Intracranial atherosclerosis: correlation between in-vivo 3T high resolution MRI and pathology

Pathology-based brain arterial disease phenotypes and their radiographic correlates

INTRODUCTION

Brain arterial diseases, including atherosclerosis, vasculitis, and dissections, are major contributors to cerebrovascular morbidity and mortality worldwide. These diseases not only increase the risk of stroke but also play a significant role in neurodegeneration and dementia. Clear and unambiguous terminology and classification of brain arterial disease phenotypes is crucial for research and clinical practice.

MATERIAL AND METHODS

This review aims to summarize and harmonize the terminology used for brain large and small arterial phenotypes based on pathology studies and relate them to imaging phenotypes used in medical research and clinical practice.

CONCLUSIONS AND RESULTS

Arteriosclerosis refers to hardening of the arteries but does not specify the underlying etiology. Specific terms such as atherosclerosis, calcification, or non-atherosclerotic fibroplasia are preferred. Atherosclerosis is defined pathologically by an atheroma. Other brain arterial pathologies occur and should be distinguished from atherosclerosis given therapeutic implications. On brain imaging, intracranial arterial luminal stenosis is usually attributed to atherosclerosis in the presence of atherosclerotic risk factors but advanced high-resolution arterial wall imaging has the potential to more accurately identify the underlying pathology. Regarding small vessel disease, arteriosclerosis is ambiguous and arteriolosclerosis is often used to denote the involvement of arterioles rather than arteries. Lipohyalinosis is sometimes used synonymously with arteriolosclerosis, but less accurately describes this common small vessel thickening which uncommonly shows lipid. Specific measures of small vessel wall thickness, the relationship to the lumen as well as changes in the layer composition might convey objective, measurable data regarding the status of brain small vessels.

Diagnostic Yield of High-Resolution Vessel Wall Magnetic Resonance Imaging in the Evaluation of Young Stroke Patients

(1) Background: The mechanism responsible for stroke in patients younger than 50 often remains unknown. This study was designed to assess whether high-resolution intracranial vessel wall MR imaging (icVWI) may be instrumental in determining stroke cause. (2) Methods: Young stroke patients with and without an identified cause of stroke despite an exhaustive investigation were prospectively included. Patients who underwent icVWI were compared to those who did not. We next compared patients with and without intracranial vulnerable plaques on icVWI. (3) Results: Overall, 47 young stroke patients were identified over the span of 2 years and included in this study. Of those, 20 (42%) underwent intracranial icVWI. Cancer prevalence was higher among patients who did not have an icVWI study (19% vs. 0% p = 0.042) but there were no other significant differences between patients who had an icVWI study and those who did not have an icVWI. Among patients who had an icVWI, 11 (55%) had vulnerable plaques and the remaining nine studies were negative. Patients with positive icVWI scans had significantly higher stroke severity at admission (mean ± SD NIHSS score 5.5 ± 3.5 vs. 1.7 ± 2.3, p = 0.012). Patients with positive icVWI scans were more often treated with antiplatelets upon discharge (100% vs. 67%, p = 0.038). (4) Conclusions: icVWI can add significant information relevant to stroke pathogenesis and secondary prevention among young stroke patients with a negative exhaustive diagnostic workup.

Impact of high-resolution intracranial vessel wall magnetic resonance imaging on diagnosis in patients with embolic stroke of unknown source

BACKGROUND

The mechanism responsible for stroke in patients with embolic stroke of unknown source (ESUS) often remains unknown despite extensive investigations. We aimed to test whether high-resolution intracranial vessel wall MR imaging (icVWI) can add to the diagnostic yield in these patients.

PATIENTS AND METHODS

Patients with ESUS were prospectively included into an ongoing registry. Patients that underwent icVWI as part of their diagnostic workup were compared to those that did not have an icVWI. Patients with icVWI positive for intracranial vulnerable plaques were than compared to those without evidence of plaque vulnerability on VWI.

RESULTS

A total of 179 patients with ESUS were included and 48 of them (27%) underwent icVWI. Patients that had an icVWI scan were significantly younger, had lower rates of ischemic heart disease and prior disability as well as significantly lower stroke severity. On regression analysis the only factor that remained associated with not obtaining an icVWI scan was increasing age (Odds ratio [OR] 0.97/year, 95% confidence intervals [CI] 0.95-0.97). Among patients that had an icVWI scan 28 (58%) had evidence of plaque enhancement on VWI in the same distribution of the stroke and the remaining 20 studies were negative. The relative proportion of stroke presumed to be secondary to intracranial non-stenotic atheromatous disease increased from 15% in patients without icVWI scans to 58% among patients with icVWI scans (p = 0.001). On regression analysis the only factor that was associated with vulnerable plaques on icVWI was smoking (OR 11.05 95% CI 1.88-65.17).

CONCLUSIONS

icVWI can add significant information relevant to stroke pathogenesis and treatment in patients with ESUS and a negative initial exhaustive diagnostic workup.

Radiomics and artificial neural networks modelling for identification of high-risk carotid plaques

Objective

In this study, we aimed to investigate the classification of symptomatic plaques by evaluating the models generated via two different approaches, a radiomics-based machine learning (ML) approach, and an end-to-end learning approach which utilized deep learning (DL) techniques with several representative model frameworks.

Methods

We collected high-resolution magnetic resonance imaging (HRMRI) data from 104 patients with carotid artery stenosis, who were diagnosed with either symptomatic plaques (SPs) or asymptomatic plaques (ASPs), in two medical centers. 74 patients were diagnosed with SPs and 30 patients were ASPs. Sampling Perfection with Application-optimized Contrasts (SPACE) by using different flip angle Evolutions was used for MRI imaging. Repeated stratified five-fold cross-validation was used to evaluate the accuracy and receiver operating characteristic (ROC) of the trained classifier. The two proposed approaches were investigated to train the models separately. The difference in the model performance of the two proposed methods was quantitatively evaluated to find a better model to differentiate between SPs and ASPs.

Results

3D-SE-Densenet-121 model showed the best performance among all prediction models (AUC, accuracy, precision, sensitivity, and F1-score of 0.9300, 0.9308, 0.9008, 0.8588, and 0.8614, respectively), which were 0.0689, 0.1119, 0.1043, 0.0805, and 0.1089 higher than the best radiomics-based ML model (MLP). Decision curve analysis showed that the 3D-SE-Densenet-121 model delivered more net benefit than the best radiomics-based ML model (MLP) with a wider threshold probability.

Conclusion

The DL models were able to accurately differentiate between symptomatic and asymptomatic carotid plaques with limited data, which outperformed radiomics-based ML models in identifying symptomatic plaques.

Intracranial plaque with large lipid core is associated with embolic stroke of undetermined source

OBJECTIVE

To investigate an association between percentage lipid-rich necrotic core (LRNC) and an index ischemic stroke in an embolic stroke of undetermined source (ESUS) cohort.

METHODS

A total of 167 ESUS patients with 259 non-stenotic intracranial plaques including 155 ipsilateral and 104 contralateral to stroke were finally enrolled in the current analysis. The multi-dimensional parameters involving remodeling index (RI), plaque burden (PB), LRNC, discontinuity of plaque surface (DPS), intraplaque hemorrhage (IPH), and vulnerable plaque defined as presence of complicated plaque were evaluated by high-resolution magnetic resonance imaging.

