Review of Perfusion Imaging in Acute Ischemic Stroke: From Time to Tissue

Modeling the effect of patient size on cerebral perfusion during veno-arterial extracorporeal membrane oxygenation

INTRODUCTION

A well-known complication of veno-arterial extracorporeal membrane oxygenation (VA ECMO) is differential hypoxia, in which poorly-oxygenated blood ejected from the left ventricle mixes with and displaces well-oxygenated blood from the circuit, thereby causing cerebral hypoxia and ischemia. We sought to characterize the impact of patient size and anatomy on cerebral perfusion under a range of different VA ECMO flow conditions.

METHODS

We use one-dimensional (1D) flow simulations to investigate mixing zone location and cerebral perfusion across 10 different levels of VA ECMO support in eight semi-idealized patient geometries, for a total of 80 scenarios. Measured outcomes included mixing zone location and cerebral blood flow (CBF).

RESULTS

Depending on patient anatomy, we found that a VA ECMO support ranging between 67-97% of a patient's ideal cardiac output was needed to perfuse the brain. In some cases, VA ECMO flows exceeding 90% of the patient's ideal cardiac output are needed for adequate cerebral perfusion.

CONCLUSIONS

Individual patient anatomy markedly affects mixing zone location and cerebral perfusion in VA ECMO. Future fluid simulations of VA ECMO physiology should incorporate varied patient sizes and geometries in order to best provide insights toward reducing neurologic injury and improved outcomes in this patient population.

Endovascular management of acute stroke

Stroke related to large vessel occlusion is a leading cause of disability and death worldwide. Advances in endovascular therapy to reopen occluded arteries have been shown to reduce patient disability and mortality. Expanded indications to treat patients with large vessel occlusion in the late window (>6 h from symptom onset), with basilar artery occlusion, and with large ischaemic core at presentation have enabled treatment of more patients with simplified imaging methods. Ongoing knowledge gaps include an understanding of which patients with large ischaemic infarct are more likely to benefit from endovascular therapy, the role of endovascular therapy in patients who present with low National Institutes of Health Stroke Scale scores or medium or distal vessel occlusion, and optimal management of patients with underlying intracranial atherosclerotic disease. As reperfusion can now be facilitated by intravenous thrombolysis, mechanical thrombectomy, or both, the development of cytoprotective or adjunctive drugs to slow infarct growth, enhance reperfusion, or decrease haemorrhagic risk has gained renewed interest with the hope to improve patient outcomes.

CT perfusion parameter estimation in stroke using neural network with transformer and physical model priors

OBJECTIVES

CT perfusion (CTP) imaging is vital in treating acute ischemic stroke by identifying salvageable tissue and the infarcted core. CTP images allow quantitative estimation of CT perfusion parameters, which can provide information on the degree of tissue hypoperfusion and its salvage potential. Traditional methods for estimating perfusion parameters, such as singular value decomposition (SVD) and its variations, are known to be sensitive to noise and inaccuracies in the arterial input function. To our knowledge, there has been no implementation of deep learning methods for CT perfusion parameter estimation.

MATERIALS & METHODS

In this work, we propose a deep learning method based on the Transformer model, named CTPerformer-Net, for CT perfusion parameter estimation. In addition, our method incorporates some physical priors. We integrate physical consistency prior, smoothness prior and the physical model prior through the design of the loss function. We also generate a simulation dataset based on physical model prior for training the network model.

RESULTS

In the simulation dataset, CTPerformer-Net exhibits a 23.4 % increase in correlation coefficients, a 95.2 % decrease in system error, and a 90.7 % reduction in random error when contrasted with block-circulant SVD. CTPerformer-Net successfully identifies hypoperfused and infarcted lesions in 103 real CTP images from the ISLES 2018 challenge dataset. It achieves a mean dice score of 0.36 for the infarct core segmentation, which is slightly higher than the commercially available software (dice coefficient: 0.34) used as a reference level by the challenge.

CONCLUSION

Experimental results on the simulation dataset demonstrate that CTPerformer-Net achieves better performance compared to block-circulant SVD. The real-world patient dataset confirms the validity of CTPerformer-Net.

Perfusion imaging predicts short-term clinical outcome in isolated posterior cerebral artery occlusion stroke

BACKGROUND AND PURPOSE

Ischemic strokes due to isolated posterior cerebral artery (PCA) occlusions represent 5% of all strokes but have significant impacts on patients' quality of life, primarily due to visual deficits and thalamic involvement. Current guidelines for acute PCA occlusion management are sparse, and the prognostic value of perfusion imaging parameters remains underexplored.

METHODS

We conducted a retrospective analysis of 32 patients with isolated PCA occlusions treated at Johns Hopkins Medical Institutions between January 2017 and March 2023. Patients underwent pretreatment perfusion imaging, with perfusion parameters analyzed using RAPID software. The primary outcome was short-term clinical outcome as measured by the National Institutes of Health Stroke Scale (NIHSS) at discharge.

RESULTS

The median age of the cohort was 70 years, with 34% female and 66% male. Significant correlations were found between NIHSS at discharge and various perfusion parameters, including time-to-maximum (Tmax) >6 seconds (ρ = .55, p = .004), Tmax >8 seconds (ρ = .59, p = .002), Tmax >10 seconds (ρ = .6, p = .001), mismatch volume (ρ = .51, p = .008), and cerebral blood volume (CBV) < 34% (ρ = .59, p = .002).

CONCLUSIONS

Tmax and CBV volumes significantly correlated with discharge NIHSS with marginal superiority of Tmax >10 seconds and CBV <42% volumes. These findings suggest that CT and MR perfusion imaging can play a crucial role in the acute management of PCA strokes, though larger, standardized studies are needed to validate these results and refine imaging thresholds specific to posterior circulation infarcts.

Perfusion Abnormalities on 24-Hour Perfusion Imaging in Patients With Complete Endovascular Reperfusion

BACKGROUND

Perfusion abnormalities in the infarct and salvaged penumbra have been proposed as a potential reason for poor clinical outcome (modified Rankin Scale score >2) despite complete angiographic reperfusion (Thrombolysis in Cerebral Infarction [TICI3]). In this study, we aimed to identify different microvascular perfusion patterns and their association with clinical outcomes among TICI3 patients.

METHODS

University Hospital Bern's stroke registry of all patients between February 2015 and December 2021. Macrovascular reperfusion was graded using the TICI scale. Microvascular reperfusion status was evaluated within the infarct area on cerebral blood volume and cerebral blood flow perfusion maps obtained 24-hour postintervention. Primary outcome was functional independence (90-day modified Rankin Scale score 0-2) evaluated with the logistic regression analysis adjusted for age, sex, and 24-hour infarct volume from follow-up imaging.

RESULTS

Based on microvascular perfusion findings, the entire cohort (N=248) was stratified into one of the 4 clusters: (1) normoperfusion (no perfusion abnormalities; n=143/248); (2) hyperperfusion (hyperperfusion on both cerebral blood volume and cerebral blood flow; n=54/248); (3) hypoperfusion (hypoperfusion on both cerebral blood volume and cerebral blood flow; n=14/248); and (4) mixed (discrepant findings, eg, cerebral blood volume hypoperfusion and cerebral blood flow hyperperfusion; n=37/248). Compared with the normoperfusion cluster, patients in the hypoperfusion cluster were less likely to achieve functional independence (adjusted odds ratio, 0.3 [95% CI, 0.1-0.9]), while patients in the hyperperfusion cluster tended to have better outcomes (adjusted odds ratio, 3.3 [95% CI, 1.3-8.8]).

CONCLUSIONS

In around half of TICI3 patients, perfusion abnormalities on the microvascular level can be observed. Microvascular hypoperfusion, despite complete macrovascular reperfusion, is rare but may explain the poor clinical course among some TICI3 patients, while a detrimental effect of hyperperfusion after reperfusion could not be confirmed.

Hypoperfusion Intensity Ratio as an Indirect Imaging Surrogate in Patients With Anterior Circulation Large-Vessel Occlusion and Association of Baseline Characteristics With Poor Collateral Status

BACKGROUND

Collateral status (CS) plays a crucial role in infarct growth rate, risk of postthrombectomy hemorrhage, and overall clinical outcomes in patients with acute ischemic stroke (AIS) secondary to anterior circulation large-vessel occlusions (LVOs). Hypoperfusion intensity ratio has been previously validated as an indirect noninvasive pretreatment imaging biomarker of CS. In addition to imaging, derangements in admission laboratory findings can also influence outcomes in patients with AIS-LVO. Therefore, our study aims to assess the relationship between admission laboratory findings, baseline characteristics, and CS, as assessed by hypoperfusion intensity ratio in patients with AIS-LVO.

METHODS AND RESULTS

In this retrospective study, consecutive patients presenting with AIS secondary to anterior circulation LVO who underwent pretreatment computed tomography perfusion were included. The computed tomography perfusion data processed by RAPID (Ischema View, Menlo Park, CA) generated the hypoperfusion intensity ratio. Binary logistic regression models were used to assess the relationship between patients' baseline characteristics, admission laboratory findings, and poor CS. A total of 221 consecutive patients with AIS-LVO between January 2017 and September 2022 were included in our study (mean±SD age, 67.0±15.8 years; 119 men [53.8%]). Multivariable logistic regression showed that patients with AIS caused by cardioembolic and cryptogenic causes (adjusted odds ratio [OR], 2.67; 95% CI, 1.20-5.97; P=0.016), those who presented with admission National Institutes of Health Stroke Scale score ≥12 (adjusted OR, 3.12; 95% CI, 1.61-6.04; P=0.001), and male patients (adjusted OR, 2.06; 95% CI, 1.13-3.77; P=0.018) were associated with poor CS.

