Intraplaque Hemorrhage in Symptomatic Intracranial Atherosclerotic Disease

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.

Evaluation of High Intracranial Plaque Prevalence in Type 2 Diabetes Using Vessel Wall Imaging on 7 T Magnetic Resonance Imaging

BACKGROUND

While type 2 diabetes (T2D) is a major risk for ischemic stroke, the associated vessel wall characteristics remain essentially unknown. This study aimed to clarify intracranial vascular changes on three-dimensional vessel wall imaging (3D-VWI) using fast spin echo by employing 7Tesla (7T) magnetic resonance imaging (MRI) in T2D patients without advanced atherosclerosis as compared to healthy controls.

METHODS

In 48 T2D patients and 35 healthy controls, the prevalence of cerebral small vessel diseases and intracranial plaques were evaluated by 3D-VWI with 7T MRI.

RESULTS

The prevalence rate of lacunar infarction was significantly higher in T2D than in controls (n = 8 in T2D vs. n = 0 in control, p = 0.011). The mean number of intracranial plaques in both anterior and posterior circulation of each subject was significantly larger in T2D than in controls (2.23 in T2D vs. 0.94 in control, p < 0.01). In T2D patients, gender was associated with the presence of intracranial plaques.

CONCLUSION

This is the first study to demonstrate the high prevalence of intracranial plaque in T2D patients with neither confirmed atherosclerotic disease nor symptoms by performing intracranial 3D-VWI employing 7TMRI. Investigation of intracranial VWI with 7T MRI is expected to provide novel insights allowing early intensive risk management for prevention of ischemic stroke in T2D patients.

Characteristics of culprit intracranial plaque without substantial stenosis in ischemic stroke using three-dimensional high-resolution vessel wall magnetic resonance imaging

Background and aims

We aim to analyze the difference in quantitative features between culprit and non-culprit intracranial plaque without substantial stenosis using three-dimensional high-resolution vessel wall MRI (3D hr-vw-MRI).

Methods

The patients with cerebral ischemic symptoms of the unilateral anterior circulation were recruited who had non-stenotic intracranial atherosclerosis (<50%) confirmed by computed tomographic angiographic (CTA) or magnetic resonance angiography (MRA). All patients underwent 3D hr-vw MRI within 1 month after symptom onset. 3D hr-vw-MRI characteristics, including wall thickness, plaque burden, enhancement ratio, plaque volume and intraplaque hemorrhage, and histogram features were analyzed based on T2-, precontrast T1-, and post-contrast T1-weighted images. Univariate and multivariate logistic regression analysis were used to identify key determinates differentiating culprit and non-culprit plaques and to calculate the odds ratios (ORs) with 95% confidence intervals (CIs).

Results

A total of 150 plaques were identified, of which 133 plaques (97 culprit and 36 non-culprit) were in the middle cerebral artery, three plaques (all culprit) were in the anterior cerebral artery (ACA) and 14 (11 culprit and three non-culprit) were in the internal carotid artery (ICA). Of all the quantitative parameters analyzed, plaque volume, maximum wall thickness, minimum wall thickness, plaque burden, enhancement ratio, coefficient of variation of the most stenotic site, enhancement ratio of whole culprit plaque in culprit plaques were significantly higher than those in non-culprit plaques. Multivariate logistic regression analysis found that plaque volume [OR, 1.527 (95% CI, 1.231-1.894); P < 0.001] and enhancement ratio of whole plaque [OR, 1.095 (95% CI, 1.021-1.175); P = 0.011] were significantly associated with culprit plaque. The combination of the two features obtained a better diagnostic efficacy for culprit plaque with sensitivity and specificity (0.910 and 0.897, respectively) than each of the two parameters alone.

Conclusion

3D hr-vw MRI features of intracranial atherosclerotic plaques provided potential values over prediction of ischemic stroke patients with non-stenotic arteries. The plaque volume and enhancement ratio of whole plaque of stenosis site were found to be effective predictive parameters.

3D Enhancement Color Maps in the Characterization of Intracranial Atherosclerotic Plaques

BACKGROUND AND PURPOSE

High-resolution MR imaging allows the identification of culprit symptomatic plaques after the administration of gadolinium. Current high-resolution MR imaging methods are limited by 2D multiplanar views and manual sampling of ROIs. We analyzed a new 3D method to objectively quantify gadolinium plaque enhancement.

MATERIALS AND METHODS

Patients with stroke due to intracranial atherosclerotic disease underwent 7T high-resolution MR imaging. 3D segmentations of the plaque and its parent vessel were generated. Signal intensity probes were automatically extended from the lumen into the plaque and the vessel wall to generate 3D enhancement color maps. Plaque gadolinium (Gd) uptake was quantified from 3D color maps as gadolinium uptake = (µPlaque T1 + Gd -µPlaque T1/SDPlaque T1). Additional metrics of enhancement such as enhancement ratio, variance, and plaque-versus-parent vessel enhancement were also calculated. Conventional 2D measures of enhancement were collected for comparison.

RESULTS

Thirty-six culprit and 44 nonculprit plaques from 36 patients were analyzed. Culprit plaques had higher gadolinium uptake than nonculprit plaques (P < .001). Gadolinium uptake was the most accurate metric for identifying culprit plaques (OR, 3.9; 95% CI 2.1-8.3). Gadolinium uptake was more sensitive (86% versus 70%) and specific (71% versus 68%) in identifying culprit plaques than conventional 2D measurements. A multivariate model, including gadolinium uptake and plaque burden, identified culprit plaques with an 83% sensitivity and 86% specificity.

CONCLUSIONS

The new 3D color map method of plaque-enhancement analysis is more accurate for identifying culprit plaques than conventional 2D methods. This new method generates a new set of metrics that could potentially be used to assess disease progression.

Sex Differences in Intracranial Atherosclerotic Plaques Among Patients With Ischemic Stroke

Objective

High-risk intracranial arterial plaques are the most common cause of ischemic stroke and their characteristics vary between male and female patients. However, sex differences in intracranial plaques among symptomatic patients have rarely been discussed. This study aimed to evaluate sex differences in intracranial atherosclerotic plaques among Chinese patients with cerebral ischemia.

