Magnetic Resonance Imaging of Plaque Morphology, Burden, and Distribution in Patients With Symptomatic Middle Cerebral Artery Stenosis

Delayed Enhancement of Intracranial Atherosclerotic Plaque Can Better Differentiate Culprit Lesions: A Multiphase Contrast-Enhanced Vessel Wall MRI Study

BACKGROUND AND PURPOSE

Intracranial plaque enhancement (IPE) identified by contrast-enhanced vessel wall MR imaging (VW-MR imaging) is an emerging marker of plaque instability related to stroke risk, but there was no standardized timing for postcontrast acquisition. We aim to explore the optimal postcontrast timing by using multiphase contrast-enhanced VW-MR imaging and to test its performance in differentiating culprit and nonculprit lesions.

MATERIALS AND METHODS

Patients with acute ischemic stroke due to intracranial plaque were prospectively recruited to undergo VW-MR imaging with 1 precontrast phase and 4 consecutive postcontrast phases (9 minutes and 13 seconds for each phase). The signal intensity (SI) values of the CSF and intracranial plaque were measured on 1 precontrast and 4 postcontrast phases to determine the intracranial plaque enhancement index (PEI). The dynamic changes of the PEI were compared between culprit and nonculprit plaques on the postcontrast acquisitions.

RESULTS

Thirty patients with acute stroke (aged 59 ± 10 years, 18 [60%] men) with 113 intracranial plaques were included. The average PEI of all intracranial plaques significantly increased (up to 14%) over the 4 phases. There was significantly increased PEI over the 4 phases for culprit plaques (an average increase of 23%), but this was not observed for nonculprit plaques. For differentiating culprit and nonculprit plaques, we observed that the performance of IPE in the second postcontrast phase (cutoff = 0.83, AUC = 0.829 [0.746-0.893]) exhibited superior accuracy when compared with PEI in the first postcontrast phase (cutoff = 0.48; AUC = 0.768 [0.680-0.843]) (P = .022).

CONCLUSIONS

A 9-minute delay of postcontrast acquisition can maximize plaque enhancement and better differentiate between culprit and nonculprit plaques. In addition, culprit and nonculprit plaques have different enhancement temporal patterns, which should be evaluated in future studies.

Predictive stroke risk model with vision transformer-based Doppler features

BACKGROUND

Acute stroke is the leading cause of death and disability globally, with an estimated 16 million cases each year. The progression of carotid stenosis reduces blood flow to the intracranial vasculature, causing stroke. Early recognition of ischemic stroke is crucial for disease treatment and management.

PURPOSE

A computer-aided diagnosis (CAD) system was proposed in this study to rapidly evaluate ischemic stroke in carotid color Doppler (CCD).

METHODS

Based on the ground truth from the clinical examination report, the vision transformer (ViT) features extracted from all CCD images (513 stroke and 458 normal images) were combined in machine learning classifiers to generate the likelihood of ischemic stroke for each image. The pretrained weights from ImageNet reduced the time-consuming training process. The accuracy, sensitivity, specificity, and area under the receiver operating characteristic curve were calculated to evaluate the stroke prediction model. The chi-square test, DeLong test, and Bonferroni correction for multiple comparisons were applied to deal with the type-I error. Only p values equal to or less than 0.00125 were considered to be statistically significant.

RESULTS

The proposed CAD system achieved an accuracy of 89%, a sensitivity of 94%, a specificity of 84%, and an area under the receiver operating characteristic curve of 0.95, outperforming the convolutional neural networks AlexNet (82%, p < 0.001), Inception-v3 (78%, p < 0.001), ResNet101 (84%, p < 0.001), and DenseNet201 (85%, p < 0.01). The computational time in model training was only 30 s, which would be efficient and practical in clinical use.

CONCLUSIONS

The experiment shows the promising use of CCD images in stroke estimation. Using the pretrained ViT architecture, the image features can be automatically and efficiently generated without human intervention. The proposed CAD system provides a rapid and reliable suggestion for diagnosing ischemic stroke.

Vessel Wall Imaging of Intracranial Arteries: Fundamentals and Clinical Applications

With the increasing use of 3-tesla MRI scanners and the development of applicable sequences, it has become possible to achieve high-resolution, good contrast imaging, which has enabled the imaging of the walls of small-diameter intracranial arteries. In recent years, the usefulness of vessel wall imaging has been reported for numerous intracranial arterial diseases, such as for the detection of vulnerable plaque in atherosclerosis, diagnosis of cerebral arterial dissection, prediction of the rupture of cerebral aneurysms, and status of moyamoya disease and cerebral vasculitis. In this review, we introduce the histological characteristics of the intracranial artery, discuss intracranial vessel wall imaging methods, and review the findings of vessel wall imaging for various major intracranial arterial diseases.

Multimodal MRI study of the relationship between plaque characteristics and hypoperfusion in patients with transient ischemic attack

Objective

Transient ischemic attack is a significant risk factor for acute cerebral infarction. Previous studies have demonstrated that hypoperfusion in patients with transient ischemic attack was associated with the recurrence of transient ischemic attack, stroke, and persistent worsening of neurological symptoms. Moreover, transient ischemic attack patients classified as high-risk group according to the ABCD2 score have a higher incidence of stroke. Therefore, the objective of this study was to investigate the plaque characteristics of transient ischemic attack patients with concomitant cerebral hypoperfusion using multimodal MRI, as well as hemodynamic changes in the high-risk group with transient ischemic attack patients.

Materials and methods

A total of 151 patients with transient ischemic attack were prospectively recruited for this study. All enrolled patients underwent multimodal MRI, including DWI, TOF-MRA, HR-VWI, and DSC-PWI. Finally, 56 patients met the inclusion criteria. Based on DSC-PWI images, patients were divided into two groups: hypoperfusion (n = 41) and non-hypoperfusion (n = 15). Clinical baseline characteristics and plaque characteristics were analyzed between the two groups. Furthermore, within the hypoperfusion group, patients were further classified into low-risk (n = 11) and high-risk (n = 30) subgroups based on the ABCD2 score. Hemodynamic differences between these subgroups were also analyzed.

Results

Compared with the non-hypoperfusion group, the hypoperfusion group had a significantly higher prevalence of hypertension (68.3% vs. 33.3%, p = 0.019) and hyperhomocysteinemia (65.9% vs. 33.3%, p = 0.029). Moreover, the hypoperfusion group exhibited more significant luminal stenosis degree [41.79 ± 31.36 vs. 17.62± 13.62, p = 0.006] and greater NWI (57.1%± 20.47% vs. 40.21%± 21.56%, p = 0.009) compared to the non-hypoperfusion group. In addition, the high-risk group identified by the ABCD2 score had a higher rMTT [117.6(109.31-128.14) vs. 108.36(100.67-119.92), p = 0.037].

Conclusion

Transient ischemic attack patients with hypoperfusion exhibited a higher prevalence of hypertension and hyperhomocysteinemia, as well as higher luminal stenosis degree, and greater NWI. Furthermore, Transient ischemic attack patients in the high-risk group demonstrated higher MTT.

MR Imaging for Intracranial Vessel Wall Imaging: Pearls and Pitfalls

Conventional vascular imaging methods have primarily focused on evaluating the vascular lumen. However, these techniques are not intended to evaluate vessel wall abnormalities where many cerebrovascular pathologies reside. With increased interest for the visualization and study of the vessel wall, high-resolution vessel wall imaging (VWI) has gained traction.Over the past two decades, there has been a rapid increase in number of VWI publications with improvements in imaging techniques and expansion on clinical applications. With increasing utility and interest in VWI, application of proper protocols and understanding imaging characteristics of vasculopathies are important for the interpreting radiologists to understand.

Baseline vessel wall magnetic resonance imaging characteristics associated with in-stent restenosis for intracranial atherosclerotic stenosis

BACKGROUND

Imaging factors, specifically baseline plaque features on high-resolution magnetic resonance vessel wall imaging (HR-VWI) that could be associated with in-stent restenosis (ISR), are still unknown. We aimed to investigate the presenting clinical and plaque features on HR-VWI associated with ISR.

METHODS

Sixty-four patients with intracranial stent placement for intracranial atherosclerotic stenosis who had pre- and post-contrast T1-weighted HR-VWI on 3.0T prior to stenting were included in this analysis. Student's t-test, Mann-Whitney U test, χ2 test, or the Cochran-Mantel-Haenszel (CMH) test were used to compare clinical and baseline HR-VWI characteristics of the patients between the ISR and non-ISR groups. Univariable and multivariable logistic analysis were used to test the clinical and imaging factors associated with ISR.

RESULTS

Among the 64 patients, 9 patients (14.06%) developed ISR during the 2-year follow-up period. Plaque burden (median 0.89 vs 0.92, P=0.04), minimum lumen area (0.009 cm² vs 0.006 cm², P=0.04), plaque eccentricity (55.6% vs 89.1%, P＜0.01), enhancement ratio (1.36 vs 0.84, P＜0.01), and enhancement involvement (type 2 represents ≥50% cross-sectional wall involvement; 100% vs 63.6%, P=0.03) all significantly differed between patients with and without ISR. Multivariable analysis revealed that lower frequency of plaque eccentricity (OR 0.18, 95% CI 0.04 to 0.96, P=0.04) and higher enhancement ratio (OR 3.57, 95% CI 1.02 to 12.48, P=0.04) were independently associated with ISR.