CONCLUSIONS

Stroke caused by cardioembolic or cryptogenic causes, admission National Institutes of Health Stroke Scale score of ≥12, and male sex were associated with poor CS, as defined by hypoperfusion intensity ratio in the patients with AIS-LVO.

Post-endovascular therapy contrast extravasation in the mesial temporal region on dual-energy CT is associated with outcome in acute ischemic stroke patients

PURPOSE

Pre- and post-endovascular treatment (EVT) imaging may aid in predicting functional outcomes in acute middle cerebral artery (MCA) ischemic stroke. Low post-EVT contrast extravasation (CE)-ASPECTS is associated with poor functional outcomes. Besides the MCA regions included in the ASPECTS score, CE may be seen in the mesial temporal (MT) region. In this study, we investigated the frequency and prognostic implication of MT-CE in acute ischemic stroke patients.

METHODS

Patients with an acute ischemic stroke due to anterior large vessel occlusion who received EVT and post-EVT DECT between 2010 and 2019 were included. Iodine overlay maps of DECT were assessed for the occurrence of CE, using the ASPECTS for occurrence in the MCA region and, calculating a CE-ASPECTS, for whether the MT region was involved. Multivariable linear and logistic regression were used to assess the relationship between involvement of MT-CE and 24-48h NIHSS, mRS, and mortality on a multiple imputed dataset. All models were adjusted significant variables in univariate analyses and for total CE-ASPECTS.

RESULTS

501/651 patients met the inclusion criteria. MT-CE occurred in 97 (19 %) patients, and was more often present in patients with internal carotid artery occlusions. MT-CE was associated with higher NIHSS scores at 24-hours (aβ 2.2, 95 % CI 0.09-4.31), with increased risk of higher mRS scores (acOR 1.88, 95 % CI 1.16-3.06), and with increased risk of mortality (aOR 2.12, 95 % CI 1.16-3.86).

CONCLUSION

MT-CE is a common finding on post-EVT DECT and is an independent predictor for worse functional outcomes.

Obstructive sleep apnea exaggeration as predictor of poor outcome post thrombolytic stroke

Obstructive sleep apnea (OSA) is a common sleep disordered breathing in stroke patients. This case report aimed to show the presence of OSA in stroke can contribute to the increasing chance of mortality and morbidity. We presented a case of first-time stroke in a 64-year-old female with a history of pre-stroke OSA. She underwent intravenous thrombolysis as main therapy within the time limit under 4.5 hours since the stroke onset. She had prolonged hospital stay due to complications from OSA, even though she only had a small ischemic core (9 mL) in follow-up radiological imaging and was discharged with a greater National Institutes of Health Stroke Scale (NIHSS) score than admission (5 to 10). OSA can be one of warning signs for poor prognosis in stroke patients. Understanding the presence of OSA not only can be beneficial toward choosing the next steps of therapy, but also important for the rehabilitation and recovery period of stroke patients.

Importance of computed tomography perfusion on assessing collateral circulation and prognosis of patients with acute anterior circulation large vessel occlusion after endovascular therapy

This study probed the importance of computed tomography perfusion (CTP) on assessing collateral circulation and prognosis in patients with acute anterior circulation large vessel occlusion (AAC-LVO) after endovascular therapy (EVT). Retrospective analysis was performed on the case data of 124 AAC-LVO patients who achieved EVT in the First People's Hospital of Lianyungang. All patients received computed tomography (CT) examination. Based on the multi-phase computed tomography angiography (mCTA) score, patients were separated into poor collateral circulation group and good collateral circulation group. Based on modified Rankin scale (mRS) score, patients were separated into good prognosis group and poor prognosis group. The receiver operating characteristic (ROC) curve was used to measure the efficacy of CTP parameters in predicting good collateral circulation or good prognosis. Correlation between CTP parameters with mCTA collateral and 90-day mRS circulation score was analyzed using the Spearman correlation analysis. The age and admission national Institutes of Health stroke scale (NIHSS) scores of the good collateral circulation group were lower than the poor collateral circulation group, and low perfusion area volume with Tmax > 6 s (VTmax>6 s), infarct core area volume (VCBF<30 %)and hypoperfusion intensity ratio (HIR) were also lower. The mCTA collateral cycle score was negatively related to VTmax>6s, VCBF<30 % and HIR. The area under the curve (AUC) values of VTmax>6s and VCBF<30 % and HIR for predicting good collateral circulation were 0.763, 0.884 and 0.842, respectively, which suggested that perfusion parameters VTmax>6s, VCBF<30 % and HIR could effectively indicate the status of patients' collateral circulation. Relative to the poor prognosis group, patients in the good prognosis group possessed lower admission NIHSS score, younger age, smaller final infarct volume, lower HIR, VCBF<30 %, VTmax>6 s, Alberta Stroke Program Early CT(ASPECT) score, and higher mCTA score. Spearman correlation analysis unveiled that ASPECT score, mCTA score and 90-day mRS were negatively correlated. The final infarct volume, perfusion parameters HIR and VCBF<30 % were positively correlated with 90-day mRS. ROC analysis showed that all variates had good prognostic value for acute anterior circulation great vessel occlusion patients, while VCBF<30 % and HIR had high diagnostic value for prognosis. To sum up, CTP can provide a comprehensive imaging assessment of the collateral circulation of patients with AAC-LVO and has a higher predictive value for the prognosis assessment of patients with EVT in terms of VCBF<30 %, HIR score and mCTA collateral circulation score.

Application of emerging technologies in ischemic stroke: from clinical study to basic research

Stroke is a primary cause of noncommunicable disease-related death and disability worldwide. The most common form, ischemic stroke, is increasing in incidence resulting in a significant burden on patients and society. Urgent action is thus needed to address preventable risk factors and improve treatment methods. This review examines emerging technologies used in the management of ischemic stroke, including neuroimaging, regenerative medicine, biology, and nanomedicine, highlighting their benefits, clinical applications, and limitations. Additionally, we suggest strategies for technological development for the prevention, diagnosis, and treatment of ischemic stroke.

Current State of Evidence for Neuroimaging Paradigms in Management of Acute Ischemic Stroke

Stroke is the chief differential diagnosis in patient presenting to the emergency room with abrupt onset focal neurological deficits. Neuroimaging, including non-contrast computed tomography (CT), magnetic resonance imaging (MRI), vascular and perfusion imaging, is a cornerstone in the diagnosis and treatment decision-making. This review examines the current state of evidence behind the different imaging paradigms for acute ischemic stroke diagnosis and treatment, including current recommendations from the guidelines. Non-contrast CT brain, or in some centers MRI, can help differentiate ischemic stroke and intracerebral hemorrhage (ICH), a pivotal juncture in stroke diagnosis and treatment algorithm, especially for early window thrombolytics. Advanced imaging such as MRI or perfusion imaging can also assist making a diagnosis of ischemic stroke versus mimics such as migraine, Todd's paresis, or functional disorders. Identification of medium-large vessel occlusions with CT or MR angiography triggers consideration of endovascular thrombectomy (EVT), with additional perfusion imaging help identify salvageable brain tissue in patients who are likely to benefit from reperfusion therapies, particularly in the ≥6 h window. We also review recent advances in neuroimaging and ongoing trials in key therapeutic areas and their imaging selection criteria to inform the readers on potential future transitions into use of neuroimaging for stroke diagnosis and treatment decision making. ANN NEUROL 2024;95:1017-1034.

Annotation-free prediction of treatment-specific tissue outcome from 4D CT perfusion imaging in acute ischemic stroke

Acute ischemic stroke is a critical health condition that requires timely intervention. Following admission, clinicians typically use perfusion imaging to facilitate treatment decision-making. While deep learning models leveraging perfusion data have demonstrated the ability to predict post-treatment tissue infarction for individual patients, predictions are often represented as binary or probabilistic masks that are not straightforward to interpret or easy to obtain. Moreover, these models typically rely on large amounts of subjectively segmented data and non-standard perfusion analysis techniques. To address these challenges, we propose a novel deep learning approach that directly predicts follow-up computed tomography images from full spatio-temporal 4D perfusion scans through a temporal compression. The results show that this method leads to realistic follow-up image predictions containing the infarcted tissue outcomes. The proposed compression method achieves comparable prediction results to using perfusion maps as inputs but without the need for perfusion analysis or arterial input function selection. Additionally, separate models trained on 45 patients treated with thrombolysis and 102 treated with thrombectomy showed that each model correctly captured the different patient-specific treatment effects as shown by image difference maps. The findings of this work clearly highlight the potential of our method to provide interpretable stroke treatment decision support without requiring manual annotations.

Computed tomography perfusion deficit volume predicts the functional outcome of endovascular therapy for basilar artery occlusion

OBJECTIVES

To investigate the relationship between baseline computed tomography perfusion deficit volumes and functional outcomes in patients with basilar artery occlusion (BAO) undergoing endovascular therapy.

METHODS

This was a single-center study in which the data of 64 patients with BAO who underwent endovascular therapy were retrospectively analyzed. All the patients underwent multi-model computed tomography on admission. The posterior-circulation Acute Stroke Prognosis Early Computed Tomography Score was applied to assess the ischemic changes. Perfusion deficit volumes were obtained using Syngo.via software. The primary outcome of the analysis was a good functional outcome (90-day modified Rankin Scale score ≤ 3). Logistic regression and receiver operating characteristic curves were used to explore predictors of functional outcome.