Methods

One hundred and ten patients who experienced ischemic events underwent 3T cardiovascular magnetic resonance vessel wall scanning for the evaluation of intracranial atherosclerotic disease. Each plaque was classified according to its likelihood of causing a stroke (as culprit, uncertain, or non-culprit). The outer wall area (OWA) and lumen area of the lesion and reference sites were measured, and the wall and plaque areas, remodeling ratio, and plaque burden (characterized by a normalized wall index) were further calculated. The composition (T1 hyperintensity, enhancement) and morphology (surface irregularity) of each plaque were analyzed. Sex differences in intracranial plaque characteristics were compared between male and female patient groups.

Results

Overall, 311 plaques were detected in 110 patients with ischemic stroke (81 and 29 male and female patients, respectively). The OWA (P &lt; 0.001) and wall area (P &lt; 0.001) of intracranial arterial lesions were significantly larger in male patients. Regarding culprit plaques, the plaque burden in male patients was similar to that in female patients (P = 0.178, odds ratio [OR]: 0.168, 95% confidence interval [CI]: −0.020 to 0.107). However, the prevalence of plaque T1 hyperintensity was significantly higher than that in female patients (P = 0.005, OR: 15.362, 95% CI: 2.280–103.49). In the overall ischemic stroke sample, intracranial T1 hyperintensity was associated with male sex (OR: 13.480, 95% CI: 2.444–74.354, P = 0.003), systolic blood pressure (OR: 1.019, 95% CI: 1.002–1.036, P = 0.031), and current smoker (OR: 3.245, 95% CI: 1.097–9.598, P = 0.033).

Conclusion

For patients with ischemic stroke, the intracranial plaque burden in male patients was similar to that in female patients; however, the plaque characteristics in male patients are associated with higher risk, especially in culprit plaques.

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.

Plaque Characteristics in Young Adults With Symptomatic Intracranial Atherosclerotic Stenosis: A Preliminary Study

Purpose

To determine how intracranial vascular wall and atherosclerosis plaque characteristics differ between young and old adults with sICAS.

Methods

Eighty-four consecutive patients with sICAS who underwent high-resolution magnetic resonance imaging (HRMRI) from December 2017 to July 2020 were retrospectively collected. These participants were divided into young adult group (18–50 years, n = 28) and old adult group (>50 years, n = 56). Reviewers were blinded to any clinical information and HRMRI scans were analyzed for qualitative and quantitative indicators of vascular walls and plaque at the maximal lumen narrowing site using the independent-sample t-test, Mann–Whitney U-test, chi-square test or Fisher exact test, and logistic regression analysis.

Results

Young patients with sICAS had significantly smaller maximum wall thickness (1.45 ± 0.38 vs.1.75 ± 0.51 mm², P = 0.003), higher prevalence of positive remodeling (53.57 vs. 21.43%, P = 0.003), and lower prevalence of diabetes mellitus (14.29 vs. 35.71%, P = 0.04) than old patients. Plaque burden and other plaque features were comparable between young and old patients.

Conclusion

Young patients with sICAS have smaller maximum wall thickness and greater ability to reconstruct, and are more likely to show positive remodeling, which may lead to some atherosclerotic lesions being missed. Young patients with evidence of vessel narrowing should be carefully examined for presence of high-risk atherosclerotic plaque.

Association between Short-Term Blood Pressure Variability and Intracranial Atherosclerotic Plaque Vulnerability: A High-Resolution Magnetic Resonance Imaging Study

Aim: short-term blood pressure variability (BPV) as a risk factor of atherosclerosis and cardiovascular events has been investigated. However, its association with atherosclerotic plaque vulnerability remains unknown. The objective of this study was to determine the association between short-term BPV and intracranial atherosclerotic plaque vulnerability.

Methods: this is a cross-sectional analysis of 267 ischemic stroke patients with symptomatic intracranial atherosclerosis (mean age, 65±12 years old; 60.3% male), which were prospectively recruited in a comprehensive stroke center. Systolic and diastolic BP SD, CV, and BP variability ratio (BPVR) from 24 hours, daytime, and nighttime were calculated from 24-h ambulatory blood pressure monitoring, intracranial atherosclerotic plaque burden and vulnerability were evaluated by high-resolution magnetic resonance vessel wall imaging. Logistic regression analysis was used to locate the correlation between short-term BPV and plaque vulnerability.

Results: a total of 36.3% subjects presented with intraplaque hemorrhage (IPH) in this study. Multivariate logistic regression suggested that nighttime diastolic BP CV and 24-h BPVR were associated with intracranial IPH independently after adjusted for cardiovascular risk factors, odds ratio (OR) and 95% confidence interval (CI) for per SD BPV changes were 1.418 (1.051, 1.914) and 0.731 (0.548, 0.976), respectively, and this association also independent of atherosclerosis burden and 24-h mean systolic BP level. Further subgroup analysis by age and hypertension history demonstrated that the statistical correlation could only establish in the elder, and subjects with hypertension.

Conclusion: nighttime diastolic BP CV and 24-h BPVR were associated with intracranial IPH independently, especially in the elderly and subjects with hypertension.

Prevalence, prognosis, and treatment of atherosclerotic intracranial stenosis in Caucasians

BACKGROUND

Intracranial atherosclerotic stenosis is a highly prevalent cause of stroke worldwide with important ethnic disparities. Widely considered to be a common cause of stroke in Asian and Afro-Caribbean populations, relatively less is known about the burden and significance of intracranial atherosclerotic stenosis in Caucasians.

AIMS

We aim to highlight recent insights and advances into the prevalence, prognosis, and treatment of symptomatic and asymptomatic atherosclerotic intracranial atherosclerotic stenosis in Caucasian patients.

