imaging including DTI of fiber tracts and activation studies during specific tasks might yield the best information on residual function, reserve capacity, and prospects for recovery after ischemic stroke.

Penumbra and re-canalization acute computed tomography in ischemic stroke evaluation: PRACTISE study protocol

Rationale Multimodal imaging, including computed tomography angiography and computed tomography perfusion imaging, yields additional information on intracranial vessels and brain perfusion and can differentiate between ischemic core and penumbra which may affect patient selection for intravenous thrombolysis. Hypothesis The use of multimodal imaging will increase the number of patients receiving intravenous thrombolysis and lead to better treatment outcomes. Sample size 400 patients. Methods and design PRACTISE is a prospective, multicenter, randomized, controlled trial in which patients presenting within 4.5 h of symptom onset are randomized to either the current evidence-based imaging (NCCT alone) or additional multimodal computed tomography imaging (NCCT + computed tomography angiography + computed tomography perfusion). Clinical decisions on intravenous recombinant tissue plasminogen activator are documented. Total imaging time in both arms and time to initiation of treatment delivery in those treated with intravenous recombinant tissue plasminogen activator, is recorded. Follow-up will include brain imaging at 24 h to document infarct size, the presence of edema and the presence of intra-cerebral hemorrhage. Clinical evaluations include NIHSS score at baseline, 24 h and day 7 ± 2, and mRS at day 90 to define functional outcomes. Study outcomes The primary outcome is the proportion of patients receiving intravenous recombinant tissue plasminogen activator. Secondary end-points evaluate times to decision-making, comparison of different image processing software and clinical outcomes at three months. Discussion Multimodal computed tomography is a widely available tool for patient selection for revascularization therapy, but it is currently unknown whether the use of additional imaging in all stroke patients is beneficial. The study opened for recruitment in March 2015 and will provide data on the value of multimodal imaging in treatment decisions for acute stroke.

Quantifying reperfusion of the ischemic region on whole-brain computed tomography perfusion

To derive the reperfusion index best predicting clinical outcome of ischemic stroke patients, we retrospectively analysed the acute and 24-h computed tomography perfusion data of 116 patients, collected from two centres equipped with whole-brain computed tomography perfusion. Reperfusion index was defined by the percentage of the ischemic region reperfused from acute to 24-h computed tomography perfusion. Recanalization was graded by arterial occlusive lesion system. Receiver operator characteristic analysis was performed to assess the prognostic value of reperfusion and recanalization in predicting good clinical outcome, defined as modified Rankin Score of 0-2 at 90 days. Among previous reported reperfusion measurements, reperfusion of the Tmax>6 s region resulted in higher prognostic value than recanalization at predicting good clinical outcome (area under the curve = 0.88 and 0.74, respectively, p = 0.002). Successful reperfusion of the Tmax>6 s region (≥60%) had 89% sensitivity and 78% specificity in predicting good clinical outcome. A reperfusion index defined by Tmax>2 s or by mean transit time>145% had much lower area under the curve in comparison to Tmax>6 s measurement (p < 0.001 and p = 0.003, respectively), and had no significant difference to recanalization at predicting clinical outcome (p = 0.58 and 0.63, respectively). In conclusion, reperfusion index calculated by Tmax>6 s is a stronger predictor of clinical outcome than recanalization or other reperfusion measures.

Evaluation of hyperacute infarct volume using ASPECTS and brain CT perfusion core volume

OBJECTIVE

To compare the accuracy of Alberta Stroke Program Early Computed Tomography Score (ASPECTS) and CT perfusion to detect established infarction in acute anterior circulation stroke.

METHODS

We performed an observational study in 59 acute anterior circulation ischemic stroke patients who underwent brain noncontrast CT, CT perfusion, and MRI within 100 minutes from CT imaging. ASPECTS scores were calculated by 4 blinded vascular neurologists. The accuracy of ASPECTS and CT perfusion core volume to detect an acute MRI diffusion lesion of ≥70 mL was evaluated using receiver operating characteristics analysis and optimum cutoff values were calculated using Youden J.

RESULTS

Median ASPECTS score was 8 (interquartile range [IQR] 5-9). Median CT perfusion core volume was 22 mL (IQR 10.4-71.9). Median MRI diffusion lesion volume was 24.5 mL (IQR 10-63.9). No significant difference was found between the accuracy of CT perfusion and ASPECTS (c statistic 0.95 vs 0.87, p value for difference = 0.17). The optimum ASPECTS cutoff score to detect a diffusion-weighted imaging lesion ≥70 mL was <7 (sensitivity 0.74, specificity 0.86, Youden J = 0.60) and the optimum CT perfusion core volume cutoff was ≥50 mL (sensitivity 0.86, specificity 0.97, Youden J = 0.84). The CT perfusion core lesion covered a median of 100% (IQR 86%-100%) of the acute MRI lesion volume (Pearson R = 0.88; R² = 0.77).

CONCLUSIONS

We found no significant difference between the accuracy of CT perfusion and ASPECTS to predict hyperacute MRI lesion volume in ischemic stroke.

White Matter and Gray Matter Segmentation in 4D Computed Tomography

Modern Computed Tomography (CT) scanners are capable of acquiring contrast dynamics of the whole brain, adding functional to anatomical information. Soft tissue segmentation is important for subsequent applications such as tissue dependent perfusion analysis and automated detection and quantification of cerebral pathology. In this work a method is presented to automatically segment white matter (WM) and gray matter (GM) in contrast- enhanced 4D CT images of the brain. The method starts with intracranial segmentation via atlas registration, followed by a refinement using a geodesic active contour with dominating advection term steered by image gradient information, from a 3D temporal average image optimally weighted according to the exposures of the individual time points of the 4D CT acquisition. Next, three groups of voxel features are extracted: intensity, contextual, and temporal. These are used to segment WM and GM with a support vector machine. Performance was assessed using cross validation in a leave-one-patient-out manner on 22 patients. Dice coefficients were 0.81 ± 0.04 and 0.79 ± 0.05, 95% Hausdorff distances were 3.86 ± 1.43 and 3.07 ± 1.72 mm, for WM and GM, respectively. Thus, WM and GM segmentation is feasible in 4D CT with good accuracy.