RESULTS

A total of 64 patients (median age, 68 years; 72 % male) were recruited, of whom 26 (41 %) patients achieved good functional outcomes, while 38 (59 %) had poor functional outcomes. Tmax > 10 s, Tmax > 6 s, and rCBF < 30 % volume were independent predictors of good functional outcomes (odds ratio range, 1.0-1.2; 95 % confidence interval [CI], 1.0-1.4]) and performed well in the receiver operating characteristic curve analyses, exhibiting positive prognostic value; the areas under the curve values were 0.85 (95 % CI, 0.75-0.94), 0.81 (95 % CI, 0.70-0.90), and 0.78 (95 % CI, 0.67-0.89).

CONCLUSION

Computed tomography perfusion deficit volume represents a valuable tool in predicting high risk of disability and mortality in patients with BAO after endovascular treatment.

Identifiability of spatiotemporal tissue perfusion models

Objective.Standard models for perfusion quantification in DCE-MRI produce a bias by treating voxels as isolated systems. Spatiotemporal models can remove this bias, but it is unknown whether they are fundamentally identifiable. The aim of this study is to investigate this question in silico using one-dimensional toy systems with a one-compartment blood flow model and a two-compartment perfusion model.Approach.For each of the two models, identifiability is explored theoretically and in-silico for three systems. Concentrations over space and time are simulated by forward propagation. Different levels of noise and temporal undersampling are added to investigate sensitivity to measurement error. Model parameters are fitted using a standard gradient descent algorithm, applied iteratively with a stepwise increasing time window. Model fitting is repeated with different initial values to probe uniqueness of the solution. Reconstruction accuracy is quantified for each parameter by comparison to the ground truth.Main results.Theoretical analysis shows that flows and volume fractions are only identifiable up to a constant, and that this degeneracy can be removed by proper choice of parameters. Simulations show that in all cases, the tissue concentrations can be reconstructed accurately. The one-compartment model shows accurate reconstruction of blood velocities and arterial input functions, independent of the initial values and robust to measurement error. The two-compartmental perfusion model was not fully identifiable, showing good reconstruction of arterial velocities and input functions, but multiple valid solutions for the perfusion parameters and venous velocities, and a strong sensitivity to measurement error in these parameters.Significance.These results support the use of one-compartment spatiotemporal flow models, but two-compartment perfusion models were not sufficiently identifiable. Future studies should investigate whether this degeneracy is resolved in more realistic 2D and 3D systems, by adding physically justified constraints, or by optimizing experimental parameters such as injection duration or temporal resolution.

The lesion core extent modulates the impact of early perfusion mismatch imaging on outcome variability after thrombectomy in stroke

Introduction

Despite profitable group effects on functional outcomes after mechanical thrombectomy (MT) in large vessel occlusion (LVO), many patients with successful reperfusion show a non-favorable long-term outcome, highlighting the necessity to identify potential biomarkers predicting outcome variability. In this regard, the role of perfusion mismatch imaging for outcome variability in the early time window within 6 h after symptom onset is a matter of debate. We attempted to investigate under which conditions early perfusion mismatch imaging accounts for variability in functional outcomes after mechanical thrombectomy.

Patients and methods

In a retrospective single-center study, we examined 190 consecutive patients with LVO who were admitted to the Medical Center Lübeck within 6 h after symptom onset, all of whom underwent MT. Perfusion mismatch was quantified by applying the Alberta Stroke Program Early CT score (ASPECTS) on CT-measured cerebral blood flow (CBF-ASPECTS) and subtracting it from an ASPECTS application on cerebral blood volume (CBV-ASPECTS), i.e., ASPECTS mismatch. Using multivariate ordinal regression models, associations between ASPECTS mismatch and modified Rankin Scale (mRS) after 90 days were assessed. Furthermore, the interaction between ASPECTS mismatch and the core lesion volume was calculated to evaluate conditional associations.

Results

ASPECTS mismatch did not correlate with functional outcomes when corrected for multiple influencing covariables. However, interactions between ASPECTS mismatch and CBV-ASPECTS [OR: 1.12 (1.06-1.18), p-value < 0.001], as well as NCCT-ASPECTS [OR: 1.15 (1.06-1.25), p-value < 0.001], did show a significant association with functional outcomes. Model comparisons revealed that, profoundly, in patients with large core lesion volumes (CBV-ASPECTS < 6 or NCCT-ASPECTS < 6), perfusion mismatch showed a negative correlation with the mRS.

Discussion and conclusion

Perfusion mismatch imaging within the first 6 h of symptom onset provides valuable insights into the outcome variability of LVO stroke patients receiving thrombectomy but only in patients with large ischemic core lesions.

The volume of steal phenomenon is associated with neurological deterioration in patients with large-vessel occlusion minor stroke not eligible for thrombectomy

INTRODUCTION

A significant number of patients who present with mild symptoms following large-vessel occlusion acute ischemic stroke (LVO-AIS) are currently considered ineligible for EVT. However, they frequently experience neurological deterioration during hospitalization. This study aimed to investigate the association between neurological deterioration and hemodynamic impairment by assessing steal phenomenon derived from blood oxygenation-level dependent cerebrovascular reactivity (BOLD-CVR) in this specific patient cohort.

PATIENTS AND METHODS

From the database of our single-center BOLD-CVR observational cohort study (June 2015-October 2023) we retrospectively identified acute ischemic stroke patients with admission NIHSS < 6, a newly detected large vessel occlusion of the anterior circulation and ineligible for EVT. Neurological deterioration during hospitalization as well as outcome at hospital discharge were rated with NIHSS score. We analyzed the association between these two outcomes and BOLD-CVR-derived steal phenomenon volume through regression analysis. Additionally, we investigated the discriminatory accuracy of steal phenomenon volume for predicting neurological deterioration.

RESULTS

Forty patients were included in the final analysis. Neurological deterioration occurred in 35% of patients. In the regression analysis, a strong association between steal phenomenon volume and neurological deterioration (OR 4.80, 95% CI 1.32-31.04, p = 0.04) as well as poorer NIHSS score at hospital discharge (OR 3.73, 95% CI 1.52-10.78, p = 0.007) was found. The discriminatory accuracy of steal phenomenon for neurological deterioration prediction had an AUC of 0.791 (95% CI 0.653-0.930).

DISCUSSION

Based on our results we may distinguish two groups of patients with minor stroke currently ineligible for EVT, however, showing hemodynamic impairment and exhibiting neurological deterioration during hospitalization: (1) patients exhibiting steal phenomenon on BOLD-CVR imaging as well as hemodynamic impairment on resting perfusion imaging; (2) patients exhibiting steal phenomenon on BOLD-CVR imaging, however, no relevant hemodynamic impairment on resting perfusion imaging.

CONCLUSION

The presence of BOLD-CVR derived steal phenomenon may aid to further study hemodynamic impairment in patients with minor LVO-AIS not eligible for EVT.

MR Imaging Techniques for Acute Ischemic Stroke and Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Acute ischemic stroke (AIS) is a leading cause of death and disability worldwide, and its prevalence is expected to increase with global population aging and the burgeoning obesity epidemic. Clinical care for AIS has evolved during the past 3 decades, and it comprises of 3 major tenants: (1) timely recanalization of occluded vessels with intravenous thrombolysis or endovascular thrombectomy, (2) prompt initiation of antithrombotic agents to prevent stroke recurrences, and (3) poststroke supportive care and rehabilitation. In this article, we summarize commonly used MR sequences for AIS and DCI and highlight their clinical applications.

Gadolinium Retention and Nephrotoxicity in a Mouse Model of Acute Ischemic Stroke: Linear Versus Macrocyclic Agents

BACKGROUND

Gadolinium (Gd)-based contrast agents (GBCAs) have been widely used for acute ischemic stroke (AIS) patients. GBCAs or AIS alone may cause the adverse effects on kidney tissue, respectively. However, whether GBCAs and AIS would generate a synergistic negative effect remains undefined.

PURPOSE

To evaluate synergistic negative effects of AIS and GBCAs on renal tissues in a mouse model of AIS, and to compare the differences of these negative effects between linear and macrocyclic GBCAs.

STUDY TYPE

Animal study.

ANIMAL MODEL

Seventy-two healthy mice underwent transient middle cerebral artery occlusion (tMCAO) and sham operation to establish AIS and sham model (N = 36/model). 5.0 mmol/kg GBCAs (gadopentetate or gadobutrol) or 250 μL saline were performed at 4.5 hours and 1 day after model establishing (N = 12/group).

ASSESSMENT

Inductively coupled plasma mass spectrometry (ICP-MS) was performed to detect Gd concentrations. Serum biochemical analyzer was performed to measure the serum creatinine (Scr), uric acid (UA), and blood urea nitrogen (BUN). Pathological staining was performed to observe tubular injury, cell apoptosis, mesangial hyperplasia, and interstitial fibrosis.

STATISTICAL TESTS

Two-way analysis of variances with post hoc Sidak's tests and independent-samples t-tests were performed. A P-value <0.05 was considered statistically significant.