SUMMARY OF REVIEW

We identified 48 articles studying intracranial atherosclerotic stenosis in Caucasian patients with ischemic stroke or transient ischemic attack. Most studies were on hospital-based cohorts of consecutive patients and half were graded as "fair" quality. There was significant variation between studies in the definition of intracranial atherosclerotic stenosis and in the imaging modalities used to detect intracranial atherosclerotic stenosis. Overall, 12.1% of Caucasian patients were found to have any intracranial atherosclerotic stenosis, 6.4% symptomatic intracranial atherosclerotic stenosis and 11.1% asymptomatic intracranial atherosclerotic stenosis, with higher rates at older ages. In studies reporting prognosis, there were 61 and 10 same-territory ischemic strokes in 1000 person-years in patients with symptomatic and asymptomatic intracranial atherosclerotic stenosis, respectively. Percutaneous stenting and angioplasty have not proven superior to intensive medical management in patients with symptomatic intracranial atherosclerotic stenosis.

CONCLUSIONS

Intracranial atherosclerotic stenosis has previously been neglected as a cause of stroke in Caucasians but is highly prevalent at older ages and frequently discovered with the growing use of noninvasive angiography. Intensive medical therapy is the treatment of choice, but there is a need to develop novel treatments or therapeutic approaches to lower the risk of stroke in higher risk patients.

The diagnostic contribution of intracranial vessel wall imaging in the differentiation of primary angiitis of the central nervous system from other intracranial vasculopathies

PURPOSE

The aim of this study is to demonstrate the diagnostic effect of VWI in differentiating PACNS from other vasculopathies and its role in post-treatment follow-up in PACNS patients in this study.

METHODS

In this prospective study, we included patients with clinical suspicion of PACNS who presented with new-onset ischemic events and had significant intracranial large vessel stenosis on DSA or MRA. VWI was performed on all patients. The imaging findings and final diagnoses were recorded. Control VWI was performed on patients with PACNS diagnosis after at least 3 months of treatment, and the change in findings was also evaluated.

RESULTS

Twenty-three patients were included in the study had a median age of 40 (range 12-58). The most common clinical manifestations were focal neurologic deficits. According to the initial clinical evaluation, 10 patients (43.5%) were classified as PACNS and 13 patients (56.5%) as indeterminate for PACNS. After incorporating the VWI findings, the diagnosis of PACNS was confirmed in all clinically diagnosed PACNS patients. Concentric wall thickening and contrast enhancement were statistically significant in the PACNS group (p <0.001). According to concentric thickening and VWE features, sensitivity and specificity in distinguishing PACNS and other vasculopathies were 95.2%, 75% and 95.2%, 68.8%, respectively. Vessel wall enhancement regressed in 7 of 9 patients during a median follow-up period of 8 months (range 5.5-11.5) in PACNS patients who followed up.

CONCLUSION

VWI seems a new and useful imaging method in the differential diagnosis of PACNS and might be a useful adjunct for post-treatment follow-up.

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.

Characterisation of symptomatic intracranial plaque without substantial stenosis using high-resolution vessel wall MRI

AIM

To characterise symptomatic intracranial plaque without substantial stenosis using three-dimensional (3D) high-resolution contrast-enhanced black-blood magnetic resonance imaging (BBMRI) and to determine plaque features associated with recent cerebrovascular events.

MATERIALS AND METHODS

The institutional review board approved this retrospective study. The case notes from patients with evidence of intracranial atherosclerosis in a large intracranial artery with preceding BBMRI were reviewed retrospectively. Symptomatic and asymptomatic plaques with substantial luminal stenosis (<50%) were matched by plaque location and patient age. All MRI images were de-identified and interpreted by two neuroradiologists who were blinded to the history of symptoms. Qualitative analyses including the presence of intraplaque haemorrhage (IPH), eccentricity, surface irregularity, and grade of plaque enhancement were recorded. Quantitative analyses including normal wall index and degree of contrast enhancement were calculated. Multivariate regression analysis was performed to identify the association with cerebrovascular ischaemic events.

RESULTS

A total of 38 pairs of symptomatic and asymptomatic plaques from 74 patients were analysed. Compared to asymptomatic plaques, symptomatic plaques demonstrated higher degree of contrast enhancement (29.77 ± 19.23 versus 18.21 ± 12.18%, p=0.039) and presence of IPH (26% versus 8%, p=0.032). No significant differences were detected regarding eccentricity, surface irregularity, and normal wall index. Events were associated with contrast enhancement (OR, 1.212; 95% confidence interval [CI], 1.086-1.352) after controlling for age, sex, cardiovascular risk factors, and stenosis degree. IPH was not associated with events.

CONCLUSION

Contrast enhancement in the intracranial plaque without substantial stenosis is associated with previous events, and may serve as the vulnerable feature, thereby stratifying stroke risk not achievable by luminal stenosis.

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.

Assessment of quantitative methods for enhancement measurement on vessel wall magnetic resonance imaging evaluation of intracranial atherosclerosis

PURPOSE

Quantitative measures of vessel wall magnetic resonance imaging (vwMRI) for the evaluation of intracranial atherosclerotic disease (ICAD) offers standardization not available with previously used qualitative approaches that may be difficult to replicate.

METHODS

vwMRI studies performed to evaluate ICAD that had caused a stroke were analyzed. Two blinded reviewers qualitatively rated culprit lesions for the presence of enhancement on T1 delay alternating with nutation for tailored excitation (DANTE) SPACE images. At least 3 months later, quantitative analysis was performed of the same images, comparing lesion enhancement to reference structures. Cohen's kappa and intraclass correlation coefficients were calculated to assess agreement. Ratios of enhancement of lesions to references were compared to qualitative ratings.

RESULTS

Studies from 54 patients met inclusion criteria. A mean of 49 (90.7%) lesions were qualitatively rated as enhancing, with good inter-rater agreement (κ = 0.783). Among reference structure candidates, low infundibulum demonstrated the highest inter-rater agreement on pre- and post-contrast imaging. The ratio of percentage increase in plaque signal following contrast to the same measure in low infundibulum demonstrated the highest agreement with qualitative assessment, with highest agreement seen with a ratio of 0.8 set as a threshold (κ = 0.675).

CONCLUSION

Quantitative metrics can yield objective data to better standardize techniques and acceptance of vwMRI evaluation of ICAD. The low infundibulum had the highest inter-rater agreement on both pre- and post-contrast images and is best suited as a normally enhancing reference structure. Such quantitative techniques should be implemented in future research of vwMRI for the evaluation of ICAD.