RESULTS

We found that %LRNC was an independent predictor for ESUS in model 1 (OR: 2.574, 95% CI: 1.854-3.573, P < 0.001), and model 2 (OR: 2.550, 95% CI: 1.835-3.545, P < 0.001), but the association was not seen in PB. In receiver operating characteristic curve analysis, the discrimination of LRNC for ESUS was significantly superior to that of PB (absolute difference: 0.121, 95% CI: 0.056-0.205, P < 0.001). Importantly, a significantly positive synergy between the remodeling pattern and LRNC in response to plaque vulnerability was found by Sankey diagram (P for interaction = 0.001).

CONCLUSION

This is the first report that LRNC, beyond PB, may be correlated with an index ESUS, and a synergistic effect between positive remodeling and larger LRNC could promote plaque vulnerability. The findings suggest that a potential target subgroup may benefit from stroke prevention with intensive statin, although this must be confirmed in future.

Intracranial plaque characteristics on high-resolution MRI and high-sensitivity C-reactive protein levels: association and clinical relevance in acute cerebral infarction

AIM

To investigate the association between intracranial plaque characteristics and high-sensitivity C-reactive protein (hs-CRP) levels, and their combined effects on the occurrence of acute cerebral infarction (ACI).

MATERIALS AND METHODS

One hundred and forty-three patients with recent ischaemic events in the territory of middle cerebral artery or basilar artery were enrolled and divided into the ACI group (n=93) and non-ACI group (n=50) according to clinical data and diffusion-weighting imaging (DWI) results. All recruited patients underwent high-resolution magnetic resonance imaging (MRI) to assess intracranial plaque characteristics, including plaque enhancement, standardised wall index, stenosis ratio, T1 hyperintense component, remodelling pattern, plaque area, plaque burden, and maximum wall thickness. hs-CRP levels were further grouped into the low group (<1 mg/l), the intermediate group (1-3 mg/l), and the high group (≥3 mg/l). Multivariate logistic regression and receiver operating characteristic curve were constructed to evaluate the association between intracranial plaque characteristics and hs-CRP levels, as well as their synergistic effects on determining the occurrence of ACI.

RESULTS

High hs-CRP levels were associated with strong plaque enhancement (p<0.001, odds ratio [OR] = 7.497). Strong plaque enhancement (p=0.002, OR=2.109) and high hs-CRP levels (p=0.009, OR=3.893) were independently associated with the occurrence of ACI after adjustments for sex, age, and other traditional atherosclerotic risk factors. The combination of hs-CRP levels and strong plaque enhancement provided incremental information to determine ACI with an AUC of 0.823, which was significantly higher than that of strong plaque enhancement (0.711) and hs-CRP levels (0.686), respectively.

CONCLUSION

High hs-CRP levels were associated with strong plaque enhancement. The synergistic effects of hs-CRP levels and strong plaque enhancement provided incremental effects on the occurrence of ACI.

Recurrent stroke risk in intracranial atherosclerotic disease

Recurrent stroke risk secondary to intracranial atherosclerotic disease remains high despite aggressive medical treatment. This risk is further amplified in subgroups possessing biomarkers of hemodynamic insufficiency and potential for embolization, which have been shown to be independently and synergistically predictive of recurrent stroke. Luminal stenosis was predominantly used as entry criteria in major treatment trials, discounting the potential role of hemodynamics from primary analyses, limiting the strength of evidence and conclusions of these biomarkers to post-hoc analyses and other natural history studies. Future treatment trials should consider stratifying patients using a combination of these high-risk biomarkers. In the absence of trials, risk stratifying patients based on the presence of these markers may lend to more individualized clinical decisions. We aimed to summarize the studies that have investigated the relationship between biomarkers and their role in predicting recurrent stroke risk in intracranial atherosclerotic disease.

Intracranial Arterial Calcifications: Potential Biomarkers of Stroke Risk and Outcome

Intracranial artery calcifications (IAC), a common and easily identifiable finding on computed tomorgraphy angiography (CTA), has gained recognition as a possible risk factor for ischemic stroke. While atherosclerosis of intracranial arteries is believed to be a mechanism that commonly contributes to ischemic stroke, and coronary artery calcification is well-established as a predictor of both myocardial infarction (MI) and ischemic stroke risk, IAC is not currently used as a prognostic tool for stroke risk or recurrence. This review examines the pathophysiology and prevalence of IAC, and current evidence suggesting that IAC may be a useful tool for prediction of stroke incidence, recurrence, and response to acute ischemic stroke therapy.

The role of cross-sectional imaging of the extracranial and intracranial vasculature in embolic stroke of undetermined source

Despite an extensive workup, nearly one third of ischemic strokes are defined as Embolic Stroke of Undetermined Source (ESUS), indicating that no clear etiologic cause has been identified. Since large vessel atherosclerotic disease is a major cause of ischemic stroke, we focus on imaging of large vessel atherosclerosis to identify further sources of potential emboli which may be contributing to ESUS. For a stroke to be considered ESUS, both the extracranial and intracranial vessels must have &lt;50% stenosis. Given the recent paradigm shift in our understanding of the role of plaque vulnerability in ischemic stroke risk, we evaluate the role of imaging specific high-risk extracranial plaque features in non-stenosing plaque and their potential contributions to ESUS. Further, intracranial vessel-wall MR is another potential tool to identify non-stenosing atherosclerotic plaques which may also contribute to ESUS. In this review, we discuss the role of cross-sectional imaging of the extracranial and intracranial arteries and how imaging may potentially uncover high risk plaque features which may be contributing to ischemic strokes.

Identification of high-risk intracranial plaques with 3D high-resolution magnetic resonance imaging-based radiomics and machine learning

BACKGROUND

Identifying high-risk intracranial plaques is significant for the treatment and prevention of stroke.

OBJECTIVE

To develop a high-risk plaque model using three-dimensional (3D) high-resolution magnetic resonance imaging (HRMRI) based radiomics features and machine learning.

METHODS

136 patients with documented symptomatic intracranial artery stenosis and available HRMRI data were included. Among these patients, 136 and 92 plaques were identified as symptomatic and asymptomatic plaques, respectively. A conventional model was developed by recording and quantifying the radiological plaque characteristics. Radiomics features from T1-weighted images (T1WI) and contrast-enhanced T1WI (CE-T1WI) were used to construct a high-risk plaque model with linear support vector classification (linear SVC). The radiological and radiomics features were combined to build a combined model. Receiver operating characteristic (ROC) curves were used to evaluate these models.

RESULTS

Plaque length, burden, and enhancement were independently associated with clinical symptoms and were included in the conventional model, which had an AUC of 0.853 vs. 0.837 in the training and test sets. While the radiomics and the combined model showed an improved AUC: 0.923 vs. 0.925 for the training sets and 0.906 vs. 0.903 in the test sets. Both the radiomics model (p = 0.024, p = 0.018) and combined model (p = 0.042, p = 0.049) outperformed the conventional model in the two sets, whereas the performance of the combined model was not significantly different from that of the radiomics model in the two sets (p = 0.583 and p = 0.606).

CONCLUSION

The radiomics model based on 3D HRMRI can accurately differentiate symptomatic from asymptomatic intracranial arterial plaques and significantly outperforms the conventional model.

