High-resolution MRI of carotid plaque with a neurovascular coil and contrast-enhanced MR angiography: one-stop shopping for the comprehensive assessment of carotid atherosclerosis

High-resolution magnetic resonance vessel wall imaging in ischemic stroke and carotid artery atherosclerotic stenosis: A review

Ischemic stroke is a significant burden on human health worldwide. Carotid Atherosclerosis stenosis plays an important role in the comprehensive assessment and prevention of ischemic stroke patients. High-resolution vessel wall magnetic resonance imaging has emerged as a successful technique for assessing carotid atherosclerosis stenosis. This advanced imaging modality has shown promise in effectively displaying a wide range of characteristics associated with the condition, leading to a comprehensive evaluation. High-resolution vessel wall magnetic resonance imaging not only enables a comprehensive evaluation of the instability of carotid atherosclerosis stenosis plaques but also provides valuable information for understanding the pathogenesis and predicting the prognosis of ischemic stroke patients. The purpose of this article is to review the application of high-resolution magnetic resonance imaging in ischemic stroke and carotid atherosclerotic stenosis.

Choice of imaging to evaluate carotid stenosis and guide management

Carotid artery disease is a cause of ischemic stroke and is associated with cognitive decline. Besides the evaluation of the degree of stenosis, it is also crucial to assess the morphology of the atherosclerotic plaque, for a prompt and accurate diagnosis, and to make the best decision for the patient. On top of noninvasive duplex ultrasound (DUS) and invasive digital subtraction angiography (DSA), compute tomography angiography (CTA) and magnetic resonance angiography (MRA) are often used effectively as noninvasive imaging tools to study carotid stenoses. This review describes the fundamental characteristics of carotid artery plaques, and how they can be best evaluated with currently available imaging methods.

High-Resolution MRI for Evaluation of the Possibility of Successful Recanalization in Symptomatic Chronic ICA Occlusion: A Retrospective Study

BACKGROUND AND PURPOSE

Accurate radiologic evaluation of the possibility of successful recanalization in symptomatic chronic ICA occlusion remains challenging. This study aimed to investigate the high-resolution MR imaging characteristics of symptomatic chronic ICA occlusion and their association with successful recanalization.

MATERIALS AND METHODS

Consecutive patients with symptomatic chronic ICA occlusion who underwent balloon dilation plus stent implantation were identified retrospectively and divided into 2 groups: a successful recanalization group and an unsuccessful recanalization group. Clinical and high-resolution MR imaging characteristics were compared between the groups. Univariate and multivariate analyses were used to identify the characteristics associated with successful recanalization.

RESULTS

A total of 114 patients were included in the study. High-resolution MR imaging characteristics independently associated with unsuccessful recanalization were longer lesion length (OR, 0.41; 95% CI, 0.36-0.55; P = .009) and larger calcification volume (OR, 0.56; 95% CI, 0.37-0.68; P = .002) for proximal occlusion and reversed distal ICA flow at the level of ophthalmic segment or above (OR, 0.14; 95% CI, 0.08-0.48; P = .001). Reversed distal ICA flow at the level of the petrous segment or below (OR, 4.07; 95% CI, 1.65-8.38; P = .001) and lumen area (OR, 1.13; 95% CI, 1.04-1.61; P = .002) for distal occlusion were risk factors of successful recanalization.

CONCLUSIONS

In symptomatic chronic ICA occlusion, lesion length and calcification volume (for proximal occlusion), the level of reversed distal ICA flow, and the lumen area (for distal occlusion) appear to be predictors of successful recanalization. High-resolution MR imaging can evaluate chronic ICA occlusion and help in clinical decision-making.

Review of imaging biomarkers for the vulnerable carotid plaque

Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis. However, histopathologic studies demonstrate considerable differences between plaques with identical degrees of stenosis and indicate that certain plaque features are associated with increased risk for ischemic events. As a result of the rapid technological evolution in medical imaging, several important steps have been taken in the field of carotid plaque imaging allowing us to visualize the carotid atherosclerotic plaque and its composition in great detail. For computed tomography, magnetic resonance imaging, positron emission tomography, and ultrasound scan, evidence has accumulated on novel imaging-based markers that confer information on carotid plaque vulnerability, such as intraplaque hemorrhage and lipid-rich necrotic cores. In terms of the imaging-based identification of individuals at high risk of stroke, routine assessments of such imaging markers are the way forward for improving current clinical practice. The current review highlights the main characteristics of the vulnerable plaque indicating their role in the etiology of ischemic stroke as identified by intensive plaque imaging.