RESULTS

AIS groups showed higher Gd concentration than sham group on day 1 p.i. regardless of gadopentetate or gadobutrol used. Increased total Gd concentration was also found in AIS + gadopentetate group compared with the sham group on day 28 p.i. Significantly higher rates for renal dysfunction, higher tubular injury scores, and higher numbers of apoptotic cells on days 1 or 28 p.i. were found for AIS mice injected with GBCA. AIS + gadopentetate group displayed more severe renal damage than the AIS + gadobutrol group.

DATA CONCLUSION

AIS and GBCAs may cause increased total Gd accumulation and nephrotoxicity in a mouse, especially linear GBCAs were used.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 4.

Utilizing imaging parameters for functional outcome prediction in acute ischemic stroke: A machine learning study

BACKGROUND AND PURPOSE

We aimed to predict the functional outcome of acute ischemic stroke patients with anterior circulation large vessel occlusions (LVOs), irrespective of how they were treated or the severity of the stroke at admission, by only using imaging parameters in machine learning models.

METHODS

Consecutive adult patients with anterior circulation LVOs who were scanned with CT angiography (CTA) and CT perfusion were queried in this single-center, retrospective study. The favorable outcome was defined as a modified Rankin score (mRS) of 0-2 at 90 days. Predictor variables included only imaging parameters. CatBoost, XGBoost, and Random Forest were employed. Algorithms were evaluated using the area under the receiver operating characteristic curve (AUROC), the area under the precision-recall curve (AUPRC), accuracy, Brier score, recall, and precision. SHapley Additive exPlanations were implemented.

RESULTS

A total of 180 patients (102 female) were included, with a median age of 69.5. Ninety-two patients had an mRS between 0 and 2. The best algorithm in terms of AUROC was XGBoost (0.91). Furthermore, the XGBoost model exhibited a precision of 0.72, a recall of 0.81, an AUPRC of 0.83, an accuracy of 0.78, and a Brier score of 0.17. Multiphase CTA collateral score was the most significant feature in predicting the outcome.

CONCLUSIONS

Using only imaging parameters, our model had an AUROC of 0.91 which was superior to most previous studies, indicating that imaging parameters may be as accurate as conventional predictors. The multiphase CTA collateral score was the most predictive variable, highlighting the importance of collaterals.

Pretreatment parameters associated with hemorrhagic transformation among successfully recanalized medium vessel occlusions

Although pretreatment radiographic biomarkers are well established for hemorrhagic transformation (HT) following successful mechanical thrombectomy (MT) in large vessel occlusion (LVO) strokes, they are yet to be explored for medium vessel occlusion (MeVO) acute ischemic strokes. We aim to investigate pretreatment imaging biomarkers representative of collateral status, namely the hypoperfusion intensity ratio (HIR) and cerebral blood volume (CBV) index, and their association with HT in successfully recanalized MeVOs. A prospectively collected registry of acute ischemic stroke patients with MeVOs successfully recanalized with MT between 2019 and 2023 was retrospectively reviewed. A multivariate logistic regression for HT of any subtype was derived by combining significant univariate predictors into a forward stepwise regression with minimization of Akaike information criterion. Of 60 MeVO patients successfully recanalized with MT, HT occurred in 28.3% of patients. Independent factors for HT included: diabetes mellitus history (p = 0.0005), CBV index (p = 0.0071), and proximal versus distal occlusion location (p = 0.0062). A multivariate model with these factors had strong diagnostic performance for predicting HT (area under curve [AUC] 0.93, p < 0.001). Lower CBV indexes, distal occlusion location, and diabetes history are significantly associated with HT in MeVOs successfully recanalized with MT. Of note, HIR was not found to be significantly associated with HT.

Reducing False-Positives in CT Perfusion Infarct Core Segmentation Using Contralateral Local Normalization

BACKGROUND AND PURPOSE

The established global threshold of rCBF <30% for infarct core segmentation can lead to false-positives, as it does not account for the differences in blood flow between GM and WM and patient-individual factors, such as microangiopathy. To mitigate this problem, we suggest normalizing each voxel not only with a global reference value (ie, the median value of normally perfused tissue) but also with its local contralateral counterpart.

MATERIALS AND METHODS

We retrospectively enrolled 2830 CTP scans with suspected ischemic stroke, of which 335 showed obvious signs of microangiopathy. In addition to the conventional, global normalization, a local normalization was performed by dividing the rCBF maps with their mirrored and smoothed counterpart, which sets each voxel value in relation to the contralateral counterpart, intrinsically accounting for GM and WM differences and symmetric patient individual microangiopathy. Maps were visually assessed and core volumes were calculated for both methods.

RESULTS

Cases with obvious microangiopathy showed a strong reduction in false-positives by using local normalization (mean 14.7 mL versus mean 3.7 mL in cases with and without microangiopathy). On average, core volumes were slightly smaller, indicating an improved segmentation that was more robust against naturally low blood flow values in the deep WM.

CONCLUSIONS

The proposed method of local normalization can reduce overestimation of the infarct core, especially in the deep WM and in cases with obvious microangiopathy. False-positives in CTP infarct core segmentation might lead to less-than-optimal therapy decisions when not correctly interpreted. The proposed method might help mitigate this problem.

CT perfusion in stroke: Comparing conventional and RAPID automated software

CT perfusion (CTP) imaging is increasingly used for routine evaluation of acute ischemic stroke. Knowledge about the different types of CTP software, imaging acquisition and post-processing, and interpretation is crucial for appropriate patient selection for reperfusion therapy. Conventional vendor-provided CTP software differentiates between ischemic penumbra and core infarct using the tiebreaker of critically reduced cerebral blood volume (CBV) values within brain regions showing abnormally elevated time parameters like mean transit time (MTT) or time to peak (TTP). On the other hand, RAPID automated software differentiates between ischemic penumbra and core infarct using the tiebreaker of critically reduced cerebral blood flow (CBF) values within brain regions showing abnormally elevated time to maximum (Tmax). Additionally, RAPID calculates certain indices that confer prognostic value, such as the hypoperfusion and CBV index. In this review, we aim to familiarize the reader with the technical principles of CTP imaging, compare CTP maps generated by conventional and RAPID software, and discuss important thresholds for reperfusion and prognostic indices. Lastly, we discuss common pitfalls to help with the accurate interpretation of CTP imaging.

Value of Immediate Flat Panel Perfusion Imaging after Endovascular Therapy (AFTERMATH): A Proof of Concept Study

BACKGROUND AND PURPOSE

Potential utility of flat panel CT perfusion imaging (FPCT-PI) performed immediately after mechanical thrombectomy (MT) is unknown. We aimed to assess whether FPCT-PI obtained directly post-MT could provide additional potentially relevant information on tissue reperfusion status.

MATERIALS AND METHODS

This was a single-center analysis of all patients with consecutive acute stroke admitted between June 2019 and March 2021 who underwent MT and postinterventional FPCT-PI (n = 26). A core lab blinded to technical details and clinical data performed TICI grading on postinterventional DSA images and qualitatively assessed reperfusion on time-sensitive FPCT-PI maps. According to agreement between DSA and FPCT-PI, all patients were classified into 4 groups: hypoperfusion findings perfectly matched by location (group 1), hypoperfusion findings mismatched by location (group 2), complete reperfusion on DSA with hypoperfusion on FPCT-PI (group 3), and hypoperfusion on DSA with complete reperfusion on FPCT-PI (group 4).

RESULTS

Detection of hypoperfusion (present/absent) concurred in 21/26 patients. Of these, reperfusion findings showed perfect agreement on location and size in 16 patients (group 1), while in 5 patients there was a mismatch by location (group 2). Of the remaining 5 patients with disagreement regarding the presence or absence of hypoperfusion, 3 were classified into group 3 and 2 into group 4. FPCT-PI findings could have avoided TICI overestimation in all false-positive operator-rated TICI 3 cases (10/26).

CONCLUSIONS

FPCT-PI may provide additional clinically relevant information in a considerable proportion of patients undergoing MT. Hence, FPCT-PI may complement the evaluation of reperfusion efficacy and potentially inform decision-making in the angiography suite.

Implications of Post-recanalization Perfusion Deficit After Acute Ischemic Stroke: a Scoping Review of Clinical and Preclinical Imaging Studies

The goal of reperfusion therapy for acute ischemic stroke (AIS) is to restore cerebral blood flow through recanalization of the occluded vessel. Unfortunately, successful recanalization does not always result in favorable clinical outcome. Post-recanalization perfusion deficits (PRPDs), constituted by cerebral hypo- or hyperperfusion, may contribute to lagging patient recovery rates, but its clinical significance remains unclear. This scoping review provides an overview of clinical and preclinical findings on post-ischemic reperfusion, aiming to elucidate the pattern and consequences of PRPD from a translational perspective. The MEDLINE database was searched for quantitative clinical and preclinical studies of AIS reporting PRPD based on cerebral circulation parameters acquired by translational tomographic imaging methods. PRPD and stroke outcome were mapped on a charting table, creating an overview of PRPD after AIS. Twenty-two clinical and twenty-two preclinical studies were included. Post-recanalization hypoperfusion is rarely reported in clinical studies (4/22) but unequivocally associated with detrimental outcome. Post-recanalization hyperperfusion is more commonly reported (18/22 clinical studies) and may be associated with positive or negative outcome. PRPD has been replicated in animal studies, offering mechanistic insights into causes and consequences of PRPD and allowing delineation of possible courses of PRPD. Complex relationships exist between PRPD and stroke outcome. Diversity in methods and lack of standardized definitions in reperfusion studies complicate the characterization of reperfusion patterns. Recommendations are made to advance the understanding of PRPD mechanisms and to further disentangle the relation between PRPD and disease outcome.