Vessel wall MR imaging of aortic arch, cervical carotid and intracranial arteries in patients with embolic stroke of undetermined source: A narrative review

Despite advancements in multi-modal imaging techniques, a substantial portion of ischemic stroke patients today remain without a diagnosed etiology after conventional workup. Based on existing diagnostic criteria, these ischemic stroke patients are subcategorized into having cryptogenic stroke (CS) or embolic stroke of undetermined source (ESUS). There is growing evidence that in these patients, non-cardiogenic embolic sources, in particular non-stenosing atherosclerotic plaque, may have significant contributory roles in their ischemic strokes. Recent advancements in vessel wall MRI (VW-MRI) have enabled imaging of vessel walls beyond the degree of luminal stenosis, and allows further characterization of atherosclerotic plaque components. Using this imaging technique, we are able to identify potential imaging biomarkers of vulnerable atherosclerotic plaques such as intraplaque hemorrhage, lipid rich necrotic core, and thin or ruptured fibrous caps. This review focuses on the existing evidence on the advantages of utilizing VW-MRI in ischemic stroke patients to identify culprit plaques in key anatomical areas, namely the cervical carotid arteries, intracranial arteries, and the aortic arch. For each anatomical area, the literature on potential imaging biomarkers of vulnerable plaques on VW-MRI as well as the VW-MRI literature in ESUS and CS patients are reviewed. Future directions on further elucidating ESUS and CS by the use of VW-MRI as well as exciting emerging techniques are reviewed.

The MRI enhancement ratio and plaque steepness may be more accurate for predicting recurrent ischemic cerebrovascular events in patients with intracranial atherosclerosis

OBJECTIVES

To assess the complementary value of high-resolution multi-contrast MRI (hrMRI) in identifying symptomatic patients with intracranial atherosclerosis (ICAS) who are likely to experience recurrent ischemic cerebrovascular events.

METHODS

In this retrospective cohort study, eighty patients with acute ischemic events attributed to ICAS who underwent hrMRI examination between January 2015 and January 2019 were included. Median follow-up for all patients was 30 months (range: 1 to 52 months) and recurrent ischemic cerebrovascular events were recorded. Cox regression analysis and time-dependent ROC were performed to quantify the association between the plaque characteristics and recurrent events.

RESULTS

During the follow-up, 14 patients experienced recurrent ischemic cerebrovascular events. Young males and those with diabetes and poor medication persistence were more likely to experience recurrent events. ICAS in patients with recurrence had significantly higher enhancement ratio and steepness which is defined as the ratio between the plaque height and length than those without (p < 0.001 and p = 0.015, respectively). After adjustment of clinical factors, enhancement ratio (HR, 13.13 [95% CI, 3.58-48.20], p < 0.001) and plaque steepness (HR, 110.27 [95% CI, 4.75-2560.91], p = 0.003) were independent imaging biomarkers associated with recurrent events. Time-dependent ROC indicated that integrated high enhancement ratio and steepness into clinical risk factors improved discrimination power with the ROC increased from 0.79 to 0.94 (p = 0.008).

CONCLUSIONS

The enhancement ratio and plaque steepness improved the accuracy over traditional clinical risk factors in predicting recurrent ischemic cerebrovascular events for patients with ICAS.

KEY POINTS

• High-resolution magnetic resonance imaging helps clinicians to evaluate high-risk Intracranial plaque. • The higher enhancement ratio and plaque steepness (= height/length) were the primary biomarkers associated with future ischemic cerebrovascular events. • High-resolution magnetic resonance imaging combined with clinical characteristics showed a higher accuracy for the prediction of recurrent events in patients with intracranial atherosclerosis.

Implementation of an International Vessel Wall MR Plaque Imaging Research Network: Experience with the ChAMPION Study

Background and Objective: Intracranial atherosclerosis (ICAS) is one of the most common causes of stroke worldwide. High-resolution Vessel Wall MR imaging (VW-MR) is commonly used to study ICAS, but in order to accelerate advances in the field of VW-MR ICAS research, the establishment of a multicenter research network is needed. We introduce our experience in establishing a collaborative international VW-MR ICAS research network in China and North America using an innovative, disease-specific ICAS imaging phantom for standardization of VW-MR sequences at the sites. Methods: Both the Medical University of South Carolina and Peking Union Medical College functioned as Central Coordinating Centers in the network. PUMC identified research centers within China that had the potential for collaboration on VW-MR ICAS research based on networking and prior experience. All selected centers refined MRI sequences using an ICAS phantom with study principal investigators virtually present in real-time during scanning. MRI sequences were efficiently calibrated utilizing the broad expertise of all members of the research team. All centers further validated MRI sequences with human subjects. Results: We identified 11 Chinese hospitals as the potential collaborating sites for the network. Of the 11 selected sites, six sites were able to complete the required VW-MR scanning and sequence refinement using the ICAS phantom and subsequent human subjects. Conclusion: The study demonstrated the feasibility of establishing a cross-continent collaborative VW-MR research network and the use of a disease-specific phantom to facilitate convenient and efficient sequence modification for image quality standardization, which is needed for future multicenter VW-MR studies.

The characteristics of intracranial plaques of unilateral, anterior circulation embolic stroke of undetermined source: an analysis of different subtypes based on high-resolution imaging

BACKGROUND AND PURPOSE

To investigate the characteristics of non-stenotic intracranial plaque (NSIP) among embolic stroke of undetermined source (ESUS) subtypes by high-resolution magnetic resonance imaging (HR-MRI).

METHODS

we retrospectively enrolled consecutive patients with ESUS who were mandatory for HR-MRI. Based the location and arterial supply of the infarct, ESUS were categorized into three types: cortical ESUS, subcortical ESUS and mixed ESUS. The NSIP parameters including plaque location, morphology (plaque distribution, remodeling index and plaque burden) and composition (thick fibrous cap, discontinuity of plaque surface, intraplaque hemorrhage and complicated plaque) were evaluated among subtypes.

RESULTS

Among 243 patients, there were 87 (35.8%) cortical ESUS, 127 (52.3%) subcortical ESUS and 29 (11.9%) mixed ESUS. We found significant differences in plaque location (P < 0.001), plaque quadrant (P < 0.001), remodeling index (P < 0.001), plaque burden (P < 0.001), discontinuity of plaque surface (P < 0.001), intraplaque hemorrhage (P = 0.001) and complicated plaque (P < 0.001) of ipsilateral NISP among different ESUS subtypes, except for fibrous cap (P = 0.135). But we found no differences among contralateral NISP. In addition, the clinical characteristics of the differences among ESUS subtypes were striking, including age (P = 0.004), initial National Institute of Health Stroke Scale (P < 0.001), coronary artery disease (P = 0.039), serum urea (P = 0.011) and creatinine (P = 0.002).

CONCLUSION

This is the first report of significantly heterogeneous characteristics of ipsilateral NSIP and clinical findings among ESUS subtypes, which may suggest their different underlying mechanisms.

Imaging Features of Symptomatic MCA Stenosis in Patients of Different Ages: A Vessel Wall MR Imaging Study

BACKGROUND AND PURPOSE

The prevalence of intracranial artery stenosis is high in Asian people. This study aimed to investigate whether there are differences in the imaging features of symptomatic MCA stenosis in patients of different ages using vessel wall MR imaging.

MATERIALS AND METHODS

We retrospectively reviewed the data of consecutive patients with unilateral MCA stenosis based on a prospectively established vessel wall MR imaging data base between January 2017 and December 2018. According to age, the patients were divided into the young group (18-45 years of age) and the middle-aged and elderly group (older than 45 years of age).

