The infarct core is well represented by the acute diffusion lesion: sustained reversal is infrequent

Computed tomography perfusion as an early predictor of malignant cerebral infarction

INTRODUCTION

Malignant middle cerebral artery infarction (MCI) needs rapid intervention. This study aimed to enhance the prediction of MCI using computed tomography perfusion (CTP) with varied quantitative benchmarks.

MATERIALS AND METHODS

We retrospectively analyzed 253 patients from a single-center registry presenting with acute, severe, proximal large vessel occlusion studied with whole-brain CTP imaging at hospital arrival within the first 24 h of symptoms-onset. MCI was defined by clinical and imaging criteria, including decreased level of consciousness, anisocoria, death due to cerebral edema, or need for decompressive craniectomy, together with midline shift ⩾6 mm, or infarction of more than 50% of the MCA territory. The predictive accuracy of baseline ASPECTS and CTP quantifications for MCI was assessed by receiver operating characteristic (ROC) area under the curve (AUC) while F-score was calculated as an indicator of precision and sensitivity.

RESULTS

Sixty-three out of 253 patients (25%) fulfilled MCI criteria and had worse clinical and imaging results than the non-MCI group. The capacity to predict MCI was lower for baseline ASPECTS (AUC 0.83, F-score 0.52, Youden's index 6), than with perfusion-based measures: relative cerebral blood volume threshold <40% (AUC 0.87, F-score 0.71, Youden's index 34 mL) or relative cerebral blood flow threshold <35% (AUC 0.87, F-score 0.62, Youden's index 67 mL). CTP based on rCBV measurements identified twice as many MCI as baseline CT ASPECTS.

DISCUSSION AND CONCLUSION

CTP-based quantifications may offer enhanced predictive capabilities for MCI compared to non-contrast baseline CT ASPECTS, potentially improving the monitoring of severe ischemic stroke patients at risk of life-threatening edema and its treatment.

Imaging in acute ischaemic stroke: assessing findings in light of evolving therapies

Acute ischaemic stroke (AIS) is a debilitating disease for which effective therapies are now available. Effective identification of candidates for therapy relies heavily on noninvasive imaging that must be interpreted accurately in a short timeframe. This review summarizes the evolution of AIS therapies and the implications for noninvasive imaging. The review concludes with consideration of longstanding assumptions about imaging of ischaemic stroke and potential paradigm shifts on the horizon.

A comprehensive review for artificial intelligence on neuroimaging in rehabilitation of ischemic stroke

Stroke is the second leading cause of death worldwide, with ischemic stroke accounting for a significant proportion of morbidity and mortality among stroke patients. Ischemic stroke often causes disability and cognitive impairment in patients, which seriously affects the quality of life of patients. Therefore, how to predict the recovery of patients can provide support for clinical intervention in advance and improve the enthusiasm of patients for rehabilitation treatment. With the popularization of imaging technology, the diagnosis and treatment of ischemic stroke patients are often accompanied by a large number of imaging data. Through machine learning and Deep Learning, information from imaging data can be used more effectively. In this review, we discuss recent advances in neuroimaging, machine learning, and Deep Learning in the rehabilitation of ischemic stroke.

Long-Term Effect of Mechanical Thrombectomy in Stroke Patients According to Advanced Imaging Characteristics

PURPOSE

Data on long-term effect of mechanical thrombectomy (MT) in patients with large ischemic cores (≥ 70 ml) are scarce. Our study aimed to assess the long-term outcomes in MT-patients according to baseline advanced imaging parameters.

METHODS

We performed a single-centre retrospective cohort study of stroke patients receiving MT between January 1, 2010 and December 31, 2018. We assessed baseline imaging to determine core and mismatch volumes and hypoperfusion intensity ratio (with low ratio reflecting good collateral status) using RAPID automated post-processing software. Main outcomes were cross-sectional long-term mortality, functional outcome and quality of life by May 2020. Analysis were stratified by the final reperfusion status.

RESULTS

In total 519 patients were included of whom 288 (55.5%) have deceased at follow-up (median follow-up time 28 months, interquartile range 1-55). Successful reperfusion was associated with lower long-term mortality in patients with ischemic core volumes ≥ 70 ml (adjusted hazard ratio (aHR) 0.20; 95% confidence interval (95% CI) 0.10-0.44) and ≥ 100 ml (aHR 0.26; 95% CI 0.08-0.87). The effect of successful reperfusion on long-term mortality was significant only in the presence of relevant mismatch (aHR 0.17; 95% CI 0.01-0.44). Increasing reperfusion grade was associated with a higher rate of favorable outcomes (mRS 0-3) also in patients with ischemic core volume ≥ 70 ml (aOR 3.58, 95% CI 1.64-7.83).

CONCLUSION

Our study demonstrated a sustainable benefit of better reperfusion status in patients with large ischemic core volumes. Our results suggest that patient deselection based on large ischemic cores alone is not advisable.

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.

The role of input imaging combination and ADC threshold on segmentation of acute ischemic stroke lesion using U-Net

BACKGROUND

To evaluate the effect of the weighting of input imaging combo and ADC threshold on the performance of the U-Net and to find an optimized input imaging combo and ADC threshold in segmenting acute ischemic stroke (AIS) lesion.

METHODS

This study retrospectively enrolled a total of 212 patients having AIS. Four combos, including ADC-ADC-ADC (AAA), DWI-ADC-ADC (DAA), DWI-DWI-ADC (DDA), and DWI-DWI-DWI (DDD), were used as input images, respectively. Three ADC thresholds including 0.6, 0.8 and 1.8 × 10-3 mm2/s were applied. Dice similarity coefficient (DSC) was used to evaluate the segmentation performance of U-Nets. Nonparametric Kruskal-Wallis test with Tukey-Kramer post-hoc tests were used for comparison. A p < .05 was considered statistically significant.

RESULTS

The DSC significantly varied among different combos of images and different ADC thresholds. Hybrid U-Nets outperformed uniform U-Nets at ADC thresholds of 0.6 × 10-3 mm2/s and 0.8 × 10-3 mm2/s (p < .001). The U-Net with imaging combo of DDD had segmentation performance similar to hybrid U-Nets at an ADC threshold of 1.8 × 10-3 mm2/s (p = .062 to 1). The U-Net using the imaging combo of DAA at the ADC threshold of 0.6 × 10-3 mm2/s achieved the highest DSC in the segmentation of AIS lesion.

CONCLUSIONS

The segmentation performance of U-Net for AIS varies among the input imaging combos and ADC thresholds. The U-Net is optimized by choosing the imaging combo of DAA at an ADC threshold of 0.6 × 10-3 mm2/s in segmentating AIS lesion with highest DSC.

KEY POINTS

• Segmentation performance of U-Net for AIS differs among input imaging combos. • Segmentation performance of U-Net for AIS differs among ADC thresholds. • U-Net is optimized using DAA with ADC = 0.6 × 10-3 mm2/s.

Amide proton transfer imaging in stroke

Amide proton transfer (APT) imaging, a variant of chemical exchange saturation transfer MRI, has shown promise in detecting ischemic tissue acidosis following impaired aerobic metabolism in animal models and in human stroke patients due to the sensitivity of the amide proton exchange rate to changes in pH within the physiological range. Recent studies have demonstrated the possibility of using APT-MRI to detect acidosis of the ischemic penumbra, enabling the assessment of stroke severity and risk of progression, monitoring of treatment progress, and prognostication of clinical outcome. This paper reviews current APT imaging methods actively used in ischemic stroke research and explores the clinical aspects of ischemic stroke and future applications for these methods.