New developments in clinical ischemic stroke prevention and treatment and their imaging implications

Acute ischemic stroke results from blockage of a cerebral artery or impaired cerebral blood flow due to cervical or intracranial arterial stenosis. Ischemic stroke prevention seeks to minimize the risk of developing impaired cerebral perfusion by controlling vascular and cardiac disease risk factors. Similarly, ischemic stroke treatment aims to restore cerebral blood flow through recanalization of an occluded artery or dilation of a severely narrowed artery that supplies cerebral tissue. Stroke prevention and treatment are increasingly informed by imaging studies, and neurovascular and cerebral perfusion imaging has become essential in in guiding ischemic stroke prevention and treatment. Here we review the latest advances in ischemic stroke prevention and treatment with an emphasis on the neuroimaging principles emphasized in recent randomized trials. Future research directions that should be explored in ischemic stroke prevention and treatment are also discussed.

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.

Clinical Significance of Intraplaque Hemorrhage in Low- and High-Grade Basilar Artery Stenosis on High-Resolution MRI

BACKGROUND AND PURPOSE

Intraplaque hemorrhage within intracranial atherosclerotic plaques identified by high-resolution MR imaging has been studied as a potential marker of stroke risk. However, previous studies only examined intracranial arteries with high-grade stenosis (degree of stenosis, >50%). This study aimed to ascertain the clinical relevance of intraplaque hemorrhage in patients with low- and high-grade stenotic basilar artery plaques.

MATERIALS AND METHODS

Patients with basilar artery stenosis (n = 126; mean age, 62 ± 10 years; 66 symptomatic and 60 asymptomatic) underwent high-resolution MR imaging. The relationship between imaging findings (intraplaque hemorrhage, contrast enhancement, degree of stenosis, minimal lumen area, and plaque burden) and symptoms was analyzed.

RESULTS

Intraplaque hemorrhage was identified in 22 patients (17.5%), including 21 (31.8%) symptomatic patients and 1 (1.7%) asymptomatic patient. Multivariate analysis showed that intraplaque hemorrhage was the strongest independent marker of symptomatic status (odds ratio, 27.5; 95% CI, 3.4-221.5; P = .002). Contrast enhancement was also independently associated with symptomatic status (odds ratio, 9.9; 95% CI, 1.5-23.6; P = .016). Stenosis, minimal lumen area, and plaque burden were not correlated with symptoms (P > .05). Intraplaque hemorrhage was present in both low- and high-grade stenotic basilar arteries (11.3% versus 16.3%, P = .63). Diagnostic performance values of intraplaque hemorrhage for patients with acute/subacute symptomatic stroke were the following: specificity, 98.3%; sensitivity, 31.8%; positive predictive value, 95.5%; and negative predictive value, 56.7%.

CONCLUSIONS

Intraplaque hemorrhage is present in both low- and high-grade stenotic basilar artery plaques and is independently associated with symptomatic stroke status. Intraplaque hemorrhage may identify high-risk plaque and provide new insight into the management of patient with stroke without significant stenosis.

Hyperintense Plaque on Intracranial Vessel Wall Magnetic Resonance Imaging as a Predictor of Artery-to-Artery Embolic Infarction

BACKGROUND AND PURPOSE

The aim of the present study was to investigate atherosclerotic plaque characteristics in patients with artery-to-artery (A-to-A) embolic infarction by whole-brain high-resolution magnetic resonance imaging.

METHODS

Seventy-four patients (mean age, 54.7±12.1 years; 59 men) with recent stroke in the territory of middle cerebral artery because of intracranial atherosclerotic disease were prospectively enrolled. Whole-brain high-resolution magnetic resonance imaging was performed in all the patients both precontrast and postcontrast administration by using a 3-dimensional T1-weighted vessel wall magnetic resonance imaging technique known as inversion-recovery prepared sampling perfection with application-optimized contrast using different flip angle evolutions. Patients were divided into A-to-A embolic infarction and non-A-to-A embolic infarction groups based on diffusion-weighted imaging findings. The characteristics of the intracranial atherosclerotic plaques were compared between groups.

RESULTS

A total of 74 intracranial atherosclerotic plaques were analyzed (36 in A-to-A embolism group and 38 in non-A-to-A embolism group). Hyperintense plaques (HIPs) were more frequently observed in A-to-A embolism group (75.0% versus 21.1%; P<0.001). Eighteen of the 27 HIPs (66.7%) demonstrated hyperintense spots or areas located adjacent to the lumen versus 9 HIPs (33.3%) located within the plaque in A-to-A embolism group. Furthermore, a higher prevalence of plaque surface irregularity was also observed in A-to-A embolism group (41.7% versus 18.4%; P=0.029). Logistic regression analysis showed that HIP was the most powerful independent predictor of A-to-A embolic infarction (P<0.001), with the odds ratio of 11.2 (95% confidence interval, 3.5-36.2).

CONCLUSIONS

A-to-A embolic infarction has distinct vulnerable plaque characteristics compared with non-A-to-A embolic infarction. HIP and plaque surface irregularity may predict A-to-A embolic infarction.

Endovascular recanalization for chronic symptomatic intracranial vertebral artery total occlusion: Experience of a single center and review of literature

OBJECTIVE

The optimal treatment of chronic symptomatic total occlusion of the intracranial vertebral artery (ICVA) remains undefined. We report a single-center experience of endovascular recanalization for patients with chronic symptomatic ICVA occlusion who were refractory to medical therapy.

METHODS

From Jan 2009 to Jan 2017, we retrospectively reviewed 14 consecutive patients presenting with recurrent symptoms attributed to the chronic ICVA occlusion. We searched previous literature using PubMed databases during the same period as comparison.