Effect of Menopause Status on Brain Perfusion Hemodynamics

BACKGROUND

The menopause transition is associated with an increasing risk of cerebrovascular disorders. However, the direct effect of menopause status on brain perfusion hemodynamics remains unclear. This study aimed to explore the influence of menopause status on cerebral blood flow (CBF) using arterial spin labeling magnetic resonance imaging.

METHODS

In this cross-sectional study, 185 subjects underwent arterial spin labeling magnetic resonance imaging at a hospital in China between September 2020 and December 2022, including 38 premenopausal women (mean age, 47.74±2.02 years), 42 perimenopausal women (mean age, 50.62±3.15 years), 42 postmenopausal women (mean age, 54.02±4.09 years), and 63 men (mean age, 52.70±4.33 years) of a similar age range. Mean CBF values in the whole brain, gray matter, white matter, cortical gray matter, subcortical gray matter, juxtacortical white matter, deep white matter, and periventricular white matter were extracted. ANCOVA was used to compare mean CBF among the 4 groups, controlling for confounding factors. Student t test was applied to compare mean CBF between the 3 female groups and age-matched males, respectively. Multivariable regression analysis was used to analysis the effect of age, sex, and menopause status on the CBF of the whole brain, gray matter, white matter, and subregions.

RESULTS

Perimenopausal and postmenopausal women showed a higher proportion of white matter hyperintensities compared with the other 2 groups (P<0.001). Premenopausal women exhibited higher CBF in the whole brain, gray matter, white matter, and subregions, compared with perimenopausal, postmenopausal women and men (P≤0.001). Multivariable regression analysis demonstrated significant effect of age and insignificant effect of sex on CBF for all participants. In addition, menopause status and the interaction between age and menopause status on CBF of whole brain, gray matter, white matter, and the subregions were observed in female participants, except for the deep and periventricular white matter regions, with premenopausal women exhibited a slight increase in CBF with age, while perimenopausal and postmenopausal women exhibited declines in CBF with age.

CONCLUSIONS

The current findings suggest that alterations of brain perfusion hemodynamics begin during the perimenopause period, which may be due to the increased burden of white matter hyperintensities.

Clinical Uncertainty in Large Vessel Occlusion ischemic stroke (CULVO): Does automated perfusion scanning make a difference? Protocol of an intrarater and interrater agreement study

BACKGROUND

Guidelines recommend the use of perfusion computed tomography (CT) to identify emergent large vessel ischemic stroke (ELVIS) patients who are likely to benefit from endovascular thrombectomy (EVT) if they present within 6-24 hour (late window) of stroke onset. We aim to determine if the interrater and intrarater reliability among physicians when recommending EVT is significantly different when perfusion CT or non-perfusion CT is reviewed.

METHODS

A total of 30 non-consecutive patients will be selected from our institutional database comprising 3144 cranial CT scans performed for acute stroke symptoms January 2018 to August 2022. The clinical and radiologic data of the 30 patients will be presented in random order to a group of 29 physicians in two separate sessions at least three weeks apart. In each session, the physicians will evaluate each patient once with automated perfusion images and once without. We will use non-overlapping 95% confidence intervals and difference in agreement classification as criteria to suggest a difference between the Gwet AC1 statistics (κG).

DISCUSSION

The results obtained from this study, combined with the clinical outcomes data of patients categorized through the two imaging techniques and a cost-effectiveness analysis, will offer a comprehensive evaluation of the clinical utility of perfusion CT neuroimaging. Should there be no significant disparity in the reliability of decisions made by clinicians using the two neuroimaging protocols, it may be necessary to revise existing recommendations regarding neuroimaging in the later time window to align with these findings.

No-reflow phenomenon in stroke patients: A systematic literature review and meta-analysis of clinical data

BACKGROUND

The no-reflow phenomenon refers to the absence of microvascular reperfusion despite macrovascular reperfusion.

AIM

The aim of this analysis was to summarize the available clinical evidence on no-reflow in patients with acute ischemic stroke.

METHODS

A systematic literature review and a meta-analysis of clinical data on definition, rates, and impact of the no-reflow phenomenon after reperfusion therapy was carried out. A predefined research strategy was formulated according to the Population, Intervention, Comparison, and Outcome (PICO) model and was used to screen for articles in PubMed, MEDLINE, and Embase up to 8 September 2022. Whenever possible, quantitative data were summarized using a random-effects model.

RESULTS

Thirteen studies with a total of 719 patients were included in the final analysis. Most studies (n = 10/13) used variations of the Thrombolysis in Cerebral Infarction scale to evaluate macrovascular reperfusion, whereas microvascular reperfusion and no-reflow were mostly assessed on perfusion maps (n = 9/13). In one-third of stroke patients with successful macrovascular reperfusion (29%, 95% confidence interval (CI), 21-37%), the no-reflow phenomenon was observed. Pooled analysis showed that no-reflow was consistently associated with reduced rates of functional independence (odds ratio (OR), 0.21, 95% CI, 0.15-0.31).

CONCLUSION

The definition of no-reflow varied substantially across studies, but it appears to be a common phenomenon. Some of the no-reflow cases may simply represent remaining vessel occlusions, and it remains unclear whether no-reflow is an epiphenomenon of the infarcted parenchyma or causes infarction. Future studies should focus on standardizing the definition of no-reflow with more consistent definitions of successful macrovascular reperfusion and experimental set-ups that could detect the causality of the observed findings.

Computer tomography perfusion patterns in iatrogenic cerebral arterial gas embolism: A retrospective cohort study

PURPOSE

Cerebral arterial gas embolism (CAGE) occurs when air or medical gas enters the systemic circulation during invasive procedures and lodges in the cerebral vasculature. Non-contrast computer tomography (CT) may not always show intracerebral gas. CT perfusion (CTP) might be a useful adjunct for diagnosing CAGE in these patients.

METHODS

This is a retrospective single-center cohort study. We included patients who were diagnosed with iatrogenic CAGE and underwent CTP within 24 h after onset of symptoms between January 2016 and October 2022. All imaging studies were evaluated by two independent radiologists. CTP studies were scored semi-quantitatively for perfusion abnormalities (normal, minimal, moderate, severe) in the following parameters: cerebral blood flow, cerebral blood volume, time-to-drain and time-to-maximum.

RESULTS

Among 27 patient admitted with iatrogenic CAGE, 15 patients underwent CTP within the designated timeframe and were included for imaging analysis. CTP showed perfusion deficits in all patients except one. The affected areas on CTP scans were in general located bilaterally and frontoparietally. The typical pattern of CTP abnormalities in these areas was hypoperfusion with an increased time-to-drain and time-to-maximum, and a corresponding minimal decrease in cerebral blood flow. Cerebral blood volume was mostly unaffected.

CONCLUSION

CTP may show specific perfusion defects in patients with a clinical diagnosis of CAGE. This suggests that CTP may be supportive in diagnosing CAGE in cases where no intracerebral gas is seen on non-contrast CT.

Cerebral haemodynamics in symptomatic intracranial atherosclerotic disease: a narrative review of the assessment methods and clinical implications

Intracranial atherosclerotic disease (ICAD) is a common cause of ischaemic stroke and transient ischaemic attack (TIA) with a high recurrence rate. It is often referred to as intracranial atherosclerotic stenosis (ICAS), when the plaque has caused significant narrowing of the vessel lumen. The lesion is usually considered 'symptomatic ICAD/ICAS' (sICAD/sICAS) when it has caused an ischaemic stroke or TIA. The severity of luminal stenosis has long been established as a prognostic factor for stroke relapse in sICAS. Yet, accumulating studies have also reported the important roles of plaque vulnerability, cerebral haemodynamics, collateral circulation, cerebral autoregulation and other factors in altering the stroke risks across patients with sICAS. In this review article, we focus on cerebral haemodynamics in sICAS. We reviewed imaging modalities/methods in assessing cerebral haemodynamics, the haemodynamic metrics provided by these methods and application of these methods in research and clinical practice. More importantly, we reviewed the significance of these haemodynamic features in governing the risk of stroke recurrence in sICAS. We also discussed other clinical implications of these haemodynamic features in sICAS, such as the associations with collateral recruitment and evolution of the lesion under medical treatment, and indications for more individualised blood pressure management for secondary stroke prevention. We then put forward some knowledge gaps and future directions on these topics.

Revolutionizing the Management of Large-Core Ischaemic Strokes: Decoding the Success of Endovascular Therapy in the Recent Stroke Trials

Endovascular therapy (EVT) has revolutionized the management of acute ischaemic strokes with large vessel occlusion, with emerging evidence suggesting its benefit also in large infarct core volume strokes. In the last two years, four randomised controlled trials have been published on this topic-RESCUE-Japan LIMIT, ANGEL-ASPECT, SELECT2 and TENSION, with overall results showing that EVT improves functional and neurological outcomes compared to medical management alone. This review aims to summarise the recent evidence presented by these four trials and highlight some of the limitations in our current understanding of this topic.

Perfusion deficits in thrombolysis-treated acute ischemic stroke patients with negative or positive diffusion-weighted imaging

OBJECTIVE

Magnetic resonance imaging (MRI) and CT perfusion may provide diagnostic information for intravenous tissue-type plasminogen activator (IV t-PA) administration in acute ischemic stroke (AIS) patients. We aimed to compare the clinical features and perfusion deficits of diffusion weighted imaging (DWI)-negative and DWI-positive AIS patients.