CONCLUSIONS

Preliminary findings showed that ISR was independently associated with plaque concentricity and higher enhancement ratios on pre-stenting HR-VWI for patients with symptomatic intracranial atherosclerotic stenosis.

Association of Plaque Morphology With Stroke Mechanism in Patients With Symptomatic Posterior Circulation ICAD

BACKGROUND AND OBJECTIVES

Although the main mechanisms of stroke in patients with intracranial atherosclerotic disease (ICAD)-perforating artery occlusion (PAO) and artery-to-artery embolism (AAE)-have been identified and described, relatively little is known about the morphology of the symptomatic plaques and how they differ between these 2 mechanisms.

METHODS

We prospectively recruited patients with acute ischemic stroke in the posterior circulation that was attributable to ICAD. Fifty-one eligible patients were enrolled and underwent magnetic resonance imaging before being assigned to the PAO or AAE group according to probable stroke mechanism. Plaque morphological properties including plaque length, lumen area, outer wall area, plaque burden, plaque surface irregularity, vessel wall remodeling, and plaque enhancement were assessed using high-resolution MRI. Plaque morphological parameters of both PAO and AAE groups were compared using nonparametric tests. A binary logistic regression model was used to identify independent predictors while a receiver operating characteristic curve tested the sensitivity and specificity of the model.

RESULTS

Among patients who met the imaging eligibility criteria, 38 (74.5%) had PAO and 13 (25.5%) had AAE. Plaque length was shorter (6.39 interquartile range [IQR, 5.18-7.7]1 mm vs 10.90 [IQR, 8.18-11.85] mm, p < 0.01) in patients with PAO. Plaque burden was lower in PAO group (78.00 [IQR, 71.94-86.35] % vs 86.37 [IQR, 82.24-93.04] %, p = 0.04). The proportion of patients with plaque surface irregularity was higher in patients with AAE than in patients with PAO (19/38, 50.00% vs 12/13, 92.30%, p = 0.008). Plaque length was significantly associated with the PAO mechanism (adjusted OR 0.57, 95% CI, 0.41-0.79).

DISCUSSION

Intracranial atherosclerotic plaque morphology differs between patients with PAO and those with AAE. Plaque with shorter length, lower plaque burden, and regular surface is more likely to cause PAO.

Diagnostic Value of Micro-Bubble Transcranial Doppler Combined with Contrast Transthoracic Echocardiography in Cryptogenic Stroke Patients with Patent Foramen Ovale

Background

In recent years, increasing attention has been paid to cryptogenic stroke (CS) caused by the patent foramen ovale (PFO).

Objective

This study aims to evaluate the value of microbubble transcranial Doppler (MB-TCD) combined with contrast transthoracic echocardiography (cTTE) in the diagnosis of cryptogenic stroke patients with PFO.

Materials and Method

From January 2014 to January 2019, patients who suffered from CS were recruited and divided into the cTTE group and MB-TCD combined with cTTE group. All patients were further checked by transesophageal echocardiography (TEE).

Results

A total of 130 patients accepted cTTE examination, and 109 patients accepted MB-TCD combined with cTTE. In the group, 52 of the 54 positive patients were finally confirmed by TEE with PFO, and 12 of the 76 negative patients were finally confirmed by TEE with PFO. In combined group, 50 patients were negative on both two examination (Negative group), 54 were positive on both two examination (Positive group) and finally confirmed by TEE indeed with patent foramen ovale (PFO), while remaining five (5) patients were positive only on MB-TCD (Suspected group). After checked by TEE, three (3) of five patients with MB-TCD positive were confirmed by TEE indeed with PFO. The sensitivity, specificity, positive likelihood ratio (+LR), and Youden's index of cTEE in diagnostic of cryptogenic stroke patients with PFO were 81.25%, 96.97%, 26.82 and 0.78, respectively, and these for MB-TCD combined with cTTE were 100%, 96.15%, 25.97 and 0.96, respectively. MB-TCD medium can sensitively discover PFO in cryptogenic stroke patients with 100% sensitivity and a missdiagnosis rate of 0.

Conclusion

The combination of MB-TCD and cTTE can improve the sensitivity and specificity of PFO diagnosis in cryptogenic stroke patients. MB-TCD medium also had high sensitivity and specificity.

A Predictive Model for the Risk of Posterior Circulation Stroke in Patients with Intracranial Atherosclerosis Based on High Resolution MRI

Intracranial vertebrobasilar atherosclerosis is the main cause of posterior circulation ischemic stroke. We aimed to construct a predictive model for the risk of posterior circulation ischemic stroke in patients with posterior circulation atherosclerosis based on high-resolution MRI (HR-MRI). A total of 208 consecutive patients with posterior circulation atherosclerosis confirmed by HR-MRI, from January 2020 to July 2021, were retrospectively assessed. They were assigned to the posterior circulation stroke (49 patients) and non-posterior circulation stroke group (159 patients) based on clinical presentation and diffusion-weighted imaging (DWI). Demographic data, risk factors of atherosclerosis, laboratory findings, and imaging characteristics were extracted from electronic health records. Plaque features were investigated by HR-MRI. Fifty-three clinical or imaging features were used to derive the model. Multivariable logistic regression analysis was employed to construct the prediction model. The nomogram was evaluated for calibration, differentiation, and clinical usefulness. Plaque enhancement, plaque irregular surface morphology, artery location of plaque, and dorsal quadrant of plaque location were significant predictors for posterior circulation stroke in patients with intracranial atherosclerosis. Subsequently, these variables were selected to establish a nomogram. The model showed good distinction (C-index 0.830, 95% CI 0.766-0.895). The calibration curve also showed excellent consistency between the prediction of the nomogram and the observed curve. Decision curve analysis further demonstrated that the nomogram conferred significantly high clinical net benefit. The nomogram calculated from plaque characteristics in HR-MRI may accurately predict the posterior circulation stroke occurrence and be of great help for stratification of stroke decision making.

Assessing the characteristics and diagnostic value of plaques for patients with acute stroke using high-resolution magnetic resonance imaging

BACKGROUND

A comprehensive understanding of atherosclerotic plaques aids physicians in evaluation and treatment of stroke. This study set out to evaluate the characteristics and diagnostic value of atherosclerotic plaques in patients with acute stroke and stenotic middle cerebral artery (MCA) using high-resolution magnetic resonance imaging.

METHODS

Sixty-five consecutive patients with transient ischemic attack or recent ischemic stroke were prospectively recruited. All enrolled patients underwent routine magnetic resonance scans and cross-sectional scans of the stenotic MCA vascular wall. Differences in vascular wall parameters and location, the enhancement degree, and remodelling patterns of plaques in the stenotic MCA were compared between symptomatic (n=30) and asymptomatic (n=35) groups of patients. The statistically significant indicators were then subjected to logistic regression analysis to identify which factors could better predict acute stroke.

RESULTS

Compared with the asymptomatic group, the symptomatic group had a smaller lumen area (LA) (P=0.027), larger plaque area (P<0.001), larger remodelling index (P<0.001), more superior/posterior plaques (P=0.001), more obviously enhanced plaques (P<0.001), and a greater number of PR patterns (P<0.001) in the stenotic MCA. Logistic regression analysis showed that the plaque area, remodelling patterns, LA in the stenotic MCA, enhancement degree, and plaque location were predictors of acute stroke. The combination of the plaque area and LA in the stenotic MCA, and the plaque enhancement degree had optimal predictive value (area under the curve =0.927).

CONCLUSIONS

A larger plaque area and smaller LA in the stenotic MCA, and obvious plaque enhancement might indicate that a patient is prone to acute stroke.

Vertebrobasilar Junction Angle Over 90°: A Potential Imaging Marker Associated With Vertebrobasilar Atherosclerosis

Objective: Whether the cerebral vascular variations play an important role in the progression of intracranial atherosclerosis is yet largely unclear. We aimed to investigate the relationship between the magnitude of the vertebrobasilar junction (VBJ) angle and the imaging features of vertebrobasilar artery atherosclerosis.

Methods: Adult patients with acute ischemic stroke or transient ischemic attack undergoing a 3.0-tesla vessel wall magnetic resonance imaging (VW-MRI) scanning were consecutively included. Imaging features of vertebrobasilar artery atherosclerosis were assessed on the reconstructed short axis of VW-MRI at the most stenotic site. The VBJ angle degree was measured on magnetic resonance angiography and classified into the angle ≥90° or <90°.

Results: Among 68 patients (mean age = 63.5 ± 9.4 years old; 63.2% were male) with vertebrobasilar atherosclerosis, 33 had a VBJ angle ≥90° and 35 had a VBJ angle <90°. Compared to the vertebrobasilar plaques with VBJ angle <90°, those with VBJ angle ≥90° had a heavier plaque burden (84.35 vs. 70.58%, p < 0.001) and higher prevalence of intraplaque hemorrhage (17.1 vs. 3.3%, p = 0.01). In the regression analyses, the VBJ angle ≥90° was also robustly associated with plaque burden (odds ratio, 1.11; 95% confidential interval, 1.043–1.18; p = 0.001) and intraplaque hemorrhage (odds ratio, 5.776; 95% confidential interval, 1.095–30.46; p = 0.039) of vertebrobasilar atherosclerosis.