Accuracy of Four Different CT Perfusion Thresholds for Ischemic Core Volume and Location Estimation Using IntelliSpace Portal

Computed tomography perfusion (CTP) is frequently used in the triage of ischemic stroke patients for endovascular thrombectomy (EVT). We aimed to quantify the volumetric and spatial agreement of the CTP ischemic core estimated with different thresholds and follow-up MRI infarct volume on diffusion-weighted imaging (DWI). Patients treated with EVT between November 2017 and September 2020 with available baseline CTP and follow-up DWI were included. Data were processed with Philips IntelliSpace Portal using four different thresholds. Follow-up infarct volume was segmented on DWI. In 55 patients, the median DWI volume was 10 mL, and median estimated CTP ischemic core volumes ranged from 10-42 mL. In patients with complete reperfusion, the intraclass correlation coefficient (ICC) showed moderate-good volumetric agreement (range 0.55-0.76). A poor agreement was found for all methods in patients with successful reperfusion (ICC range 0.36-0.45). Spatial agreement (median Dice) was low for all four methods (range 0.17-0.19). Severe core overestimation was most frequently (27%) seen in Method 3 and patients with carotid-T occlusion. Our study shows moderate-good volumetric agreement between ischemic core estimates for four different thresholds and subsequent infarct volume on DWI in EVT-treated patients with complete reperfusion. The spatial agreement was similar to other commercially available software packages.

Post-reperfusion acute MR diffusion in stroke is a potential predictor for clinical outcome in rats

Middle cerebral artery occlusion (MCAO) models show substantial variability in outcome, introducing uncertainties in the evaluation of treatment effects. Early outcome predictors would be essential for prognostic purposes and variability control. We aimed to compare apparent diffusion coefficient (ADC) MRI data obtained during MCAO and shortly after reperfusion for their potentials in acute-phase outcome prediction. Fifty-nine male rats underwent a 45-min MCAO. Outcome was defined in three ways: 21-day survival; 24 h midline-shift and neurological scores. Animals were divided into two groups: rats surviving 21 days after MCAO (survival group, n = 46) and rats dying prematurely (non-survival/NS group, n = 13). At reperfusion, NS group showed considerably larger lesion volume and lower mean ADC of the initial lesion site (p < 0.0001), while during occlusion there were no significant group differences. At reperfusion, each survival animal showed decreased lesion volume and increased mean ADC of the initial lesion site compared to those during occlusion (p < 10^-6), while NS group showed a mixed pattern. At reperfusion, lesion volume and mean ADC of the initial lesion site were significantly associated with 24 h midline-shift and neurological scores. Diffusion MRI performed soon after reperfusion has a great impact in early-phase outcome prediction, and it works better than the measurement during occlusion.

Imaging of Central Nervous System Ischemia

OBJECTIVE

This article describes imaging modalities used in the evaluation of patients presenting with symptoms of acute ischemic stroke.

LATEST DEVELOPMENTS

The year 2015 marked the beginning of a new era in acute stroke care with the widespread adoption of mechanical thrombectomy. Subsequent randomized controlled trials in 2017 and 2018 brought the stroke community even further into this new territory with the expansion of the eligibility window for thrombectomy using imaging-based patient selection, which led to an increase in the use of perfusion imaging. Now, after several years of routine use, the debate is ongoing as to when this additional imaging is truly required and when it results in unnecessary delays in time-sensitive stroke care. At this time, more than ever, a robust understanding of neuroimaging techniques, applications, and interpretation is essential for the practicing neurologist.

ESSENTIAL POINTS

CT-based imaging is the first step in most centers for the evaluation of patients presenting with symptoms of acute stroke because of its wide availability, speed, and safety. Noncontrast head CT alone is sufficient for IV thrombolysis decision making. CT angiography is very sensitive for the detection of large-vessel occlusion and can be used reliably to make this determination. Advanced imaging including multiphase CT angiography, CT perfusion, MRI, and MR perfusion can provide additional information useful for therapeutic decision making in specific clinical scenarios. In all cases, it is essential that neuroimaging be performed and interpreted rapidly to allow for timely reperfusion therapy.

Neuroimaging of Acute Ischemic Stroke: Multimodal Imaging Approach for Acute Endovascular Therapy

Advances in acute ischemic stroke (AIS) treatment have been contingent on innovations in neuroimaging. Neuroimaging plays a pivotal role in the diagnosis and prognosis of ischemic stroke and large vessel occlusion, enabling triage decisions in the emergent care of the stroke patient. Current imaging protocols for acute stroke are dependent on the available resources and clinicians' preferences and experiences. In addition, differential application of neuroimaging in medical decision-making, and the rapidly growing evidence to support varying paradigms have outpaced guideline-based recommendations for selecting patients to receive intravenous or endovascular treatment. In this review, we aimed to discuss the various imaging modalities and approaches used in the diagnosis and treatment of AIS.

Agreement between estimated computed tomography perfusion ischemic core and follow-up infarct on diffusion-weighted imaging

BACKGROUND

Computed tomography perfusion (CTP) is frequently performed during the diagnostic workup of acute ischemic stroke patients. Yet, ischemic core estimates vary widely between different commercially available software packages. We assessed the volumetric and spatial agreement of the ischemic core on CTP with the follow-up infarct on diffusion-weighted imaging (DWI) using an automated software.

METHODS

We included successfully reperfused patients who underwent endovascular treatment (EVT) with CTP and follow-up DWI between November 2017 and September 2020. CTP data were processed with a fully automated software using relative cerebral blood flow (rCBF) < 30% to estimate the ischemic core. The follow-up infarct was segmented on DWI imaging data, which were acquired at approximately 24 h. Ischemic core on CTP was compared with the follow-up infarct lesion on DWI using intraclass correlation coefficient (ICC) and Dice similarity coefficient (Dice).

RESULTS

In 59 patients, the median estimated core volume on CTP was 16 (IQR 8-47) mL. The follow-up infarct volume on DWI was 11 (IQR 6-42) mL. ICC was 0.60 (95% CI 0.33-0.76), indicating moderate volumetric agreement. Median Dice was 0.20 (IQR 0.01-0.35). The median positive predictive value was 0.24 (IQR 0.05-0.57), and the median sensitivity was 0.3 (IQR 0.13-0.47). Severe core overestimation on computed tomography perfusion > 50 mL occurred in 4/59 (7%) of the cases.

CONCLUSIONS

In patients with successful reperfusion after EVT, CTP-estimated ischemic core showed moderate volumetric and spatial agreement with the follow-up infarct lesion on DWI, similar to the most used commercially available CTP software packages. Severe ischemic core overestimation was relatively uncommon.

Clinical Impact and Predictors of Diffusion Weighted Imaging (DWI) Reversal in Stroke Patients with Diffusion Weighted Imaging Alberta Stroke Program Early CT Score 0-5 Treated by Thrombectomy : Diffusion Weighted Imaging Reversal in Large Volume Stroke

PURPOSE

To determine whether reversal of DWI lesions (DWIr) on the DWI-ASPECTS (diffusion weighted imaging Alberta Stroke Program CT Score) template should serve as a predictor of 90-day clinical outcome in acute ischemic stroke (AIS) patients with pretreatment diffusion-weighted imaging (DWI)-ASPECTS 0-5 treated with thrombectomy, and to determine its predictors in current practice.