New technique: the use of the THRIVE sequence in the follow-up of patients who received endovascular intracranial aneurysm treatment

PURPOSE

To determine the diagnostic accuracy of 3D time of flight MR angiography (TOF-MRA), contrast enhanced MR angiography (CE-MRA), and T1-weighted high-resolution isotropic volume examination (THRIVE) at 3 T for the evaluation of intracranial aneurysm occlusion after endovascular treatment and to evaluate the usability of the THRIVE sequence in endovascular treatment follow-up.

METHODS

In 3 T MR follow-up examinations of 66 aneurysms in 50 patients treated endovascularly, 3D TOF-MRA (index test), THRIVE (index test), and CE-MRA (reference standard) examinations were performed in a retrospective consecutive case series. Source images were classified as class 1, class 2, and class 3 according to the Raymond criteria using MIP (maximum intensity projection) techniques. The compatibility between sequences was evaluated with the Kappa test. The sensitivity and specificity were also calculated.

RESULTS

In the evaluation of THRIVE and CE-MRA sequences, compatibility was determined in 61 cases in total, with an overall fit of 61/66 (92.42%). A statistically significant correlation was found between THRIVE and CE-MRA (p < 0.001, κ = 0.800). In the evaluation of TOF and CE-MRA sequences, compatibility was determined in 54 cases in total, and the overall fit was 54/66 (81.8%). A statistically significant agreement was found between TOF and CE-MRA (p < 0.001, κ = 0.502). Assuming that CE-MRA is a reference standard, the sensitivity and specificity of the TOF sequence were 44.4% and 97.9%, respectively, and the sensitivity and specificity of the THRIVE sequence were 77.8% and 97.9%, respectively.

CONCLUSION

The THRIVE sequence can be used as a noncontrast method for monitoring endovascularly treated intracranial aneurysms.

Influence of Vertebrobasilar Stenotic Lesion Rigidity on the Outcome of Angioplasty and Stenting

Stenotic lesion rigidity (SLR) has an unclear influence on the outcome of percutaneous transluminal angioplasty and stenting (PTAS) for intracranial arterial stenosis. This study evaluated the outcome of PTAS and the relationship of vertebrobasilar SLR to features on vessel wall MRI (VW-MRI) for identifying pathologies of vertebrobasilar stenosis (VBS) and evaluating PTAS outcome. We retrospectively evaluated the results of PTAS in 31 patients with severe VBS. Stenotic lesions were classified as soft (based on predilatation pressure [PP] ≦ 4 atm) in 15 patients or hard (PP >4 atm) in 16 patients. We examined the relationship of SLR to clinical and MR findings. Patients with hard vs soft lesions had atherosclerosis (8/16 [50.0%] vs 2/15 [13.3%]), dissection (0/16 [0.0%] vs 12/15 [80.0%]), and dissection in atherosclerosis (8/16 [50.0%] vs 1/15 [6.7%], P < 0.0001); high intensity signal on the T1WI of VW-MRI (5/16 [31.3%] vs 14/15 [93.3%]) and iso- to low intensity signal (11/16 [68.7%] vs 1/15 [6.7], P = 0.001), and significant in-stent restenosis (>50%) in 5/15 (33.3%) vs 0/15 (0.0%) (P = 0.0421) in the 30 patients who successfully completed PTAS. Vertebrobasilar SLR correlated well with lesion etiology, findings on VW-MRI, and PTAS outcome. Patients with hard stenotic lesions need close follow-up after PTAS.

Contrast agents for cardiovascular magnetic resonance imaging: an overview

Contrast agents for Cardiovascular Magnetic Resonance (CMR) play a major role in research and clinical cardiology.

Visualizing the atherosclerotic plaque: a chemical perspective

Atherosclerosis is the major underlying pathologic cause of coronary artery disease. An early detection of the disease can prevent clinical sequellae such as angina, myocardial infarction, and stroke. The different imaging techniques employed to visualize the atherosclerotic plaque provide information of diagnostic and prognostic value. Furthermore, the use of contrast agents helps to improve signal-to-noise ratio providing better images. For nuclear imaging techniques and optical imaging these agents are absolutely necessary. We report on the different contrast agents that have been used, are used or may be used in future in animals, humans, or excised tissues for the distinct imaging modalities for atherosclerotic plaque imaging.

3D high-resolution contrast enhanced MRI of carotid atheroma--a technical update

OBJECTIVE

Development of a fast 3D high-resolution magnetic resonance imaging (MRI) protocol for improved carotid artery plaque imaging.

METHODS

Two patients with carotid atherosclerosis disease underwent 3D high-resolution MRI which included time-of-flight and T1-weighted variable flip angle, fast-spin-echo (FSE) imaging, pre- and post-intravenous gadolinium-based contrast agent administration.

RESULTS

Good quality images with intrinsic blood suppression were obtained pre- and post-contrast administration using a 3D FSE sequence. The plaque burden, lipid core volume, hemorrhage volume and fibrous cap thickness were well determined.