RESULTS

Overall, 131 patients with unilateral MCA stenosis were included (45.8% in the young group and 54.2% in the middle-aged and elderly group). Middle-aged and elderly patients had a higher prevalence of hypertension (P = .01) and diabetes (P = .05). The lesion length (P < .0001), proportion of circular involvement (P = .006), and proportion of circular enhancement (P = .03) were higher in the young group than in the middle-aged and elderly group. The analysis of the atherosclerotic subgroup showed that compared with middle-aged and elderly patients, young patients had longer lesions (P = .002). The atherosclerotic-versus-nonatherosclerotic subgroup analysis showed that the maximal wall thickness in the patients with atherosclerosis was larger than that of patients without it (P = .002).

CONCLUSIONS

Compared with the middle-aged and elderly group, young patients with MCA stenosis tended to have longer lesions and more circular wall involvement and circular enhancement, which may indicate the differences in underlying vascular pathophysiologic and developmental mechanisms in symptomatic MCA stenosis.

Intraplaque Enhancement Is Associated With Artery-to-Artery Embolism in Symptomatic Vertebrobasilar Atherosclerotic Diseases

Objective: There are limited data regarding the characteristics of intracranial plaques according to stroke mechanism in the posterior circulation. This study aims to compare whether the plaque characteristics and baseline features are different in patients with artery-to-artery (A-to-A) embolism and those with parent artery disease in the intracranial vertebrobasilar atherosclerotic disease.

Methods: From September 2014 to January 2017, patients with recent posterior circulation stroke due to intracranial vertebrobasilar atherosclerotic disease were retrospectively analyzed. Patients with the following eligibility criteria were included: (1) age ≥18 years old, (2) ischemic stroke in the vertebrobasilar territory, (3) 70–99% stenosis of the intracranial vertebral artery or basilar artery, and (4) two or more atherosclerotic risk factors. Patients with concomitant ipsilateral or bilateral extracranial vertebral artery >50% stenosis, cardio-embolism, or non-atherosclerotic stenosis were excluded. The plaque characteristics, including intraplaque compositions (intraplaque hemorrhage and intraplaque calcification), intraplaque enhancement, and remodeling index, were evaluated by using 3T high-resolution magnetic resonance imaging (HRMRI). The baseline features including vascular risk factors and the involved artery were collected. Patients were divided into A-to-A embolism and parent artery disease groups based on the diffusion-weighted images, T2-weighted images, or computed tomography. The plaque characteristics and baseline features were compared between the two groups.

Results: Among consecutive 298 patients, 51 patients were included. Twenty-nine patients had A-to-A embolism and 22 patients had parent artery disease. Compared with parent artery disease, the occurrence rates of intraplaque enhancement and intracranial vertebral involvement were higher in the A-to-A embolism group (79.3 vs. 36.4%; p = 0.002 and 62.1 vs. 18.2%; p = 0.002, respectively). Multivariable logistic regression analysis showed that intraplaque enhancement and intracranial vertebral artery plaques were also associated with A-to-A embolism (adjusted OR, 7.31; 95% CI 1.58–33.77; p = 0.011 and adjusted OR, 9.42; 95% CI 1.91–46.50; p = 0.006, respectively).

Conclusion: Intraplaque enhancement and intracranial vertebral artery plaques seem to be more closely associated with A-to-A embolism than parent artery disease in patients with symptomatic intracranial vertebrobasilar disease.

Clinical Trial Registration:http://www.clinicaltrials.gov, identifier: NCT02705599.

Current Clinical Applications of Intracranial Vessel Wall MR Imaging

Intracranial vessel wall MR imaging (VWI) is increasingly being used as a valuable adjunct to conventional angiographic imaging techniques. This article will provide an updated review on intracranial VWI protocols and image interpretation. We review VWI technical considerations, describe common VWI imaging features of different intracranial vasculopathies and show illustrative cases. We review the role of VWI for differentiating among steno-occlusive vasculopathies, such as intracranial atherosclerotic plaque, dissections and Moyamoya disease. We also highlight how VWI may be used for the diagnostic work-up and surveillance of patients with vasculitis of the central nervous system and cerebral aneurysms.

Gadolinium enhancement of atherosclerotic plaque in the intracranial artery

Background: Gadolinium enhancement on high resolution magnetic resonance imaging (HR-MRI) has been considered a sign of instability and inflammation of intracranial atherosclerotic plaques. Our research objective was to explore the relationship between the extent of plaque enhancement (PE), the degree of intracranial artery stenosis, and acute ischemic stroke events.Methods: HR-MRI was performed in 91 patients with intracranial vascular stenosis to determine the existence and intensity of PE.Results: Among 91 patients enrolled in the trial, there were 43 patients in the acute/subacute group (≤1 month from ischemic stroke event), 15 patients in the chronic group (>1 month from ischemic stroke event), and 33 patients in the non-culprit plaques group (no ischemic stroke event). A total of 105 intracranial atherosclerotic plaques were detected in 91 patients. 14 (13.3%) were mild-stenosis plaques, 22 (21.0%) were moderate-stenosis plaques, and 69 (65.7%) were severe-stenosis plaques. There were 12 (11.4%), 18 (17.1%), and 75 (71.4%) plaques in the non-enhanced plaque group, the mild-enhancement group, and the significant-enhancement group, respectively. The degree of PE among the acute/subacute group, the chronic group, and the non-culprit plaque group had a significant difference (P = 0.005). Enhanced plaques were more often observed in culprit plaques (acute/subacute group and chronic group) than non-culprit plaques (96.7% vs 77.3%). Non-enhanced plaques were more often observed in non-culprit plaques than culprit plaques (acute/subacute group and chronic group) (22.7% vs 3.3%). And 36.6% of the enhanced plaques were non-culprit plaques. After performing univariate and multivariate logistic regression analysis, the results showed that strong plaque enhancement (P = 0.025, odds ratio [OR] 3.700, 95% confidence interval [95% CI] 1.182-11.583) and severe stenosis (P = 0.008, OR 4.393, 95%CI 1.481-13.030) were significantly associated with acute ischemic events.Conclusion: Enhanced plaques were more often observed in culprit plaques, and non-enhanced plaques were more often observed in non-culprit plaques. Moreover, significant plaque enhancement and severe ICAS were closely associated with acute ischemic events.

Optical Coherence Tomography for Neurovascular Disorders

Diagnosis of cerebrovascular disease includes vascular neuroimaging techniques such as computed tomography (CT) angiography, magnetic resonance (MR) angiography (with or without use of contrast agents) and catheter digital subtraction angiography (DSA). These techniques provide mostly information about the vessel lumen. Vessel wall imaging with MR seeks to characterize cerebrovascular pathology, but with resolution that is often insufficient for small lesions. Intravascular imaging techniques such as ultrasound and optical coherence tomography (OCT), used for over a decade in the peripheral circulation, is not amendable to routine deployment in the intracranial circulation due to vessel caliber and tortuosity. However, advances in OCT technology including the probe profile, stiffness and unique distal rotation solution, holds the promise for eventual translation of OCT into the clinical arena. As such, it is apropos to review this technology and present the rationale for utilization of OCT in the cerebrovasculature.

High-Resolution Magnetic Resonance Vessel Wall Imaging for the Evaluation of Intracranial Vascular Pathology

Intracranial vessel wall imaging (IVWI) is an advanced MR imaging technique that allows for direct visualization of the walls of intracranial blood vessels and detection of subtle pathologic vessel wall changes before they become apparent on conventional luminal imaging. When performed correctly, IVWI can increase diagnostic confidence, aid in the differentiation of intracranial vasculopathies, and assist in patient risk stratification and prognostication. This review covers the essential technical underpinnings of IVWI and presents emerging clinical research highlighting its utility for the evaluation of multiple intracranial vascular pathologies.

