Imaging in Acute Anterior Circulation Ischemic Stroke: Current and Future

Strategies to Improve the Robustness and Generalizability of Deep Learning Segmentation and Classification in Neuroimaging

Artificial Intelligence (AI) and deep learning models have revolutionized diagnosis, prognostication, and treatment planning by extracting complex patterns from medical images, enabling more accurate, personalized, and timely clinical decisions. Despite its promise, challenges such as image heterogeneity across different centers, variability in acquisition protocols and scanners, and sensitivity to artifacts hinder the reliability and clinical integration of deep learning models. Addressing these issues is critical for ensuring accurate and practical AI-powered neuroimaging applications. We reviewed and summarized the strategies for improving the robustness and generalizability of deep learning models for the segmentation and classification of neuroimages. This review follows a structured protocol, comprehensively searching Google Scholar, PubMed, and Scopus for studies on neuroimaging, task-specific applications, and model attributes. Peer-reviewed, English-language studies on brain imaging were included. The extracted data were analyzed to evaluate the implementation and effectiveness of these techniques. The study identifies key strategies to enhance deep learning in neuroimaging, including regularization, data augmentation, transfer learning, and uncertainty estimation. These approaches address major challenges such as data variability and domain shifts, improving model robustness and ensuring consistent performance across diverse clinical settings. The technical strategies summarized in this review can enhance the robustness and generalizability of deep learning models for segmentation and classification to improve their reliability for real-world clinical practice.

Multiphase CTA vs. MRA collateral map for predicting functional outcomes after acute ischemic stroke

PURPOSE

To compare the prognostic abilities of multiphase CT angiography (mCTA) and multiphase MR angiography (MRA) collateral map in acute anterior circulation ischemic stroke.

METHODS

This secondary analysis of a prospective observational study included data from participants with acute ischemic stroke due to steno-occlusion of the internal carotid artery and/or middle cerebral artery within 8 h of symptom onset between January 1, 2016, and March 31, 2021. The intermethod agreement of the collateral scores (CSs) from mCTA and the collateral perfusion scores (CPSs) from the MRA collateral map was analyzed. Multiple logistic regression analyses were conducted to determine the prognostic value of mCTA and MRA collateral maps.

RESULTS

169 participants (106 men and 63 women, mean age 69 years ± 13) were included. The agreement between the CSs of mCTA and the CPSs of the MRA collateral map (weighted kappa = 0.44, 95% confidence interval [CI]: 0.37-0.52) of 168 participants was moderate. Younger age (Odds ratio [OR], 0.51; 95% CI, 0.34-0.76; p = 0.001), lower baseline NIHSS scores (OR, 0.89; 95% CI, 0.81-0.99; p = 0.024), CPS 4 (OR, 36.66; 95% CI, 1.79-750.29; p = 0.019) and CPS 5 (OR, 144.10; 95% CI, 1.11-18788.93; p = 0.046) on the MRA collateral map, and successful reperfusion (OR, 9.63; 95% CI, 3.00-30.94; p < 0.001) were independently associated with favorable functional outcomes.

CONCLUSIONS

Only the MRA collateral map demonstrated clinical prognostic value in acute anterior circulation ischemic stroke patients, demonstrating the superiority of the MRA collateral map over mCTA in collateral assessment.

MCC950 mitigates SIRT3-NLRP3-driven inflammation and rescues post-stroke neurogenesis

Sustained activation of the SIRT3-NLRP3 inflammasome has been associated with worse outcomes after ischemic stroke. The objective of this study was to examine the potential mechanism by which the SIRT3-NLRP3 inflammasome affects neural stem and progenitor cells (NSPCs) after transient middle cerebral artery occlusion (tMCAO) in rats. Following tMCAO, significantly elevated levels of NLRP3, ASC, cleaved caspase 1, IL-1β, and IL-18 were observed in the ischemic subventricular zone. Moreover, tMCAO increased NLRP3 expression while decreasing SIRT3 levels, suggesting a connection between these two processes. Furthermore, we discovered that inflammation induced by the NLRP3 inflammasome impaired post-stroke hippocampal and subventricular neurogenesis, while nestin (a marker for NSPCs) and Sox2 (a marker for stem cell pluripotency) were downregulated after tMCAO. However, systemic administration of MCC950 reduced inflammatory signaling and effectively restored neurogenesis. Overall, our results suggest that protecting NSPCs and neurogenesis in the ischemically damaged brain by mitigating the impact of the SIRT3-NLRP3 inflammasome may be a feasible treatment strategy for ischemic stroke.