METHODS

We analyzed data of all consecutive patients included in the prospective multicenter national Endovascular Treatment in Ischemic Stroke Registry between 1 January 2015 and 31 December 2020 with a premorbid mRS ≤ 2, who presented with a pretreatment DWI-ASPECTS 0-5 score, underwent thrombectomy and had an available 24 h post-interventional MRI follow-up. Multivariable analyses were performed to evaluate the clinical impact of DWIr on early neurological improvement (ENI), 3‑month modified Rankin scale (mRS) score distribution (shift analysis) and to define independent predictors of DWIr.

RESULTS

Early neurological improvement was detected in 82/211 (41.7%) of patients while 3‑month functional independence was achieved by 75 (35.5%) patients. The DWI reversal (39/211, 18.9%) resulted an independent predictor of both ENI (aOR 3.6, 95% CI 1.2-7.7; p 0.018) and 3‑month clinical outcome (aOR for mRS shift: 2.2, 95% CI 1-4.6; p 0.030). Only successful recanalization (mTICI 2c-3) independently predicted DWIr in the studied population (aOR 3.3, 95% CI 1.3-7.9; p 0.009).

CONCLUSION

The DWI reversal occurs in a non-negligible proportion of DWI-ASPECTS 0-5 patients subjected to thrombectomy and significantly influences clinical outcome. The mTICI 2c-3 recanalization emerged as an independent DWIr predictor.

ADC Level is Related to DWI Reversal in Patients Undergoing Mechanical Thrombectomy: A Retrospective Cohort Study

BACKGROUND AND PURPOSE

In patients with ischemic stroke, DWI lesions can occasionally be reversed by reperfusion therapy. This study aimed to ascertain the relationship between ADC levels and DWI reversal in patients with acute ischemic stroke who underwent recanalization treatment.

MATERIALS AND METHODS

We conducted a retrospective cohort study in patients with acute ischemic stroke who underwent endovascular mechanical thrombectomy with successful recanalization between April 2017 and March 2021. DWI reversal was assessed through follow-up MR imaging approximately 24 hours after treatment.

RESULTS

In total, 118 patients were included. DWI reversal was confirmed in 42 patients. The ADC level in patients with reversal was significantly higher than that in patients without reversal. Eighty-three percent of patients with DWI reversal areas had mean ADC levels of ≥520 × 10^-6 mm²/s, and 71% of patients without DWI reversal areas had mean ADC levels of <520 × 10^-6 mm²/s. The mean ADC threshold was 520 × 10^-6 mm²/s with a sensitivity and specificity of 71% and 83%, respectively. In multivariate analysis, the mean ADC level (OR, 1.023; 95% CI, 1.013-1.033; P < .0001) was independently associated with DWI reversal. Patients with DWI reversal areas had earlier neurologic improvement (NIHSS at 7 days) than patients without reversal areas (P < .0001).

CONCLUSIONS

In acute ischemic stroke, the ADC value is independently associated with DWI reversal. Lesions with a mean ADC of ≥520 × 10^-6 mm²/s are salvageable by mechanical thrombectomy, and DWI reversal areas regain neurologic function. The ADC value is easily assessed and is a useful tool to predict viable lesions.

Diabetes is an Independent Growth Factor of Ischemic Stroke During Reperfusion Phase Leading to Poor Clinical Outcome

OBJECTIVES

Despite the success of recanalization by bridging therapy, about half of treated stroke patients remain disabled. While numerous reports propose clinical predictors of stroke clinical outcome in this context, we originally aimed to study pre-therapeutic factors influencing infarct growth (IG) and poor clinical outcome in strokes due to large vessel occlusion (LVO) successfully recanalized.

MATERIALS AND METHODS

We enrolled 87 consecutive successfully recanalized patients (mTICI: 2b/2c/3) by mechanical thrombectomy (±rt-PA) after stroke due to middle cerebral artery (M1) occlusion within 6 h according to AHA guidelines. IG was defined by subtracting the initial DWI volume to the final 24 h-TDM volume. Statistical associations between poor clinical outcome (mRS≥2), IG and pertinent clinico-radiological variables, were measured using logistic and linear regression models.

RESULTS

Among 87 enrolled patients (Age(y): 68.4 ± 17.5; NIHSS: 16.0 ± 5.4), 42/87 (48,28%) patients had a mRS ≥ 2 at 3 months. Diabetic history (OR: 3.70 CI95%[1.03;14.29] and initial NIHSS (/1 point: OR: 1.16 CI95%[1.05;1.27]) were independently associated with poor outcome. IG was significantly higher in stroke patients with poor outcome (+7.57 ± 4.52 vs -7.81 ± 1.67; p = 0.0024). Initial volumes were not significantly different (mRS≥2: 16.18 ± 2.67; mRS[0-1]: 14.70 ± 2.30; p = 0.6771). Explanatory variables of IG in linear regression were diabetic history (β: 21.26 CI95%[5.43; 37.09]) and NIHSS (β: 0.83 CI95%[0.02; 1.64]). IG was higher in diabetic stroke patients (23.54 ± 1.43 vs -6.20 ± 9.36; p = 0.0061).

CONCLUSIONS

We conclude that diabetes leads to continued IG after complete recanalization, conditioning clinical outcome in LVO strokes successfully recanalized by bridging therapy. We suggest that poor tissular reperfusion by diabetic microangiopathy could explain this result.

Comparison of Two Automated Computed Tomography Perfusion Applications to Predict the Final Infarct Volume After Thrombolysis in Cerebral Infarction 3 Recanalization

BACKGROUND AND PURPOSE

Several automated computed tomography perfusion software applications have been developed to provide support in the definition of ischemic core and penumbra in acute ischemic stroke. However, the degree of interchangeability between software packages is not yet clear. Our study aimed to evaluate 2 commonly used automated perfusion software applications (Syngo.via and RAPID) for the indication of ischemic core with respect to the follow-up infarct volume (FIV) after successful recanalization and with consideration of the clinical impact.

METHODS

Retrospectively, 154 patients with large vessel occlusion of the middle cerebral artery or the internal carotid artery, who underwent endovascular therapy with a consequent Thrombolysis in Cerebral Infarction 3 result within 2 hours after computed tomography perfusion, were included. Computed tomography perfusion core volumes were assessed with both software applications with different thresholds for relative cerebral blood flow (rCBF). The results were compared with the FIV on computed tomography within 24 to 36 hours after recanalization. Bland-Altman was applied to display the levels of agreement and to evaluate systematic differences.

RESULTS

Highest correlation between ischemic core volume and FIV without significant differences was found at a threshold of rCBF<38% for the RAPID software (r=0.89, P<0.001) and rCBF<25% for the Syngo software (r=0.87, P<0.001). Bland-Altman analysis revealed best agreement in these settings. In the vendor default settings (rCBF<30% for RAPID and rCBF<20% for Syngo) correlation between ischemic core volume and FIV was also high (RAPID: r=0.88, Syngo: r=0.86, P<0.001), but mean differences were significant (P<0.001). The risk of critical overestimation of the FIV was higher with rCBF<38% (RAPID) and rCBF<25% (Syngo) than in the default settings.

CONCLUSIONS

By adjusting the rCBF thresholds, comparable results with reliable information on the FIV after complete recanalization can be obtained both with the RAPID and Syngo software. Keeping the software specific default settings means being more inclusive in patient selection, but forgo the highest possible accuracy in the estimation of the FIV.

Outcomes of Mechanical Thrombectomy in Patients with Large Diffusion-Weighted Imaging Lesions

Objective

Despite many advancements in endovascular treatment, the benefits of mechanical thrombectomy (MT) in patients with large infarctions remain uncertain due to hemorrhagic complications. Therefore, we aimed to investigate the efficacy and safety of recanalization via MT within 6 hours after stroke in patients with large cerebral infarction volumes (>70 mL).