Conclusion: The VBJ angle over 90° might aggravate the vessel wall condition of the atherosclerotic vertebrobasilar arteries, which might serve as a potential risk factor for vertebrobasilar atherosclerosis.

Symptomatic and Asymptomatic Chronic Carotid Artery Occlusion on High-Resolution MR Vessel Wall Imaging

BACKGROUND AND PURPOSE

Chronic carotid artery occlusion remains a poorly understood risk factor for subsequent stroke, and potential revascularization is dependent on understanding the anatomy and nature of the occlusion. Luminal imaging cannot assess the nature of an occlusion, so the internal structure of the occlusion must be inferred. The present study examines the signal characteristics of symptomatic and asymptomatic carotid occlusion that may point to management differentiation.

MATERIALS AND METHODS

We prospectively recruited patients who were diagnosed with chronic carotid artery occlusion defined as longer than 4 weeks and confirmed by DSA. All patients underwent high-resolution MR vessel wall imaging examinations after enrollment. Baseline characteristics, vessel wall imaging features, and DSA features were collected and evaluated. The vessel wall imaging features included segment involvement, signal intensity, contrast enhancement, and vessel wall thickness. The symptomatic and asymptomatic chronic carotid artery occlusions were compared.

RESULTS

A total of 44 patients with 48 lesions were included in this study from February 2020 to December 2020. Of the 48 lesions, 35 (72.9%) were symptomatic and 13 (27.1%) were asymptomatic. There was no difference in baseline and DSA features. On vessel wall imaging, C1 and C2 were the most commonly involved segments (91.7% and 68.8%, respectively). Compared with symptomatic lesions, asymptomatic lesions were more often isointense (69.2%) in the distal segment (P = .03). Both groups had diffuse wall thickening (80% and 100%).

CONCLUSIONS

Signal characteristics between those with symptomatic and asymptomatic carotid artery occlusions differ in a statistically significant fashion, indicating a different structure of the occlusion.

The Relationship between Patterns of Remodeling and Degree of Enhancement in Patients with Atherosclerotic Middle Cerebral Artery Stenosis: A High-Resolution MRI Study

PURPOSE

The aim of this research was to investigate the relationship between remodeling patterns and degree of enhancement in patients with atherosclerotic middle cerebral artery (MCA) stenosis using high-resolution magnetic resonance imaging (HR-MRI).

MATERIALS AND METHODS

From August 2015 to May 2016, 38 consecutive patients with unilateral MCA stenosis on time-of-flight (TOF) MR angiography were prospectively enrolled. The routine MR scan and cross-sectional images of the stenotic MCA vessel wall on HR-MRI were performed in all patients. Among them, 17 patients displayed positive remodeling (PR) and the other 21 patients displayed negative remodeling or non-remodeling (non-PR). The patients displaying hyperintense on diffusion-weighted imaging (DWI) in the territory of ipsilateral stenotic MCA were considered to have had acute stroke. Subsequently, the differences in the degree of enhancement and the number of acute stroke patients between the PR group and the non-PR group were compared. The Spearman rank correlation analysis of the enhancement degree (ED) and the remodeling index (RI) was calculated. Then, receiver operating curve (ROC) was used to evaluate diagnostic efficiency of RI and ED for acute infarction.

RESULTS

The PR group had more obvious enhancement plaques than the non-PR group (10 versus 3, P = 0.006). The PR group also had a larger number of acute stroke patients than the non-PR group (15 versus 4, P = 0.000). The spear-man rank correlation analysis showed that the degree of enhancement had a weak positive correlation with the remodeling index (r = 0.379, P = 0.019). The area under the curve (AUC) of RI and ED was higher than that of RI (0.924: 0.842).

CONCLUSION

The PR, obvious enhancement predicted vulnerable plaques that were more prone to causing acute stroke. RI and ED had valuable diagnostic efficiency for acute infarction.

Plaque Elasticity and Intraplaque Neovascularisation on Carotid Artery Ultrasound: A Comparative Histological Study

OBJECTIVE

Plaque elasticity and intraplaque neovascularisation are strongly suggestive of vulnerable plaque. This study aimed to investigate the relationship between intraplaque neovascularisation and plaque elasticity, and to compare the ultrasound findings with histopathological changes.

METHODS

Patients enrolled in this study presented with symptomatic carotid stenosis (> 70%) and later underwent both pre-operative ultrasonography and endarterectomy. Contrast enhanced ultrasound (CEUS) and shear wave elastography (SWE) were used to measure the neovascularisation and elasticity of the plaque, respectively. After removal, plaques were histologically assessed to determine the microvessel density (MVD), matrix metalloproteinase (MMP)-9 expression, and type I/type III collagen ratio using immunohistochemistry staining and morphometry. A correlation analysis was used to establish the relationship among the aforementioned quantitative parameters. Inter- and intra-observer consistency evaluations were performed using the intraclass correlation coefficient and Bland-Altman plots.

RESULTS

Ninety-four symptomatic patients with 98 plaques were included. The area under the curve (AUC) of the carotid plaque detected using CEUS correlated with its shear wave velocity (SWV) (r = -.714; p < .001), MVD (r = .842; p < .001), collagen type I/III ratio (r = -.833; p < .001), and MMP-9 (r = .738; p < .001). SWE was positively correlated with the type I/III collagen ratio (r = .805; p < .001). The overall interexaminer consistency of the SWE was acceptable (r = .638; p < .001). The interobserver correlation coefficient of the AUC, time to peak (TP), mean transit time (MTT), and SWV were .719, .756, .733, and .686, respectively. The intra-observer variability values of the AUC, TP, MTT, and SWV were .826, .845, .633, and .748, respectively.

CONCLUSION

SWE and CEUS can comprehensively evaluate the vulnerability of the carotid plaque by assessing the elasticity of the plaque and neovascularisation within it. The negative correlation between the intraplaque neovascularisation and elasticity, further validated by histological findings, suggests that the more abundant the neovascularisation, the less elasticity.

Intracranial vessel wall imaging

PURPOSE OF REVIEW

To give an overview regarding the potential usefulness of vessel wall imaging (VWI) in distinguishing various intracranial vascular diseases, their common imaging features, and potential pitfalls.

RECENT FINDINGS

VWI provides direct visualization of the vessel wall and allows the discrimination of different diseases such as vasculitis, atherosclerosis, dissection, Moyamoya disease, and reversible cerebral vasoconstriction syndrome. Recent studies showed that concentric and eccentric involvement in the vessel wall, as well as the enhancement pattern were found important for the distinguishing these diseases and evaluating their activity.

SUMMARY

Most of the imaging techniques currently used are based on luminal imaging. However, these imaging methods are not adequate to distinguish different diseases that can demonstrate similar radiological findings. VWI is being increasingly used as a noninvasive imaging method to offset this limitation.

Advances in imaging acute ischemic stroke: evaluation before thrombectomy

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

Progression of Plaque Burden of Intracranial Atherosclerotic Plaque Predicts Recurrent Stroke/Transient Ischemic Attack: A Pilot Follow-Up Study Using Higher-Resolution MRI

BACKGROUND

Patients with intracranial atherosclerotic disease (ICAD) have a high frequency of stroke recurrence. However, there has been little investigation into the prognostic value of higher-resolution magnetic resonance imaging (HR-MRI).

PURPOSE

To investigate the use of intracranial atherosclerotic plaques features in predicting risk of recurrent cerebrovascular ischemic events using HR-MRI.

STUDY TYPE

Prospective.

POPULATION

Fifty-eight patients with acute/subacute stroke (N = 46) or transient ischemic attack (N = 12).

FIELD STRENGTH/SEQUENCE

A 3.0 T, 3D time-of-flight gradient echo sequence and T1- and T2-weighted fast spin echo sequences with 0.31 x 0.39 mm² in-plane resolution, twice (with >3 months between scans) following the initial event.

ASSESSMENT

Patients were also followed clinically for recurrent ischemic events for up to 48 months or until a subsequent event occurred. The degree of stenosis, plaque burden (PB), minimal lumen area (MLA), and contrast enhancement ratio were assessed at each scanning session and the percentage change of each over time was calculated.

STATISTICAL TESTS

Univariable and multivariable Cox regression analyses were used to calculate the hazard ratio (HR) and 95% confidence interval (CI) for predicting recurrent events.

RESULTS

The mean time interval between baseline and follow-up MRI scans was 6.2 ± 4.1 months. After the second MRI scan, 20.7% of patients (N = 12) had experienced ipsilateral recurrent TIA/stroke within 10.9 ± 9.2 months. Univariable analyses showed that baseline triglyceride, percentage change of PB, and progression of PB were significantly associated with recurrent events (all P < 0.05). Multivariable Cox regression indicated that progression of PB (HR, 6.293; 95% CI, 1.620-24.444; P < 0.05) was a significant independent imaging feature for recurrent ischemic events.