Clinical feasibility of deep learning-driven magnetic resonance angiography collateral map in acute anterior circulation ischemic stroke

To validate the clinical feasibility of deep learning-driven magnetic resonance angiography (DL-driven MRA) collateral map in acute ischemic stroke. We employed a 3D multitask regression and ordinal regression deep neural network, called as 3D-MROD-Net, to generate DL-driven MRA collateral maps. Two raters graded the collateral perfusion scores of both conventional and DL-driven MRA collateral maps and measured the grading time. They also qualitatively assessed the image quality of both collateral maps. Interrater and inter-method agreements for collateral perfusion grading between the two collateral maps were analyzed, along with a comparison of grading time and image quality. In the analysis of the 296 acute ischemic stroke patients, the inter-method agreement for collateral perfusion grading was almost perfect (κ = 0.96, 95% CI: 0.95-0.98). Compared to conventional MRA collateral maps, the time taken for collateral perfusion grading on DL-driven MRA collateral maps was shorter (P < 0.001 for rater 1 and P = 0.003 for rater 2), and the image quality of the DL-driven MRA collateral maps was superior (P < 0.001 for rater 1 and P = 0.002 for rater 2). The DL-driven MRA collateral map demonstrates clinical feasibility for collateral perfusion grading in acute ischemic stroke, with the added benefits of reduced generation and interpretation time, along with improved image quality of the MRA collateral map.

Iatrogenic emboli during mechanical thrombectomy for acute ischemic stroke: comparison between stent retriever technique and contact aspiration-a retrospective case-control study

BACKGROUND

Mechanical thrombectomy (MT) is an effective treatment for acute ischemic stroke from large vessel occlusion (LVO). While embolization to a new territory (ENT) after MT is well-documented, data on embolization in the same distal territory (EDT) are limited. Achieving modified Treatment In Cerebral Infarction (mTICI) 3 reperfusion presents significant clinical benefits over mTICI 2b/2c, necessitating strategies to reduce both ENT and EDT. Previous studies suggest higher rates of EDTs with contact aspiration compared with stentrievers. However, comprehensive comparison studies in clinical practice are scarce. This study compares the rates of overall clot emboli (OCE) between these MT strategies.

METHODS

A retrospective, multicenter observational study was conducted at four university hospitals in France from January 2015 to November 2019. Adult patients (≥18 years) with acute ischemic stroke due to LVO, treated with either contact aspiration (ADAPT, A Direct Aspiration First Pass Technique) or stentrievers, specifically using the Embotrap device to maintain sample homogeneity, were included. Digital subtraction angiography was used for imaging, with two independent, blinded reviewers assessing OCE post-first MT pass. Propensity score full matching and independent sample testing were employed to evaluate OCE after the first MT pass.

RESULTS

A significant difference in OCE rates was observed between contact aspiration and stentriever techniques, with the stentriever technique resulting in fewer embolic events compared with ADAPT, based on a propensity score analysis that accounts for key confounding factors.

CONCLUSION

A statistically significant reduction in embolic events was observed with the stentriever technique compared with contact aspiration. These results suggest that the stentriever method may offer a safer profile in terms of embolic risk for LVO interventions, and should be considered over contact aspiration when embolic risk is a primary concern, while also considering individual patient factors.

The enhanced reliability of higher national institute of health stroke scale thresholds over the conventional 6-point scale

INTRODUCTION

It is still uncertain if higher thresholds on National Institute of Health Stroke Scale (NIHSS) are better predictors of large infarctions than the conventional 6-point cutoff.

METHODS

We used 6-point and higher NIHSS thresholds including 8, 9, and 10-point to predict relative infarct areas, expressed as percentage of the affected hemisphere on axial brain computed tomography images, beginning at 5% with 5% increments each time until reaching the 40% cutoff for large infarctions, or achieving 100% sensitivity. Results were compared using area under the receiver operating characteristic curves (AUROC).