METHODS

This retrospective and observational study included thrombolysis-treated AIS patients undergoing multimodel CT imaging before treatment and DWI after treatment between 2021 and 2022. Two experienced neuroradiologists blindly and independently examined the images to identify perfusion deficits in AIS patients. The patients were divided into DWI-positive and DWI-negative groups based on visible hyperintense lesions on DWI. A modified Rankin scale (mRS) score of ≤ 2 indicated good functional outcomes at discharge. Sensitivity analysis was conducted to determine whether CT perfusion was an independent predictor of positive DWI imaging on follow-up.

RESULTS

This study included 151 patients, of whom 35 (23.2%) patients were DWI-negative on follow-up. These DWI-negative patients were less likely to have a medical history of atrial fibrillation; they had lower triglyceride levels, a shorter admission time, lower National Institutes of Health Stroke Scale (NIHSS) scores after IV t-PA and lower mRS scores at discharge, and had better functional outcomes. A total of 37.1% of DWI-positive and 25.7% of DWI-negative patients had vascular stenosis (P = 0.215). A total of 47.4% of DWI-positive and 37.1% of DWI-negative patients had CT perfusion deficits (P = 0.284). A total of 73.5% of patients with normal CT perfusion had positive DWI, while 19.1% of patients with perfusion deficits had negative DWI. The sensitivity and specificity of NCCT were 14.8% and 97.1% (Kappa = 0.061, P = 0.074), CTP was 47.4% and 62.9% for predicting DWI lesion (Kappa = 0.069, P = 0.284).

CONCLUSIONS

About 23.2% of AIS patients who received intravenous thrombolysis treatment did not have a relevant DWI-MRI lesion on follow-up. Over one-third of patients in the DWI-MRI negative group showed CT perfusion deficits, with a sensitivity of 47.4% for predicting DWI lesions in non-mechanical thrombectomy patients.

The value of computed tomography perfusion deficit volumes in acute isolated brainstem infarction

Purpose

Diagnosis of acute isolated brainstem infarction is challenging owing to non-specific, variable symptoms, and the effectiveness of non-contrast computed tomography (NCCT) is poor owing to limited spatial resolution and artifacts. Computed tomography perfusion (CTP) imaging parameters are significantly associated with functional outcomes in posterior circulation acute ischemic stroke; however, the role of CTP in isolated brainstem infarction remains unclear. We aimed to determine the value of CTP imaging parameters in predicting functional outcomes for affected patients.

Methods

In total, 116 consecutive patients with isolated pontine/midbrain hypoperfusion who underwent CTP and follow-up by magnetic resonance imaging (MRI) between January 2018 and March 2022, were retrospectively analyzed. Perfusion deficit volumes on all maps, and the final infarction volume (FIV) on MRI were quantified. "Good" functional outcome was defined as a 90-day modified Rankin Scale score of 0 and 1. Statistical analysis included uni- and multivariate regression analyses, binary logistic regressions, and receiver operating characteristics (ROC) analyses.

Results

In total, 113 patients had confirmed isolated pontine/midbrain infarction on follow-up MRI. Onset-to-scan time, visibility of ischemic lesions on NCCT, the baseline National Institutes of Health Stroke Scale (NIHSS) score, and perfusion deficit volumes on all CTP maps were significantly associated with FIV (p < 0.05). In a multivariate linear regression model, adjusted for age, sex, NIHSS score, onset-to-scan time, and visibility of NCCT, perfusion deficit volumes remained significantly associated with FIV. In binary logistic regression analyses, perfusion deficit volumes on all CTP maps remained independent predictors of a good functional outcome. In ROC analyses, the cerebral blood flow deficit volume showed a slightly higher discriminatory value with the largest area under the curve being 0.683 [(95% CI, 0.587-0.780), p = 0.001].

Conclusion

Perfusion deficit volumes of CTP imaging could reflect the FIV and contain prognostic information on functional outcomes in patients with acute isolated brainstem infarction.

Cerebral perfusion in post-stroke aphasia and its relationship to residual language abilities

Stroke alters blood flow to the brain resulting in damaged tissue and cell death. Moreover, the disruption of cerebral blood flow (perfusion) can be observed in areas surrounding and distal to the lesion. These structurally preserved but suboptimally perfused regions may also affect recovery. Thus, to better understand aphasia recovery, the relationship between cerebral perfusion and language needs to be systematically examined. In the current study, we aimed to evaluate (i) how stroke affects perfusion outside of lesioned areas in chronic aphasia and (ii) how perfusion in specific cortical areas and perilesional tissue relates to language outcomes in aphasia. We analysed perfusion data from a large sample of participants with chronic aphasia due to left hemisphere stroke (n = 43) and age-matched healthy controls (n = 25). We used anatomically defined regions of interest that covered the frontal, parietal, and temporal areas of the perisylvian cortex in both hemispheres, areas typically known to support language, along with several control regions not implicated in language processing. For the aphasia group, we also looked at three regions of interest in the perilesional tissue. We compared perfusion levels between the two groups and investigated the relationship between perfusion levels and language subtest scores while controlling for demographic and lesion variables. First, we observed that perfusion levels outside the lesioned areas were significantly reduced in frontal and parietal regions in the left hemisphere in people with aphasia compared to the control group, while no differences were observed for the right hemisphere regions. Second, we found that perfusion in the left temporal lobe (and most strongly in the posterior part of both superior and middle temporal gyri) and inferior parietal areas (supramarginal gyrus) was significantly related to residual expressive and receptive language abilities. In contrast, perfusion in the frontal regions did not show such a relationship; no relationship with language was also observed for perfusion levels in control areas and all right hemisphere regions. Third, perilesional perfusion was only marginally related to language production abilities. Cumulatively, the current findings demonstrate that blood flow is reduced beyond the lesion site in chronic aphasia and that hypoperfused neural tissue in critical temporoparietal language areas has a negative impact on behavioural outcomes. These results, using perfusion imaging, underscore the critical and general role that left hemisphere posterior temporal regions play in various expressive and receptive language abilities. Overall, the study highlights the importance of exploring perfusion measures in stroke.

Is the optimal Tmax threshold identifying perfusion deficit volumes variable across MR perfusion software packages? A pilot study

PURPOSE

Accurate quantification of ischemic core and ischemic penumbra is mandatory for late-presenting acute ischemic stroke. Substantial differences between MR perfusion software packages have been reported, suggesting that the optimal Time-to-Maximum (Tmax) threshold may be variable. We performed a pilot study to assess the optimal Tmax threshold of two MR perfusion software packages (A: RAPID®; B: OleaSphere®) by comparing perfusion deficit volumes to final infarct volumes as ground truth.

METHODS

The HIBISCUS-STROKE cohort includes acute ischemic stroke patients treated by mechanical thrombectomy after MRI triage. Mechanical thrombectomy failure was defined as a modified thrombolysis in cerebral infarction score of 0. Admission MR perfusion were post-processed using two packages with increasing Tmax thresholds (≥ 6 s, ≥ 8 s and ≥ 10 s) and compared to final infarct volume evaluated with day-6 MRI.

RESULTS

Eighteen patients were included. Lengthening the threshold from ≥ 6 s to ≥ 10 s led to significantly smaller perfusion deficit volumes for both packages. For package A, Tmax ≥ 6 s and ≥ 8 s moderately overestimated final infarct volume (median absolute difference: - 9.5 mL, interquartile range (IQR) [- 17.5; 0.9] and 0.2 mL, IQR [- 8.1; 4.8], respectively). Bland-Altman analysis indicated that they were closer to final infarct volume and had narrower ranges of agreement compared with Tmax ≥ 10 s. For package B, Tmax ≥ 10 s was closer to final infarct volume (median absolute difference: - 10.1 mL, IQR: [- 17.7; - 2.9]) versus - 21.8 mL (IQR: [- 36.7; - 9.5]) for Tmax ≥ 6 s. Bland-Altman plots confirmed these findings (mean absolute difference: 2.2 mL versus 31.5 mL, respectively).

CONCLUSIONS

The optimal Tmax threshold for defining the ischemic penumbra appeared to be most accurate at ≥ 6 s for package A and ≥ 10 s for package B. This implies that the widely recommended Tmax threshold ≥ 6 s may not be optimal for all available MRP software package. Future validation studies are required to define the optimal Tmax threshold to use for each package.

Correlation between EEG spectral power and cerebral perfusion in patients with acute ischemic stroke

Dry electrode electroencephalography (EEG) has the potential to diagnose ischemic stroke in the acute phase. In the current study we determined the correlation between EEG spectral power and ischemic stroke size and location as determined by computed tomography perfusion (CTP). Dry electrode EEG recordings were performed in patients with acute ischemic stroke in the emergency room. CTP preceded the EEG recordings as part of standard imaging protocol. Infarct core volume, total hypoperfused volume and local cerebral blood flow (CBF) were estimated with CTP. Additionally, global and local EEG spectral power were determined. We used Spearman's correlation coefficients to evaluate the correlation between variables. We included 27 patients (median age 72 [IQR:69-80] years, 15/27 [56%] men). Median CTP-to-EEG time was 32 (range:8-138) minutes. Hypoperfused volumes were estimated for 12/27 (44%) patients. Infarct core volume correlated best with global delta power (ρ = 0.76, p < 0.01), total hypoperfused volume with global alpha power (ρ = -0.58, p = 0.05), and local CBF with local alpha power (ρ = 0.43, p < 0.01). We conclude that dry electrode EEG signals slow down with increasing hypoperfused volume, which could potentially be used to discriminate between small and large ischemic strokes.