Methods

We retrospectively reviewed the medical data of 30 patients with large lesions on initial diffusion-weighted imaging (>70 mL) who underwent MT at our institution within 6 hours after stroke onset. Baseline data, recanalization rate, and 3-month clinical outcomes were analyzed. Successful recanalization was defined as a modified treatment in cerebral ischemia score of 2b or 3.

Results

The recanalization rate was 63.3%, and symptomatic intracerebral hemorrhage occurred in six patients (20%). The proportion of patients with modified Rankin Scale (mRS) scores of 0-3 was significantly higher in the recanalization group than in the non-recanalization group (47.4% vs. 9.1%, p=0.049). The mortality rate was higher in the non-recanalization group, this difference was not significant (15.8% vs. 36.4%, p=0.372). In the analysis of 3-month clinical outcomes, only successful recanalization was significantly associated with mRS scores of 0-3 (90% vs. 50%, p=0.049). The odds ratio of recanalization for favorable outcomes (mRS 0-3) was 9.00 (95% confidence interval, 0.95-84.90; p=0.055).

Conclusion

Despite the risk of symptomatic intracerebral hemorrhage, successful recanalization via MT 6 hours after stroke may improve clinical outcomes in patients with large vessel occlusion.

Prediction of Tissue Damage Using a User-Independent Machine Learning Algorithm vs. Tmax Threshold Maps

(1) Background: To test the accuracy of a fully automated stroke tissue estimation algorithm (FASTER) to predict final lesion volumes in an independent dataset in patients with acute stroke; (2) Methods: Tissue-at-risk prediction was performed in 31 stroke patients presenting with a proximal middle cerebral artery occlusion. FDA-cleared perfusion software using the AHA recommendation for the Tmax threshold delay was tested against a prediction algorithm trained on an independent perfusion software using artificial intelligence (FASTER). Following our endovascular strategy to consequently achieve TICI 3 outcome, we compared patients with complete reperfusion (TICI 3) vs. no reperfusion (TICI 0) after mechanical thrombectomy. Final infarct volume was determined on a routine follow-up MRI or CT at 90 days after the stroke; (3) Results: Compared to the reference standard (infarct volume after 90 days), the decision forest algorithm overestimated the final infarct volume in patients without reperfusion. Underestimation was observed if patients were completely reperfused. In cases where the FDA-cleared segmentation was not interpretable due to improper definitions of the arterial input function, the decision forest provided reliable results; (4) Conclusions: The prediction accuracy of automated tissue estimation depends on (i) success of reperfusion, (ii) infarct size, and (iii) software-related factors introduced by the training sample. A principal advantage of machine learning algorithms is their improved robustness to artifacts in comparison to solely threshold-based model-dependent software. Validation on independent datasets remains a crucial condition for clinical implementations of decision support systems in stroke imaging.

Ischemic Penumbra: A Personal View

The concept of the ischemic penumbra was defined over 40 years ago by Lindsay Symon and his group and is now an established principle of all acute ischemic stroke therapies. These reperfusion treatments rescue threatened, critically hypoperfused brain tissue and have been proven to improve clinical outcomes. We have been fortunate to have observed and played a small part in the penumbral story from its beginnings in the 1970s to its pivotal position today. Over this period, we have witnessed penumbral imaging evolve from positron emission tomography through to magnetic resonance imaging and now predominantly computed tomography perfusion, with the advent of automated imaging facilitating case selection for reperfusion therapies. We and others have conducted clinical trials using penumbral imaging to extend the time window for intravenous thrombolysis and select patients for thrombectomy. Together with the concept of fast- and slow-growing ischemic infarct patterns, this embeds the penumbral principle in everyday clinical management. The opportunity now exists to make penumbral imaging even more portable, affordable, and more widely available using mobile platforms, novel imaging techniques, digital linkage, and artificial intelligence.

AIFNet: Automatic vascular function estimation for perfusion analysis using deep learning

Perfusion imaging is crucial in acute ischemic stroke for quantifying the salvageable penumbra and irreversibly damaged core lesions. As such, it helps clinicians to decide on the optimal reperfusion treatment. In perfusion CT imaging, deconvolution methods are used to obtain clinically interpretable perfusion parameters that allow identifying brain tissue abnormalities. Deconvolution methods require the selection of two reference vascular functions as inputs to the model: the arterial input function (AIF) and the venous output function, with the AIF as the most critical model input. When manually performed, the vascular function selection is time demanding, suffers from poor reproducibility and is subject to the professionals' experience. This leads to potentially unreliable quantification of the penumbra and core lesions and, hence, might harm the treatment decision process. In this work we automatize the perfusion analysis with AIFNet, a fully automatic and end-to-end trainable deep learning approach for estimating the vascular functions. Unlike previous methods using clustering or segmentation techniques to select vascular voxels, AIFNet is directly optimized at the vascular function estimation, which allows to better recognise the time-curve profiles. Validation on the public ISLES18 stroke database shows that AIFNet almost reaches inter-rater performance for the vascular function estimation and, subsequently, for the parameter maps and core lesion quantification obtained through deconvolution. We conclude that AIFNet has potential for clinical transfer and could be incorporated in perfusion deconvolution software.

Acute Stroke Imaging Research Roadmap IV: Imaging Selection and Outcomes in Acute Stroke Clinical Trials and Practice

BACKGROUND AND PURPOSE

The Stroke Treatment Academic Industry Roundtable (STAIR) sponsored an imaging session and workshop during the Stroke Treatment Academic Industry Roundtable XI via webinar on October 1 to 2, 2020, to develop consensus recommendations, particularly regarding optimal imaging at primary stroke centers.

METHODS

This forum brought together stroke neurologists, neuroradiologists, neuroimaging research scientists, members of the National Institute of Neurological Disorders and Stroke, industry representatives, and members of the US Food and Drug Administration to discuss imaging priorities in the light of developments in reperfusion therapies, particularly in an extended time window, and reinvigorated interest in brain cytoprotection trials.

RESULTS

The imaging session summarized and compared the imaging components of recent acute stroke trials and debated the optimal imaging strategy at primary stroke centers. The imaging workshop developed consensus recommendations for optimizing the acquisition, analysis, and interpretation of computed tomography and magnetic resonance acute stroke imaging, and also recommendations on imaging strategies for primary stroke centers.

CONCLUSIONS

Recent positive acute stroke clinical trials have extended the treatment window for reperfusion therapies using imaging selection. Achieving rapid and high-quality stroke imaging is therefore critical at both primary and comprehensive stroke centers. Recommendations for enhancing stroke imaging research are provided.

Predicting Infarct Core From Computed Tomography Perfusion in Acute Ischemia With Machine Learning: Lessons From the ISLES Challenge

BACKGROUND AND PURPOSE

The ISLES challenge (Ischemic Stroke Lesion Segmentation) enables globally diverse teams to compete to develop advanced tools for stroke lesion analysis with machine learning. Detection of irreversibly damaged tissue on computed tomography perfusion (CTP) is often necessary to determine eligibility for late-time-window thrombectomy. Therefore, the aim of ISLES-2018 was to segment infarcted tissue on CTP based on diffusion-weighted imaging as a reference standard.

METHODS

The data, from 4 centers, consisted of 103 cases of acute anterior circulation large artery occlusion stroke who underwent diffusion-weighted imaging rapidly after CTP. Diffusion-weighted imaging lesion segmentation was performed manually and acted as a reference standard. The data were separated into 63 cases for training and 40 for testing, upon which quality metrics (dice score coefficient, Hausdorff distance, absolute lesion volume difference, etc) were computed to rank methods based on their overall performance.