DATA CONCLUSION

Progression of PB was independently associated with recurrent ischemic cerebrovascular events. HR-MRI may help risk stratification of patients at risk of recurrent stroke.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 4.

Hemodynamics is associated with vessel wall remodeling in patients with middle cerebral artery stenosis

OBJECTIVES

To evaluate the relationship between hemodynamics and vessel wall remodeling patterns in middle cerebral artery (MCA) stenosis based on high-resolution magnetic resonance imaging and computational fluid dynamics (CFD).

METHODS

Forty consecutive patients with recent ischemic stroke or transient ischemic attack attributed to unilateral atherosclerotic MCA stenosis (50-99%) were prospectively recruited. All patients underwent a cross-sectional scan of the stenotic MCA vessel wall. The parameters of the vessel wall, the number of patients with acute infarction, translesional wall shear stress ratio (WSSR), wall shear stress in stenosis (WSSs), and translesional pressure ratio were obtained. The patients were divided into positive remodeling (PR) and negative remodeling (NR) groups. The differences in vessel wall parameters and hemodynamics were compared. Correlations between the parameters of the vessel wall and hemodynamics were calculated.

RESULTS

Of the 40 patients, 16 had PR, 19 had NR, and the other 5 displayed non-remodeling. The PR group had a smaller lumen area (p = 0.004), larger plaque area (p < 0.001), normal wall index (p = 0.004), and higher WSSR (p = 0.004) and WSSs (p = 0.023) at the most narrowed site. The PR group had more enhanced plaques (12 vs 6, p = 0.03). The number of patients with acute stroke in the PR group was more than that in the NR group (11 vs 4, p = 0.01). The remodeling index (r = 0.376, p = 0.026) and plaque area (r = 0.407, p = 0.015) showed a positive correlation with WSSR, respectively.

CONCLUSIONS

Hemodynamics plays a role in atherosclerotic plaques and vessel wall remodeling. Individuals with greater hemodynamic values might be more prone to stroke.

KEY POINTS

• Stenotic plaques in middle cerebral artery with positive remodeling have smaller lumen area and larger resp. higher plaque area, normal wall index, translesional wall shear stress ratio, and wall shear stress than negative remodeling. • The remodeling index and plaque area are positively correlated with translesional wall shear stress ratio. • Hemodynamic may help to understand the role of positive remodeling in the development of acute stroke.

Plaque Wall Distribution Pattern of the Atherosclerotic Middle Cerebral Artery Associates With the Circle of Willis Completeness

Objective: Investigating the relevance of the incomplete circle of Willis (COW) to the plaque wall distribution in the atherosclerotic middle cerebral arteries (MCAs) through utilizing high-resolution magnetic resonance imaging (HR-MRI), and its potential clinical impact.

Methods: This hospital-based study enrolled consecutive adult patients with acute ischemic stroke or transient ischemic attack, who received a 3.0T Achieva MR system scanning. The COW completeness was evaluated on MR angiography imaging, including anterior (A) and posterior (P)-COW sections. The MCA plaque wall distribution was assessed on HR-MRI. The occurrence of perforator infarction was detected on diffusion-weighted imaging.

Results: Among 87 patients (mean age = 62.39 ± 11.64 years old) with atherosclerotic plaques in the MCA M1 segments, the incomplete COW types were more prevalent than the complete COW type (incomplete P-COW, 83.9%; incomplete A-COW, 36.8%; complete COW, 8.1%). The incomplete A-COW had more inferior but fewer ventral plaques of MCA atherosclerosis than the complete A-COW, while the incomplete P-COW had fewer inferior MCA plaques than the complete P-COW. Moreover, symptomatic MCA plaques causing perforator infarctions were more likely to locate on the superior wall.

Conclusion: Our findings suggested that the COW completeness could influence the vessel wall distribution of the MCA plaques, among which the superior plaques of symptomatic MCA atherosclerosis was associated with branch occlusive disease.

Understanding the Clinical Implications of Intracranial Arterial Calcification Using Brain CT and Vessel Wall Imaging

Background and Purpose: Intracranial arterial calcification (IAC) has been the focus of much attention by clinicians and researchers as an indicator of intracranial atherosclerosis, but correlations of IAC patterns (intimal or medial) with the presence of atherosclerotic plaques and plaque stability are still a matter of debate. Our study aimed to assess the associations of IAC patterns identified on computed tomography (CT) with the presence of plaque detected on vessel wall magnetic resonance imaging and plaque stability. Materials and Methods: Patients with stroke or transient ischemic attack and intracranial artery stenosis were recruited. IAC was detected and localized (intima or media) on non-contrast CT images. Intracranial atherosclerotic plaques were identified using vessel wall magnetic resonance imaging and matched to corresponding CT images. Associations between IAC patterns and culprit atherosclerotic plaques were assessed by using multivariate regression. Results: Seventy-five patients (mean age, 63.4 ± 11.6 years; males, 46) were included. Two hundred and twenty-one segments with IAC were identified on CT in 66 patients, including 86 (38.9%) predominantly intimal calcifications and 135 (61.1%) predominantly medial calcifications. A total of 72.0% of intimal calcifications coexisted with atherosclerotic plaques, whereas only 10.2% of medial calcifications coexisted with plaques. Intimal calcification was more commonly shown in non-culprit plaques than culprit plaques (25.9 vs. 9.4%, P = 0.008). The multivariate mixed logistic regression adjusted for the degree of stenosis showed that intimal calcification was significantly associated with non-culprit plaques (OR, 2.971; 95% CI, 1.036-8.517; P = 0.043). Conclusion: Our findings suggest that intimal calcification may indicate the existence of a stable form of atherosclerotic plaque, but plaques can exist in the absence of intimal calcification especially in the middle cerebral artery.

Detection and Quantification of Symptomatic Atherosclerotic Plaques With High-Resolution Imaging in Cryptogenic Stroke

BACKGROUND AND PURPOSE

High-resolution vessel wall imaging (HR-VWI) is a powerful tool in diagnosing intracranial vasculopathies not detected on routine imaging. We hypothesized that 7T HR-VWI may detect the presence of atherosclerotic plaques in patients with intracranial atherosclerosis disease initially misdiagnosed as cryptogenic strokes.

METHODS

Patients diagnosed as cryptogenic stroke but suspected of having an intracranial arteriopathy by routine imaging were prospectively imaged with HR-VWI. If intracranial atherosclerotic plaques were identified, they were classified as culprit or nonculprit based on the likelihood of causing the index stroke. Plaque characteristics, such as contrast enhancement, degree of stenosis, and morphology, were analyzed. Contrast enhancement was determined objectively after normalization with the pituitary stalk. A cutoff value for plaque-to-pituitary stalk contrast enhancement ratio (CR) was determined for optimal prediction of the presence of a culprit plaque. A revised stroke cause was adjudicated based on clinical and HR-VWI findings.

RESULTS

A total of 344 cryptogenic strokes were analyzed, and 38 eligible patients were imaged with 7T HR-VWI. Intracranial atherosclerosis disease was adjudicated as the final stroke cause in 25 patients. A total of 153 intracranial plaques in 374 arterial segments were identified. Culprit plaques (n=36) had higher CR and had concentric morphology when compared with nonculprit plaques (P≤0.001). CR ≥53 had 78% sensitivity for detecting culprit plaques and a 90% negative predictive value. CR ≥53 (P=0.008), stenosis ≥50% (P<0.001), and concentric morphology (P=0.030) were independent predictors of culprit plaques.

CONCLUSIONS

7T HR-VWI allows identification of underlying intracranial atherosclerosis disease in a subset of stroke patients with suspected underlying vasculopathy but otherwise classified as cryptogenic. Plaque analysis in this population demonstrated that culprit plaques had more contrast enhancement (CR ≥53), caused a higher degree of stenosis, and had a concentric morphology.

High-Resolution Vessel Wall Magnetic Resonance Imaging of the Middle Cerebral Artery: Comparison of 3D CUBE T1-Weighted Sequence with and without Fat Suppression

Background

Fat suppression is an important technique in magnetic resonance imaging (MRI). Comprehensive and quantitative assessment of the influence of fat suppression (FS) on T1-weighted imaging of intracranial vessel wall imaging is needed. In this study, we compared the three-dimensional (3D) variable-flip-angle turbo-spin-echo (CUBE) T1-weighted sequence with and without FS to investigate the differences between the 2 sequences in imaging of the middle cerebral artery (MCA) vessel walls.

Material/Methods

A 3D CUBE T1-weighted sequence with and without FS by 3.0T MRI was used to obtain intracranial vessel wall images of 105 MCA stenosis patients. The image signal intensity, signal-to-noise ratio, and contrast-to-noise ratio were calculated and compared. Two observers evaluated the image quality of the 2 sequences twice, and interobserver and intraobserver consistency were determined. Differences between the 2 sequences in the area of lumen and plaque were compared.

Results

The signal intensity, signal-to-noise ratio, and contrast-to-noise ratio of the 3D CUBE T1-weighted sequence without FS were higher, whereas the noise level was lower. In terms of subjective scores, the 3D CUBE T1-weighted sequence without FS performed better. No significant difference was observed in the measurement of the vascular lumen area between the 2 sequences, although there were statistically significant differences in the measurement of plaque area (i.e., the measurement obtained with 3D CUBE T1-weighted sequence without FS was larger).