Intracranial Atherosclerotic Plaque as a Potential Cause of Embolic Stroke of Undetermined Source

BACKGROUND

Previous studies investigated the potential mechanism of embolic stroke of undetermined source (ESUS) from extracranial artery plaque, but there has been no study other than a case report on high-risk intracranial plaque in ESUS.

OBJECTIVES

The aim of this study was to investigate the issue by evaluating the morphology and composition of intracranial plaque in patients with ESUS and small-vessel disease (SVD) using 3.0-T high-resolution magnetic resonance imaging.

METHODS

Two hundred forty-three consecutive patients with ESUS and 160 patients with SVD-associated stroke between January 2015 and December 2019 were retrospectively enrolled. Multidimensional parameters involving the presence of plaque on both sides, including remodeling index (RI), plaque burden, presence of discontinuity of plaque surface, thick fibrous cap, intraplaque hemorrhage, and complicated American Heart Association type VI plaque at the maximal luminal narrowing site, were evaluated using intracranial high-resolution magnetic resonance imaging.

RESULTS

Among 243 patients with ESUS, the prevalence of intracranial plaque was much higher in the ipsilateral than the contralateral side (63.8% vs. 42.8%; odds ratio [OR]: 5.25; 95% confidence interval [CI]: 2.83 to 9.73), a finding that was not evident in patients with SVD (35.6% vs. 30.6%; OR: 2.14; 95% CI: 0.87 to 5.26; p = 0.134). Logistic analysis showed that RI was independently associated with ESUS in model 1 (OR: 2.329; 95% CI: 1.686 to 3.217; p < 0.001) and model 2 (OR: 2.295; 95% CI: 1.661 to 3.172; p < 0.001). RI alone with an optimal cutoff of 1.162, corresponding to an area under the curve of 0.740, had good diagnostic efficiency for ESUS.

CONCLUSIONS

The present study supports an etiologic role of high-risk nonstenotic intracranial plaque in ESUS.

A High Resolution MRI Study of the Relationship Between Plaque Enhancement and Perforator Stroke after Stenting for Symptomatic Vertebrobasilar Artery Stenosis

BACKGROUND AND PURPOSE

Perforator stroke is one of the most common complications of vertebrobasilar arterial stenting. We investigated whether perforator stroke after vertebrobasilar arterial stenting is associated with plaque enhancement in patients with severe vertebrobasilar artery stenosis.

METHODS

We studied patients with symptomatic vertebrobasilar arterial stenosis who underwent stenting from January 2017 to July 2020. Patients who underwent high resolution magnetic resonance imaging were recruited among them. Demographic data, risk factors of atherosclerosis, procedure details, and characteristics of imaging were extracted from electronic health records and imaging data. Plaque features were investigated by high resolution magnetic resonance imaging.

RESULTS

136 patients were enrolled in this study, 39 of whom fulfilled the inclusion criteria. 18 patients (46.2%) had obvious plaque enhancement among the 39 patients, and 21 (53.8%) had plaque non-enhancement. 21 patients (53.8%) had diffuse distribution, and 22 patients (56.4%) had irregular plaques surface. Patients were divided into plaque enhanced and plaque non-enhanced groups according to the degree of plaque enhancement. Clinical characteristics and other plaque features were similar between two groups. Procedure-related perforator stroke was identified in 4 patients (10.3%). Patients with plaque enhancement were more likely to have perforator stroke after stenting compared with those with plaque non-enhancement (22.2% versus 0%, P = 0.037).

CONCLUSIONS

Plaque enhancement in high resolution magnetic resonance imaging may be associated with perforator stroke after vertebrobasilar artery stenting.

Vessel Wall Magnetic Resonance Imaging Biomarkers of Symptomatic Intracranial Atherosclerosis: A Meta-Analysis

BACKGROUND AND PURPOSE

Intracranial atherosclerotic disease is a common cause of stroke worldwide. Intracranial vessel wall magnetic resonance imaging may be able to identify imaging biomarkers of symptomatic plaque. We performed a meta-analysis to evaluate the strength of association of imaging features of symptomatic plaque leading to downstream ischemic events. Effects on the strength of association were also assessed accounting for possible sources of bias and variability related to study design and magnetic resonance parameters.

METHODS

PubMed, Scopus, Web of Science, EMBASE, and Cochrane databases were searched up to October 2019. Two independent reviewers extracted data on study design, vessel wall magnetic resonance imaging techniques, and imaging end points. Per-lesion odds ratios (OR) were calculated and pooled using a bivariate random-effects model. Subgroup analyses, sensitivity analysis, and evaluation of publication bias were also performed.

RESULTS

Twenty-one articles met inclusion criteria (1750 lesions; 1542 subjects). Plaque enhancement (OR, 7.42 [95% CI, 3.35-16.43]), positive remodeling (OR, 5.60 [95% CI, 2.23-14.03]), T1 hyperintensity (OR, 2.05 [95% CI, 1.27-3.32]), and surface irregularity (OR, 4.50 [95% CI, 1.39-8.57]) were significantly associated with downstream ischemic events. T2 signal intensity was not significant (P=0.59). Plaque enhancement was significantly associated with downstream ischemic events in all subgroup analyses and showed stronger associations when measured in retrospectively designed studies (P=0.02), by a radiologist as a rater (P<0.001), and on lower vessel wall magnetic resonance imaging spatial resolution sequences (P=0.02).

CONCLUSIONS

Plaque enhancement, positive remodeling, T1 hyperintensity, and surface irregularity emerged as strong imaging biomarkers of symptomatic plaque in patients with ischemic events. Plaque enhancement remained significant accounting for sources of bias and variability in both study design and instrument. Future studies evaluating plaque enhancement as a predictive marker for stroke recurrence with larger sample sizes would be valuable.

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.

Infarct Recurrence in Intracranial Atherosclerosis: Results from the MyRIAD Study

BACKGROUND

Intracranial atherosclerotic disease (ICAD) is a common cause of ischemic stroke with a high risk of clinical stroke recurrence. Multiple mechanisms may underlie cerebral ischemia in this condition. The study's objective is to discern the mechanisms of recurrent ischemia in ICAD through imaging biomarkers of impaired antegrade flow, poor distal perfusion, abnormal vasoreactivity, and artery-to-artery embolism.

METHODS

This prospective multicenter observational study enrolled patients with recent (≤21 days) ischemic stroke or transient ischemic attack (TIA) caused by ICAD with 50-99% stenosis treated medically. We obtained baseline quantitative MRA (QMRA), perfusion MRI (PWI), transcranial Doppler vasoreactivity (VMR), and emboli detection studies (EDS). The primary outcome was ischemic stroke in the territory of the stenotic artery within 1 year of follow-up; secondary outcomes were TIA at 1 year and new infarcts in the territory on MRI at 6-8 weeks.

RESULTS

Amongst 102 of 105 participants with clinical follow-up (mean 253±131 days), the primary outcome occurred in 8.8% (12.7/100 patient-years), while 5.9% (8.5/100 patient-years) had a TIA. A new infarct in the territory of the symptomatic artery was noted in 24.7% at 6-8 weeks. A low flow state on QMRA was noted in 25.5%, poor distal perfusion on PWI in 43.5%, impaired vasoreactivity on VMR in 67.5%, and microemboli on EDS in 39.0%. No significant association was identified between these imaging biomarkers and primary or secondary outcomes.