CONCLUSIONS

3D high-resolution MR imaging of carotid plaque using TOF and 3D FSE can achieve high isotropic resolution, large coverage, and excellent image quality within a short acquisition time.

Association between carotid artery occlusion and ultrasonographic plaque type

BACKGROUND

Internal carotid artery (ICA) occlusion is associated with acute stroke and carries significant morbidity and mortality. The aim of this study was to examine whether ultrasonographic carotid plaque type may be associated with ICA occlusion.

METHODS

Two hundred eleven patients (85% men, mean age 66.0±9.5 years, 28.9% asymptomatic) with ICA occlusion were included in this case-control study. Ultrasonographic Gray-Weale plaque type (I-IV, echolucent to echogenic) characterization was obtained in both the occluded and the contralateral ICA. Univariate and conditional logistic regression analyses with 1:1 pair matching per artery were undertaken. Each contralateral carotid artery with stenosis was treated as control to the ipsilateral-occluded ICA of the same patient.

RESULTS

A total of 261 ICAs (61.9%) were recorded with type I-II plaque, of which 165 (63.2%) were among the occluded and 96 (36.8%) were among the contralateral ICAs with stenosis (P<0.001). Mean contralateral ICA stenosis was 58.2%±20.4%. Regression analysis showed that carotid plaque type I-II was significantly associated with carotid artery occlusion compared with plaque type III-IV (crude odds ratio [OR]=4.29, 95% confidence intervals [CI]=2.81-6.57%, P<0.001, adjusted OR=5.60, 95% CI=3.23-9.70, P<0.001). Previous neurological events did not seem to be significantly associated with plaque echolucency (OR=0.62, 95% CI=0.29-1.35, P=0.23).

CONCLUSIONS

A significant association between echolucent plaque and ICA occlusion was observed. This observational hypothesis may prompt for further investigation of the causal mechanism between carotid plaque type and ICA occlusion by larger cohort studies.

Grading of carotid artery stenosis in the presence of extensive calcifications: dual-energy CT angiography in comparison with contrast-enhanced MR angiography

PURPOSE

We investigated the agreement of dual-energy computed tomography angiography (DE-CTA) and contrast-enhanced magnetic resonance angiography (CE-MRA)in the quantitative measurement of stenoses of the internal carotid artery in comparison with digital subtraction angiography (DSA).

METHODS

A total of 21 patients with stenoses of the external carotid artery were investigated with a DE-CTA and CE-MRA before undergoing carotid angioplasty. The grade of the stenoses was assessed in axial multiplanar reformations (MPR) before and multi-intensity projections (MIP) after plaque subtraction (PS) and compared with results from CE-MRA and DSA according to the North American Symptomatic Carotid Endarterectomy Trial.

RESULTS

Average grades of stenoses were 80.7 ± 16.1 % (DSA), 81.4 ± 15.3 % (MRA), 80.0 ± 16.7 % (DE-CTA-MPR), and 85.2 ± 14.7 % (DE-CTA-PS-MIP). Of 21 stenoses, 6 were filiform (stenosis grade, 99 %) in the DSA examination. Five of these cases were identified as pseudo-occlusions in MRA, while four were considered as occlusions in DE-CTA-PS-MIP. Another four cases were identified as pseudo-occlusion in DE-CTA-PS-MIP, which were identified as 90 % stenosis in the DSA examination.

CONCLUSIONS

In comparison with the gold standard DSA, DE-CTA-MPR had a slightly better agreement in measuring the degree of stenosis of the internal carotid arteries than CE-MRA. In DE-CTA-PS-MIP images, a systematic overestimation has to be taken into account due to partial extinction of the lumen by the PS algorithm. Nevertheless, DE-CTA should be preferred in imaging patients with carotid artery stenosis in the presence of extensive calcifications.

Gadofosveset trisodium: abdominal and peripheral vascular applications

OBJECTIVE

The purpose of this review is to illustrate various applications of gadofosveset trisodium in evaluating abdominal and peripheral vascular disease. The basic properties, technical considerations, and clinical and potential future applications of gadofosveset are described.

CONCLUSION

Gadofosveset trisodium facilitates comprehensive high-resolution arterial and venous MR angiography. Because of its prolonged intravascular residence time, gadofosveset trisodium is particularly useful for evaluating venous, dynamic, and functional vascular disease with a single low-dose contrast injection.

MRI plaque imaging detects carotid plaques with a high risk for future cerebrovascular events in asymptomatic patients

PURPOSE

The aim of this study was to investigate prospectively whether MRI plaque imaging can identify patients with asymptomatic carotid artery stenosis who have an increased risk for future cerebral events. MRI plaque imaging allows categorization of carotid stenosis into different lesion types (I-VIII). Within these lesion types, lesion types IV-V and VI are regarded as rupture-prone plaques, whereas the other lesion types represent stable ones.