RESULTS

Twenty-four different teams participated in the challenge. Median time to CTP was 185 minutes (interquartile range, 180-238), the time between CTP and magnetic resonance imaging was 36 minutes (interquartile range, 25-79), and the median infarct lesion size was 15.2 mL (interquartile range, 5.7-45). The best performance for Dice score coefficient and absolute volume difference were 0.51 and 10.1 mL, respectively, from different teams. Based on the ranking criteria, the top team's algorithm demonstrated for average Dice score coefficient and average absolute volume difference 0.51 and 10.2 mL, respectively, outperforming the conventional threshold-based method (dice score coefficient, 0.3; volume difference, 15.3). Diverse algorithms were used, almost all based on deep learning, with top-ranked approaches making use of the raw perfusion data as well as methods to synthetically generate complementary information to boost prediction performance.

CONCLUSIONS

Machine learning methods may predict infarcted tissue from CTP with improved accuracy compared with threshold-based methods used in clinical routine. This dataset will remain public and can be used to test improvement in algorithms over time.

Current perspectives on neuroimaging techniques used to identify stroke mimics in clinical practice

INTRODUCTION

Urgent clinical assessment and brain imaging are essential for differentiating stroke mimics from stroke and to avoid unnecessary initiation of reperfusion and other therapies in stroke mimic patients.

AREAS COVERED

In this article, the authors will review acute stroke imaging and then the imaging patterns of the most common stroke mimics. The authors have focused our review on brain CT scan, and more specifically CT perfusion, as this is the most commonly available and emerging tool in emergency settings. The authors also provide information on acute brain MRI and MR perfusion.

EXPERT OPINION

Imaging can contribute to the detection and diagnosis of acute stroke mimics. Knowledge of imaging findings in different stroke mimics can help distinguish these from patients with stroke who require timely reperfusion therapy. CT and MRI perfusion and diffusion-weighted imaging (DWI) MRI are useful imaging modalities for the assessment of acute stroke patients as they provide more accurate information than plain CT scan. Some of these modalities should be available in the emergency setting. The authors recommended CT perfusion as a useful tool for stroke management and differentiation with stroke mimics.

Diffusion weighted imaging in acute ischemic stroke: A review of its interpretation pitfalls and advanced diffusion imaging application

Diffusion weighted imaging (DWI) is a widely used imaging technique to evaluate patients with stroke. It can detect brain ischemia within minutes of stroke onset. However, DWI has few potential pitfalls that should be recognized during interpretation. DWI lesion could be reversible in the early hours of stroke and the entire lesion may not represent ischemic core. False negative DWI could lead to diagnosis of DWI negative stroke or to a missed stroke diagnosis. Ischemic stroke mimics can occur on DWI with non-cerebrovascular neurological conditions. In this article, the history of DWI, its clinical applications, and potential pitfalls for use in acute ischemic stroke are reviewed. Advanced diffusion imaging techniques with reference to Diffusion Kurtosis Imaging and Diffusion Tensor Imaging that has been studied to evaluate ischemic core are discussed.

Diagnosis and Management of Transient Ischemic Attack and Acute Ischemic Stroke: A Review

IMPORTANCE

Stroke is the fifth leading cause of death and a leading cause of disability in the United States, affecting nearly 800 000 individuals annually.

OBSERVATIONS

Sudden neurologic dysfunction caused by focal brain ischemia with imaging evidence of acute infarction defines acute ischemic stroke (AIS), while an ischemic episode with neurologic deficits but without acute infarction defines transient ischemic attack (TIA). An estimated 7.5% to 17.4% of patients with TIA will have a stroke in the next 3 months. Patients presenting with nondisabling AIS or high-risk TIA (defined as a score ≥4 on the age, blood pressure, clinical symptoms, duration, diabetes [ABCD2] instrument; range, 0-7 [7 indicating worst stroke risk]), who do not have severe carotid stenosis or atrial fibrillation, should receive dual antiplatelet therapy with aspirin and clopidigrel within 24 hours of presentation. Subsequently, combined aspirin and clopidigrel for 3 weeks followed by single antiplatelet therapy reduces stroke risk from 7.8% to 5.2% (hazard ratio, 0.66 [95% CI, 0.56-0.77]). Patients with symptomatic carotid stenosis should receive carotid revascularization and single antiplatelet therapy, and those with atrial fibrillation should receive anticoagulation. In patients presenting with AIS and disabling deficits interfering with activities of daily living, intravenous alteplase improves the likelihood of minimal or no disability by 39% with intravenous recombinant tissue plasminogen activator (IV rtPA) vs 26% with placebo (odds ratio [OR], 1.6 [95% CI, 1.1-2.6]) when administered within 3 hours of presentation and by 35.3% with IV rtPA vs 30.1% with placebo (OR, 1.3 [95% CI, 1.1-1.5]) when administered within 3 to 4.5 hours of presentation. Patients with disabling AIS due to anterior circulation large-vessel occlusions are more likely to be functionally independent when treated with mechanical thrombectomy within 6 hours of presentation vs medical therapy alone (46.0% vs 26.5%; OR, 2.49 [95% CI, 1.76-3.53]) or when treated within 6 to 24 hours after symptom onset if they have a large ratio of ischemic to infarcted tissue on brain magnetic resonance diffusion or computed tomography perfusion imaging (modified Rankin Scale score 0-2: 53% vs 18%; OR, 4.92 [95% CI, 2.87-8.44]).

CONCLUSIONS AND RELEVANCE

Dual antiplatelet therapy initiated within 24 hours of symptom onset and continued for 3 weeks reduces stroke risk in select patients with high-risk TIA and minor stroke. For select patients with disabling AIS, thrombolysis within 4.5 hours and mechanical thrombectomy within 24 hours after symptom onset improves functional outcomes.

Advances in imaging acute ischemic stroke: evaluation before thrombectomy

Recent advances in neuroimaging have demonstrated significant assessment benefits and appropriate triage of patients based on specific clinical and radiological features in the acute stroke setting. Endovascular thrombectomy is arguably the most important aspect of acute stroke management with an extended time window. Imaging-based physiological information may potentially shift the treatment paradigm from a rigid time-based model to a more flexible and individualized, tissue-based approach, increasing the proportion of patients amenable to treatment. Various imaging modalities are routinely used in the diagnosis and management of acute ischemic stroke, including multimodal computed tomography (CT) and magnetic resonance imaging (MRI). Therefore, these imaging methods should provide information beyond the presence or absence of intracranial hemorrhage as well as the presence and extent of the ischemic core, collateral circulation and penumbra in patients with neurological symptoms. Target mismatch may optimize selection of patients with late or unknown symptom onset who would potentially be eligible for revascularization therapy. The purpose of this study was to provide a comprehensive review of the current evidence about efficacy and theoretical basis of present imaging modalities, and explores future directions for imaging in the management of acute ischemic stroke.

Automated estimation of ischemic core prior to thrombectomy: comparison of two current algorithms

PURPOSE

Endovascular thrombectomy (EVT) improves clinical outcomes in ischemic stroke with large vessel occlusion. Clinical benefits are inversely proportional to size of the pre-treatment ischemic core. This study compared estimated ischemic core volumes by two different CT perfusion (CTP) automated algorithms to the gold standard follow-up infarct volume using diffusion-weighted imaging (DWI) to assess for congruence, and thus eligibility for EVT.