RESULTS

We enrolled 151 patients of acute ischemic stroke (Mean age: 62.88 years ± 12.71; Female: 48.34%). 77 patients (50.99%) exhibited left hemisphere strokes, while 74 (49%) had right hemisphere involvement. Sensitivity values of the 6-point for infarcts measuring 5%, 10%, 20%, 30%, and 40% were 62%, 64%, 77%, 82%, and 100%, respectively. At 40% infarct-size, 8-point achieved comparable results (52%, 55%, 69%, 76%, 100%), closely aligning with the 9-point (50%, 53%, 69%, 76%, 100%). The10-point was slightly trailing behind in sensitivity at 40% infarct-core (96%). Moreover, higher thresholds exhibited improved false-positive rates (FPR). At 40% infarct size, the FPRs of 6, 8, 9, and 10 points were 39%, 27%, 27%, and 21% respectively. Higher thresholds had augmented AUROC values (0.86, 0.86, 0.89) as compared to the 6-point (0.80). Logistic regression identified 14-point as definitive cutoff for large infarctions.

CONCLUSION

Higher thresholds can better differentiate small and medium infarcts as true-negatives and substantially reduce false-positive referrals for mechanical thrombectomy.

The collateral map: prediction of lesion growth and penumbra after acute anterior circulation ischemic stroke

OBJECTIVES

This study evaluated the collateral map's ability to predict lesion growth and penumbra after acute anterior circulation ischemic strokes.

METHODS

This was a retrospective analysis of selected data from a prospectively collected database. The lesion growth ratio was the ratio of the follow-up lesion volume to the baseline lesion volume on diffusion-weighted imaging (DWI). The time-to-maximum (Tmax)/DWI ratio was the ratio of the baseline Tmax  > 6 s volume to the baseline lesion volume. The collateral ratio was the ratio of the hypoperfused lesion volume of the phase_FU (phase with the hypoperfused lesions most approximate to the follow-up DWI lesion) to the hypoperfused lesion volume of the phase_baseline of the collateral map. Multiple logistic regression analyses were conducted to identify independent predictors of lesion growth. The concordance correlation coefficients of Tmax/DWI ratio and collateral ratio for lesion growth ratio were analyzed.

RESULTS

Fifty-two patients, including twenty-six males (mean age, 74 years), were included. Intermediate (OR, 1234.5; p < 0.001) and poor collateral perfusion grades (OR, 664.7; p = 0.006) were independently associated with lesion growth. Phase_FUs were immediately preceded phases of the phase_baselines in intermediate or poor collateral perfusion grades. The concordance correlation coefficients of the Tmax/DWI ratio and collateral ratio for the lesion growth ratio were 0.28 (95% CI, 0.17-0.38) and 0.88 (95% CI, 0.82-0.92), respectively.

CONCLUSION

Precise prediction of lesion growth and penumbra can be possible using collateral maps, allowing for personalized application of recanalization treatments. Further studies are needed to generalize the findings of this study.

CLINICAL RELEVANCE STATEMENT

Precise prediction of lesion growth and penumbra can be possible using collateral maps, allowing for personalized application of recanalization treatments.

KEY POINTS

• Cell viability in cerebral ischemia due to proximal arterial steno-occlusion mainly depends on the collateral circulation. • The collateral map shows salvageable brain extent, which can survive by recanalization treatments after acute anterior circulation ischemic stroke. • Precise estimation of salvageable brain makes it possible to make patient-specific treatment decision.

Impact of Collateral Circulation on Futile Endovascular Thrombectomy in Acute Anterior Circulation Ischemic Stroke

OBJECTIVE

Collateral circulation is associated with the differential treatment effect of endovascular thrombectomy (EVT) in acute ischemic stroke. We aimed to verify the ability of the collateral map to predict futile EVT in patients with acute anterior circulation ischemic stroke.

METHODS

This secondary analysis of a prospective observational study included data from participants underwent EVT for acute ischemic stroke due to occlusion of the internal carotid artery and/or the middle cerebral artery within 8 hours of symptom onset. Multiple logistic regression analyses were conducted to identify independent predictors of futile recanalization (modified Rankin scale score at 90 days of 4-6 despite of successful reperfusion).

RESULTS

In a total of 214 participants, older age (odds ratio [OR], 2.40; 95% confidence interval [CI], 1.56 to 3.67; p<0.001), higher baseline National Institutes of Health Stroke Scale (NIHSS) scores (OR, 1.12; 95% CI, 1.04 to 1.21; p=0.004), very poor collateral perfusion grade (OR, 35.09; 95% CI, 3.50 to 351.33; p=0.002), longer door-to-puncture time (OR, 1.08; 95% CI, 1.02 to 1.14; p=0.009), and failed reperfusion (OR, 3.73; 95% CI, 1.30 to 10.76; p=0.015) were associated with unfavorable functional outcomes. In 184 participants who achieved successful reperfusion, older age (OR, 2.30; 95% CI, 1.44 to 3.67; p<0.001), higher baseline NIHSS scores (OR, 1.12; 95% CI, 1.03 to 1.22; p=0.006), very poor collateral perfusion grade (OR, 4.96; 95% CI, 1.42 to 17.37; p=0.012), and longer door-to-reperfusion time (OR, 1.09; 95% CI, 1.03 to 1.15; p=0.003) were associated with unfavorable functional outcomes.