Baseline collateral status and infarct topography in post-ischaemic perilesional hyperperfusion: An arterial spin labelling study

Focal hyperperfusion after acute ischaemic stroke could be of prognostic value depending upon its spatial localisation and temporal dynamics. Factors associated with late stage (12-24 h) perilesional hyperperfusion, identified using arterial spin labelling, are poorly defined. A prospective cohort of acute ischaemic stroke patients presenting within 4.5 h of symptom onset were assessed with multi-modal computed tomography acutely and magnetic resonance imaging at 24 ± 8 h. Multivariate logistic regression analysis and receiver operating characteristics curves were used. One hundred and nineteen hemispheric acute ischaemic stroke patients (mean age = 71 ± 12 years) with 24 h arterial spin labelling imaging were included. Forty-two (35.3%) patients showed perilesional hyperperfusion on arterial spin labelling at 24 h. Several factors were independently associated with perilesional hyperperfusion: good collaterals (71% versus 29%, P < 0.0001; OR = 5, 95% CI = [1.6, 15.7], P = 0.005), major reperfusion (81% versus 48%, P = < 0.0001; OR = 7.5, 95% CI = [1.6, 35.1], P = 0.01), penumbral salvage (76.2% versus 47%, P = 0.002; OR = 6.6, 95% CI = [1.8, 24.5], P = 0.004), infarction in striatocapsular (OR = 9.5, 95% CI = [2.6, 34], P = 0.001) and in cortical superior division middle cerebral artery (OR = 4.7, 95% CI = [1.4, 15.7], P = 0.012) territory. The area under the receiver operating characteristic curve was 0.91. Our results demonstrate good arterial collaterals, major reperfusion, penumbral salvage, and infarct topographies involving cortical superior middle cerebral artery and striatocapsular are associated with perilesional hyperperfusion.

Computed tomography perfusion and computed tomography angiography for prediction of clinical outcomes in ischemic stroke patients after thrombolysis

Cerebral blood perfusion and cerebrovascular lesions are important factors that can affect the therapeutic efficacy of thrombolysis. At present, the majority of studies focus on assessing the accuracy of lesion location using imaging methods before treatment, with less attention to predictions of outcomes after thrombolysis. Thus, in the present study, we assessed the efficacy of combined computed tomography (CT) perfusion and CT angiography in predicting clinical outcomes after thrombolysis in ischemic stroke patients. The study included 52 patients who received both CT perfusion and CT angiography. Patients were grouped based on the following criteria to compare clinical outcomes: (1) thrombolytic and non-thrombolytic patients, (2) thrombolytic patients with CT angiography showing the presence or absence of a vascular stenosis, (3) thrombolytic patients with CT perfusion showing the presence or absence of hemodynamic mismatch, and (4) different CT angiography and CT perfusion results. Short-term outcome was assessed by the 24-hour National Institution of Health Stroke Scale score change. Long-term outcome was assessed by the 3-month modified Rankin Scale score. Of 52 ischemic stroke patients, 29 were treated with thrombolysis and exhibited improved short-term outcomes compared with those without thrombolysis treatment (23 patients). Patients with both vascular stenosis and blood flow mismatch (13 patients) exhibited the best short-term outcome, while there was no correlation of long-term outcome with CT angiography or CT perfusion findings. These data suggest that combined CT perfusion and CT angiography are useful for predicting short-term outcome, but not long-term outcome, after thrombolysis.

Association of Cortical Vein Filling with Clot Location and Clinical Outcomes in Acute Ischaemic Stroke Patients

Delay in cortical vein filling during the late-venous phase (delayed-LCVF) is characterized by opacification of cerebral veins despite contrast clearance from contralateral veins on dynamic computed tomography angiography (dCTA) in acute ischemic stroke (AIS) patients. The aim of the study was to investigate the associations of delayed-LCVF with clot location, reperfusion status at 24 hours, and 90-days functional outcome in AIS patients who received reperfusion therapy. A prospective cohort of AIS patients treated with intravenous thrombolysis was studied. Groupwise comparison, univariate, and multivariate regression analyses were used to study the association of delayed-LCVF with clot location and clinical outcomes. Of 93 patients (mean age = 72 ± 12 years) with hemispheric AIS included in the study, 46 (49%) demonstrated delayed-LCVF. Patients with delayed-LCVF demonstrated a significantly higher proportion of proximal occlusion (72% vs 13%, P =< 0.0001), and poor reperfusion at 24 hours (41% vs 11%, P = 0.001). The proportion of poor functional outcome at 90 days was not significantly different (22/56 (48%) vs 17/61 (36%), P = 0.297). The appearance of delayed-LCVF on baseline dCTA may be a surrogate for large vessel occlusion, and an early marker for poor 24-hour angiographic reperfusion.

A 4D CT digital phantom of an individual human brain for perfusion analysis

Brain perfusion is of key importance to assess brain function. Modern CT scanners can acquire perfusion maps of the cerebral parenchyma in vivo at submillimeter resolution. These perfusion maps give insights into the hemodynamics of the cerebral parenchyma and are critical for example for treatment decisions in acute stroke. However, the relations between acquisition parameters, tissue attenuation curves, and perfusion values are still poorly understood and cannot be unraveled by studies involving humans because of ethical concerns. We present a 4D CT digital phantom specific for an individual human brain to analyze these relations in a bottom-up fashion. Validation of the signal and noise components was based on 1,000 phantom simulations of 20 patient imaging data. This framework was applied to quantitatively assess the relation between radiation dose and perfusion values, and to quantify the signal-to-noise ratios of penumbra regions with decreasing sizes in white and gray matter. This is the first 4D CT digital phantom that enables to address clinical questions without having to expose the patient to additional radiation dose.

The establishment of a telestroke service using multimodal CT imaging decision assistance: "Turning on the fog lights"

Telestroke services have been shown to increase stroke therapy access in rural areas. The implementation of advanced CT imaging for patient assessment may improve patient selection and detection of stroke mimics in conjunction with telestroke. We implemented a telestroke service supported by multimodal CT imaging in a rural hospital in Australia. Over 21months we conducted an evaluation of service activation, thrombolysis rates and use of multimodal imaging to assess the feasibility of the service. Rates of symptomatic intracranial haemorrhage and 90-day modified Rankin Score were used as safety outcomes. Fifty-eight patients were assessed using telestroke, of which 41 were regarded to be acute ischemic strokes and 17 to be stroke mimics on clinical grounds. Of the 41 acute stroke patients, 22 patients were deemed eligible for thrombolysis. Using multimodal CT imaging, 8 more patients were excluded from treatment because of lack of treatment target. Multimodal imaging failed to be obtained in one patient. For the 14 treated patients, median door-imaging time was 38min. Median door-treatment time was 91min. A 90-day mRS ⩽2 was achieved in 40% of treated patients. We conclude that a telestroke service using advanced CT imaging for therapy decision assistance can be successfully implemented in regional Australia and can be used to guide acute stroke treatment decision-making and improve access to thrombolytic therapy. Efficiency and safety is comparable to established telestroke services.