METHODS

Retrospective, single-center cohort study of 102 patients presenting to a comprehensive stroke center between 2012 and 2018. Inclusion criteria were CT perfusion prior to EVT, successful EVT with mTIBI 2b-3 reperfusion, and DWI post-EVT. CTP data were retrospectively processed by two algorithms: "delay and dispersion insensitive deconvolution" (DISD, RAPID software) versus "delay and dispersion corrected single value decomposition" (ddSVD, Mistar software), using commercially available software. Core volumes were compared to follow up DWI using independent software (MRIcron). Agreement between each algorithm and DWI was estimated using Lin's concordance coefficient and analyzed using reduced major axis regression.

RESULTS

We included 102 patients. Both algorithms had excellent agreement with DWI (Lin's concordance coefficients: DISD 0.8 (95% CI: 0.73; 0.87), ddSVD 0.92 (95% CI: 0.89; 0.95). Compared to ddSVD (reduced major axis slope = 0.95), DISD exhibited a larger extent of proportional bias (slope = 1.12).

CONCLUSION

The ddSVD algorithm better correlates with DWI follow-up infarct volume than DISD processing. The DISD algorithm overestimated larger ischemic cores which may lead to patient exclusion from thrombectomy based on selection by core volume.

Identifying large ischemic core volume ranges in acute stroke that can benefit from mechanical thrombectomy

BACKGROUND

We aimed to identify the large ischemic core (LIC) volume ranges in acute ischemic stroke patients that can benefit from mechanical thrombectomy (MT).

METHODS

Consecutive patients within 24 hours of onset of anterior circulation ischemic stroke with large vessel occlusion and ischemic core volumes of 70-300 mL were included from our single-center prospective database from March 2014 to December 2019. Subjects were divided into three groups by baseline ischemic core volume (A: 70-100 mL; B: 101-130 mL; C: >130 mL). We compared modified Rankin Scale (mRS) score 0-2 at 3 months and parenchymal hematoma between patients receiving MT and standard medical treatment (SMT), and determined clinically treatable core volume ranges for MT.

RESULTS

Of 157 patients (86 women; median age, 81 years; median ischemic core volume, 123 mL), 49 patients underwent MT. In Group A (n=52), MT patients (n=31) showed a higher proportion of mRS 0-2 at 3 months (52% vs 5%, P<0.05) versus SMT, respectively. Group B (n=36) MT patients (n=14) also had a higher proportion of mRS 0-2 at 3 months (29% vs 9%, P=0.13) versus SMT, respectively. In Group C (n=69), only four patients received MT. The 95% confidence intervals for the probability of mRS 0-2 at 3 months in patients with MT (n=49) versus SMT (n=108) intersected at 120-130 mL.

CONCLUSIONS

Ischemic core volumes between 70 and 100 mL may benefit from MT. The treatable upper core limit is approximately 120 mL in selected patients with LIC of 70-300 mL.

Which Imaging Approach Should Be Used for Stroke of Unknown Time of Onset?

Reperfusion therapy with intravenous thrombolysis or mechanical thrombectomy is effective in improving outcome for ischemic stroke but remains underused. Patients presenting with stroke of unknown onset are a common clinical scenario and a common reason for not offering reperfusion therapy. Recent studies have demonstrated the efficacy of reperfusion therapy in stroke of unknown time of onset, when guided by advanced brain imaging. However, translation into clinical practice is challenged by variability in the available data. Comparison between studies is difficult because of use of different imaging modalities (magnetic resonance imaging or computed tomography), different imaging paradigms (imaging biomarkers of lesion age versus imaging biomarkers of tissue viability), and different populations studied (ie, both patients with large vessel occlusion or those with less severe strokes). Physicians involved in acute stroke care are faced with the key question of which imaging approach they should use to guide reperfusion treatment for stroke with unknown time of onset. In this review, we provide an overview of the available evidence for selecting and treating patients with strokes of unknown onset, based on the underlying imaging concepts. The perspective provided is from the viewpoint of the clinician seeing these patients acutely, to provide pragmatic recommendations for clinical practice.

The ischemic penumbra: From concept to reality

The discovery that brain tissue could potentially be salvaged from ischaemia due to stroke, has led to major advances in the development of therapies for ischemic stroke. In this review, we detail the advances in the understanding of this area termed the ischaemic penumbra, from its discovery to the evolution of imaging techniques, and finally some of the treatments developed. Evolving from animal studies from the 70s and 80s and translated to clinical practice, the field of ischemic reperfusion therapy has largely been guided by an array of imaging techniques developed to positively identify the ischemic penumbra, including positron emission tomography, computed tomography and magnetic resonance imaging. More recently, numerous penumbral identification imaging studies have allowed for a better understanding of the progression of the ischaemic core at the expense of the penumbra, and identification of patients than can benefit from reperfusion therapies in the acute phase. Importantly, 40 years of critical imaging research on the ischaemic penumbra have allowed for considerable extension of the treatment time window and better patient selection for reperfusion therapy. The translation of the penumbra concept into routine clinical practice has shown that "tissue is at least as important as time."

Predictors of malignant middle cerebral artery infarction after mechanical thrombectomy

INTRODUCTION

Several predictors have been described to early diagnose malignant middle cerebral artery infarction (MMI) and select patient for hemicraniectomy. Nevertheless, few studies have assessed them among patients with acute ischemic stroke undergoing mechanical endovascular thrombectomy (MET). The overall objective in this study was to evaluate these predictors in patients undergoing MET in the purpose to guide the medical care in the acute phase.

METHODS

We selected patients from a prospective local database which reference all patients eligible for treatment with Alteplase thrombolysis and/or mechanical endovascular thrombectomy in acute stroke. We investigated demographic, clinical, and radiological data. Multivariate regression analysis was used to identify clinical and imaging predictors of MMI.

RESULTS

In 32 months, 66 patients were included. Eighteen (27.3%) developed MMI. Malignant evolution was associated with: severity of neurological deficit and level of consciousness at admission, infarct size in DWI sequence and involvement of other vascular territories. Study groups didn't differ in terms of successful reperfusion. Two variables were identified as independent predictors of MMI: DWI infarct volume (p<0.001) and time to thrombectomy (p=0.018). A decision tree based on these two factors was able to predict malignant evolution with high specificity (100%) and sensibility (73%).

CONCLUSION

Our study proposes a practical decision tree including DWI lesion volume and delay before thrombectomy to early and accurately predict MMI in a subgroup of patients with MCA infarction undergoing MET regardless to the status of reperfusion.

Within-lesion heterogeneity of subcortical DWI lesion evolution, and stroke outcome: A voxel-based analysis

The fate of subcortical diffusion-weighted imaging (DWI) lesions in stroke patients is highly variable, ranging from complete tissue loss to no visible lesion on follow-up. Little is known about within-lesion heterogeneity and its relevance for stroke outcome. Patients with subcortical stroke and recruited through the prospective DEDEMAS study (NCT01334749) were examined at baseline (n = 45), six months (n = 45), and three years (n = 28) post-stroke. We performed high-resolution structural MRI including DWI. Tissue fate was determined voxel-wise using fully automated tissue segmentation. Within-lesion heterogeneity at baseline was assessed by free water diffusion imaging measures. The majority of DWI lesions (66%) showed cavitation on six months follow-up but the proportion of tissue turning into a cavity was small (9 ± 13.5% of the DWI lesion). On average, 69 ± 25% of the initial lesion resolved without any visually apparent signal abnormality. The extent of cavitation at six months post-stroke was independently associated with clinical outcome, i.e. modified Rankin scale score at six months (OR = 4.71, p = 0.005). DWI lesion size and the free water-corrected tissue mean diffusivity at baseline independently predicted cavitation. In conclusion, the proportion of cavitating tissue is typically small, but relevant for clinical outcome. Within-lesion heterogeneity at baseline on advanced diffusion imaging is predictive of tissue fate.