CONCLUSION

The assessment of collateral perfusion status using the collateral map can predict futile EVT, which may help select ineligible patients for EVT, thereby potentially reducing the rate of futile EVT.

Prognostic value of multiphase CT angiography: estimated infarct core volume in the patients with acute ischaemic stroke after mechanical thrombectomy

BACKGROUND AND PURPOSE

Recent studies reported the feasibility of quantifying a reliable infarct core (IC) volume using multiphase computed tomography (mCTA) based on deep learning, however its prognostic value was not fully clarified. Therefore, we aimed to evaluate the prognostic value of mCTA-estimated IC volume in patients with acute ischemic stroke (AIS) after mechanical thrombectomy (MT).

MATERIALS AND METHODS

We retrospectively reviewed patients who underwent mCTA and MT for large vessel occlusion in middle cerebral artery and (or) internal carotid artery within 6 hours after symptom onset between January 2018 and November 2019. Patients were dichotomized into good (modified Rankin Scale [mRS] score, 0-2) and poor (mRS, 3-6) outcome groups. mCTA-estimated IC volume were generated based on a multi-scale three-dimensional convolutional neural network. Univariate, multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were used to identify the independent variables, and evaluate their performances in predicting the clinical outcome.

RESULTS

Of 44 included patients, 27 (61.4%) patients achieved good outcome. National Institutes of Health Stroke Scale scores at admission [NIHSSpre] (odds ratio [OR], 1.191; 95%confidence interval [CI], 1.028-1.379; P=0.020) and mCTA-estimated IC volume (OR, 1.076; 95%CI, 1.016-1.140; P=0.013) were found to be independently associated with functional outcome in patients with AIS after MT. After integrating NIHSSpre and mCTA-estimated IC volume, optimal performance (area under the ROC curve, 0.874; 95%CI, 0.739-0.954) could be obtained in predicting the clinical outcome.

CONCLUSIONS

mCTA-estimated IC volume might be promising for predicting the prognosis, and assisting in making individualized treatment decision in patients with AIS.

Role of arterial spin labeling magnetic resonance perfusion in acute ischemic stroke

Background

Arterial spin labeling (ASL) is a recently used magnetic resonance imaging (MRI) perfusion technique in acute cerebrovascular stroke conditions; it can detect the hypo perfused areas on basis of qualitative and quantitative measurements and also identify the area at risk known as penumbra by detecting the diffusion/perfusion mismatch. The purpose of this study was to assess the role of ASL perfusion technique in management of acute ischemic stroke and its ability to predict the clinical outcome of acute stroke patients. The study was prospectively carried out on 33 patients clinically presented with acute stroke from the first of August 2020 till the first of August 2021. All cases were clinically assessed by stroke consultant followed by brain imaging including conventional MRI and ASL perfusion technique, based upon which management was established. These imaging data were correlated with the clinical outcome after 3 months using Modified Rankin Scale.

Results

Sixteen cases (48.48%) showed ischemic penumbra with diffusion perfusion mismatch with three cases presenting within the first 4 h managed by intravenous thrombolytic therapy and 13 cases presenting later than 4 h, 10 of whom were managed by endovascular intervention. The group with ischemic penumbra showed significant positive correlation with favorable clinical outcome while the group without ischemic penumbra showed significant positive correlation with poor clinical outcome. Quantitative ASL values were statistically significantly higher (p ≤ 0.05) in patients with favorable clinical outcome than those with poor clinical outcome. The estimated cut off values of ASL absolute cerebral blood flow and relative cerebral blood flow to predict favorable or poor outcome using ROC curve analysis were 19 ml/100gm/min and 74% compared to the contralateral side respectively.

Conclusion

The use of MRI as a primary diagnostic tool in arterial ischemic stroke with the application of non-contrast ASL perfusion sequence allows precise detection of perfusion deficit and diffusion perfusion mismatch (penumbra) and provides a reliable insight into outcome prediction.