RESULTS

Eleven patients out of 14 presented initial symptoms to intervention less than 90days. The occlusion course was extrapolated on simultaneous two-vessel injection angiography or high-resolution MR imaging (HRMRI) in 13 cases. Nine patients had the occlusion beyond the origin of posterior inferior cerebellar artery (PICA) and 5 had the occlusion proximal to the PICA origin. The technical success rate of recanalization was 85.7% (12/14). Two patients (14.3%, 2/14) had peri-procedural complications: 1 developed TIA and 1 presented with perforator occlusion syndrome. Using the keyword-based search, we identified 6 studies at the same period. A total of 34 patients underwent recanalization with the successful recanalization rate at 94.1%, peri-procedural complication rate at 17.6% and mortality at 2.9%, respectively.

CONCLUSION

Our single-center study illustrated the feasibility and safety of ICVA recanalization. Great care should be taken as revascularization is of high risk. When patient selection, occlusion course and stage as well as neuroimaging evaluation are considered, endovascular recanalization may be a useful therapeutic modality.

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.

Quantitative Analysis of Intracranial Vertebrobasilar Dissecting Aneurysm with Intramural Hematoma After Endovascular Treatment Using 3-T High-Resolution Magnetic Resonance Imaging

OBJECTIVE

Quantitative measurements of intracranial vessel walls are reliable in 3-T high-resolution magnetic resonance imaging (HR-MRI). However, few reports have assessed the arterial wall after endovascular treatment (EVT) by 3-T HR-MRI. This study aimed to quantitatively analyze vessel walls in vertebrobasilar artery dissecting aneurysms after EVT.

METHODS

From May 2012 to December 2015, a total of 21 patients with 21 intracranial vertebrobasilar dissecting aneurysms (VBDAs) were enrolled in this consecutive study. All the VBDAs were characterized by intramural hematomas (IMHs ≥5 mm) and treated with reconstructive EVT. Images of preoperative and follow-up 3-T HR-MRI were used to evaluate the arterial wall. The relative signal intensity (RSI) of IMHs was quantified on T1-weighted imaging (T1WI) and magnetization-prepared rapid acquisition gradient-echo (MPRAGE).

RESULTS

Angiographic follow-up was performed for a mean of 9.19 ± 3.22 months. According to angiographic results at follow-up, 21 patients were divided into 2 groups (progressive group, n = 6; stable group, n = 15). In the progressive group, RSI of IMHs was significantly increased on MPRAGE of follow-up 3-T HR-MRI compared with that before treatment (P < 0.05), and the difference was not significant on T1WI. However, in the stable group, RSI of IMHs was significantly reduced after treatment (P < 0.05).

CONCLUSIONS

Persistent high signal intensity of IMHs in VBDAs after reconstructive EVT may be associated with the progression of VBDAs. It may also indicate an unsteady state of the aneurysm, which suggests that reconstruction of the parent artery is not satisfactory.

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.

Added Value of 3D Proton-Density Weighted Images in Diagnosis of Intracranial Arterial Dissection

Background

An early and reliable diagnosis of intracranial arterial dissection is important to reduce the risk of neurological complication. The purpose of this study was to assess the clinical usefulness of three-dimensional high-resolution MRI (3D-HR-MRI) including pre- and post-contrast T1-weighted volumetric isotropic turbo spin echo acquisition with improved motion-sensitized driven equilibrium preparation (3D-iMSDE-T1) and proton-density weighted image (3D-PD) in detecting dissection and to evaluate the added value of 3D-PD in diagnosing intracranial arterial dissection.

Methods

We retrospectively recruited patients who underwent 3D-HR-MRI with clinical suspicion of arterial dissection. Among them, we selected patients who were diagnosed with definite dissection according to the Spontaneous Cervicocephalic Arterial Dissections Study criteria. For each patient, the presence of intimal flap, intramural hematoma, and vessel dilatation were evaluated independently by two neuroradiologists on each sequence. Interobserver agreement was assessed.

Results

Seventeen patients (mean age: 41 ± 10 [SD] years; 13 men) were diagnosed with definite dissection. The intimal flaps were more frequently detected on 3D-PD (88.2%, 15/17) than on 3D-iMSDE-T1 (29.4%, 5/17), and post-contrast 3D-iMSDE-T1 (35.3%, 6/17; P = 0.006 and P = 0.004, respectively). No significant difference was found in the detection rate of intramural hematomas (59–71%) and vascular dilatations (47%) on each sequence. Interobserver agreement for detection of dissection findings showed almost perfect agreement (k = 0.84–1.00), except for detection of intimal flaps on pre-contrast 3D-iMSDE-T1 (k = 0.62). After addition of 3D-PD to pre- and post-contrast 3D-iMSDE-T1, more patients were diagnosed with definite dissection with the initial MRI (88.2% vs. 47.1%; P = 0.039).

Conclusions

The intimal flap might be better visualized on the 3D-PD sequence than the 3D-iMSDE-T1 sequences, allowing diagnosis of definite dissection without follow-up imaging.

Qualitative Evaluation of a High-Resolution 3D Multi-Sequence Intracranial Vessel Wall Protocol at 3 Tesla MRI

Background and Purpose

Intracranial vessel wall imaging using MRI has great potential as a clinical method for assessing intracranial atherosclerosis. The purpose of the current study was to compare three 3T MRI vessel wall sequences with different contrast weightings (T₁w, PD, T₂w) and dedicated sagittal orientation perpendicular to the middle cerebral artery, to the reconstructed sagittal image from a transverse 3D T₁w volumetric isotropically reconstructed turbo spin-echo acquisition (VIRTA), and provide a clinical recommendation.

Materials and Methods

The above-mentioned sequences were acquired in 10 consecutive Chinese ischemic stroke or TIA patients (age: 68 years, sex: 4 females) with angiographic-confirmed MCA stenosis at 3T. Institutional review board approval was obtained. Two raters qualitatively scored all images on overall image quality, presence of artifacts, and visibility of plaques. Data were compared using Repeated measures ANOVA and Sidak’s adjusted post hoc tests.

Results

All sequences except the T₂w sequence were able to depict the walls of the large vessels of the Circle of Willis (p<0.05). T₁w sagittal oblique VIRTA showed significantly more artifacts (p<0.01). Peripherally located plaques were sometimes missed on the sagittal sequences, but could be appreciated on the transverse T₁w VIRTA.