Optimal Computed Tomographic Perfusion Scan Duration for Assessment of Acute Stroke Lesion Volumes

BACKGROUND AND PURPOSE

The minimal scan duration needed to obtain reliable lesion volumes with computed tomographic perfusion (CTP) has not been well established in the literature.

METHODS

We retrospectively assessed the impact of gradual truncation of the scan duration on acute ischemic lesion volume measurements. For each scan, we identified its optimal scan time, defined as the shortest scan duration that yields measurements of the ischemic lesion volumes similar to those obtained with longer scanning, and the relative height of the fitted venous output function at its optimal scan time.

RESULTS

We analyzed 70 computed tomographic perfusion scans of acute stroke patients. An optimal scan time could not be determined in 11 scans (16%). For the other 59 scans, the median optimal scan time was 32.7 seconds (90th percentile 52.6 seconds; 100th percentile 68.9 seconds), and the median relative height of the fitted venous output function at the optimal scan times was 0.39 (90th percentile 0.02; 100th percentile 0.00). On the basis of a linear model, the optimal scan time was T₀ plus 1.6 times the width of the venous output function (P<0.001; R²=0.49).

CONCLUSIONS

This study shows how the optimal duration of a computed tomographic perfusion scan relates to the arrival time and width of the contrast bolus. This knowledge can be used to optimize computed tomographic perfusion scan protocols and to determine whether a scan is of sufficient duration. Provided a baseline (T₀) of 10 seconds, a total scan duration of 60 to 70 seconds, which includes the entire downslope of the venous output function in most patients, is recommended.

Utility of perfusion imaging in acute stroke treatment: a systematic review and meta-analysis

BACKGROUND

Variability in imaging protocols and techniques has resulted in a lack of consensus regarding the incorporation of perfusion imaging into stroke triage and treatment. The objective of our study was to evaluate the available scientific evidence regarding the utility of perfusion imaging in determining treatment eligibility in patients with acute stroke and in predicting their clinical outcome.

METHODS

We performed a systematic review of the literature using PubMed, Web of Science, and Cochrane Library focusing on themes of medical imaging, stroke, treatment, and outcome (CRD42016037817). We included randomized controlled trials, cohort studies, and case-controlled studies published from 2011 to 2016. Two independent reviewers conducted the study appraisal, data abstraction, and quality assessments of the studies.

RESULTS

Our literature search yielded 13 studies that met our inclusion criteria. In total, 994 patients were treated with the aid of perfusion imaging compared with 1819 patients treated with standard care. In the intervention group 51.1% of patients had a favorable outcome at 3 months compared with 45.6% of patients in the control group (p=0.06). Subgroup analysis of studies that used multimodal therapy (IV tissue plasminogen activator, endovascular thrombectomy) showed a significant benefit of perfusion imaging (OR 1.89, 95% CI 1.43 to 2.51, p<0.01).

CONCLUSIONS

Perfusion imaging may represent a complementary tool to standard radiographic assessment in enhancing patient selection for reperfusion therapy, with a subset of patients having up to 1.9 times the odds of achieving independent functional status at 3 months. This is particularly important as patients selected based on perfusion status often included individuals who did not meet the current treatment eligibility criteria.

A benchmarking tool to evaluate computer tomography perfusion infarct core predictions against a DWI standard

Differences in research methodology have hampered the optimization of Computer Tomography Perfusion (CTP) for identification of the ischemic core. We aim to optimize CTP core identification using a novel benchmarking tool. The benchmarking tool consists of an imaging library and a statistical analysis algorithm to evaluate the performance of CTP. The tool was used to optimize and evaluate an in-house developed CTP-software algorithm. Imaging data of 103 acute stroke patients were included in the benchmarking tool. Median time from stroke onset to CT was 185 min (IQR 180-238), and the median time between completion of CT and start of MRI was 36 min (IQR 25-79). Volumetric accuracy of the CTP-ROIs was optimal at an rCBF threshold of <38%; at this threshold, the mean difference was 0.3 ml (SD 19.8 ml), the mean absolute difference was 14.3 (SD 13.7) ml, and CTP was 67% sensitive and 87% specific for identification of DWI positive tissue voxels. The benchmarking tool can play an important role in optimizing CTP software as it provides investigators with a novel method to directly compare the performance of alternative CTP software packages.

How many stroke patients might be eligible for mechanical thrombectomy?

Introduction

Recent studies showed improved patient outcomes with endovascular treatment of acute stroke compared to medical care, including IV rtPA, alone. Seven trials have reported results, each using different clinical and imaging criteria for patient selection. We compared eligibility for different trial protocols to estimate the number of patients eligible for treatment.

Patients and methods

Patient data were extracted from a single centre database that combined patients recruited to three clinical studies, each of which obtained both CTA and CTP within 6 h of stroke onset. The published inclusion and exclusion criteria of seven intervention trials (MR CLEAN, EXTEND-IA, ESCAPE, SWIFT-PRIME, REVASCAT, THERAPY and THRACE) were applied to determine the proportion that would be eligible for each of these studies.

Results

A total of 263 patients was included. Eligibility for IAT in individual trials ranged from 53% to 3% of patients; 17% were eligible for four trials and under 10% for two trials. Only three patients (1%) were eligible for all studies. The most common cause of exclusion was absence of large artery occlusion (LAO) on CTA. When applying simplified criteria requiring an ASPECT score > 6, 16% were eligible for IAT, but potentially 40% of these patients were excluded by perfusion criteria and more than half by common NIHSS thresholds.

Conclusion

Around 15% of patients presenting within 6 h of stroke onset were potentially eligible for IAT, but clinical trial eligibility criteria have much more limited overlap than is commonly assumed and only 1% of patients fulfilled criteria for all recent trials.

Admission CT perfusion may overestimate initial infarct core: the ghost infarct core concept

Background

Identifying infarct core on admission is essential to establish the amount of salvageable tissue and indicate reperfusion therapies. Infarct core is established on CT perfusion (CTP) as the severely hypoperfused area, however the correlation between hypoperfusion and infarct core may be time-dependent as it is not a direct indicator of tissue damage. This study aims to characterize those cases in which the admission core lesion on CTP does not reflect an infarct on follow-up imaging.

Methods

We studied patients with cerebral large vessel occlusion who underwent CTP on admission but received endovascular thrombectomy based on a non-contrast CT Alberta Stroke Program Early CT Score (ASPECTS) >6. Admission infarct core was measured on initial cerebral blood volume (CBV) CTP and final infarct on follow-up CT. We defined ghost infarct core (GIC) as initial core minus final infarct >10 mL.