Conclusions

3D CUBE T1-weighted sequence without FS performed better for MCA vessel walls imaging than 3D CUBE T1-weighted sequence with FS.

Plaque characteristics and hemodynamics contribute to neurological impairment in patients with ischemic stroke and transient ischemic attack

OBJECTIVES

We aimed to investigate differential characteristics of plaque in the middle cerebral artery (MCA) and hemodynamics in patients with ischemic stroke and transient ischemic attack (TIA), and to develop a predictive model for the presence of ischemic stroke and neurological impairment.

METHODS

Sixty-seven patients with acute ischemic events in MCA territory who underwent high-resolution vessel wall imaging between September 2016 and August 2018 were reviewed retrospectively. Patients were assigned to either the stroke group or TIA group, according to diffusion-weighted imaging and neurological examination. Plaque characteristics and anterograde score (AnS) were calculated. Tmax > 6.0-s volume was acquired by RApid Processing of perfusIon and Diffusion software. Multivariate logistic regression analysis and multiple linear regression analysis were performed to establish a predictive model for irreversible infarction occurrence and clinical severity.

RESULTS

Forty-five patients were assigned to the stroke group, and 22 were assigned to the TIA group. Plaque length, intraplaque hemorrhage (IPH), enhancement, AnS, and Tmax > 6.0-s volumes were significantly different between the two groups (p < 0.05). IPH and AnS were independent predictors for patients with stroke (p = 0.020 and 0.034, respectively). Tmax > 6.0-s volume, IPH, hypertension, and AnS were associated with high National Institutes of Health Stroke Scale (NIHSS) scores (all p < 0.05, R = 0.725, and adjusted R² = 0.494).

CONCLUSIONS

IPH and AnS are useful in predicting stroke occurrence. Tmax > 6.0-s volume, IPH, hypertension, and AnS are associated with neurological impairment of the patients.

KEY POINTS

• Ischemic stroke and TIA patients have different plaque characteristics and hemodynamics. • Intraplaque hemorrhage and anterograde score have high diagnostic efficiency for ischemic stroke. • The combination of Tmax > 6.0-s volume, intraplaque hemorrhage, hypertension, and anterograde score can predict the National Institutes of Health Stroke Scale scores of patients.

Plaque characteristics of middle cerebral artery assessed using strategically acquired gradient echo (STAGE) and vessel wall MR contribute to misery downstream perfusion in patients with intracranial atherosclerosis

OBJECTIVES

To assess plaque vulnerability of the middle cerebral artery (MCA) using strategically acquired gradient echo (STAGE) versus high-resolution vessel wall MRI (hr-vwMRI), and explore the relationship between plaque characteristics and misery downstream perfusion.

METHODS

Ninety-one patients with single MCA atherosclerotic plaques underwent STAGE and hr-vwMRI were categorized into a group with misery perfusion and a group without based on the Alberta Stroke Program Early CT score (MTT-ASPECTS) with a threshold of 6. Plaque characteristics including inner lumen area (IWA), susceptibility, presence of hyperintensity within plaque (HIP), surface irregularity, stenosis degree, remodeling index, lipid ratio, and enhancement grade were compared between the two groups. The vulnerability of each plaque was retrospectively assessed on both STAGE and hr-vwMRI according to the combination of plaque features. Logistic regression analysis and ROC curve were performed to evaluate the effect of plaque characteristics on the presence of misery perfusion.

RESULTS

Taking hr-vwMRI as the reference, STAGE showed good efficiency in detecting vulnerable plaques. Patients with misery perfusion had less IWA, higher stenosis degree, more irregular surface and HIP, higher enhancement grade, and susceptibility (p < 0.01 for all). Higher susceptibility and stenosis degree were independent predictors for the occurrence of misery perfusion (p = 0.025, p = 0.048). The AUC was 0.900 for the combination of the two variables.

CONCLUSION

STAGE shows good efficiency to assess MCA plaque vulnerability versus hr-vwMRI. Plaque susceptibility evaluated using STAGE provides incremental value to predict misery perfusion combined with hr-vwMRI plaque features.

KEY POINTS

• STAGE has good efficiency in evaluating MCA plaque vulnerability versus hr-vwMRI. • Higher plaque susceptibility assessed using STAGE and higher grade luminal stenosis based on hr-vwMRI attribute to misery downstream perfusion. • STAGE provides incremental value on the understanding of plaque vulnerability in addition to conventional hr-vwMRI.

Imaging of intracranial atherosclerotic plaques using 3.0 T and 7.0 T magnetic resonance imaging-current trends and future perspectives

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of ischemic stroke and carries a relatively high risk of stroke recurrence. Advances in high-resolution magnetic resonance imaging (HRMRI) techniques of intracranial arteries now have made it possible to directly visualize atherosclerotic plaque itself, allowing detailed assessments of plaque morphology and components. Currently available intracranial HRMRI could be performed with 2-dimensional (2D) and 3D acquisitions, and multicontrast weightings in clinically reasonable scan times. Until now, HRMRI research of ICAD has focused on the identification of plaque vulnerability, and the relationship between plaque characteristics and ischemic stroke. HRMRI at ultra-high-field strength (7.0 T) holds promise in better visualizing intracranial vessel walls, as well as identifying early lesions and total burden of ICAD. As a result, intracranial HRMRI provides great insights into pathology of intracranial atherosclerotic plaques, stroke mechanisms, and future stroke risk. In this article, we will review the technical implementation, preclinical research, clinical applications, and future directions of HRMRI for the evaluation of ICAD at 3.0 T and 7.0 T.

Vessel wall MR imaging of intracranial atherosclerosis

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of ischemic stroke worldwide. Along with high recurrent stroke risk from ICAD, its association with cognitive decline and dementia leads to a substantial decrease in quality of life and a high economic burden. Atherosclerotic lesions can range from slight wall thickening with plaques that are angiographically occult to severely stenotic lesions. Recent advances in intracranial high resolution vessel wall MR (VW-MR) imaging have enabled imaging beyond the lumen to characterize the vessel wall and its pathology. This technique has opened new avenues of research for identifying vulnerable plaque in the setting of acute ischemic stroke as well as assessing ICAD burden and its associations with its sequela, such as dementia. We now understand more about the intracranial arterial wall, its ability to remodel with disease and how we can use VW-MR to identify angiographically occult lesions and assess medical treatment responses, for example, to statin therapy. Our growing understanding of ICAD with intracranial VW-MR imaging can profoundly impact diagnosis, therapy, and prognosis for ischemic stroke with the possibility of lesion-based risk models to tailor and personalize treatment. In this review, we discuss the advantages of intracranial VW-MR imaging for ICAD, the potential of bioimaging markers to identify vulnerable intracranial plaque, and future directions of artificial intelligence and its utility for lesion scoring and assessment.

Regression of Plaque Enhancement Within Symptomatic Middle Cerebral Artery Atherosclerosis: A High-Resolution MRI Study

Objective: Contrast enhancement is a vital feature of the intracranial atherosclerotic plaque on high-resolution magnetic resonance imaging (HRMRI), but its clinical significance is still unclear. We aimed to quantitatively assess plaque enhancement patterns in the middle cerebral artery (MCA) atherosclerotic plaque. Methods: We conducted a cross-sectional study by prospectively recruiting stroke or transient ischemic attack patients with >30% of MCA stenosis of either side. All patients underwent contrast-enhanced HRMRI scans. Enrolled patients were classified into acute phase (<4 weeks), subacute phase (4-12 weeks) and chronic phase (>12 weeks) groups based on the time interval from stroke onset to imaging scan. Plaque enhancement index was calculated for each MCA lesion at the maximal narrowing site. Results: We identified a total of 89 MCA plaques [53 (60%) symptomatic and 36 (40%) asymptomatic; 57 (64%) acute, 18 (20%) subacute and 14 (16%) chronic] in 58 patients on HRMRI. Among the acute lesions, symptomatic plaques had a significantly stronger plaque enhancement than asymptomatic plaques (symptomatic vs. asymptomatic: 38.9 ± 18.2 vs. 18.2 ± 16.2, p < 0.001). Among the symptomatic lesions, plaque enhancement diminished with increasing time after stroke onset (38.9 ± 18.2, 22.0 ± 22.8, and 5.0 ± 10.1 for acute, subacute, and chronic phase, respectively; p = 0.001). Conclusion: Plaque enhancement in the acute atherosclerotic plaque is closely related to recent ischemic events. In symptomatic atherosclerosis, plaque enhancement regresses over time after ischemic stroke, which may offer the potential to monitor the plaque activity in intracranial atherosclerosis using HRMRI.