METHODS

Eighty-three consecutive patients (45 male (54.2%); age 54-88 years (mean 73.2 years)) presenting with an asymptomatic carotid stenosis of 50-99% according to ECST-criteria were recruited. Patients were imaged with a 1.5-T scanner. T1-, T2-, time-of-flight-, and proton-density weighted studies were performed. The carotid plaques were classified as lesion type I-VIII. Clinical endpoints were ischemic stroke, TIA or amaurosis fugax. Survival analysis and log rank test were used to ascertain statistical significance.

RESULTS

Six out of 83 patients (7.2%) were excluded: 4 patients had insufficient MR image quality; 1 patient was lost-to-follow-up; 1 patient died shortly after the baseline MRI plaque imaging. The following results were obtained by analyzing the remaining 77 patients. The mean time of follow-up was 41.1 months. During follow-up, n = 9 (11.7%) ipsilateral ischemic cerebrovascular events occurred. Only patients presenting with the high-risk lesion types IV-V and VI developed an ipsilateral cerebrovascular event versus none of the patients presenting with the stable lesion types III, VII, and VIII (n = 9 (11.7%) vs. n = 0 (0%) during follow-up). Event-free survival was higher among patients with the MRI-defined stable lesion types (III, VII, and VIII) than in patients with the high-risk lesion types (IV-V and VI) (log rank test P<0.0001).

CONCLUSIONS

MRI plaque imaging has the potential to identify patients with asymptomatic carotid stenosis who are particularly at risk of developing future cerebral ischemia. MRI could improve selection criteria for invasive therapy in the future.

MRI of carotid atherosclerosis

OBJECTIVE

Although MRI is widely used to observe atherosclerosis impacts on the vessel lumen, MRI also depicts the size of the plaque itself, its composition, and plaque inflammation, providing information beyond simple stenosis. This article summarizes the state of evidence for a clinical role for MRI of carotid atherosclerosis.

CONCLUSION

MRI of carotid atherosclerosis has a proven role in pharmaceutical trials and may improve patient management once large-scale clinical trials have been completed.

An initial evaluation of analyser-based phase-contrast X-ray imaging of carotid plaque microstructure

Carotid artery plaque instability can result in rupture and lead to ischaemic stroke. Stability of plaques appears to be a function of composition. Current non-invasive imaging techniques are limited in their ability to classify distinct histological regions within plaques. Phase-contrast (PC) X-ray imaging methods are an emerging class of techniques that have shown promise for identifying soft-tissue features without use of exogenous contrast agents. This is the first study to apply analyser-based X-ray PC imaging in CT mode to provide three-dimensional (3D) images of excised atherosclerotic plaques. The results provide proof of principle for this technique as a promising method for analysis of carotid plaque microstructure. Multiple image radiography CT (MIR-CT), a tomographic implementation of X-ray PC imaging that employs crystal optics, was employed to image excised carotid plaques. MIR-CT imaging yields three complementary images of the plaque's 3D X-ray absorption, refraction and scatter properties. These images were compared with histological sections of the tissue. X-ray PC images were able to identify the interface between the plaque and the medial wall. In addition, lipid-rich and highly vascularized regions were visible in the images as well as features depicting inflammation. This preliminary research shows MIR-CT imaging can reveal details about plaque structure not provided by traditional absorption-based X-ray imaging and appears to identify specific histological regions within plaques. This is the first study to apply analyser-based X-ray PC imaging to human carotid artery plaques to identify distinct soft-tissue regions.

Stratifying risk: asymptomatic carotid disease

Stroke generates significant healthcare expenses and it is also a social and economic burden. The carotid artery atherosclerotic plaque instability is responsible for a third of all embolic strokes. The degree of stenosis has been deliberately used to justify carotid artery interventions in thousands of patients worldwide. However, the annual risk of stroke in asymptomatic carotid artery disease is low. Plaque morphology and its kinetics have gained ground to explain cerebrovascular and retinal embolic events. This review provides the readers with an insightful and critical analysis of the risk stratification of asymptomatic carotid artery disease in order to assist in selecting potential candidates for a carotid intervention.

Stroke prevention-surgical and interventional approaches to carotid stenosis

Extracranial carotidartery stenosis is an important cause of stroke that often needs treatment with carotid revascularization. To prevent stroke recurrence, carotid endarterectomy has been well-established for many years in treating symptomatic high- and moderate-grade stenosis. Carotid stenting is an appealing, less invasive alternative to carotid endarterectomy, and several recent trials have compared the efficacy of the 2 procedures in patients with carotid stenosis. Carotid artery stenting has emerged as an important mode of therapy for high-risk patients with symtomatic high-grade stenosis. This review focuses on the current data available that will enable the clinician to decide optimal treatment strategies for patients with carotid stenosis.