Results

79 patients were studied. Median National Institutes of Health Stroke Scale (NIHSS) score was 17 (11–20), median time from symptoms to CTP was 215 (87–327) min, and recanalization rate (TICI 2b–3) was 77%. Thirty patients (38%) presented with a GIC >10 mL. GIC >10 mL was associated with recanalization (TICI 2b–3: 90% vs 68%; p=0.026), admission glycemia (<185 mg/dL: 42% vs 0%; p=0.028), and time to CTP (<185 min: 51% vs >185 min: 26%; p=0.033). An adjusted logistic regression model identified time from symptom to CTP imaging <185 min as the only predictor of GIC >10 mL (OR 2.89, 95% CI 1.04 to 8.09). At 24 hours, clinical improvement was more frequent in patients with GIC >10 mL (66.6% vs 39%; p=0.017).

Conclusions

CT perfusion may overestimate final infarct core, especially in the early time window. Selecting patients for reperfusion therapies based on the CTP mismatch concept may deny treatment to patients who might still benefit from reperfusion.

Interaction of Recanalization, Intracerebral Hemorrhage, and Cerebral Edema After Intravenous Thrombolysis

BACKGROUND AND PURPOSE

Both intracerebral hemorrhage (ICH) and brain edema have been attributed to reperfusion after intravenous thrombolysis. We explored the interaction of recanalization and core size for imaging outcomes (ICH and vasogenic brain edema).

METHODS

In patients with anterior circulation occlusion given intravenous thrombolysis <4.5 hours and imaged with computed tomographic (CT) perfusion and CT angiography, we defined volumes of core (relative delay time >2 s and relative cerebral blood flow <40%) and penumbra (relative delay time >2 s). CT and CT angiography at 24 hours were reviewed for ICH (European Cooperative Acute Stroke Study [ECASS]-2 definition), early vasogenic edema (third International Stroke Trial [IST-3] criteria), and recanalization (thrombolysis in myocardial infarction 2-3). Independent effects of recanalization, core volume and potential interactions on edema, ICH and day 90 outcomes were estimated by logistic regression.

RESULTS

In 123 patients, there was a trend for recanalization to be associated with H1/2 ICH (odds ratio [OR], 2.3 [0.97-5.5]; P=0.06) but not with PH1/2 ICH (OR, 1.7 [0.33-8.8]; P=0.5), any edema, or significant brain edema (OR, 1.45 [0.4-4.9]; P=0.55). Ischemic core (>50 mL) was associated with any ICH (OR, 4.0 [1.6-9.5]; P=0.003), edema (OR, 5.4 [2-14]; P<0.01), and significant brain edema (OR, 17.4 [5.3-57]; P<0.01) but not with PH1/2 ICH (OR, 1.2 [0.23-6.5]; P=0.8), after controlling for recanalization. There was no significant interaction of recanalization and large core for any adverse outcomes.

CONCLUSIONS

Large ischemic core was associated with poorer outcomes and both early vasogenic brain edema and ICH, but recanalization on 24-hour CT angiography was associated with clinically favorable outcome. There was no significant interaction of recanalization and large core volume for any outcomes. The association of hemorrhage or brain edema with post-thrombolysis reperfusion is unclear.

Defining Core and Penumbra in Ischemic Stroke: A Voxel- and Volume-Based Analysis of Whole Brain CT Perfusion

Whole brain computed tomography perfusion (CTP) has the potential to select eligible patients for reperfusion therapy. We aimed to find the optimal thresholds on baseline CTP for ischemic core and penumbra in acute ischemic stroke. We reviewed patients with acute ischemic stroke in the anterior circulation, who underwent baseline whole brain CTP, followed by intravenous thrombolysis and perfusion imaging at 24 hours. Patients were divided into those with major reperfusion (to define the ischemic core) and minimal reperfusion (to define the extent of penumbra). Receiver operating characteristic (ROC) analysis and volumetric consistency analysis were performed separately to determine the optimal threshold by Youden’s Index and mean magnitude of volume difference, respectively. From a series of 103 patients, 22 patients with minimal-reperfusion and 47 with major reperfusion were included. Analysis revealed delay time ≥ 3 s most accurately defined penumbra (AUC = 0.813; 95% CI, 0.812-0.814, mean magnitude of volume difference = 29.1 ml). The optimal threshold for ischemic core was rCBF ≤ 30% within delay time ≥ 3 s (AUC = 0.758; 95% CI, 0.757-0.760, mean magnitude of volume difference = 10.8 ml). In conclusion, delay time ≥ 3 s and rCBF ≤ 30% within delay time ≥ 3 s are the optimal thresholds for penumbra and core, respectively. These results may allow the application of the mismatch on CTP to reperfusion therapy.

Peripheral Immune Cell Counts and Advanced Imaging as Biomarkers of Stroke Outcome

Introduction

Circulating neutrophil and lymphocyte levels may be modifiable outcome predictors of ischemic stroke. We sought to compare these immune cell parameters with advanced imaging assessment and the 90-day clinical outcome.

Methods

We used a retrospectively collected cohort of consecutive ischemic stroke patients presenting within 4.5 h of symptom onset who had acute CT perfusion and routine blood collection before treatment with intravenous thrombolysis and 24-hour MRI scanning at the John Hunter Hospital. Full blood counts were performed acutely at 24 h and 7 days. Patient outcomes were assed at 90 days after stroke with the modified Rankin Scale (mRS).

Results

Overall, 142 patients were assessed during the study period. Patients with a poor outcome (mRS 3-6) had increased neutrophils (44% increase, p = 0.016), decreased lymphocytes (7% decrease, p = 0.491) and an increased lymphocyte-to-neutrophil ratio (196% increase, p < 0.001). Patients with good outcomes (mRS 0-2) did not have significant changes in their full blood counts. There was no relationship between the neutrophil count at 24 h and penumbral volume (r² = 0.217, p = 0.212), reperfusion (r² = 0.111, p = 0.085), or core growth (r² = 0.297, p = 0.107). A backward multivariate analysis containing the 24-hour core volume and 24-hour neutrophil count was strongly related to the 3-month outcome (r² = 0.477, area under the curve = 0.902, p < 0.001).

Conclusions

Peripheral neutrophils have potential as a biomarker of outcome when used in conjunction with advanced imaging. Peripherally measured neutrophil counts change significantly over time after stroke and may be potential targets for immunomodulatory therapy in patients with a severe stroke or a large infarct volume.

A comprehensive analysis of metabolic changes in the salvaged penumbra

INTRODUCTION

We aimed to assess metabolite profiles in peri-infarct tissue with magnetic resonance spectroscopy (MRS) and correlate these with early and late clinical recovery.