Cerebral artery signal intensity gradient from Time-of-Flight Magnetic Resonance Angiography and clinical outcome in lenticulostriate infarction: a retrospective cohort study

Purpose

Lenticulostriate infarction requires further research of arterial hemodynamic factors, as the disease is diagnosed in the absence of major arterial stenosis or cardioembolism.

Methods

In this multicenter retrospective cohort study, we included patients who were hospitalized for lenticulostriate infarction from January 2015 to March 2021 at three stroke centers in South Korea. We obtained hemodynamic information on cerebral arteries using signal intensity gradient (SIG), an in-vivo approximated wall shear stress (WSS) derived from Time-of-Flight Magnetic Resonance Angiography (TOF-MRA). A favorable outcome was defined as a modified Rankin Scale of 0 to 2 at hospital discharge.

Results

A total of 294 patients were included, of whom 146 (49.7%) had an unfavorable outcome. The unfavorable outcome group showed significantly lower SIG in both middle cerebral arteries (MCAs) than the favorable group (5.2 ± 1.2 SI/mm vs. 5.9 ± 1.2, p < 0.001), and similar findings were observed in other cerebral arteries. The SIGs in both MCAs were independently associated with favorable outcome, with an odds ratio of 1.42 (95% confidence interval, 1.11-1.80; p = 0.005) for the right MCA and 1.49 (95% CI, 1.15-1.93; p = 0.003) for the left MCA, after adjusting for potential confounders. Similar findings were observed in other cerebral artery SIGs.

Conclusion

Cerebral artery SIG from TOF-MRA was significantly associated with short-term functional outcomes in patients with lenticulostriate infarction. Further studies are needed to investigate the temporal relationships of SIG in patients with cerebral infarction.

Contemporary Methods for Detection and Intervention of Distal Medium and Small Vessel Occlusions

The efficacy of using mechanical thrombectomy for proximal large vessel occlusions has been demonstrated in multiple large-scale trials and has further raised the question of its potential utility for distal medium and small vessel occlusions (DMSVOs). Their longer, more tortuous course and smaller corresponding vascular territories render a significant challenge for detection and intervention. The aim of this study is to provide a comprehensive overview of the current imaging and endovascular intervention options for DMSVOs and review the current works in the literature. Compared with traditional computed tomography angiography (CTA) and CT perfusion, recent advances such as multiphase CTA and maps derived from the time-to-maximum parameter coupled with artificial intelligence have demonstrated increased sensitivity for the detection of DMSVOs. Furthermore, newer generations of mini stent retrievers and thromboaspiration devices have allowed for the access and navigation of smaller and more fragile distal arteries. Preliminary studies have suggested that mechanical thrombectomy using this newer generation of devices is both safe and feasible in distal medium-sized vessels, such as M2. However, endovascular intervention utilizing such contemporary methods and devices must be balanced at the discretion of operator experience and favorable vascular anatomy. Further large-scale multicenter clinical trials are warranted to elucidate the indications for as well as to strengthen the safety and efficacy of this approach.

Stroke: Hospital Nursing Management Within the First 24 Hours

Within the United States, someone will have a stroke approximately every 40 seconds. Eighty-five percent of strokes are ischemic, with 15% classified as either intracranial or subarachnoid hemorrhage. Stroke care is complex, and nurses play a critical role in identification, assessment, management, and coordination throughout the stroke continuum of care. This article will explore the nursing care of the patient with ischemic and hemorrhagic stroke during the first 24 hours.

Ghost infarct core: A systematic review of the frequency, magnitude, and variables of CT perfusion overestimation

BACKGROUND AND PURPOSE

CT perfusion (CTP) imaging is now widely used to select patients with large vessel occlusions for mechanical thrombectomy. Ghost infarct core (GIC) phenomenon has been coined to describe CTP core overestimation and has been investigated in several retrospective studies. Our aim is to review the frequency, magnitude, and variables associated with this phenomenon.

METHODS

A primary literature search resulted in eight studies documenting median time from symptom onset to CTP, median estimated core size, median final infarct volume, median core overestimation of the GIC population, recanalization rates, good outcomes, and collateral status for this systematic review.

RESULTS

All the studies investigated patients who underwent CTP within 6 hours of symptom onset, ranging from median times of 105 to 309 minutes. The frequency of core overestimation varied from 6% to 58.4%, while the median estimated ischemic core and final infarction volume ranged from 7 to 27 mL and 12 to 31 mL, respectively. The median core overestimation ranged from 3.6 to 30 mL with upper quartile ranges up to 58 mL. GIC was found to be a highly time-and-collateral-dependent process that increases in frequency and magnitude as the time from symptom onset to imaging decreases and in the presence of poor collaterals.

CONCLUSIONS

CTP ischemic core overestimation appears to be a relatively common phenomenon that is most frequent in patients with poor collaterals imaged within the acute time window. Early perfusion imaging should be interpreted with caution to prevent the inadvertent exclusion of patients from highly effective reperfusion therapies.

Stroke imaging modality for endovascular therapy in the extended window: systematic review and meta-analysis

BACKGROUND

In anterior circulation large vessel occlusion (LVO) in the extended time window, the guidelines recommend advanced imaging (ADVI) to select patients for endovascular therapy (EVT). However, questions remain regarding its availability and applicability in the real world. It is unclear whether an approach to the extended window EVT that does not use ADVI would be equivalent.

METHODS

In April 2022, a literature search was performed to identified randomized controlled trials (RCT) and observational studies describing 90-day outcomes. We performed a meta-analysis of the proportion of aggregate using a random effect to estimate rates of functional independence, defined as modified Rankin Scale (mRS) score ≤2 at 90 days, mean mRS, mortality and symptomatic intracranial hemorrhage (sICH) stratified by imaging modality.

RESULTS

Four RCTs and 28 observational studies were included. The pooled proportion of functional independence among patients selected by ADVI was 44% (95% CI 39% to 48%; I2=80%) and 48% (95% CI 41% to 55%; I2=75%) with non-contrast CT/CT angiography (NCCT/CTA) (p=0.36). Mean mRS with ADVI was 2.88 (95% CI 2.36 to 3.41; I2=0.0%) and 2.79 (95% CI 2.31 to 3.27; I2=0.0%) with NCCT (p=0.79). Mortality in patients selected by ADVI was 13% (95% CI 10% to 17%; I2=81%) and 16% (95% CI 12% to 22%; I2=69%) with NCCT (p=0.29). sICH with ADVI was 4% (95% CI 3% to 7%; I2=73%) and 6% with NCCT/CTA (95% CI 4% to 8%; I2=6%, p=0.27).

CONCLUSIONS

Our study suggests that, in anterior circulation LVO, the rates of functional independence may be similar when patients are selected using ADVI or NCCT for EVT in the extended time window. A simplified triage protocol does not seem to increase mortality or sICH. PROTOCOL REGISTRATION NUMBER: (PROSPERO ID: CRD42021236092).

CT Perfusion Imaging Guides Clinical Decision-Making in a Case of Thalamic Stroke: A Case Report

This case highlights a patient presenting with a stroke code in the emergency department with decreased consciousness. The patient was later found to have bilateral thalamic strokes due to ischemia of the artery of Percheron. Initial head computed tomography (CT) and CT angiogram (CTA) of the head and neck showed no abnormalities. CT perfusion (CTP) showed a perfusion deficit of 169 mL with a T-max greater than 4 s and 4 mL with a T-max greater than 6 s in the posterior circulation. The patient received IV alteplase. This case report emphasizes the importance of perfusion neuroimaging in the evaluation of acute ischemic stroke.

Artificial Intelligence in Neuroradiology: A Review of Current Topics and Competition Challenges

There is an expanding body of literature that describes the application of deep learning and other machine learning and artificial intelligence methods with potential relevance to neuroradiology practice. In this article, we performed a literature review to identify recent developments on the topics of artificial intelligence in neuroradiology, with particular emphasis on large datasets and large-scale algorithm assessments, such as those used in imaging AI competition challenges. Numerous applications relevant to ischemic stroke, intracranial hemorrhage, brain tumors, demyelinating disease, and neurodegenerative/neurocognitive disorders were discussed. The potential applications of these methods to spinal fractures, scoliosis grading, head and neck oncology, and vascular imaging were also reviewed. The AI applications examined perform a variety of tasks, including localization, segmentation, longitudinal monitoring, diagnostic classification, and prognostication. While research on this topic is ongoing, several applications have been cleared for clinical use and have the potential to augment the accuracy or efficiency of neuroradiologists.

Perfusion-weighted software written in Python for DSC-MRI analysis

Introduction

Dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion studies in magnetic resonance imaging (MRI) provide valuable data for studying vascular cerebral pathophysiology in different rodent models of brain diseases (stroke, tumor grading, and neurodegenerative models). The extraction of these hemodynamic parameters via DSC-MRI is based on tracer kinetic modeling, which can be solved using deconvolution-based methods, among others. Most of the post-processing software used in preclinical studies is home-built and custom-designed. Its use being, in most cases, limited to the institution responsible for the development. In this study, we designed a tool that performs the hemodynamic quantification process quickly and in a reliable way for research purposes.