Conclusion

With the 3T multi-sequence vessel wall protocol we were able to assess the intracranial plaque with two different image contrast weightings. The sequence of preference to include in a clinical protocol would be the transverse 3D T₁w VIRTA based on absence of artifacts, larger coverage including the whole Circle of Willis, and excellent lesion depiction.

High-resolution intracranial vessel wall imaging: imaging beyond the lumen

Accurate and timely diagnosis of intracranial vasculopathies is important due to significant risk of morbidity with delayed and/or incorrect diagnosis both from the disease process as well as inappropriate therapies. Conventional vascular imaging techniques for analysis of intracranial vascular disease provide limited information since they only identify changes to the vessel lumen. New advanced MR intracranial vessel wall imaging (IVW) techniques can allow direct characterisation of the vessel wall. These techniques can advance diagnostic accuracy and may potentially improve patient outcomes by better guided treatment decisions in comparison to previously available invasive and non-invasive techniques. While neuroradiological expertise is invaluable in accurate examination interpretation, clinician familiarity with the application and findings of the various vasculopathies on IVW can help guide diagnostic and therapeutic decision-making. This review article provides a brief overview of the technical aspects of IVW and discusses the IVW findings of various intracranial vasculopathies, differentiating characteristics and indications for when this technique can be beneficial in patient management.

Quantitative Analysis Using High-Resolution 3T MRI in Acute Intracranial Artery Dissection

BACKGROUND AND PURPOSE

Quantitative measurements, as well as qualitative characterizations, of the vessel walls of the small intracranial arteries became clinically available and reliable beyond the resolution limit of 1.5 T high-resolution magnetic resonance imaging (HR-MRI) with the development of 3 T HR-MRI. We present the quantitative dissection findings of spontaneous and unruptured acute intracranial artery dissection (SID) using 3 T HR-MRI and investigate the differences between each cerebral artery.

METHODS

Twenty-eight lesions (anterior cerebral artery = 6; middle cerebral artery = 4; vertebral artery = 18) from 26 patients (17 male and 9 female patients; mean age = 47 years; age range = 32-74 years) with presumptive diagnoses of SID were included. The diagnosis was determined based on the clinical features, findings on luminal angiography (such as digital subtraction angiography, computed tomography, or magnetic resonance angiography), and HR-MRI. HR-MRI was performed within one month from onset. The neuroimaging indices (maximal outer diameter and area, remodeling index and modified remodeling index, and wall thickness and wall area index) of aneurysmal dilatation and the signal intensities of the intramural hematomas were rated using HR-MRI. The results were compared between each cerebral artery.

RESULTS

The maximal outer diameter and area, remodeling index and modified remodeling index, and wall thickness index and length were significantly different between anterior and posterior circulation (P < .05). The mean relative signal intensities of the intramural hematoma showed consistent values, regardless of the cerebral arteries, without significant difference.

CONCLUSIONS

Neuroimaging indices of aneurysmal dilatation may be adjunctive indicators in the evaluation of SID.

Quantitative Intracranial Atherosclerotic Plaque Characterization at 7T MRI: An Ex Vivo Study with Histologic Validation

BACKGROUND AND PURPOSE

In recent years, several high-resolution vessel wall MR imaging techniques have emerged for the characterization of intracranial atherosclerotic vessel wall lesions in vivo. However, a thorough validation of MR imaging results of intracranial plaques with histopathology is still lacking. The aim of this study was to characterize atherosclerotic plaque components in a quantitative manner by obtaining the MR signal characteristics (T1, T2, T2*, and proton density) at 7T in ex vivo circle of Willis specimens and using histopathology for validation.

MATERIALS AND METHODS

A multiparametric ultra-high-resolution quantitative MR imaging protocol was performed at 7T to identify the MR signal characteristics of different intracranial atherosclerotic plaque components, and using histopathology for validation. In total, 38 advanced plaques were matched between MR imaging and histology, and ROI analysis was performed on the identified tissue components.

RESULTS

Mean T1, T2, and T2* relaxation times and proton density values were significantly different between different tissue components. The quantitative T1 map showed the most differences among individual tissue components of intracranial plaques with significant differences in T1 values between lipid accumulation (T1 = 838 ± 167 ms), fibrous tissue (T1 = 583 ± 161 ms), fibrous cap (T1 = 481 ± 98 ms), calcifications (T1 = 314 ± 39 ms), and the intracranial arterial vessel wall (T1 = 436 ± 122 ms).

CONCLUSIONS

Different tissue components of advanced intracranial plaques have distinguishable imaging characteristics with ultra-high-resolution quantitative MR imaging at 7T. Based on this study, the most promising method for distinguishing intracranial plaque components is T1-weighted imaging.

In Vivo Validation of Simultaneous Non-Contrast Angiography and intraPlaque Hemorrhage (SNAP) Magnetic Resonance Angiography: An Intracranial Artery Study

Objectives

Simultaneous Non-contrast Angiography and intraPlaque hemorrhage (SNAP) technique was recently proposed for joint MRA and intraplaque hemorrhage (IPH) imaging. The purpose of this study is to validate SNAP’s MRA performance in patients with suspected intracranial artery disease.

Methods

SNAP and time-of-flight (TOF) techniques with matched field of view and resolution were applied on 15 patients with suspected intracranial artery disease. Both techniques were evaluated based on their detection of luminal stenosis of bilateral middle cerebral arteries (MCA) and the delineation of smallest visible branches (SVB) of the MCA. Statistical analysis was conducted on the artery level.

Results

The SNAP MRA was found to provide similar stenosis detection performance when compared with TOF (Cohen’s κ 0.79; 95% Confidence Interval: 0.56–0.99). For the SVB comparison, SNAP was found to provide significantly better small artery delineation than TOF (p = 0.017). Inter-reader reproducibility for both measurements on SNAP was over 0.7. SNAP also detected IPH lesions on 13% of the patients.

Conclusions

The SNAP technique’s MRA performance was optimized and compared against TOF for intracranial artery atherosclerosis imaging and was found to provide comparable stenosis detection accuracy. Along with its IPH detection capability, SNAP holds the potential to become a first-line screening tool for high risk intracranial atherosclerosis disease evaluation.