METHODS

One hundred ten anterior circulation ischemic stroke patients presenting to hospital within 4.5 h of symptom onset and treated with intravenous thrombolysis were studied. Patients underwent computer tomography perfusion (CTP) scanning and subsequently 3-T magnetic resonance imaging (MRI) 24 h after stroke onset, including single-voxel, short-echo-time (30 ms) MRS, and diffusion- and perfusion-weighted imaging (DWI and PWI). MRS voxels were placed in the peri-infarct region in reperfused penumbral tissue. A control voxel was placed in the contralateral homologous area.

RESULTS

The concentrations of total creatine (5.39 vs 5.85 mM, p = 0.044) and N-acetylaspartic acid (NAA, 6.34 vs 7.13 mM ± 1.57, p < 0.001) were reduced in peri-infarct tissue compared to the matching contralateral region. Baseline National Institutes of Health Stroke Score was correlated with glutamate concentration in the reperfused penumbra at 24 h (r (2) = 0.167, p = 0.017). Higher total creatine was associated with better neurological outcome at 24 h (r (2) = 0.242, p = 0.004). Lower peri-infarct glutamate was a stronger predictor of worse 3-month clinical outcome (area under the curve (AUC) 0.89, p < 0.001) than DWI volume (AUC = 0.79, p < 0.001).

CONCLUSION

Decreased glutamate, creatine, and NAA concentrations are associated with poor neurological outcome at 24 h and greater disability at 3 months. The significant metabolic variation in salvaged tissue may potentially explain some of the variability seen in stroke recovery despite apparently successful reperfusion.

What is the relationship among penumbra volume, collaterals, and time since onset in the first 6 h after acute ischemic stroke?

Background

The steep, time-dependent loss of benefit from reperfusion in clinical trials is consistent with loss of penumbra over the early hours of ischemia, as observed in animal models. Human imaging studies, however, show persistent penumbra for up to 48 h. We investigated core and penumbra volumes and collateral status in relation to time after stroke onset within the first 6 h.

Methods

Using data from three multimodal computer tomography-based studies in acute ischemic stroke patients <6 h after onset, we measured core and penumbra volumes, collateral status, and target mismatch (defined as core volume < 50 ml, perfusion lesion volume > 15 ml, mismatch ratio > 1.8). Patients were grouped by onset to imaging time (<3, 3–4.5, 4.5–6 h). We explored correlates of penumbra proportion by multivariable linear regression.

Results

Analysis included 144 subjects. Across time epochs, neither proportions of penumbra (59%, 64%, 75% at <3, 3–4.5, >4. 5 h, respectively, p = 0.4) nor poor collaterals (15/56 (27%), 14/47 (30%), 4/15 (27%) at <3, 3–4.5, >4.5 h, p = 0.9) differed significantly. Penumbra proportion was not clearly related to time to imaging ( R2 = 0.003; p = 0.5) but a trend for divergent effects by collateral status was seen (slight increase in penumbra over time with good collaterals versus reduced with poor, interaction = 0.08). The proportion of patients with target mismatch did not vary by time (56%, 74%, and 67% at <3, 3–4.5, >4.5 h, p = 0.09).

Conclusions

In a cross-sectional sample imaged within 6 h, neither the proportions of penumbral tissue nor “target mismatch” varied by time from onset. A trend for reducing penumbra proportion only among those with poor collaterals may have pathophysiological and therapeutic importance.

Influence of Thin Slice Reconstruction on CT Brain Perfusion Analysis

Objectives

Although CT scanners generally allow dynamic acquisition of thin slices (1 mm), thick slice (≥5 mm) reconstruction is commonly used for stroke imaging to reduce data, processing time, and noise level. Thin slice CT perfusion (CTP) reconstruction may suffer less from partial volume effects, and thus yield more accurate quantitative results with increased resolution. Before thin slice protocols are to be introduced clinically, it needs to be ensured that this does not affect overall CTP constancy. We studied the influence of thin slice reconstruction on average perfusion values by comparing it with standard thick slice reconstruction.

Materials and Methods

From 50 patient studies, absolute and relative hemisphere averaged estimates of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and permeability-surface area product (PS) were analyzed using 0.8, 2.4, 4.8, and 9.6 mm slice reconstructions. Specifically, the influence of Gaussian and bilateral filtering, the arterial input function (AIF), and motion correction on the perfusion values was investigated.

Results

Bilateral filtering gave noise levels comparable to isotropic Gaussian filtering, with less partial volume effects. Absolute CBF, CBV and PS were 22%, 14% and 46% lower with 0.8 mm than with 4.8 mm slices. If the AIF and motion correction were based on thin slices prior to reconstruction of thicker slices, these differences reduced to 3%, 4% and 3%. The effect of slice thickness on relative values was very small.

Conclusions

This study shows that thin slice reconstruction for CTP with unaltered acquisition protocol gives relative perfusion values without clinically relevant bias. It does however affect absolute perfusion values, of which CBF and CBV are most sensitive. Partial volume effects in large arteries and veins lead to overestimation of these values. The effects of reconstruction slice thickness should be taken into account when absolute perfusion values are used for clinical decision making.

In Acute Stroke, Can CT Perfusion-Derived Cerebral Blood Volume Maps Substitute for Diffusion-Weighted Imaging in Identifying the Ischemic Core?

Background and Purpose

In the treatment of patients with suspected acute ischemic stroke, increasing evidence suggests the importance of measuring the volume of the irreversibly injured “ischemic core.” The gold standard method for doing this in the clinical setting is diffusion-weighted magnetic resonance imaging (DWI), but many authors suggest that maps of regional cerebral blood volume (CBV) derived from computed tomography perfusion imaging (CTP) can substitute for DWI. We sought to determine whether DWI and CTP-derived CBV maps are equivalent in measuring core volume.

Methods

58 patients with suspected stroke underwent CTP and DWI within 6 hours of symptom onset. We measured low-CBV lesion volumes using three methods: “objective absolute,” i.e. the volume of tissue with CBV below each of six published absolute thresholds (0.9–2.5 mL/100 g), “objective relative,” whose six thresholds (51%-60%) were fractions of mean contralateral CBV, and “subjective,” in which two radiologists (R1, R2) outlined lesions subjectively. We assessed the sensitivity and specificity of each method, threshold, and radiologist in detecting infarction, and the degree to which each over- or underestimated the DWI core volume. Additionally, in the subset of 32 patients for whom follow-up CT or MRI was available, we measured the proportion of CBV- or DWI-defined core lesions that exceeded the follow-up infarct volume, and the maximum amount by which this occurred.