Plaque features and vascular geometry in basilar artery atherosclerosis

Hemodynamic changes occurring at the segments of arterial bifurcations, up and down stream of stenotic vessels appear to play a critical role in the development of atherosclerosis. Therefore, we hypothesized that basilar artery (BA) geometry may be related to the distribution of atherosclerotic plaque.In this retrospective cross-sectional study, all patients hospitalized with ischemic stroke and intracranial atherosclerotic disease were sifted from March 2017 to October 2017. Sixty-seven patients with intracranial atherosclerotic disease (39 with and 28 without BA atherosclerosis) were analyzed. Magnetic resonance imaging, magnetic resonance angiography, and high-resolution black-blood MRI were performed within 7 days after symptoms onset. BA tortuosity, plaque location, and plaque enhancement were assessed. Plaque burden and vascular remodeling were measured.Of the 39 patients with BA atherosclerosis, plaques preferred to be formed at the inner arc than the outer arc (27/39, 69% vs 12/39, 31%) in the tortuous BA. In addition, patients with BA plaque had a greater vascular tortuosity compared with those without plaque (113.1 ± 10.2 vs 107 ± 4.6; P = .034). Finally, patients with apparent BA plaque had greater plaque enhancement (14/21, 67% vs 5/18, 28%; P = .017) and plaque burden (0.76 ± 0.15 vs 0.70 ± 0.09; P = .036) compared with those with minimal plaque.Plaque may be more likely to form at the inner arc of tortuous BA with atherosclerotic disease, and increased BA tortuosity is associated with its likelihood to form plaque.

Intracranial vessel wall imaging: applications, interpretation, and pitfalls

Vessel wall imaging (VWI) is being increasingly used as a non-invasive diagnostic method to evaluate the intra- and extracranial vascular bed. Whereas conventional vascular imaging primarily assesses the vessel lumen, VWI changes the focus of analysis toward the vessel wall. As the technical challenges of high spatial resolution, signal-to-noise ratio, and contrast-to-noise ratio and long scans times are addressed, interest in the clinical applications of this technique has steadily increased over the years. In this review, the authors will discuss the various applications of VWI as well as principles of interpretation and common imaging findings, focusing on intracranial atherosclerosis, vascular dissection, vasculitides (such as primary angiitis of the central nervous system (PACNS) and neurosarcoidosis), vasculopathies (such as reversible cerebral vasoconstriction syndrome (RCVS), cocaine-induced vasculopathy, moyamoya disease, and radiation-induced arteriopathy), aneurysms, and post-thrombectomy changes. The authors will also discuss the potential pitfalls of VWI and helpful cues to avoid being tricked.

Different risk factors in identical features of intracranial atherosclerosis plaques in the posterior and anterior circulation in high-resolution MRI

Background:

We constructed a high-volume registry to identify whether risk factors of intracranial atherosclerotic plaque (ICAP) features differ in the posterior and anterior circulation in patients with symptomatic intracranial atherosclerotic stenosis (ICAS) investigated by high-resolution magnetic resonance imaging (HRMRI).

Methods:

The registry was constructed for patients with symptomatic ICAS who underwent HRMRI for culprit plaques. ICAP-vulnerable features included positive remodelling, diffuse distribution, intraplaque haemorrhage and strong enhancement.

Results:

We analysed risk factors for the same ICAP features between the posterior and anterior circulation in data of 97 patients in the posterior circulation and 105 patients in the anterior circulation ICAPs. In patients with diffuse distribution, the probability of being female were lower [odds ratio (OR):0.08; 95% confidence interval (CI):0.02–0.34; p = 0.001] and having diabetes mellitus was higher (OR: 7.75; 95% CI:1.75–34.39; p = 0.007) in posterior circulation patients. In patients with strong enhancement, the probability of having diabetes was higher in posterior circulation patients (OR:6.71; 95% CI:1.37–32.81; p = 0.019).

Conclusions:

Our results demonstrate more risk factors in the posterior than in the anterior circulation in patients with the same ICAP-vulnerable features, highlighting the need for stratification of risk factors in symptomatic ICAPs.

Trial Registration:

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02705599.

Qualitative Assessment and Reporting Quality of Intracranial Vessel Wall MR Imaging Studies: A Systematic Review

BACKGROUND

Over the last quarter-century, the number of publications using vessel wall MR imaging has increased. Although many narrative reviews offer insight into technique and diagnostic applications, a systematic review of publication trends and reporting quality has not been conducted to identify unmet needs and future directions.

PURPOSE

We aimed to identify which intracranial vasculopathies need more data and to highlight areas of strengths and weaknesses in reporting.

DATA SOURCES

PubMed, EMBASE, and MEDLINE databases were searched up to September 2018 in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

DATA ANALYSIS

Two independent reviewers screened and extracted data from 128 articles. The Strengthening the Reporting of Observational Studies in Epidemiology guidelines were used to assess the reporting quality of analytic observational studies.

DATA SYNTHESIS

There has been an exponentially increasing trend in the number of vessel wall MR imaging publications during the past 24 years (P < .0001). Intracranial atherosclerosis is the most commonly studied intracranial vasculopathy (49%), followed by dissections (13%), aneurysms (8%), and vasculitis (5%). Analytic observational study designs composed 48% of the studies. Transcontinental collaborations showed nonsignificantly higher reporting quality compared with work originating from single continents (P = .20).

LIMITATIONS

A limitation is the heterogeneity in study designs.

CONCLUSIONS

Investigations on the diagnostic utility of vessel wall MR imaging in less commonly studied intracranial vasculopathies such as dissections, aneurysms, and vasculitis are warranted. More consistent adherence to the Strengthening the Reporting of Observational Studies in Epidemiology guidelines should improve transparency and maximize effective synthesis for clinical translation. Diverse collaborative teams are encouraged to advance the understanding of intracranial vasculopathies using vessel wall MR imaging.

Vessel wall MRI characteristics of endovascularly treated aneurysms: association with angiographic vasospasm

OBJECTIVE

The aim of this paper was to evaluate the association between intracranial vessel wall MRI enhancement characteristics and the development of angiographic vasospasm in endovascularly treated aneurysm patients.

METHODS

Consecutive cases of both ruptured and unruptured intracranial aneurysms that were treated endovascularly, followed by intracranial vessel wall MRI in the immediate postoperative period, were included. Two raters blinded to clinical data and follow-up imaging independently evaluated for the presence, pattern, and intensity of wall enhancement. Development of angiographic vasospasm was independently evaluated. Delayed cerebral ischemia; cerebral infarct; procedural details; and presence and grade of subarachnoid, parenchymal, and intraventricular hemorrhage were evaluated. Statistical associations were determined on a per-vessel segment and per-patient basis.

RESULTS

Twenty-nine patients with 30 treated aneurysms (8 unruptured and 22 ruptured) were included in this study. Interobserver agreement was substantial for the presence of enhancement (κ = 0.67) and nearly perfect for distribution (κ = 0.87) and intensity (κ = 0.84) of wall enhancement. Patients with ruptured aneurysms had a significantly greater number of enhancing segments than those with unruptured aneurysms (29.9% vs 7.2%; OR 5.5, 95% CI 2.2-13.7). For ruptured cases, wall enhancement was significantly associated with subsequent angiographic vasospasm while controlling for grade of hemorrhage (adjusted OR 3.9, 95% CI 1.7-9.4). Vessel segments affected by balloon, stent, or flow-diverter use demonstrated greater enhancement than those not affected (OR 22.7, 95% CI 5.3-97.2 for ruptured; and OR 12.9, 95% CI 3.3-49.8 for unruptured).

CONCLUSIONS

Vessel wall enhancement after endovascular treatment of ruptured aneurysms is associated with subsequent angiographic vasospasm.

High-Resolution MRI Vessel Wall Imaging in Acute Aneurysmal Subarachnoid Hemorrhage : Spatiotemporal Pattern and Clinicoradiologic Implications

PURPOSE

The spatiotemporal pattern of vessel wall changes was investigated on two time point magnetic resonance images (MRI) in patients with aneurysmal subarachnoid hemorrhages (aSAH) and its association with clinicoradiologic severity score and delayed cerebral ischemia (DCI) was analyzed.

METHODS

A total of 32 prospectively enrolled patients with aSAH (mean age 56.94 years; 9 male and 23 female) underwent vessel wall imaging (VWI) MRI. Of the patients 20 completed two time point MRIs early and late during the admission, 10 patients only had early MRI and 2 patients only had late MRI. Timing of early MRI had a mean of 2.5 days (range 1-6 days) and late MRI had a mean of 10.5 days (range 7-16 days) from time of admission. Spatiotemporal pattern of vessel wall enhancement (VWE), vasospasm, diffusion-weighted imaging (DWI) lesion burden (grade 0-III) and infarcts were analyzed against the clinicoradiologic severity score (high-risk: vasograde red and yellow, low-risk: vasograde green) and DCI.

RESULTS

On the early MRI, mild VWE alone was significantly more frequent in the high-risk group (36.7% versus 20.0%; P = 0.024). On the late MRI, vasospasm was significantly more frequent in the high-risk group (27.2% versus 4.5%; P = 0.022). Vasospasm infrequently showed mild VWE (6.67% on early MRI and 9.09% on late MRI). Both mild VWE alone on early MRI and on late MRI were significantly associated with development of DCI during the admission (P = 0.034 and P = 0.035, respectively).

CONCLUSION

Mild VWE on early MRI and vasospasm on late MRI were significantly more prevalent in high-risk and DCI patients suggesting VWI might enable imaging of early neuroinflammatory changes which are part of the pathomechanism of vasospasm and DCI.