CONCLUSIONS

Despite intensive medical management in ICAD, there is a high risk of clinical cerebrovascular events at 1 year and an even higher risk of new imaging-evident infarcts in the subacute period after index stroke. Hemodynamic and plaque instability biomarkers did not identify a higher risk group. Further work is needed to identify mechanisms of ischemic stroke and infarct recurrence and their consequence on long-term physical and cognitive outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02121028.

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.

Pterostilbene reduces endothelial cell apoptosis by regulation of the Nrf2-mediated TLR-4/MyD88/NF-κB pathway in a rat model of atherosclerosis

Endothelial cell injury in vascular arterial walls plays a crucial role in the pathological process of atherosclerosis. Pterostilbene, a stilbenoid chemically related to resveratrol, has anti-inflammatory, anti-apoptosis and antioxidant properties. However, the underlying mechanisms mediated by pterostilbene in regards to endothelial cell injury in vascular arterial walls are not fully understood. The purpose of the present study was to investigate the benefits of pterostilbene in a rat model of atherosclerosis. The possible mechanism of pterostilbene was also analyzed in regards to endothelial cell injury in vascular arterial walls in vitro. A rat model of atherosclerosis was established using endothelial injury of the iliac arteries. CCK-8 assay, TUNEL, immunofluorescence, western blot analysis and hematoxylin and eosin (H&E) staining were used to analyze the role of pterostilbene in the pathological processes of atherosclerosis. In vivo results showed that pterostilbene decreased cholesterol (CHO), high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) in plasma and attenuated interleukin (IL)-1, tumor necrosis factor (TNF)-α and IL-6 and oxidative stress injury in serum in the experimental animals. Pterostilbene treatment reduced atherogenesis, aortic plaques, macrophage infiltration and apoptosis of vascular arterial walls in the atherosclerosis rat model. In vitro assay demonstrated that pterostilbene administration increased viability of the endothelial cells, attenuated oxidative stress injury and apoptosis of endothelial cells. The results found that pterostilbene regulated endothelial cell apoptosis via the Nrf2-mediated TLR-4/MyD88/NF-κB pathway. In conclusion, data from the present study revealed that pterostilbene protects rats against atherosclerosis by regulation of the Nrf2-mediated TLR-4/MyD88/NF-κB pathway.

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.

Middle Cerebral Artery Plaque Hyperintensity on T2-Weighted Vessel Wall Imaging Is Associated with Ischemic Stroke

BACKGROUND AND PURPOSE

Vessel wall imaging can identify intracranial atherosclerotic plaque and give clues about its components. We aimed to investigate whether the plaque hyperintensity in the middle cerebral artery on T2-weighted vessel wall imaging is associated with ischemic stroke.

MATERIALS AND METHODS

We retrospectively reviewed our institutional vessel wall MR imaging data base. Patients with an acute ischemic stroke within 7-day onset in the MCA territory were enrolled. Patients with stroke and stenotic MCA plaque (stenosis degree, ≥50%) were included for analysis. Ipsilateral MCA plaque was defined as symptomatic, and contralateral plaque, as asymptomatic. Plaque was manually delineated on T2-weighted vessel wall imaging. The plaque signal was normalized to the ipsilateral muscle signal. The thresholds and volume of normalized plaque signal were investigated using logistic regression and receiver operating characteristic analysis to determine the association between normalized plaque signal and stroke.

RESULTS

One hundred eight stenotic MCAs were analyzed (from 88 patients, 66 men; mean age, 58 ± 15 years), including 72 symptomatic and 36 asymptomatic MCA plaques. Symptomatic MCA plaque showed larger plaque hyperintensity volume compared with asymptomatic MCA plaque. The logistic regression model incorporating stenosis degree, remodeling ratio, and normalized plaque signal 1.3-1.4 (OR, 6.25; 95% CI, 1.90-20.57) had a higher area under curve in differentiating symptomatic/asymptomatic MCA plaque, compared with a model with only stenosis degree and remodeling ratio (area under curve, 0.884 versus 0.806; P =.008).

CONCLUSIONS

The MCA plaque hyperintensity on T2-weighted vessel wall imaging is independently associated with ischemic stroke and adds value to symptomatic MCA plaque classification. Measuring the normalized signal intensity may serve as a practical and integrative approach to the analysis of intracranial atherosclerotic plaque.

Determinants of Gadolinium-Enhancement of the Aneurysm Wall in Unruptured Intracranial Aneurysms

BACKGROUND

Recent studies suggest that gadolinium-enhancement of the aneurysm wall may reflect aneurysm wall inflammation, which might increase the risk of aneurysm growth or rupture.

OBJECTIVE

To determine the prevalence of gadolinium-enhancement and its determinants in patients with predominantly small (<7 mm) unruptured intracranial aneurysms.

METHODS

We performed 3 T MRI aneurysm wall imaging in patients with ≥1 unruptured aneurysm. With Poisson regression analysis, we calculated crude and adjusted risk ratios (RRs) with 95% confidence intervals (CI) to assess determinants of gadolinium-enhancement.

RESULTS

Gadolinium-enhancement was observed in 25/79 patients (32%; 95% CI: 21%-42%) and 26/89 aneurysms (29%; 95% CI: 20%-39%). With aneurysms 1.0-2.9 mm as reference, RRs were 4.6 (95% CI: 0.6-36.5) for 3.0 to 4.9 mm, 9.4 (95% CI: 1.3-67.2) for 5.0 to 6.9 mm, and 14.8 (95% CI: 2.1-104.6) for ≥7.0 mm. With internal carotid artery as reference, RRs adjusted for aneurysm size were 3.6 (95% CI: 1.1-11.4) for posterior communicating artery and 3.0 (95% CI: 1.0-8.6) for middle cerebral artery. RRs were 0.8 (95% CI: 0.4-1.8) for acetylsalicylic acid use, 0.9 (95% CI: 0.5-1.8) for statin use, 1.4 (95% CI: 0.7-2.8) for hypertension, 0.9 (95% CI: 0.4-1.8) for previous smoking, 0.9 (95% CI: 0.3-2.6) for never smoking, and 1.4 (95% CI: 0.7-2.7) for irregular aneurysm shape.

CONCLUSION

Approximately one-third of patients had gadolinium-enhancement. Because aneurysm size is the strongest determinant of gadolinium-enhancement and also an established predictor for aneurysm growth and rupture, prospective studies with serial imaging need to investigate if gadolinium-enhancement predicts aneurysm growth and rupture.

Lipid-Rich Necrotic Core of Basilar Artery Atherosclerotic Plaque: Contrast-Enhanced Black Blood Imaging on Vessel Wall Imaging

Purpose: We wished to evaluate the lipid-rich necrotic core (LRNC) using contrast-enhanced T1-weighted (CE-T1W) black-blood (BB) imaging for vessel walls. Methods: Ninety-five patients with basilar artery (BA) stenosis who underwent magnetic resonance angiography between January 2016 and August 2018 were enrolled into this present study. CE-T1W BB imaging was considered as a reference method for identifying an LRNC. Results: Ten (10.5%) patients were identified as having an LRNC on CE-T1W BB imaging. Of these patients, 9 had acute symptoms. The extent of stenosis in patients with an LRNC on CE-T1W BB imaging was significantly greater than that of patients without an LRNC (p < 0.001). The maximum wall thickness in patients with an LRNC on CE-T1W imaging was significantly thicker than that of patients without an LRNC (p = 0.008). Conclusions: Identification of an LRNC on CE-T1W BB imaging was associated with high-grade stenosis and massive plaque burden from BA atherosclerosis.

