Functional evaluation of intracranial atherosclerotic stenosis by pressure ratio measurements

Advancements in imaging of intracranial atherosclerotic disease: beyond the arterial lumen to the vessel wall

Intracranial atherosclerotic disease (ICAD) significantly increases the risk of ischemic stroke. It involves the accumulation of plaque within arterial walls and narrowing or blockage of blood vessel lumens. Accurate imaging is crucial for the diagnosis and management of ICAD at both acute and chronic stages. However, imaging the small, tortuous intracranial arterial walls amidst complex structures is challenging. Clinicians have employed diverse approaches to improve imaging quality, with a particular emphasis on optimizing the acquisition of images using new techniques, enhancing spatial and temporal resolution of images, and refining post-processing techniques. ICAD imaging has evolved from depicting lumen stenosis to assessing blood flow reserve and identifying plaque components. Advanced techniques such as fractional flow reserve (FFR), high-resolution vessel wall magnetic resonance (VW-MR), optical coherence tomography (OCT), and radial wall strain (RWS) now allow direct visualization of flow impairment, vulnerable plaques, and blood flow strain to plaque, aiding in the selection of high-risk stroke patients for intervention. This article reviews the progression of imaging modalities from lumen stenosis to vessel wall pathology and compares their diagnostic value for risk stratification in ICAD patients.

Correlation of computed fractional flow and in-stent restenosis in patients with intracranial atherosclerotic stenosis

OBJECTIVE

Fractional flow (FF) reserve has been developed as a gold standard for coronary intervention. Intracranial FF is also a valuable hemodynamic index to assess the severity of narrowing in intracranial atherosclerotic stenosis (ICAS). This study aims to investigate the predictive value of FF in assessing restenosis following endovascular treatment in patients with symptomatic ICAS.

METHODS

This retrospective study recruited 67 patients with symptomatic ICAS who received intracranial stenting between March 2019 and January 2024. FF was measured by dedicated software (AccuICAD) before and after stenting. During follow-up, patients were categorized into two groups based on the occurrence of in-stent restenosis (ISR): ISR group and non-ISR group. Multivariate regression analysis and Kaplan-Meier survival analysis were performed to identify the predictive factors for ISR.

RESULTS

Post-FF was significantly different between the ISR and non-ISR groups (0.84±0.09 vs 0.92±0.06, respectively, P<0.01). Univariate and multivariate Cox regression analyses identified post-FF (HR 0.0, 95% CI 0.0 to 0.08, P=0.005) and smoking (HR 3.06, 95% CI 1.02 to 9.19, P=0.047) as the two predictors of ISR. Receiver operating characteristic curve analysis confirmed the predictive value of post-FF for ISR (AUC=0.783, 95% CI 0.645 to 0.920, P=0.003), with a cut-off value of 0.94. Kaplan-Meier survival analysis further demonstrated that patients with a post-FF value >0.94 had a significantly lower incidence of ISR (P=0.001).

CONCLUSION

In this study, post-FF effectively predicted ISR, providing an intraoperative evaluation value for stenting in ICAS.

Clinical implications of haemodynamics in symptomatic intracranial atherosclerotic stenosis by computational fluid dynamics modelling: a systematic review

BACKGROUND

Recently, computational fluid dynamics (CFD) has been used to simulate blood flow of symptomatic intracranial atherosclerotic stenosis (sICAS) and investigate the clinical implications of its haemodynamic features, which were systematically reviewed in this study.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Meta-analysis of Observational Studies in Epidemiology statements, we searched PubMed and Embase up to March 2024 and screened for articles reporting clinical implications of haemodynamic parameters in sICAS derived from CFD models.

RESULTS

19 articles met the inclusion criteria, all studies recruiting patients from China. Most studies used CT angiography (CTA) as the source image for vessel segmentation, and generic boundary conditions, rigid vessel wall and Newtonian fluid assumptions for CFD modelling, in patients with 50%-99% sICAS. Pressure and wall shear stress (WSS) were quantified in almost all studies, and the translesional changes in pressure and WSS were usually quantified with a poststenotic to prestenotic pressure ratio (PR) and stenotic-throat to prestenotic WSS ratio (WSSR). Lower PR was associated with more severe stenosis, better leptomeningeal collaterals, prolonged perfusion time and internal borderzone infarcts. Higher WSSR and other WSS measures were associated with positive vessel wall remodelling, regression of luminal stenosis and artery-to-artery embolism. Lower PR and higher WSSR were both associated with the presence and severity of cerebral small vessel disease. Moreover, translesional PR and WSSR were promising predictors for stroke recurrence in medically treated patients with sICAS and outcomes after acute reperfusion therapy, which also provided indicators to assess the effects of stenting treatment on focal haemodynamics.

CONCLUSIONS

CFD is a promising tool in investigating the pathophysiology of ICAS and in risk stratification of patients with sICAS. Future studies are warranted for standardisation of the modelling methods and validation of the simulation results in sICAS, for its wider applications in clinical research and practice.