Vascular Morphology has No Direct Relationship with Atherosclerotic Plaque Burden in Patients with Symptomatic Middle Cerebral Artery Stenosis

BACKGROUND

The vascular morphology and the characteristics of atherosclerotic plaques in the middle cerebral artery (MCA) have not been fully studied with high-resolution magnetic resonance imaging (HR-MRI).

OBJECTIVE

HR-MRI was applied to investigate vascular morphology and atherosclerotic plaque in patients with symptomatic MCA stenosis.

MATERIALS AND METHODS

A total of 343 patients with symptomatic MCA stenosis were enrolled in this study. All the patients were examined by HR-MRI to analyze the morphology of MCA and the M1 segment (MCA-M1), the characteristics and the location of the plaques.

RESULTS

The proportion of L-shaped MCA-M1 decreased, while the proportion of S-shaped MCAM1 increased with age. The anterior plaques were the most common in all the patients. The superior plaques were relatively common in patients with L-shaped and U-shaped MCA-M1, while the inferior plaques were relatively common in patients with inverted U-shaped and S-shaped MCAM1. Among all the plaques, the majority were isointense or heterogeneous. The MCA-M1 morphology had no direct relationship with the common risk factors of atherosclerosis and the clinical outcomes of the patients after 12 months of follow up.

CONCLUSION

The morphology of MCA-M1 is not directly related to the plaque burden or the degree of stenosis in patients with symptomatic MCA stenosis. The morphology of MCA-M1 is not associated with the risk factors of atherosclerosis, or the clinical outcomes of the patients.

A comparison of contrast transthoracic echocardiography and contrast transcranial Doppler in cryptogenic stroke patients with patent foramen ovale

OBJECTIVE

In recent years, increasing attention has been paid to cryptogenic stroke (CS) caused by the patent foramen ovale (PFO). This study aims to compare contrast transthoracic echocardiography (cTTE) and contrast transcranial Doppler (cTCD) to determine whether cTTE is more suitable and reliable than cTCD for clinical use.

METHODS

From March 2017 to May 2018, patients who suffered from migraines, stroke, hypomnesis, or asymptomatic stroke found casually were included in our study. Patients with CS were semirandomly divided into two groups (cTTE and cTCD) according to the date of the outpatient visit. Patients with either of the examination above found positive were selected to finish transesophageal echocardiography (TEE).

RESULTS

In our study, the sensitivities of group cTTE positive (group cTTE+) and group cTCD positive (group cTCD+) did not have any statistical difference (89% vs. 80%, p = 0.236). Focusing on group cTCD+, we discovered that the semiquantitative shunt grading was not correlated with whether a PFO was present or not (p = 0.194). However, once the PFO has been diagnosed, the shunt grading was shown to be related to the width of the gaps (p = 0.032, p_deviation  = 0.03).

CONCLUSION

Both cTTE and the cTCD can be used for preliminary PFO findings. The semiquantitative shunt grading of cTCD and cTTE can suggest the size of the PFO and the next course of treatment. The cTTE may be more significant to a safe PFO (a PFO does not have right-to-left shunts, RLSs). Combining cTTE and TEE could help diagnose PFO and assess CS risk.

Intracranial arterial wall imaging: Techniques, clinical applicability, and future perspectives

Purpose

To review the current state of the art and future development of intracranial vessel wall imaging.

Methods

Recent literature review and expert opinion about intracranial arterial wall imaging.

Results

Intracranial large artery diseases represent an important cause of stroke and vascular cognitive impairment worldwide. Our traditional understanding of intracranial large artery diseases is based on the observation of luminal narrowing or occlusion with angiographic or ultrasound techniques. Recently, novel imaging techniques have made the intracranial artery wall accessible for noninvasive visualization. The main advantage of vessel-wall imaging as compared to conventional imaging techniques for visualization of intracranial arteries is the ability to detect vessel wall changes even before they get to cause any significant luminal stenosis. This diagnostic capacity is provoking a revolutionary change in the way we see the intracranial circulation. In this article, we will review the current state of magnetic resonance imaging and computed tomography-based intracranial arterial wall imaging, focusing on technical considerations and their clinical applicability. Moreover, we will provide the readers with our vision on the future development of vessel-wall imaging techniques.

Conclusion

Intracranial arterial wall imaging methods are gaining increasing potential to impact the diagnosis and treatment of patients with cerebrovascular diseases.

Inter-rater and scan-rescan reproducibility of the detection of intracranial atherosclerosis on contrast-enhanced 3D vessel wall MRI

OBJECTIVE

The objective is to establish interscan, inter- and intra-rater reproducibility of a multicontrast three-dimensional contrast-enhanced intracranial vessel wall (IVW) MRI protocol with 0.6 mm acquired (0.3 mm interpolated) isotropic resolution in the detection of intracranial atherosclerosis.

METHODS

Subjects with established intracranial atherosclerosis were prospectively recruited and underwent two contrast-enhanced three-dimensional IVW scans within a 2-week period. Four raters with varying degrees of vessel wall imaging interpretation experience, through an iterative training process developed guidelines for plaque identification with no, possible and definite plaque categories. Using these guidelines, the raters reviewed the cases in pairs (consensus rating), while blinded to the interpretations of the other pair, clinical reports and patient history. The rater pairs reviewed 19 segments per patient for the presence and location of atherosclerotic plaques. Inter-scan, inter rater and intra rater reproducibility were assessed.

RESULTS

19 subjects were scanned twice, with 361 total segments reviewed and 304-324 evaluable segments analyzed in the different reproducibility assessments. Overall inter-rater agreement for possible and definite plaque was 88.9 % [κ = 0.73; 95% confidence interval (CI) (0.62-0.81)], inter-scan/intra-rater agreement was 82.1 % [κ = 0.58; 95% CI (0.48-0.70)] and inter-scan/inter-rater agreement of 84.5% [κ = 0.64; 95% CI (0.51 - 0.76)].

CONCLUSION

Contrast-enhanced IVW imaging, with the utilization of detailed plaque definition guidelines for image review, can be a reproducible technique for the evaluation of intracranial atherosclerosis.

ADVANCES IN KNOWLEDGE

This work is the first to establish reproducibility of IVW for plaque identification with and without contrast. Reproducibility using contrast is important as most IVW applications rely on lesion enhancement.

Intracranial Vessel Wall Segmentation Using Convolutional Neural Networks

OBJECTIVE

To develop an automated vessel wall segmentation method using convolutional neural networks to facilitate the quantification on magnetic resonance (MR) vessel wall images of patients with intracranial atherosclerotic disease (ICAD).

METHODS

Vessel wall images of 56 subjects were acquired with our recently developed whole-brain three-dimensional (3-D) MR vessel wall imaging (VWI) technique. An intracranial vessel analysis (IVA) framework was presented to extract, straighten, and resample the interested vessel segment into 2-D slices. A U-net-like fully convolutional networks (FCN) method was proposed for automated vessel wall segmentation by hierarchical extraction of low- and high-order convolutional features.

RESULTS

The network was trained and validated on 1160 slices and tested on 545 slices. The proposed segmentation method demonstrated satisfactory agreement with manual segmentations with Dice coefficient of 0.89 for the lumen and 0.77 for the vessel wall. The method was further applied to a clinical study of additional 12 symptomatic and 12 asymptomatic patients with >50% ICAD stenosis at the middle cerebral artery (MCA). Normalized wall index at the focal MCA ICAD lesions was found significantly larger in symptomatic patients compared to asymptomatic patients.

CONCLUSION

We have presented an automated vessel wall segmentation method based on FCN as well as the IVA framework for 3-D intracranial MR VWI.

SIGNIFICANCE

This approach would make large-scale quantitative plaque analysis more realistic and promote the adoption of MR VWI in ICAD management.

A High-Resolution MRI Study of the Relationship Between Plaque Enhancement and Ischemic Stroke Events in Patients With Intracranial Atherosclerotic Stenosis

Purpose: To investigate the relationships among the degree of intracranial atherosclerotic stenosis (ICAS), plaque enhancement (PE), and ischemic stroke events (ISEs) using 3. 0 T high-resolution magnetic resonance imaging (HR-MRI). Materials and Methods: Fifty-two ICAS patients who underwent HR-MRI were retrospectively analyzed. The patients were divided into two groups according to the results of whole-brain digital subtraction angiography (DSA): the mild-moderate stenosis group (group MID) and the severe stenosis group (group SEV). According to the onset time of the ISEs, the plaques were divided into the acute/sub-acute phase culprit plaque group (group ACU, within 1 month), the chronic-phase culprit plaque group (group CHR, more than 1 month), and the non-culprit plaque group (group NON). Two neuroradiologists independently measured the signal intensity of PE and pituitary enhancement in the HR-MRI and calculated the ratio of the two indices. According to the ratio, the patients were divided into three groups: the marked enhancement group (group MA), the mild enhancement group (group ME), and the no enhancement plaque group (group NO). The relationships among the degree of ICAS, the degree of PE and ISEs were analyzed. Results: Seventy-two ICAS plaques were identified in 52 patients. The multiple independent samples Kruskal-Wallis H test showed that the differences among group ACU, CHR, and NON were significant in the degree of PE (P = 0.002). Group CHR and group NON were combined as the non-acute phase group (group non-ACU). Group NO and group ME were combined as the non-marked enhancement group (group non-MA). The comparison between group ACU and group non-ACU showed significant differences in the degree of both ICAS (P = 0.014) and PE (P = 0.006) according to the univariate logistic regression. The multivariate logistic regression model was used to analyze the impact of the degree of ICAS and PE on ISEs, and the results showed that severe stenosis (P = 0.036) and marked PE (P = 0.013) were independent risk factors for acute ISEs, respectively. Conclusion: Severe intracranial arterial stenosis and marked plaque enhancement are independent risk factors for acute ischemic stroke events, respectively. The study provides new ideas for further exploring the pathogenesis of stroke caused by intracranial atherosclerotic stenosis.