Comparison of Predictive Ability of Computed Tomography and Magnetic Resonance Imaging in Patients with Carotid Atherosclerosis Complicated with Stroke

BACKGROUND

To investigate the characterizations of CT (computed tomography) and MRI (magnetic resonance imaging) in patients with carotid atherosclerosis.

METHODS

A retrospective analysis was performed on the medical records of 264 patients with carotid atherosclerosis underwent CT and MRI in Linyi Central Hospital, Linyi, China from January 2010 to January 2016. Among them, 142 patients with ischemic stroke were in experimental group (test group), another 122 patients in control group. The lumen stenosis degree, plaque fibrous cap status, calcification information and vascular plaque hemorrhage in the carotid artery fork of patients detected by CT and MRI were collected.

RESULTS

The detection rate of the plaque calcification of patients detected by MRI was lower than that detected by CT in the experimental group (P<0.05). Patients in the experimental group had higher average vascular stenosis degree detected by CT and MRI than those in the control group (P<0.01). The average vascular stenosis degree of patients detected by MRI was higher than that detected by CT in the experimental group (P<0.05). Patients in the experimental group had higher unstable fibrous cap number detected by CT and MRI than those in the control group (P<0.01). Patients in the experimental group had significantly higher number of vascular plaque small focus hemorrhage than those in the control group (P<0.05).

CONCLUSION

Patients with carotid atherosclerotic complicated with stroke have higher plaque calcification number, vascular stenosis degree and unstable fibrous cap number. Both CT and MRI can better predict the risk of stroke.

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.

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.

Quantitative assessment of symptomatic intracranial atherosclerosis and lenticulostriate arteries in recent stroke patients using whole-brain high-resolution cardiovascular magnetic resonance imaging

BACKGROUND

It has been shown that intracranial atherosclerotic stenosis (ICAS) has heterogeneous features in terms of plaque instability and vascular remodeling. Therefore, quantitative information on the changes of intracranial atherosclerosis and lenticulostriate arteries (LSAs) may potentially improve understanding of the pathophysiological mechanisms underlying stroke and may guide the treatment and work-up strategies. Our present study aimed to use a novel whole-brain high-resolution cardiovascular magnetic resonance imaging (WB-HRCMR) to assess both ICAS plaques and LSAs in recent stroke patients.

METHODS

Twenty-nine symptomatic and 23 asymptomatic ICAS patients were enrolled in this study from Jan 2015 through Sep 2017 and all patients underwent WB-HRCMR. Intracranial atherosclerotic plaque burden, plaque enhancement volume, plaque enhancement index, as well as the number and length of LSAs were evaluated in two groups. Enhancement index was calculated as follows: ([Signal intensity (SI)plaque/SInormal wall on post-contrast imaging] - [SIplaque/SInormal wall on matched pre-contrast imaging])/(SIplaque / SInormal wall on matched pre-contrast imaging). Logistic regression analysis was used to investigate the independent high risk plaque and LSAs features associated with stroke.

RESULTS

Symptomatic ICAS patients exhibited larger enhancement plaque volume (20.70 ± 3.07 mm3 vs. 6.71 ± 1.87 mm3 P = 0.001) and higher enhancement index (0.44 ± 0.08 vs. 0.09 ± 0.06 P = 0.001) compared with the asymptomatic ICAS. The average length of LSAs in symptomatic ICAS (20.95 ± 0.87 mm) was shorter than in asymptomatic ICAS (24.04 ± 0.95 mm) (P = 0.02). Regression analysis showed that the enhancement index (100.43, 95% CI - 4.02-2510.96; P = 0.005) and the average length of LSAs (0.80, 95% CI - 0.65-0.99; P = 0.036) were independent factors for predicting of stroke.

CONCLUSION

WB-HRCMR enabled the comprehensive quantitative evaluation of intracranial atherosclerotic lesions and perforating arteries. Symptomatic ICAS had distinct plaque characteristics and shorter LSA length compared with asymptomatic ICAS.

Intracranial Vessel Wall Imaging with Magnetic Resonance Imaging: Current Techniques and Applications

Vessel wall magnetic resonance imaging (VW-MRI) is a modern imaging technique with expanding applications in the characterization of intracranial vessel wall pathology. VW-MRI provides added diagnostic capacity compared with conventional luminal imaging methods. This review explores the principles of VW-MRI and typical imaging features of various vessel wall pathologies, such as atherosclerosis, dissection, and vasculitis. Radiologists should be familiar with this important imaging technique, given its increasing use and future relevance to everyday practice.

Intracranial Atherosclerosis: From Microscopy to High-Resolution Magnetic Resonance Imaging

Intracranial atherosclerosis is one of the leading causes of ischemic stroke and occurs more commonly in patients of Asian, African or Hispanic origin than in Caucasians. Although the histopathology of intracranial atherosclerotic disease resembles extracranial atherosclerosis, there are some notable differences in the onset and severity of atherosclerosis. Current understanding of intracranial atherosclerotic disease has been advanced by the high-resolution magnetic resonance imaging (HRMRI), a novel emerging imaging technique that can directly visualize the vessel wall pathology. However, the pathological validation of HRMRI signal characteristics remains a key step to depict the plaque components and vulnerability in intracranial atherosclerotic lesions. The purpose of this review is to describe the histological features of intracranial atherosclerosis and to state current evidences regarding the validation of MR vessel wall imaging with histopathology.

Etiology of intracranial stenosis in young patients: a high-resolution magnetic resonance imaging study

BACKGROUND

Using high-resolution magnetic resonance imaging (HRMRI), we sought to investigate the underlying etiology of intracranial stenosis in young patients.

METHODS

We retrospectively studied 122 Chinese young adult patients (from 18 to 45 years old, mean age 36.2±7.5 years) with unilateral middle cerebral artery (MCA) stenosis based on a prospectively established HRMRI database. The eccentricity, degree of stenosis, and remodeling types of MCA lesions were analyzed. The MCA lesions were classified as eccentric (presumed atherosclerosis) or concentric stenosis (presumed non-atherosclerosis). The clinical data and vessel wall properties were compared between the patients >35 years old and the patients ≤35 years old.

RESULTS

Eccentric stenosis was observed in 98 (80.3%) patients and concentric stenosis in 24 (19.7%) patients. The patients with eccentric stenosis were older (37.5±6.8 vs. 31.4±8.4 years old, P<0.001) and more likely had atherosclerosis risk factors (56.1% vs. 25.0%, P=0.006). The patients >35 years old had higher prevalence (90.1% vs. 66.7%, P=0.001) of eccentric stenosis and atherosclerosis factors (60.6% vs. 35.3%, P=0.006) than the patients ≤35 years old. Most of the patients with concentric stenosis were ≤35 years old (17/24, 70.8%) and were female (16/24, 66.7%). Binary Logistic analysis suggested smoking (OR =3.171; 95% CI, 1.210-8.314) and remodeling ratio (OR =1.625; 95% CI, 1.001-2.636) were independent predictive factors for symptomatic stenosis.