Panvascular concept in the evaluation and treatment of intracranial atherosclerotic stenosis

Cerebrovascular disease is the leading causes of death and disability worldwide. Intracranial atherosclerotic stenosis (ICAS) is one of the major causes of ischemic stroke, especially in the Asian population. It is urgent to explore effective screening methods for early diagnosis to improve prognosis of patients with ICAS. Recently, the concept of panvascular medicine has provided a direction for the exploration of evaluation of ICAS. Based on the concept of "panvascular medicine," atherosclerosis is the common pathological feature of panvascular disease, such as ICAS and coronary artery disease (CAD). In-depth research on the formation and development of plaques, the development and application of more precise preoperative assessment and detection methods, and the utilization of new interventional equipment have greatly enhanced the precision of diagnosis and treatment of CAD. Studies attempt to apply similar evaluation and treatment in ICAS. The deeper understanding, the more accurate diagnosis and treatment, contributing to improve the prognosis of patients with ICAS. This review focuses on these evaluations and treatment of CAD applied in the field of ICAS.

Diagnostic accuracy of hemodynamic assessment of intracranial atherosclerotic stenosis from a single angiographic view: a validation study

BACKGROUND

The aim of this study is to assess the feasibility of identifying the hemodynamic status of intracranial atherosclerotic stenosis (ICAS) using angio-based fractional flow (FF) calculated from a single angiographic view, with wire-based FF as the reference standard.

METHOD

The study retrospectively recruited 100 ICAS patients who underwent pressure wire measurement and digital subtraction angiography. The AccuICAD software was used to calculate angio-based FF, with the wire-measured value serving as the reference standard for evaluating the accuracy, consistency, and diagnostic performance of angio-based FF.

RESULTS

The mean±SD value of wire-based FF was 0.77±0.18, while the mean value of angio-based FF was 0.77±0.19. A good correlation between angio-based FF and wire-based FF was evident (r=0.90, P<0.001), with good agreement (mean difference 0.00±0.08). The diagnostic accuracy of angio-based FF and percent diameter stenosis (DS%) were 93.23% versus 72.18%, 91.73% versus 72.93%, and 89.47% versus 78.95% for predicted wire-based FF thresholds of 0.70, 0.75, and 0.80, respectively. The area under the curve (AUC) values for angio-based FF and DS% were 0.975 versus 0.822, 0.970 versus 0.814, and 0.943 versus 0.826 at the respective thresholds, respectively.

CONCLUSION

The FF calculated from a single angiographic view can be considered an effective tool for functional assessment of cerebral arterial stenosis.

Hemodynamic Impairments of Evaluating Symptomatic Intracranial Atherosclerotic Stenosis using Quantitative Flow Ratio on Digital Subtraction Angiography : A Comparison with Computed Tomography Perfusion, MRI and Fractional Flow Reserve

PURPOSE

Cerebral hemodynamics are important for the management of intracranial atherosclerotic stenosis (ICAS). The quantitative flow ratio (QFR) is a novel angiography-derived index for assessing the functional relevance of ICAS without pressure wires and adenosine. Good diagnostic yield with the hyperemic fractional flow reserve (FFR) have been reported, while data on the comparison of QFR to FFR are scarce.

METHODS

In this prospective study 56 patients with anterior circulation symptomatic ICAS who received endovascular treatment were included. The new method of computing QFR from a single angiographic view, i.e., the Murray law-based QFR (μQFR), was applied to the examined vessels. An artificial intelligence algorithm was developed to realize the automatic delineation of vascular contour. Pressure gradients were measured before and after treatment within the lesion vessel using a pressure guidewire and the FFR was calculated.

RESULTS

There was a good correlation between μQFR and FFR. Preoperative FFR predicted DWI watershed infarction (FFR optimal cut-off level: 0.755). Preoperative μQFR predicted DWI watershed infarction (μQFR optimal cut-off level: 0.51). Preoperative FFR predicted CTP hypoperfusion (FFR best predictive value: 0.62). Preoperative μQFR predicted CTP hypoperfusion (μQFR best predictive value: 0.375).

CONCLUSION

The μQFR based on DSA images can be used as an indicator to assess the functional status of the lesion in patients with ICAS.

Differential sensitivities to blood pressure variations in internal carotid and intracranial arteries: a numerical approach to stroke prediction

Stroke remains a global health concern, necessitating early prediction for effective management. Atherosclerosis-induced internal carotid and intra cranial stenosis contributes significantly to stroke risk. This study explores the relationship between blood pressure and stroke prediction, focusing on internal carotid artery (ICA) branches: middle cerebral artery (MCA), anterior cerebral artery (ACA), and their role in hemodynamics. Computational fluid dynamics (CFD) informed by the Windkessel model were employed to simulate patient-specific ICA models with introduced stenosis. Central to our investigation is the impact of stenosis on blood pressure, flow velocity, and flow rate across these branches, incorporating Fractional Flow Reserve (FFR) analysis. Results highlight differential sensitivities to blood pressure variations, with M1 branch showing high sensitivity, ACA moderate, and M2 minimal. Comparing blood pressure fluctuations between ICA and MCA revealed heightened sensitivity to potential reverse flow compared to ICA and ACA comparisons, emphasizing MCA's role. Blood flow adjustments due to stenosis demonstrated intricate compensatory mechanisms. FFR emerged as a robust predictor of stenosis severity, particularly in the M2 branch. In conclusion, this study provides comprehensive insights into hemodynamic complexities within major intracranial arteries, elucidating the significance of blood pressure variations, flow attributes, and FFR in stenosis contexts. Subject-specific data integration enhances model reliability, aiding stroke risk assessment and advancing cerebrovascular disease understanding.