Results

DWI was positive in 72% (42/58) of patients. CBV maps’ sensitivity/specificity in identifying DWI-positive patients were 100%/0% for both objective methods with all thresholds, 43%/94% for R1, and 83%/44% for R2. Mean core overestimation was 156–699 mL for objective absolute thresholds, and 127–200 mL for objective relative thresholds. For R1 and R2, respectively, mean±SD subjective overestimation were -11±26 mL and -11±23 mL, but subjective volumes differed from DWI volumes by up to 117 and 124 mL in individual patients. Inter-rater agreement regarding the presence of infarction on CBV maps was poor (kappa = 0.21). Core lesions defined by the six objective absolute CBV thresholds exceeded follow-up infarct volumes for 81%-100% of patients, by up to 430–1002 mL. Core estimates produced by objective relative thresholds exceeded follow-up volumes in 91% of patients, by up to 210-280 mL. Subjective lesions defined by R1 and R2 exceeded follow-up volumes in 18% and 26% of cases, by up to 71 and 15 mL, respectively. Only 1 of 23 DWI lesions (4%) exceeded final infarct volume, by 3 mL.

Conclusion

CTP-derived CBV maps cannot reliably substitute for DWI in measuring core volume, or even establish which patients have DWI lesions.

Multimodality Imaging of Carotid Stenosis

Four diagnostic modalities are used to image the following internal carotid artery: digital subtraction angiography (DSA), duplex ultrasound (DUS), computed tomography angiography (CTA), and magnetic resonance angiography (MRA). The aim of this article is to describe the potentials of these techniques and to discuss their advantages and disadvantages. Invasive DSA is still considered the gold standard and is an indivisible part of the carotid stenting procedure. DUS is an inexpensive but operator-dependent tool with limited visibility of the carotid artery course. Conversely, CTA and MRA allow assessment of the carotid artery from the aortic arch to intracranial parts. The disadvantages of CTA are radiation and iodine contrast medium administration. MRA is without radiation but contrast-enhanced MRA is more accurate than noncontrast MRA. The choice of methods depends on the clinical indications and the availability of methods in individual centers. However, the general approach to patient with suspected carotid artery stenosis is to first perform DUS and then other noninvasive methods such as CTA, MRA, or transcranial Doppler US.

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

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

Predictors of reperfusion in patients with acute ischemic stroke

BACKGROUND AND PURPOSE

Ischemic stroke studies emphasize a difference between reperfusion and recanalization, but predictors of reperfusion have not been elucidated. The aim of this study was to evaluate the relationship between reperfusion and recanalization and identify predictors of reperfusion.

MATERIALS AND METHODS

From the Dutch Acute Stroke Study, 178 patients were selected with an MCA territory deficit on admission CTP and day 3 follow-up CTP and CTA. Reperfusion was evaluated on CTP, and recanalization on CTA, follow-up imaging. Reperfusion percentages were calculated in patients with and without recanalization. Patient admission and treatment characteristics and admission CT imaging parameters were collected. Their association with complete reperfusion was analyzed by using univariate and multivariate logistic regression.

RESULTS

Sixty percent of patients with complete recanalization showed complete reperfusion (relative risk, 2.60; 95% CI, 1.63-4.13). Approximately one-third of patients showed some discrepancy between recanalization and reperfusion status. Lower NIHSS score (OR, 1.06; 95% CI, 1.01-1.11), smaller infarct core size (OR, 3.11; 95% CI, 1.46-6.66; and OR, 2.40; 95% CI, 1.14-5.02), smaller total ischemic area (OR, 4.20; 95% CI, 1.91-9.22; and OR, 2.35; 95% CI, 1.12-4.91), lower clot burden (OR, 1.35; 95% CI, 1.14-1.58), distal thrombus location (OR, 3.02; 95% CI, 1.76-5.20), and good collateral score (OR, 2.84; 95% CI, 1.34-6.02) significantly increased the odds of complete reperfusion. In multivariate analysis, only total ischemic area (OR, 6.12; 95% CI, 2.69-13.93; and OR, 1.91; 95% CI, 0.91-4.02) was an independent predictor of complete reperfusion.

CONCLUSIONS

Recanalization and reperfusion are strongly associated but not always equivalent in ischemic stroke. A smaller total ischemic area is the only independent predictor of complete reperfusion.

Acute Multi-modal Neuroimaging in a Porcine Model of Endothelin-1-Induced Cerebral Ischemia: Defining the Acute Infarct Core

In a porcine ischemic stroke model, we sought to compare the acute predicted infarct core volume (PIV) defined by CT perfusion (CTP)-hemodynamic parameters and MR-diffusion-weighted imaging (MR-DWI)/apparent diffusion coefficient (ADC), with the true infarct core volume (TIV) as defined by histology. Ten Duroc-cross pigs had a CTP scan prior to injection of endothelin-1 (ET-1) into the left striatum. CTP scans were used to monitor ischemic progression. A second dose of ET-1 was injected 2 h from the first injection. The animal was moved to a 3-T MRI scanner where DWI was performed. CTP imaging was acquired immediately after the MR imaging. Next, the brain was removed and stained with tetrazolium chloride (TTC). Linear regression and Bland-Altman plots were used to correlate the PIV measured by each imaging modality to that of the TIV from the histological gold standard. The CTP-cerebral blood flow (CBF) parameter had the highest R (2) value and slope closest to unity, while the CTP-cerebral blood volume (CBV) had the lowest R(2) value and slope furthest away from unity. The CTP-CBF • CBV product parameter had a higher R(2) value but lower slope than both MR parameers. The best Bland-Altman agreement was observed with the CTP-CBF parameter. PIV from MR-DWI, ADC, and CTP-CBF overestimated the TIV defined with histology. We show that the PIV defined with absolute gray and white matter CT-CBF thresholds correlates best with the TIV and is similar to both MR-DWI and ADC-defined PIVs. Further, the acute CBF • CBV mismatch may not indicate penumbral tissue in the acute stroke setting.

Is CT-Based Perfusion and Collateral Imaging Sensitive to Time Since Stroke Onset?

Purpose

CT-based perfusion and collateral imaging is increasingly used in the assessment of patients with acute stroke. Time of stroke onset is a critical factor in determining eligibility for and benefit from thrombolysis. Animal studies predict that the volume of ischemic penumbra decreases with time. Here, we evaluate if CT is able to detect a relationship between perfusion or collateral status, as assessed by CT, and time since stroke onset.