CONCLUSIONS

Atherosclerosis is the most common cause of intracranial stenosis in Chinese young patients. Non-atherosclerosis disease is an important etiology in young female, especially in the patients aged 35 years old or younger.

Identification and Quantitative Assessment of Different Components of Intracranial Atherosclerotic Plaque by Ex Vivo 3T High-Resolution Multicontrast MRI

BACKGROUND AND PURPOSE

High-resolution 3T MR imaging can visualize intracranial atherosclerotic plaque. However, histologic validation is still lacking. This study aimed to evaluate the ability of 3T MR imaging to identify and quantitatively assess intracranial atherosclerotic plaque components ex vivo with histologic validation.

MATERIALS AND METHODS

Fifty-three intracranial arterial specimens with atherosclerotic plaques from 20 cadavers were imaged by 3T MR imaging with T1, T2, and proton-density-weighted FSE and STIR sequences. The signal characteristics and areas of fibrous cap, lipid core, calcification, fibrous tissue, and healthy vessel wall were recorded on MR images and compared with histology. Fibrous cap thickness and maximum wall thickness were also quantified. The percentage of areas of the main plaque components, the ratio of fibrous cap thickness to maximum wall thickness, and plaque burden were calculated and compared.

RESULTS

The signal intensity of the lipid core was significantly lower than that of the fibrous cap on T2-weighted, proton-density, and STIR sequences (P < .01) and was comparable on T1-weighted sequences (P = 1.00). Optimal contrast between the lipid core and fibrous cap was found on T2-weighted images. Plaque component mean percentages were comparable between MR imaging and histology: fibrous component (81.86% ± 10.59% versus 81.87% ± 11.59%, P = .999), lipid core (19.51% ± 10.76% versus 19.86% ± 11.56%, P = .863), and fibrous cap (31.10% ± 11.28% versus 30.83% ± 8.51%, P = .463). However, MR imaging overestimated mean calcification (9.68% ± 5.21% versus 8.83% ± 5.67%, P = .030) and plaque burden (65.18% ± 9.01% versus 52.71% ± 14.58%, P < .001).

CONCLUSIONS

Ex vivo 3T MR imaging can accurately identify and quantitatively assess intracranial atherosclerotic plaque components, providing a direct reference for in vivo intracranial plaque imaging.

Imaging Atherosclerotic Plaque Calcification: Translating Biology

Calcification of atherosclerotic lesions was long thought to be an age - related, passive process, but increasingly data has revealed that atherosclerotic calcification is a more active process, involving complex signaling pathways and bone-like genetic programs. Initially, imaging of atherosclerotic calcification was limited to gross assessment of calcium burden, which is associated with total atherosclerotic burden and risk of cardiovascular mortality and of all cause mortality. More recently, sophisticated molecular imaging studies of the various processes involved in calcification have begun to elucidate information about plaque calcium composition and consequent vulnerability to rupture, leading to hard cardiovascular events like myocardial infarction. As such, there has been renewed interest in imaging calcification to advance risk assessment accuracy in an evolving era of precision medicine. Here we summarize recent advances in our understanding of the biologic process of atherosclerotic calcification as well as some of the molecular imaging tools used to assess it.

High-resolution Magnetic Resonance Vessel Wall Imaging for Intracranial Arterial Stenosis

OBJECTIVE

To discuss the feasibility and clinical value of high-resolution magnetic resonance vessel wall imaging (HRMR VWI) for intracranial arterial stenosis.

DATE SOURCES

We retrieved information from PubMed database up to December 2015, using various search terms including vessel wall imaging (VWI), high-resolution magnetic resonance imaging, intracranial arterial stenosis, black blood, and intracranial atherosclerosis.

STUDY SELECTION

We reviewed peer-reviewed articles printed in English on imaging technique of VWI and characteristic findings of various intracranial vasculopathies on VWI. We organized this data to explain the value of VWI in clinical application.

RESULTS

VWI with black blood technique could provide high-quality images with submillimeter voxel size, and display both the vessel wall and lumen of intracranial artery simultaneously. Various intracranial vasculopathies (atherosclerotic or nonatherosclerotic) had differentiating features including pattern of wall thickening, enhancement, and vessel remodeling on VWI. This technique could be used for determining causes of stenosis, identification of stroke mechanism, risk-stratifying patients, and directing therapeutic management in clinical practice. In addition, a new morphological classification based on VWI could be established for predicting the efficacy of endovascular therapy.

CONCLUSIONS

This review highlights the value of HRMR VWI for discrimination of different intracranial vasculopathies and directing therapeutic management.

High-Resolution Magnetic Resonance Imaging Evidence for Intracranial Vessel Wall Inflammation Following Endovascular Thrombectomy

Intracranial high-resolution vessel wall magnetic resonance imaging evidence of vessel wall inflammation is present following stent retriever manipulation but absent following aspiration thrombectomy. This is presented in a case of rotatory vertebral artery compression causing multiple posterior circulation infarctions requiring multiple separate aspiration and stent retriever thrombectomies.

Vessel wall differences between middle cerebral artery and basilar artery plaques on magnetic resonance imaging

A recent study showed that posterior circulation plaques have a greater capacity for positive remodeling in a non-Asian population. We aimed to investigate if the features of plaques in the middle cerebral artery (MCA) were different from those in the basilar artery (BA) in a northern Chinese population. We retrospectively analysed the records of 71 consecutive patients with acute ischemic stroke. All patients had at least one MCA or BA plaque with early or mild (<50% stenosis) atherosclerosis identified using vessel wall magnetic resonance imaging. The remodeling ratio, eccentricity index, and plaque range were compared between MCA and BA plaques using multilevel analysis. A total of 101 plaques were included. There were 70 plaques located in the MCA and 31 plaques located in the BA. The features of non-advanced atherosclerotic plaques did not differ between the MCA and BA when accounting for the degree of stenosis or plaque burden in a northern Chinese population. Symptomatic plaques were associated with a higher eccentricity index and smaller plaque range than asymptomatic plaques under the same plaque burden. Further studies are warranted to investigate the progression of atherosclerosis in different intracranial arteries.

Pathological Characteristics

Within the intracranial vasculature, atherosclerosis occurs in two distinctive patterns: (1) in Western populations who have severe extracranial and systemic atherosclerosis, the severity of intracranial involvement is consistently less than that within extracranial arteries; and (2) in Asians, Africans, and Hispanics, who often have isolated intracranial arterial disease that is found to be more often accompanied by brain infarction than comparable extracranial atherosclerotic disease. Compared to coronary and extracranial carotid atherosclerosis, intracranial atherosclerosis has distinct pathological characteristics compared to that of extracranial arteries. Intracranial atherosclerosis (ICAS) had been understudied due to the relative inaccessibility of cerebral artery specimens under current treatment strategies. Acquiring post-mortem cerebral vessel specimens for histology processing is the most direct method to analyze the pathological characteristics of ICAS, in order to analyze both lumen stenosis and plaque components contributing to brain infarctions. The developments in high resolution magnetic resonance imaging (HRMRI) make it feasible to assess human ICAS in vivo. It is nevertheless challenging to understand vessel wall changes within brain vasculature demonstrated on HRMRI, as well as to identify biomarkers for stroke risk stratification and treatment strategy modification. Knowledge about intracranial atherosclerosis remains limited due to lack of human arterial specimens, and the development of proper animal models of human cerebral atherosclerosis is necessary to explore the pathogenesis of intracranial atherosclerosis and to assess various strategies preventing or treating ICAS-related stroke.