Thrombolysis beyond 4.5 h in Acute Ischemic Stroke

PURPOSE OF REVIEW

The purpose of this article is to review the current approaches using neuroimaging techniques to expand eligibility for intravenous thrombolytic therapy in acute ischemic stroke patients with stroke of unknown symptom onset.

RECENT FINDINGS

In recent years, several randomized, placebo-controlled trials have shown neuroimaging-guided approaches to be feasible in determining eligibility for alteplase beyond 4.5 h from last known well, and efficacious for reducing disability. DWI-FLAIR mismatch on MRI is an effective tool to identify stroke lesions less than 4.5 h in onset in patients with stroke of unknown symptom onset. Additionally, an automated perfusion-based approach, assessing for a disproportionate amount of salvageable tissue, is effective in identifying patients likely to benefit from late window alteplase treatment. In patients with stroke of unknown symptom onset, an individualized approach using neuroimaging to determine time of stroke onset or presence of salvageable brain tissue is feasible in the acute setting and associated with improved long-term outcomes.

Association of pretreatment pontine infarction with extremely poor outcome after endovascular thrombectomy in acute basilar artery occlusion

BACKGROUND

The association between pretreatment brain stem infarction and thrombectomy outcomes remains to be elucidated in patients with acute basilar artery occlusion (BAO). We aimed to assess the association between pretreatment pontine infarction and extremely poor outcome in patients who underwent endovascular thrombectomy due to acute BAO.

METHODS

We retrospectively reviewed data from a stroke database to identify patients with acute BAO who underwent thrombectomy between January 2011 and August 2019. Patient characteristics, pretreatment diffusion-weighted imaging (DWI) data, and outcomes were evaluated. The largest infarct core was expressed as the percentage of infarct core area in each brain stem region on the DWI slice displaying the largest lesion. Extremely poor outcome was defined as a 90-day modified Rankin Scale score of 5 or 6.

RESULTS

A total of 113 patients were included, 37 of whom had extremely poor outcome. Among the 15 patients with extensive pontine infarction (largest pontine infarct core of ≥70%), 93.3% had extremely poor outcome. Multivariate logistic regression analysis revealed that the following variables were independent predictors of extremely poor outcome: extensive pontine infarction (adjusted OR 22.494; 95% CI 2.335 to 216.689; p=0.007), posterior circulation ASPECTS on DWI (adjusted OR per 1-point decrease 1.744; 95% CI 1.197 to 2.541; p=0.004), age (adjusted OR per 1-year increase 1.067; 95% CI 1.009 to 1.128; p=0.023), and baseline NIHSS (adjusted OR per 1-point increase 1.105; 95% CI 1.004 to 1.216; p=0.040).

CONCLUSION

Our results showed that a large pontine infarct core of ≥70% on pretreatment DWI was strongly associated with extremely poor outcome among patients treated with endovascular thrombectomy for acute BAO.

Diffusion MRI Reversibility in Ischemic Stroke Following Thrombolysis: A Meta-Analysis

BACKGROUND AND PURPOSE

Diffusion-weighted magnetic resonance imaging (DWI) detects early infarction in acute stroke. With the substantial progress in stroke therapies, the frequency of posttreatment DWI reversibility in modern stroke cohorts is currently unknown. The purpose of this study was to perform a systematic literature review examining the relationship between characteristics of patients with ischemic stroke and DWI reversibility following treatment with lytic therapy.

METHODS

A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, yielding a total of 422 unique articles. Studies that were nonclinical or did not report data pertaining to DWI reversibility in the context of an acute stroke series were excluded. Characteristics regarding presentation, diagnosis, intervention, and the timing of DWI reversibility were collected for each study.

RESULTS

After full-text review, 10 studies were identified as meeting inclusion criteria. The number of patients with DWI reversal ranged from .9% to 50%, whereas the extent of reversal ranged from 1.8% to 72.7%. Studies reporting on younger patients describe greater rates of reversibility following stroke treatment.

CONCLUSIONS

These data suggest that early DWI signal may not represent the definitive DWI burden in recanalized populations. However, substantial heterogeneity exists regarding the rate of DWI reversal following recanalization. Additional studies are needed to elucidate the relationship among time to treatment, early reversal rates, and clinical outcomes. Physicians should use caution when basing clinical decisions on DWI lesion volumes, as these likely change to some degree with recanalization.

Reversible diffusion-weighted imaging lesions in acute ischemic stroke: A systematic review

OBJECTIVES

To systematically review the literature for reversible diffusion-weighted imaging (DWIR) lesions and to describe its prevalence, predictors, and clinical significance.

METHODS

Studies were included if the first DWI MRI was performed within 24 hours of stroke onset and follow-up DWI or fluid-attenuated inversion recovery (FLAIR)/T2 was performed within 7 or 90 days, respectively, to measure DWIR. We abstracted clinical, imaging, and outcomes data.

RESULTS

Twenty-three studies met the study criteria. The prevalence of DWIR was 26.5% in DWI-based studies and 6% in FLAIR/T2-based studies. DWIR was associated with recanalization or reperfusion of the ischemic tissue with or without the use of tissue plasminogen activator (t-PA) or endovascular therapy, earlier treatment with t-PA, shorter time to endovascular therapy after MRI, and absent or less severe perfusion deficit within the DWI lesion. DWIR was associated with early neurologic improvement in 5 of 6 studies (defined as improvement in the NIH Stroke Scale (NIHSS) score by 4 or 8 points from baseline or NIHSS score 0 to 2 at 24 hours after treatment or at discharge or median NIHSS score at 7 days) and long-term outcome in 6 of 7 studies (defined as NIHSS score ≤1, improvement in the NIHSS score ≥8 points, or modified Rankin Scale score up to ≤2 at 30 or 90 days) likely due to reperfusion.

CONCLUSIONS

DWIR is seen in up to a quarter of patients with acute ischemic stroke, and it is associated with good clinical outcome following reperfusion. Our findings highlight the pitfalls of DWI to define ischemic core in the early hours of stroke.

Multiparametric classification of sub-acute ischemic stroke recovery with ultrafast diffusion, 23 Na, and MPIO-labeled stem cell MRI at 21.1 T

MRI leverages multiple modes of contrast to characterize stroke. High-magnetic-field systems enhance the performance of these MRI measurements. Previously, we have demonstrated that individually sodium and stem cell tracking metrics are enhanced at ultrahigh field in a rat model of stroke, and we have developed robust single-scan diffusion-weighted imaging approaches that utilize spatiotemporal encoding (SPEN) of the apparent diffusion coefficient (ADC) for these challenging field strengths. Here, we performed a multiparametric study of middle cerebral artery occlusion (MCAO) biomarker evolution focusing on comparison of these MRI biomarkers for stroke assessment during sub-acute recovery in rat MCAO models at 21.1 T. T₂ -weighted MRI was used as the benchmark for identification of the ischemic lesion over the course of the study. The number of MPIO-induced voids measured by gradient-recalled echo, the SPEN measurement of ADC, and ²³ Na MRI values were determined in the ischemic area and contralateral hemisphere, and relative performances for stroke classification were compared by receiver operator characteristic analysis. These measurements were associated with unique time-dependent trajectories during stroke recovery that changed the sensitivity and specificity for stroke monitoring during its evolution. Advantages and limitations of these contrasts, and the use of ultrahigh field for multiparametric stroke assessment, are discussed.