Materials and methods

We studied 53 consecutive patients with proximal vessel occlusions, mean (SD) age of 71.3 (14.9) years, at a mean (SD) of 125.2 (55.3) minutes from onset, using whole-brain CT perfusion (CTp) imaging. Penumbra was defined using voxel-based thresholds for cerebral blood flow (CBF) and mean transit time (MTT); core was defined by cerebral blood volume (CBV). Normalized penumbra fraction was calculated as Penumbra volume/(Penumbra volume + Core volume) for both CBF and MTT (Pen_CBF and Pen_MTT, respectively). Collaterals were assessed on CT angiography (CTA). CTp ASPECTS score was applied visually, lower scores indicating larger lesions. ASPECTS ratios were calculated corresponding to penumbra fractions.

Results

Both Pen_CBF and Pen_MTT showed decremental trends with increasing time since onset (Kendall’s tau-b = −0.196, p = 0.055, and −0.187, p = 0.068, respectively). The CBF/CBV ASPECTS ratio, which showed a relationship to Pen_CBF (Kendall’s tau-b = 0.190, p = 0.070), decreased with increasing time since onset (Kendall’s tau-b = −0.265, p = 0.006). Collateral response did not relate to time (Kendall’s tau-b = −0.039, p = 0.724).

Conclusion

Even within 4.5 h since stroke onset, a decremental relationship between penumbra and time, but not between collateral status and time, may be detected using perfusion CT imaging. The trends that we demonstrate merit evaluation in larger datasets to confirm our results, which may have potential wider applications, e.g., in the setting of strokes of unknown onset time.

Alteplase versus tenecteplase for thrombolysis after ischaemic stroke (ATTEST): a phase 2, randomised, open-label, blinded endpoint study

BACKGROUND

In most countries, alteplase given within 4·5 h of onset is the only approved medical treatment for acute ischaemic stroke. The newer thrombolytic drug tenecteplase has been investigated in one randomised trial up to 3 h after stroke and in another trial up to 6 h after stroke in patients selected by advanced neuroimaging. In the Alteplase-Tenecteplase Trial Evaluation for Stroke Thrombolysis (ATTEST), we aimed to assess the efficacy and safety of tenecteplase versus alteplase within 4·5 h of stroke onset in a population not selected on the basis of advanced neuroimaging, and to use imaging biomarkers to inform the design of a definitive phase 3 clinical trial.

METHODS

In this single-centre, phase 2, prospective, randomised, open-label, blinded end-point evaluation study, adults with supratentorial ischaemic stroke eligible for intravenous thrombolysis within 4·5 h of onset were recruited from The Institute of Neurological Sciences, Glasgow, Scotland. Patients were randomly assigned (1:1) to receive tenecteplase 0·25 mg/kg (maximum 25 mg) or alteplase 0·9 mg/kg (maximum 90 mg). Treatment allocation used a mixed randomisation and minimisation algorithm including age and National Institutes of Health Stroke Scale score, generated by an independent statistician. Patients were not informed of treatment allocation; treating clinicians were aware of allocation but those assessing the primary outcome were not. Imaging comprised baseline CT, CT perfusion, and CT angiography; and CT plus CT angiography at 24-48 h. The primary endpoint was percentage of penumbra salvaged (CT perfusion-defined penumbra volume at baseline minus CT infarct volume at 24-48 h). Analysis was per protocol. This study is registered with ClinicalTrials.gov, number NCT01472926.

FINDINGS

Between Jan 1, 2012, and Sept 7, 2013, 355 patients were screened, of whom 157 were eligible for intravenous thrombolysis, and 104 patients were enrolled. 52 were assigned to the alteplase group and 52 to tenecteplase. Of 71 patients (35 assigned tenecteplase and 36 assigned alteplase) contributing to the primary endpoint, no significant differences were noted for percentage of penumbral salvaged (68% [SD 28] for the tenecteplase group vs 68% [23] for the alteplase group; mean difference 1·3% [95% CI -9·6 to 12·1]; p=0·81). Neither incidence of symptomatic intracerebral haemorrhage (by SITS-MOST definition, 1/52 [2%] tenecteplase vs 2/51 [4%] alteplase, p=0·55; by ECASS II definition, 3/52 [6%] vs 4/51 [8%], p=0·59) nor total intracerebral haemorrhage events (8/52 [15%] vs 14/51 [29%], p=0·091) differed significantly. The incidence of serious adverse events did not differ between groups (32 in the tenecteplase group, three considered probably or definitely related to drug treatment; 16 in the alteplase group, five were considered drug-related).

INTERPRETATION

Neurological and radiological outcomes did not differ between the tenecteplase and alteplase groups. Evaluation of tenecteplase in larger trials of patients with acute stroke seems warranted.

FUNDING

The Stroke Association.

Endovascular therapy for ischemic stroke with perfusion-imaging selection

BACKGROUND

Trials of endovascular therapy for ischemic stroke have produced variable results. We conducted this study to test whether more advanced imaging selection, recently developed devices, and earlier intervention improve outcomes.

METHODS

We randomly assigned patients with ischemic stroke who were receiving 0.9 mg of alteplase per kilogram of body weight less than 4.5 hours after the onset of ischemic stroke either to undergo endovascular thrombectomy with the Solitaire FR (Flow Restoration) stent retriever or to continue receiving alteplase alone. All the patients had occlusion of the internal carotid or middle cerebral artery and evidence of salvageable brain tissue and ischemic core of less than 70 ml on computed tomographic (CT) perfusion imaging. The coprimary outcomes were reperfusion at 24 hours and early neurologic improvement (≥8-point reduction on the National Institutes of Health Stroke Scale or a score of 0 or 1 at day 3). Secondary outcomes included the functional score on the modified Rankin scale at 90 days.

RESULTS

The trial was stopped early because of efficacy after 70 patients had undergone randomization (35 patients in each group). The percentage of ischemic territory that had undergone reperfusion at 24 hours was greater in the endovascular-therapy group than in the alteplase-only group (median, 100% vs. 37%; P<0.001). Endovascular therapy, initiated at a median of 210 minutes after the onset of stroke, increased early neurologic improvement at 3 days (80% vs. 37%, P=0.002) and improved the functional outcome at 90 days, with more patients achieving functional independence (score of 0 to 2 on the modified Rankin scale, 71% vs. 40%; P=0.01). There were no significant differences in rates of death or symptomatic intracerebral hemorrhage.

CONCLUSIONS

In patients with ischemic stroke with a proximal cerebral arterial occlusion and salvageable tissue on CT perfusion imaging, early thrombectomy with the Solitaire FR stent retriever, as compared with alteplase alone, improved reperfusion, early neurologic recovery, and functional outcome. (Funded by the Australian National Health and Medical Research Council and others; EXTEND-IA ClinicalTrials.gov number, NCT01492725, and Australian New Zealand Clinical Trials Registry number, ACTRN12611000969965.).