Accelerated multi-contrast high isotropic resolution 3D intracranial vessel wall MRI using a tailored k-space undersampling and partially parallel reconstruction strategy

OBJECTIVE

To develop a 3D multi-contrast IVW protocol with 0.5-mm isotropic resolution and a scan time of 5 min per sequence.

MATERIALS AND METHODS

Pre-contrast T1w VISTA, DANTE prepared PDw VISTA, SNAP, and post-contrast T1w VISTA were accelerated using cartesian undersampling with target ordering method (CUSTOM) and self-supporting tailored k-space estimation for parallel imaging reconstruction (STEP). CUSTOM + STEP IVW was compared to full-sample IVW, SENSE-accelerated IVW, and CUSTOM + zero-filled Fourier reconstruction in normal volunteers and subjects with intracranial atherosclerotic disease (ICAD). Image quality, vessel delineation, CSF suppression, and blood suppression were compared.

RESULTS

CUSTOM + STEP vessel wall delineation was comparable to full-sample IVW and better than SENSE IVW for vessel wall delineation on T1w VISTA and luminal contrast on SNAP. Average image quality and wall depiction were significantly improved using STEP reconstruction compared with zero-filled Fourier reconstruction, with no significant difference in CSF or blood suppression.

CONCLUSIONS

CUSTOM + STEP allowed multi-contrast 3D 0.5-mm isotropic IVW within 30 min. Although some quantitative and qualitative scores for CUSTOM - STEP were lower than fully sampled IVW, CUSTOM + STEP provided comparable vessel wall delineation as full-sample IVW and was superior to SENSE. CUSTOM + STEP IVW was well tolerated by patients and showed good delineation of ICAD plaque.

Variable impact of CSF flow suppression on quantitative 3.0T intracranial vessel wall measurements

BACKGROUND

Flow suppression techniques have been developed for intracranial (IC) vessel wall imaging (VWI) and optimized using simulations; however, simulation results may not translate in vivo.

PURPOSE

To evaluate experimentally how IC vessel wall and lumen measurements change in identical subjects when evaluated using the most commonly available blood and cerebrospinal fluid (CSF) flow suppression modules and VWI sequences.

STUDY TYPE

Prospective.

POPULATION/SUBJECTS

Healthy adults (n = 13; age = 37 ± 15 years) were enrolled.

FIELD STRENGTH/SEQUENCE

A 3.0T 3D T1 /proton density (PD)-weighted turbo-spin-echo (TSE) acquisition with post-readout anti-driven equilibrium module, with and without Delay-Alternating-with-Nutation-for-Tailored-Excitation (DANTE) was applied. DANTE flip angle (8-12°) and TSE refocusing angle (sweep = 40-120° or 50-120°) were varied.

ASSESSMENT

Basilar artery and internal carotid artery (ICA) wall thicknesses, CSF signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and signal ratio (SR) were assessed. Measurements were made by two readers (radiology resident and board-certified neuroradiologist).

STATISTICAL TESTS

A Wilcoxon signed-rank test was applied with corrected two-sided P < 0.05 required for significance (critical P = 0.008, 0.005, and 0.05 for SNR/CNR, SR, and wall thickness, respectively).

RESULTS

A TSE pulse sweep = 40-120° and sweep = 50-120° provided similar (P = 0.55) CSF suppression. Addition of the DANTE preparation reduced CSF SNR from 17.4 to 6.7, thereby providing significant (P < 0.008) improvement in CSF suppression. The DANTE preparation also resulted in a significant (P < 0.008) reduction in vessel wall SNR, but variable vessel wall to CSF CNR improvement (P = 0.87). There was a trend for a difference in blood SNR with vs. without DANTE (P = 0.05). The outer vessel wall diameter and wall thickness values were lower (P < 0.05) with (basilar artery 4.45 mm, 0.81 mm, respectively) vs. without (basilar artery 4.88 mm, 0.97 mm, respectively) DANTE 8°.

DATA CONCLUSION

IC VWI with TSE sweep = 40-120° and with DANTE flip angle = 8° provides the best CSF suppression and CNR of the approaches evaluated. However, improvements are heterogeneous, likely owing to intersubject vessel pulsatility and CSF flow variations, which can lead to variable flow suppression efficacy in these velocity-dependent modules.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1120-1128.

Differential Features of Culprit Intracranial Atherosclerotic Lesions: A Whole-Brain Vessel Wall Imaging Study in Patients With Acute Ischemic Stroke

Background

Intracranial atherosclerotic disease tends to affect multiple arterial segments. Using whole‐brain vessel wall imaging, we sought to study the differences in plaque features among various types of plaques in patients with a recent unilateral anterior circulation ischemic stroke.

Methods and Results

Sixty‐one patients with unilateral anterior circulation ischemic stroke were referred to undergo whole‐brain vessel wall imaging (before and after contrast) within 1 month of symptom onset for intracranial atherosclerotic disease evaluations. Each plaque was classified as a culprit, probably culprit, or nonculprit lesion, according to its likelihood of causing the stroke. The associations between plaque features (thickening pattern, plaque‐wall contrast ratio, high signal on T1‐weighted images, plaque contrast enhancement ratio, enhancement grade, and enhancement pattern) and culprit lesions were estimated using mixed multivariable logistic regression after adjustment for maximum wall thickness. In 52 patients without motion corruption in whole‐brain vessel wall imaging, a total of 178 intracranial plaques in the anterior circulation were identified, including 52 culprit lesions (29.2%), 51 probably culprit lesions (28.7%), and 75 nonculprit lesions (42.1%). High signal on T1‐weighted images (adjusted odds ratio, 9.1; 95% confidence interval, 1.9–44.1; P=0.006), grade 2 (enhancement ratio of plaque ≥ enhancement ratio of pituitary) contrast enhancement (adjusted odds ratio, 17.4; 95% confidence interval, 1.8–164.9; P=0.013), and type 2 (≥50% cross‐sectional wall involvement) enhancement pattern (adjusted odds ratio, 10.1; 95% confidence interval, 1.3–82.2; P=0.030) were independently associated with culprit lesions.

Conclusions

High signal on T1‐weighted images, grade 2 contrast enhancement, and type 2 enhancement pattern are associated with cerebrovascular ischemic events, which may provide valuable insights into risk stratification.

3D whole-brain vessel wall cardiovascular magnetic resonance imaging: a study on the reliability in the quantification of intracranial vessel dimensions

BACKGROUND

One of the potentially important applications of three-dimensional (3D) intracranial vessel wall (IVW) cardiovascular magnetic resonance (CMR) is to monitor disease progression and regression via quantitative measurement of IVW morphology during medical management or drug development. However, a prerequisite for this application is to validate that IVW morphologic measurements based on the modality are reliable. In this study we performed comprehensive reliability analysis for the recently proposed whole-brain IVW CMR technique.

METHODS

Thirty-four healthy subjects and 10 patients with known intracranial atherosclerotic disease underwent repeat whole-brain IVW CMR scans. In 19 of the 34 subjects, two-dimensional (2D) turbo spin-echo (TSE) scan was performed to serve as a reference for the assessment of vessel dimensions. Lumen and wall volume, normalized wall index, mean and maximum wall thickness were measured in both 3D and 2D IVW CMR images. Scan-rescan, intra-observer, and inter-observer reproducibility of 3D IVW CMR in the quantification of IVW or plaque dimensions were respectively assessed in volunteers and patients as well as for different healthy subjectsub-groups (i.e. < 50 and ≥ 50 years). The agreement in vessel wall and lumen measurements between the 3D technique and the 2D TSE method was also investigated. In addition, the sample size required for future longitudinal clinical studies was calculated.

RESULTS

The intra-class correlation coefficient (ICC) and Bland-Altman plots indicated excellent reproducibility and inter-method agreement for all morphologic measurements (All ICCs > 0.75). In addition, all ICCs of patients were equal to or higher than that of healthy subjects except maximum wall thickness. In volunteers, all ICCs of the age group of ≥50 years were equal to or higher than that of the age group of < 50 years. Normalized wall index and mean and maximum wall thickness were significantly larger in the age group of ≥50 years. To detect 5% - 20% difference between placebo and treatment groups, normalized wall index requires the smallest sample size while lumen volume requires the highest sample size.

CONCLUSIONS

Whole-brain 3D IVW CMR is a reliable imaging method for the quantification of intracranial vessel dimensions and could potentially be useful for monitoring plaque progression and regression.