Intracranial vessel wall MRI

There are many different methods of imaging the intracranial arteries; however, the vast majority of currently used techniques are based on luminal imaging. Although this is useful, it does have limitations as many different pathological processes can produce the same appearance. Therefore, directly imaging the site of the pathology - the vessel wall itself - offers the hope of discriminating between different disease processes. In this review, we will discuss the current status of vessel wall magnetic resonance imaging alongside its potential usefulness in differentiating between various disease entities.

Vessel Wall Imaging of the Intracranial and Cervical Carotid Arteries

Vessel wall imaging can depict the morphologies of atherosclerotic plaques, arterial walls, and surrounding structures in the intracranial and cervical carotid arteries beyond the simple luminal changes that can be observed with traditional luminal evaluation. Differentiating vulnerable from stable plaques and characterizing atherosclerotic plaques are vital parts of the early diagnosis, prevention, and treatment of stroke and the neurological adverse effects of atherosclerosis. Various techniques for vessel wall imaging have been developed and introduced to differentiate and analyze atherosclerotic plaques in the cervical carotid artery. High-resolution magnetic resonance imaging (HR-MRI) is the most important and popular vessel wall imaging technique for directly evaluating the vascular wall and intracranial artery disease. Intracranial artery atherosclerosis, dissection, moyamoya disease, vasculitis, and reversible cerebral vasoconstriction syndrome can also be diagnosed and differentiated by using HR-MRI. Here, we review the radiologic features of intracranial artery disease and cervical carotid artery atherosclerosis on HR-MRI and various other vessel wall imaging techniques (e.g., ultrasound, computed tomography, magnetic resonance, and positron emission tomography-computed tomography).

An assessment on the incremental value of high-resolution magnetic resonance imaging to identify culprit plaques in atherosclerotic disease of the middle cerebral artery

Objective

Although certain morphological features depicted by high resolution, multi-contrast magnetic resonance imaging (hrMRI) have been shown to be different between culprit and non-culprit middle cerebral artery (MCA) atherosclerotic lesions, the incremental value of hrMRI to define culprit lesions over stenosis has not been assessed.

Methods

Patients suspected with MCA stenosis underwent hrMRI. Lumen and outer wall were segmented to calculate stenosis, plaque burden (PB), volume (PV), length (PL) and minimum luminal area (MLA).

Results

Data from 165 lesions (112 culprit and 53 non-culprit) in 139 individuals were included. Culprit lesions were larger and longer with a narrower lumen and increased PB compared with non-culprit lesions. More culprit lesions showed contrast enhancement. Both PB and MLA were better indicators than stenosis in differentiating lesion types (AUC were 0.649, 0.732 and 0.737 for stenosis, PB and MLA, respectively). Combinations of PB, MLA and stenosis could improve positive predictive value (PPV) and specificity significantly. An optimal combination of stenosis ≥ 50 %, PB ≥ 77 % and MLA ≤ 2.0 mm² produced a PPV = 85.7 %, negative predictive value = 54.1 %, sensitivity = 69.6 %, specificity = 75.5 %, and accuracy = 71.5 %.

Conclusions

hrMRI plaque imaging provides incremental information to luminal stenosis in identifying culprit lesions.

Key points

• High resolution MRI provides incremental information in defining culprit MCA atherosclerotic lesions.

• Both plaque burden and minimum luminal area are better indicators than stenosis.

• An optimal combination includes stenosis ≥ 50 %, PB ≥ 77 % and MLA ≤ 2.0 mm².

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-015-4008-5) contains supplementary material, which is available to authorized users.

Basilar plaque on high-resolution MRI predicts progressive motor deficits after pontine infarction

BACKGROUND

The association between progressive motor deficits (PMD) in acute pontine infarction and basilar stenosis is unclear. High resolution MRI (HRMRI) is an emerging tool for basilar artery evaluation and might provide more accurate information. We aimed to analyze the association between basilar plaque assessed by HRMRI and PMD after acute pontine infarction.

METHODS

We identified consecutive patients with unilateral pontine infarction within 24 h of stroke onset. All the patients underwent diffusion weighted MRI, MR angiography and HRMRI within 24 h of admission. PMD was defined as an increase in National Institutes of Health Stroke Scale score by ≥1 during hospitalization. Factors potentially associated with PMD were validated by multivariate analyses.

RESULTS

Of a total of 87 patients, 63 (72%) had paramedian pontine infarction (PPI) and PMD was observed in 28 (32%) patients. Apparent basilar plaque assessed by HRMRI was more frequent in those with PMD than in those without PMD (52% versus 33%, p<0.001). In contrast, the frequency of basilar stenosis (>30%) assessed by MR angiography was similar regardless of PMD. In the patients with PPI, PMD was associated with hypertension and apparent plaque on HRMRI. After adjusting covariates, PMD was independently associated with apparent plaque on HRMRI (OR, 9.1; 95% CI 1.4-58.9).

CONCLUSIONS

Our results suggest that basilar plaque assessed by HRMRI is associated with PMD in patients with acute unilateral pontine infarction. Since basilar stenosis may be underestimated by MR angiography, HRMRI may provide additional information for predicting PMD and evaluating basilar artery stenosis.

Imaging the intracranial atherosclerotic vessel wall using 7T MRI: initial comparison with histopathology

BACKGROUND AND PURPOSE

Several studies have attempted to characterize intracranial atherosclerotic plaques by using MR imaging sequences. However, dedicated validation of these sequences with histology has not yet been performed. The current study assessed the ability of ultra-high-resolution 7T MR imaging sequences with different image contrast weightings to image plaque components, by using histology as criterion standard.

MATERIALS AND METHODS

Five specimens of the circle of Wills were imaged at 7T with 0.11 × 0.11 mm in-plane-resolution proton attenuation-, T1-, T2-, and T2*-weighted sequences (through-plane resolution, 0.11-1 mm). Tissue samples from 13 fiducial-marked locations (per specimen) on MR imaging underwent histologic processing and atherosclerotic plaque classification. Reconstructed MR images were matched with histologic sections at corresponding locations.