Multimodal imaging in acute ischemic stroke

OPINION STATEMENT

Recent years have seen the development of novel neuroimaging techniques whose roles in the management of acute stroke are sometimes confusing and controversial. This may be attributable in part to a focus on establishing simplified algorithms and terminology that omit consideration of the basic pathophysiology of cerebral ischemia and, consequently, of the full potential for optimizing patients' care based upon their individual imaging findings. This review begins by discussing cerebral hemodynamic physiology and of the effects of hemodynamic disturbances upon the brain. Particular attention will be paid to the hemodynamic measurements and markers of tissue injury that are provided by common clinical imaging techniques, with the goal of enabling greater confidence and flexibility in understanding the potential uses of these techniques in various clinical roles, which will be discussed in the remainder of the review.

Prediction of infarction and reperfusion in stroke by flow- and volume-weighted collateral signal in MR angiography

BACKGROUND AND PURPOSE

In proximal anterior circulation occlusive strokes, collateral flow is essential for good outcome. Collateralized vessel intensity in TOF- and contrast-enhanced MRA is variable due to different acquisition methods. Our purpose was to quantify collateral supply by using flow-weighted signal in TOF-MRA and blood volume-weighted signal in contrast-enhanced MRA to determine each predictive contribution to tissue infarction and reperfusion.

MATERIALS AND METHODS

Consecutively (2009-2013), 44 stroke patients with acute proximal anterior circulation occlusion met the inclusion criteria with TOF- and contrast-enhanced MRA and penumbral imaging. Collateralized vessels in the ischemic hemisphere were assessed by TOF- and contrast-enhanced MRA using 2 methods: 1) visual 3-point collateral scoring, and 2) collateral signal quantification by an arterial atlas-based collateral index. Collateral measures were tested by receiver operating characteristic curve and logistic regression against 2 imaging end points of tissue-outcome: final infarct volume and percentage of penumbra saved.

RESULTS

Visual collateral scores on contrast-enhanced MRA but not TOF were significantly higher in patients with good outcome. Visual collateral scoring on contrast-enhanced MRA was the best rater-based discriminator for final infarct volume < 90 mL (area under the curve, 0.81; P < .01) and percentage of penumbra saved >50% (area under the curve, 0.67; P = .04). Atlas-based collateral index of contrast-enhanced MRA was the overall best independent discriminator for final infarct volume of <90 mL (area under the curve, 0.94; P < .01). Atlas-based collateral index combining the signal of TOF- and contrast-enhanced MRA was the overall best discriminator for effective reperfusion (percentage of penumbra saved >50%; area under the curve, 0.89; P < .001).

CONCLUSIONS

Visual scoring of contrast-enhanced but not TOF-MRA is a reliable predictor of infarct outcome in stroke patients with proximal arterial occlusion. By atlas-based collateral assessment, TOF- and contrast-enhanced MRA both contain predictive signal information for penumbral reperfusion. This could improve risk stratification in further studies.

Limited reliability of computed tomographic perfusion acute infarct volume measurements compared with diffusion-weighted imaging in anterior circulation stroke

BACKGROUND AND PURPOSE

Diffusion-weighted imaging (DWI) can reliably identify critically ischemic tissue shortly after stroke onset. We tested whether thresholded computed tomographic cerebral blood flow (CT-CBF) and CT-cerebral blood volume (CT-CBV) maps are sufficiently accurate to substitute for DWI for estimating the critically ischemic tissue volume.

METHODS

Ischemic volumes of 55 patients with acute anterior circulation stroke were assessed on DWI by visual segmentation and on CT-CBF and CT-CBV with segmentation using 15% and 30% thresholds, respectively. The contrast:noise ratios of ischemic regions on the DWI and CT perfusion (CTP) images were measured. Correlation and Bland-Altman analyses were used to assess the reliability of CTP.

RESULTS

Mean contrast:noise ratios for DWI, CT-CBF, and CT-CBV were 4.3, 0.9, and 0.4, respectively. CTP and DWI lesion volumes were highly correlated (R(2)=0.87 for CT-CBF; R(2)=0.83 for CT-CBV; P<0.001). Bland-Altman analyses revealed little systemic bias (-2.6 mL) but high measurement variability (95% confidence interval, ±56.7 mL) between mean CT-CBF and DWI lesion volumes, and systemic bias (-26 mL) and high measurement variability (95% confidence interval, ±64.0 mL) between mean CT-CBV and DWI lesion volumes. A simulated treatment study demonstrated that using CTP-CBF instead of DWI for detecting a statistically significant effect would require at least twice as many patients.

CONCLUSIONS

The poor contrast:noise ratios of CT-CBV and CT-CBF compared with those of DWI result in large measurement error, making it problematic to substitute CTP for DWI in selecting individual acute stroke patients for treatment. CTP could be used for treatment studies of patient groups, but the number of patients needed to identify a significant effect is much higher than the number needed if DWI is used.

A Randomized Controlled Trial of the Effect of Early Upper-Limb Training on Stroke Recovery and Brain Activation

Background. Upper-limb (UL) dysfunction is experienced by up to 75% of patients poststroke. The greatest potential for functional improvement is in the first month. Following reperfusion, evidence indicates that neuroplasticity is the mechanism that supports this recovery. Objective. This preliminary study hypothesized increased activation of putative motor areas in those receiving intensive, task-specific UL training in the first month poststroke compared with those receiving standard care. Methods. This was a single-blinded, longitudinal, randomized controlled trial in adult patients with an acute, first-ever ischemic stroke; 23 participants were randomized to standard care (n = 12) or an additional 30 hours of task-specific UL training in the first month poststroke beginning week 1. Patients were assessed at 1 week, 1 month, and 3 months poststroke. The primary outcome was change in brain activation as measured by functional magnetic resonance imaging. Results. When compared with the standard-care group, the intensive-training group had increased brain activation in the anterior cingulate and ipsilesional supplementary motor areas and a greater reduction in the extent of activation ( P = .02) in the contralesional cerebellum. Intensive training was associated with a smaller deviation from mean recovery at 1 month (Pr>F0 = 0.017) and 3 months (Pr>F = 0.006), indicating more consistent and predictable improvement in motor outcomes. Conclusion. Early, more-intensive, UL training was associated with greater changes in activation in putative motor (supplementary motor area and cerebellum) and attention (anterior cingulate) regions, providing support for the role of these regions and functions in early recovery poststroke.