Methods

The DSC-MRI quantification tool, developed as a Python project, performs the basic mathematical steps to generate the parametric maps: cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), signal recovery (SR), and percentage signal recovery (PSR). For the validation process, a data set composed of MRI rat brain scans was evaluated: i) healthy animals, ii) temporal blood-brain barrier (BBB) dysfunction, iii) cerebral chronic hypoperfusion (CCH), iv) ischemic stroke, and v) glioblastoma multiforme (GBM) models. The resulting perfusion parameters were then compared with data retrieved from the literature.

Results

A total of 30 animals were evaluated with our DSC-MRI quantification tool. In all the models, the hemodynamic parameters reported from the literature are reproduced and they are in the same range as our results. The Bland-Altman plot used to describe the agreement between our perfusion quantitative analyses and literature data regarding healthy rats, stroke, and GBM models, determined that the agreement for CBV and MTT is higher than for CBF.

Conclusion

An open-source, Python-based DSC post-processing software package that performs key quantitative perfusion parameters has been developed. Regarding the different animal models used, the results obtained are consistent and in good agreement with the physiological patterns and values reported in the literature. Our development has been built in a modular framework to allow code customization or the addition of alternative algorithms not yet implemented.

Tmax volume can predict clinical type in patients with acute ischemic stroke

OBJECTIVE

Endovascular therapy (EVT) is performed for acute ischemic stroke (AIS) with large vessel occlusion (LVO), however, the treatment strategies and clinical outcomes differ between cardiac embolism (CE) and intracranial arteriosclerosis-derived LVO (ICAS-LVO). We analyzed whether the time-to-max (Tmax) volume derived from perfusion imaging predicted clinical classification in AIS patients before EVT.

METHODS

Consecutive AIS patients with anterior circulation LVO evaluated by automated imaging software were retrospectively identified. Patients were classified into a CE group and an ICAS-LVO group, and parameters were compared between groups.

RESULTS

Thirty-nine patients were included and Tmax volume and Tmax > 6 s volume/Tmax > 4 s volume were significantly greater in the CE group than in the ICAS-LVO group (Tmax > 4 s volume: 261 mL vs. 149 mL, p = .01, Tmax > 6 s volume: 143 mL vs. 59 mL, p = .001, Tmax > 6 s volume/Tmax > 4 s volume: 0.59 vs. 0.40, p < .001). Multiple logistic regression analysis indicated an association between clinical classification and high Tmax > 6 s volume/Tmax > 4 s volume (p = .04).

CONCLUSION

The Tmax volume derived from perfusion imaging predicts the clinical classification of AIS patients before EVT.

Stroke-GFCN: ischemic stroke lesion prediction with a fully convolutional graph network

Purpose

The interpretation of image data plays a critical role during acute brain stroke diagnosis, and promptly defining the requirement of a surgical intervention will drastically impact the patient's outcome. However, determining stroke lesions purely from images can be a daunting task. Many studies proposed automatic segmentation methods for brain stroke lesions from medical images in different modalities, though heretofore results do not satisfy the requirements to be clinically reliable. We investigate the segmentation of brain stroke lesions using a geometric deep learning model that takes advantage of the intrinsic interconnected diffusion features in a set of multi-modal inputs consisting of computer tomography (CT) perfusion parameters.

Approach

We propose a geometric deep learning model for the segmentation of ischemic stroke brain lesions that employs spline convolutions and unpooling/pooling operators on graphs to excerpt graph-structured features in a fully convolutional network architecture. In addition, we seek to understand the underlying principles governing the different components of our model. Accordingly, we structure the experiments in two parts: an evaluation of different architecture hyperparameters and a comparison with state-of-the-art methods.

Results

The ablation study shows that deeper layers obtain a higher Dice coefficient score (DCS) of up to 0.3654. Comparing different pooling and unpooling methods shows that the best performing unpooling method is the proportional approach, yet it often smooths the segmentation border. Unpooling achieves segmentation results more adapted to the lesion boundary corroborated with systematic lower values of Hausdorff distance. The model performs at the level of state-of-the-art models without optimized training methods, such as augmentation or patches, with a DCS of 0.4553 ± 0.0031 .

Conclusions

We proposed and evaluated an end-to-end trainable fully convolutional graph network architecture using spline convolutional layers for the ischemic stroke lesion prediction. We propose a model that employs graph-based operations to predict acute stroke brain lesions from CT perfusion parameters. Our results prove the feasibility of using geometric deep learning to solve segmentation problems, and our model shows a better performance than other models evaluated. The proposed model achieves improved metric values for the DCS metric, ranging from 8.61% to 69.05%, compared with other models trained under the same conditions. Next, we compare different pooling and unpooling operations in relation to their segmentation results, and we show that the model can produce segmentation outputs that adapt to irregular segmentation boundaries when using simple heuristic unpooling operations.

Deep-learning-enabled brain hemodynamic mapping using resting-state fMRI

Cerebrovascular disease is a leading cause of death globally. Prevention and early intervention are known to be the most effective forms of its management. Non-invasive imaging methods hold great promises for early stratification, but at present lack the sensitivity for personalized prognosis. Resting-state functional magnetic resonance imaging (rs-fMRI), a powerful tool previously used for mapping neural activity, is available in most hospitals. Here we show that rs-fMRI can be used to map cerebral hemodynamic function and delineate impairment. By exploiting time variations in breathing pattern during rs-fMRI, deep learning enables reproducible mapping of cerebrovascular reactivity (CVR) and bolus arrival time (BAT) of the human brain using resting-state CO2 fluctuations as a natural "contrast media". The deep-learning network is trained with CVR and BAT maps obtained with a reference method of CO2-inhalation MRI, which includes data from young and older healthy subjects and patients with Moyamoya disease and brain tumors. We demonstrate the performance of deep-learning cerebrovascular mapping in the detection of vascular abnormalities, evaluation of revascularization effects, and vascular alterations in normal aging. In addition, cerebrovascular maps obtained with the proposed method exhibit excellent reproducibility in both healthy volunteers and stroke patients. Deep-learning resting-state vascular imaging has the potential to become a useful tool in clinical cerebrovascular imaging.

Understanding recovery of language after stroke: insights from neurovascular MRI studies

Stroke causes a disruption in blood flow to the brain that can lead to profound language impairments. Understanding the mechanisms of language recovery after stroke is crucial for the prognosis and effective rehabilitation of people with aphasia. While the role of injured brain structures and disruptions in functional connectivity have been extensively explored, the relationship between neurovascular measures and language recovery in both early and later stages has not received sufficient attention in the field. Fully functioning healthy brain tissue requires oxygen and nutrients to be delivered promptly via its blood supply. Persistent decreases in blood flow after a stroke to the remaining non-lesioned tissue have been shown to contribute to poor language recovery. The goal of the current paper is to critically examine stroke studies looking at the relationship between different neurovascular measures and language deficits and mechanisms of language recovery via changes in neurovascular metrics. Measures of perfusion or cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) provide complementary approaches to understanding neurovascular mechanisms post stroke by capturing both cerebral metabolic demands and mechanical vascular properties. While CBF measures indicate the amount of blood delivered to a certain region and serve as a proxy for metabolic demands of that area, CVR indices reflect the ability of the vasculature to recruit blood flow in response to a shortage of oxygen, such as when one is holding their breath. Increases in CBF during recovery beyond the site of the lesion have been shown to promote language gains. Similarly, CVR changes, when collateral vessels are recruited to help reorganize the flow of blood in hypoperfused regions, have been related to functional recovery post stroke. In the current review, we highlight the main findings in the literature investigating neurovascular changes in stroke recovery with a particular emphasis on how language abilities can be affected by changes in CBF and CVR. We conclude by summarizing existing methodological challenges and knowledge gaps that need to be addressed in future work in this area, outlining a promising avenue of research.

Predictive value of ischemia location on multimodal CT in thrombectomy-treated patients

OBJECTIVE

Alberta Stroke Program Early CT Score (ASPECTS) applied to CT-perfusion (CTP) and CT-angiography-source-images (CTA-SI) may improve outcome prediction in large vessel occlusion (LVO) stroke if compared to non-contrast CT (NCCT) alone. Besides, ischemia location may have enhanced capabilities, compared to ischemia volume alone, in predicting stroke outcomes. We aim to evaluate the association between ischemia location as measured by ASPECTS regions in NCCT, CTP maps and CTA-SI and 3 months outcome in patients with LVO treated with mechanical thrombectomy (MT).

MATERIAL AND METHODS

Consecutive patients with anterior circulation stroke treated with MT were recorded in a prospectively maintained database at a single center. Modified Rankin scale (mRS) at 3 months >2 was considered a poor outcome. Association of patients' characteristics, NCCT, CTP, and CTA-SI parameters with outcome was evaluated using single-variable analysis and binary logistic regression multivariate analysis for each imaging technique.

RESULTS

177 patients were included. 115 (65%) patients reached a favorable outcome. The involvement of lenticular, caudate, M1, or M2 in all imaging techniques, insula in NCCT and CTA-SI and M5 in CBV maps and CTA-SI was related to functional outcome in bivariate analysis. However, in the multivariate analysis, none ischemia location was independently related to outcome, no matter the imaging technique studied. This finding remained unchanged when restricted to patients with good recanalization and when analyzing subpopulations according to hemisphere involvement or territories association.

CONCLUSIONS

Our study suggests ischemia location shouldn't be used solely for decision-making in LVO stroke patients. Its predictive value may be taken in consideration together with other clinical and radiological variables.