RESULTS

Forty-four samples were available for subsequent evaluation of agreement or disagreement between plaque components and image contrast differences. Of samples, 52.3% (n = 23) showed no image contrast heterogeneity; this group comprised solely no lesions or early lesions. Of samples, 25.0% (n = 11, mostly advanced lesions) showed good correlation between the spatial organization of MR imaging heterogeneities and plaque components. Areas of foamy macrophages were generally seen as proton attenuation-, T2-, and T2*- hypointense areas, while areas of increased collagen content showed more ambiguous signal intensities. Five samples showed image-contrast heterogeneity without corresponding plaque components on histology; 5 other samples showed contrast heterogeneity based on intima-media artifacts.

CONCLUSIONS

MR imaging at 7T has the image contrast capable of identifying both focal intracranial vessel wall thickening and distinguishing areas of different signal intensities spatially corresponding to plaque components within more advanced atherosclerotic plaques.

Luminal thrombosis in middle cerebral artery occlusions: a high-resolution MRI study

BACKGROUND AND PURPOSE

High signals within occluded vessels on T1-weighted fat-suppressed images (HST1) are highly suggestive of luminal thrombosis. We sought to investigate the feasibility of in vivo identification of luminal thrombosis in middle cerebral artery (MCA) occlusions using high-resolution magnetic resonance imaging (HR-MRI).

METHODS

We retrospectively reviewed the HR-MRI data of 25 patients with unilateral symptomatic MCA occlusion. HST1 were defined as an area of high signal within the cross-section of occluded MCA, the intensity of which was >150% of the signal of adjacent muscles. The prevalence of HST1 and their relationship to infarct sizes and infarct patterns were analyzed.

RESULTS

The average time from stroke onset to HR-MRI examination was 9±6 days. There were 18 (72%) occluded vessels with HST1 on HR-MRI. HST1 were observed in 5/7 patients with a large territory infarct (≥1/3 MCA distribution) and 13/18 patients without (P=0.37). In the patients with non-large territory infarcts, the presence of HST1 was similar in those with and without border zone infarcts (9/13 vs. 4/5, P=0.42).

CONCLUSIONS

It's feasible to in vivo identify luminal thrombosis in occluded MCA. HR-MRI is a potentially powerful tool for investigating the mechanisms of stroke due to MCA occlusions.

Intracranial atherosclerotic disease

Atherosclerotic disease of the intracranial arteries is responsible for at least 10% of ischaemic strokes worldwide. Symptomatic disease has been extensively studied in the past few years, using diagnostic methods including multi-slice computed tomography and high resolution magnetic resonance imaging. A literature search was performed using PubMed and OvidSP between 1984 and May 2013. Variations of the terms 'intracranial atherosclerosis' plus 'ischemic stroke', 'plaque', 'morphology', 'imaging' were used and a combination of them. The reference lists of identified articles were also consulted for additional references. Amongst symptomatic patients the prevalence of intracranial atherosclerotic disease is around 10%, depending on race ethnicity, and the diagnosis requires the presence of ≥50% stenosis in the territory of the symptomatic vessel in a patient with stroke or transient ischaemic attack. The prognosis of intracranial atherosclerotic disease related stroke is poor. Although risk factor control can lead to a better outcome of intracranial atherosclerotic disease related strokes, the significance of asymptomatic disease is still a matter of debate.

Reproducibility of high-resolution MRI for the middle cerebral artery plaque at 3T

PURPOSE

To assess the reproducibility of HR-MRI for the identification of MCA atherosclerotic plaque components and quantification of stenosis.

MATERIALS AND METHODS

Seventy-three consecutive subjects who initially had ischemic stroke or asymptomatic MCA stenosis (>50%) were enrolled in the study. All subjects were scanned using 3.0T MRI. Two independent readers reviewed all images and one reader reevaluated all images four weeks later. The tissue components of plaques were analyzed qualitatively and the vessels were quantitative measured.

RESULTS

HR-MRI displayed the artery wall and lumen clearly. The intra-observer reproducibility was excellent for the identification of plaques (kappa [κ]=0.96; 95% CI: 0.83-1.04) and contrast enhancement (κ=0.89; 0.78-0.95); it was substantial for intra-plaque hemorrhage (κ=0.79; 0.57-0.96) and the fibrous cap (κ=0.65; 0.42-0.86). The inter-observer reproducibility was excellent for plaques (κ=0.92; 0.73-1.06), substantial for contrast enhancement (κ=0.80; 0.65-0.93), intra-plaque hemorrhage (κ=0.68; 0.47-0.92) and moderate for the fibrous cap (κ=0.58; 0.44-0.79). Both intra-observer and inter-observer reproducibility were excellent for quantitative vessel, lumen and wall measurements with intraclass correlation coefficients ranging from 0.91 to 0.97 and 0.87 to 0.96, respectively. However, vessel and wall areas and the intervals defined by the Bland-Altman plots were wide in comparison to the mean.

CONCLUSIONS

The identification of MCA atherosclerotic plaque components and the quantification of vessel and lumen measurements are reproducible. The reproducibility is overall acceptable. HR-MRI may provide a useful tool for clinical risk evaluation in MCA atherosclerosis.

Advances in imaging of intracranial atherosclerotic disease and implications for treatment

OPINION STATEMENT

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of ischemic stroke worldwide and is associated with a high risk of recurrent stroke despite aggressive therapy. ICAD may lead to cerebral ischemia through a variety of mechanisms, the interactions of which are largely unknown. The use of endovascular therapy for the prevention of stroke related to severe ICAD has been studied but was associated with a higher risk of recurrent stroke and death in the Stenting and Aggressive Medical Management for Preventing Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) study. With advances in diagnostic testing, it may be possible to better delineate the specific mechanism of stroke from ICAD and identify those patients at higher risk for recurrent ischemia. There may be a subset of patients less responsive to medical interventions, such as those with hemodynamic failure as opposed to those with perforator syndromes, who would benefit from medical plaque stabilization or safer endovascular approaches such as angioplasty alone. These will need to be tested in future clinical trials. Overall, symptomatic ICAD remains a high risk condition with suboptimal treatment options.