Proposed Standardized Neurological Endpoints for Cardiovascular Clinical Trials: An Academic Research Consortium Initiative

Surgical and catheter-based cardiovascular procedures and adjunctive pharmacology have an inherent risk of neurological complications. The current diversity of neurological endpoint definitions and ascertainment methods in clinical trials has led to uncertainties in the neurological risk attributable to cardiovascular procedures and inconsistent evaluation of therapies intended to prevent or mitigate neurological injury. Benefit-risk assessment of such procedures should be on the basis of an evaluation of well-defined neurological outcomes that are ascertained with consistent methods and capture the full spectrum of neurovascular injury and its clinical effect. The Neurologic Academic Research Consortium is an international collaboration intended to establish consensus on the definition, classification, and assessment of neurological endpoints applicable to clinical trials of a broad range of cardiovascular interventions. Systematic application of the proposed definitions and assessments will improve our ability to evaluate the risks of cardiovascular procedures and the safety and effectiveness of preventive therapies.

Ischaemic stroke

Stroke is the second highest cause of death globally and a leading cause of disability, with an increasing incidence in developing countries. Ischaemic stroke caused by arterial occlusion is responsible for the majority of strokes. Management focuses on rapid reperfusion with intravenous thrombolysis and endovascular thrombectomy, which both reduce disability but are time-critical. Accordingly, improving the system of care to reduce treatment delays is key to maximizing the benefits of reperfusion therapies. Intravenous thrombolysis reduces disability when administered within 4.5 h of the onset of stroke. Thrombolysis also benefits selected patients with evidence from perfusion imaging of salvageable brain tissue for up to 9 h and in patients who awake with stroke symptoms. Endovascular thrombectomy reduces disability in a broad group of patients with large vessel occlusion when performed within 6 h of stroke onset and in patients selected by perfusion imaging up to 24 h following stroke onset. Secondary prevention of ischaemic stroke shares many common elements with cardiovascular risk management in other fields, including blood pressure control, cholesterol management and antithrombotic medications. Other preventative interventions are tailored to the mechanism of stroke, such as anticoagulation for atrial fibrillation and carotid endarterectomy for severe symptomatic carotid artery stenosis.

Cerebral Blood Flow Predicts the Infarct Core: New Insights From Contemporaneous Diffusion and Perfusion Imaging

Background and Purpose- The aim of this study is to determine the spatial and volumetric accuracy of infarct core estimates from relative cerebral blood flow (rCBF) by comparison with near-contemporaneous diffusion-weighted imaging (DWI), and evaluate whether it is sufficient for patient triage to reperfusion therapies. Methods- One hundred ninety-three patients enrolled in the DEFUSE 2 (Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution) and SENSE 3 (Sensitivity Encoding) stroke studies were screened, and 119 who underwent acute magnetic resonance imaging with DWI and perfusion imaging within 24 hours of onset were included. Infarct core was estimated using reduced rCBF at 12 thresholds (<0.20-<0.44) and compared against DWI (apparent diffusion coefficient <620 10^-6mm2/s). For each threshold, volumetric agreement between the rCBF and DWI core estimates was assessed using Bland-Altman, correlation, and linear regression analyses; spatial agreement was assessed using receiver operating characteristic analysis. Results- An rCBF threshold of 0.32 yielded the smallest mean absolute volume difference (14.7 mL), best linear regression fit (R²=0.84), and best spatial agreement (Youden index, 0.38; 95% CI, 0.34-0.41) between rCBF and DWI, with high correlation (r=0.91, P<0.05), a small mean volume difference (1.3 mL) and no fixed bias (P<0.05). At this threshold, 110 of 119 (92.4%) patients were correctly triaged when applying 70 mL as the volume limit for thrombectomy. Spatial agreement was better for prediction of large infarcts (>70 mL) than small infarcts (≤70 mL), with Youden indices of 0.53 (95% CI, 0.49-0.56) and 0.34 (95% CI, 0.30-0.37), respectively. Conclusions- Strong correlation and agreement with near-contemporaneous DWI indicate that infarct core estimates obtained using rCBF are sufficiently accurate for patient triage to reperfusion therapies. The identified optimal rCBF threshold of 0.32 closely approximates the threshold currently used in clinical practice.

Imaging After Thrombolysis and Thrombectomy: Rationale, Modalities and Management Implications

PURPOSE OF REVIEW

Urgent reperfusion treatment with intravenous thrombolysis or mechanical thrombectomy reduces disability after ischaemic stroke. Imaging plays an important role in identifying patients who benefit, particularly in extended time windows. However, the role of post-treatment neuroimaging is less well established. We review recent advances in neuroimaging after reperfusion treatment and provide a practical guide to the options and management implications.

RECENT FINDINGS

Post-treatment imaging is critical to identify patients with reperfusion-related haemorrhage and oedema requiring intervention. It also can guide the timing and intensity of antithrombotic medication. The degree of reperfusion on post-thrombectomy angiography and infarct volume and topography using CT or MRI carry important prognostic significance. Perfusion-weighted MRI and permeability analysis may help detect persistent perfusion abnormalities post-treatment and predict haemorrhagic complications. Post-treatment neuroimaging provides clinically relevant information to identify complications, assess prognosis and perform quality assurance after acute ischaemic stroke. Recent advances in neuroimaging represent a potential avenue to explore post-reperfusion pathophysiology and uncover therapeutic targets for secondary ischaemic and haemorrhagic injury.

Rapid Apparent Diffusion Coefficient Evolution After Early Revascularization

Background and Purpose- In this era of endovascular therapy (EVT) with early, complete recanalization and reperfusion, we have observed an even more rapid apparent diffusion coefficient (ADC) normalization within the acute ischemic lesion compared with the natural history or IV-tPA-treated patient. In this study, we aimed to evaluate the effect of revascularization on ADC evolution within the core lesion in the first 24 hours in acute ischemic stroke patients. Methods- This retrospective study included anterior circulation acute ischemic stroke patients treated with EVT with or without intravenous tPA (IVT) from 2015 to 2017 compared with a consecutive cohort of IVT-only patients treated before 2015. Diffusion-weighted imaging and ADC maps were used to quantify baseline core lesions. Median ADC value change and core reversal were determined at 24 hours. Diffusion-weighted imaging lesion growth was measured at 24 hours and 5 days. Good clinical outcome was defined as modified Rankin Scale score of 0 to 2 at 90 days. Results- Twenty-five patients (50%) received IVT while the other 25 patients received EVT (50%) with or without IVT. Between these patient groups, there were no differences in age, sex, baseline National Institutes of Health Stroke Scale, interhospital transfer, or IVT rates. Thirty-two patients (64%) revascularized with 69% receiving EVT. There was a significant increase in median ADC value of the core lesion at 24 hours in patients who revascularized compared with further ADC reduction in nonrevascularization patients. Revascularization patients had a significantly higher rate of good clinical outcome at 90 days, 63% versus 9% (P=0.003). Core reversal at 24 hours was significantly higher in revascularization patients, 69% versus 22% (P=0.002). Conclusions- ADC evolution in acute ischemic stroke patients with early, complete revascularization, now more commonly seen with EVT, is strikingly different from our historical understanding. The early ADC normalization we have observed in this setting may include a component of secondary injury and serve as a potential imaging biomarker for the development of future adjunctive therapies. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT00009243.