Current status and future developments of contrast-enhanced ultrasound of carotid atherosclerosis.

B-mode and Doppler ultrasound are commonly used for the evaluation of atherosclerosis in the carotid arteries. Recently, contrast-enhanced ultrasound (CEUS) has been introduced as a technique to improve the detection of carotid atherosclerosis and evaluate the presence of intraplaque neovascularization, which is considered a marker of plaque vulnerability. The present review focuses on the role of CEUS for the assessment of atherosclerosis and plaque instability. Currently available literature and future developments with CEUS are discussed.

Molecular imaging of inflammation and intraplaque vasa vasorum: a step forward to identification of vulnerable plaques?

Current developments in cardiovascular biology and imaging enable the noninvasive molecular evaluation of atherosclerotic vascular disease. Intraplaque neovascularization sprouting from the adventitial vasa vasorum has been identified as an independent predictor of intraplaque hemorrhage and plaque rupture. These intraplaque vasa vasorum result from angiogenesis, most likely under influence of hypoxic and inflammatory stimuli. Several molecular imaging techniques are currently available. Most experience has been obtained with molecular imaging using positron emission tomography and single photon emission computed tomography. Recently, the development of targeted contrast agents has allowed molecular imaging with magnetic resonance imaging, ultrasound and computed tomography. The present review discusses the use of these molecular imaging techniques to identify inflammation and intraplaque vasa vasorum to identify vulnerable atherosclerotic plaques at risk of rupture and thrombosis. The available literature on molecular imaging techniques and molecular targets associated with inflammation and angiogenesis is discussed, and the clinical applications of molecular cardiovascular imaging and the use of molecular techniques for local drug delivery are addressed.

New quantification methods for carotid intra-plaque neovascularization using contrast-enhanced ultrasound.

As carotid intra-plaque neovascularization (IPN) is linked to progressive atherosclerotic disease and plaque vulnerability, its accurate quantification might allow early detection of plaque vulnerability. We therefore developed several new quantitative methods for analyzing IPN perfusion and structure. From our analyses, we derived six quantitative parameters-IPN surface area (IPNSA), IPN surface ratio (IPNSR), plaque mean intensity, plaque-to-lumen enhancement ratio, mean plaque contrast percentage and number of micro-vessels (MVN)-and compared these with visual grading of IPN by two independent physicians. A total of 45 carotid arteries with symptomatic stenosis in 23 patients were analyzed. IPNSA (correlation r = 0.719), IPNSR (r = 0.538) and MVN (r = 0.484) were found to be significantly correlated with visual scoring (p < 0.01). IPNSA was the best match to visual scoring. These results indicate that IPNSA, IPNSR and MVN may have the potential to replace qualitative visual scoring and to measure the degree of carotid IPN.

Carotid intima-media thickness for cardiovascular risk assessment: systematic review and meta-analysis.

OBJECTIVE: B-mode ultrasound measurement of the carotid intima-media thickness (CIMT) is a widely used marker for atherosclerosis and is associated with future cardiovascular events. This article provides a review and meta-analysis of the published evidence on the association of CIMT with future cardiovascular events and its additional value to traditional cardiovascular risk prediction models. METHODS: A systematic review and meta-analysis of the evidence on the association of CIMT with future cardiovascular events and the additional value of CIMT to traditional cardiovascular risk prediction models was conducted. The association of CIMT with future cardiovascular events and the additional value of CIMT were calculated using random effects analysis. RESULTS: The literature search yielded 1196 articles of which 15 articles provided sufficient data for the meta-analysis. A 1 SD increase in CIMT was predictive for myocardial infarction (HR 1.26, 95% CI 1.20-1.31) and for stroke (HR 1.31, 95% CI 1.26-1.36). A 0.1 mm increase in CIMT was predictive for myocardial infarction (HR 1.15, 95% CI 1.12-1.18) and for stroke (HR 1.17, 95% CI 1.15-1.21). The overall performance of risk prediction models did not significantly increase after addition of CIMT data. The areas under the curve increased from 0.726 to 0.729 (p = 0.8). CONCLUSIONS: CIMT as measured by B-mode ultrasound is associated with future cardiovascular events. However, the addition of CIMT to traditional cardiovascular risk prediction models does not lead to a statistical significantly increase in performance of those models.

Effect of carotid plaque screening using contrast-enhanced ultrasound on cardiovascular risk stratification.

Cardiovascular risk stratification of asymptomatic patients is based on the assessment of risk factors. Noninvasive imaging of subclinical atherosclerosis may improve cardiovascular risk stratification, especially in patients with co-morbidities. The aim of this study was to investigate the effect of contrast-enhanced ultrasound (CEUS) of the carotid arteries on cardiovascular risk assessment. The study population consisted of 100 consecutive asymptomatic patients with ≥1 clinical risk factor for atherosclerosis. Cardiovascular risk was estimated by calculating the Prospective Cardiovascular Münster Heart Study (PROCAM) risk score. This score was divided into 3 subgroups: low (≤5%), intermediate (6% to 19%), and high (≥20%). Subclinical carotid atherosclerosis was assessed using standard ultrasound for intima-media thickness and plaque screening and CEUS for additional plaque screening. CEUS was performed using SonoVue contrast agent. Patients with subclinical atherosclerosis were considered to be at high cardiovascular risk. McNemar's test was used to compare PROCAM score to ultrasound findings. The mean PROCAM risk score was 9 ± 10; the PROCAM risk score was low in 72 patients (72%), intermediate in 17 patients (17%), and high in 11 patients (11%). A total of 21 patients (21%) had abnormal carotid intima-media thickness, 77% had plaques on conventional carotid ultrasound, and 88% had plaques on standard carotid ultrasound combined with CEUS. Detection of atherosclerosis led to the reclassification of 79 patients (79%) to high cardiovascular risk (p <0.001). In conclusion, CEUS changes the risk category as estimated by a traditional risk stratification model in most asymptomatic patients. CEUS may thus be an additional method for cardiovascular risk prediction in patient groups with co-morbidities.

Carotid plaque burden as a measure of subclinical coronary artery disease in patients with heterozygous familial hypercholesterolemia.

Patients with familial hypercholesterolemia (FH) are at markedly increased risk of developing premature coronary artery disease. The objective of the present study was to evaluate the role of carotid ultrasonography as a measure of subclinical coronary artery disease in patients with FH. The present prospective study compared the presence of subclinical carotid and coronary artery disease in 67 patients with FH (mean age 55 ± 8 years, 52% men) to that in 30 controls with nonanginal chest pain (mean age 56 ± 9 years, 57% men). The carotid intima-media thickness and carotid plaque burden were assessed using B-mode ultrasonography, according to the Mannheim consensus. Coronary artery disease was assessed using computed tomographic coronary angiography. A lumen reduction >50% was considered indicative of obstructive coronary artery disease. The patients with FH and the controls had a comparable carotid intima-media thickness (0.64 vs 0.66 mm, p = 0.490), prevalence of carotid plaque (93% vs 83%, p = 0.361), and median carotid plaque score (3 vs 2, p = 0.216). Patients with FH had a significantly greater median coronary calcium score than did the controls (62 vs 5, p = 0.015). However, the prevalence of obstructive coronary artery disease was comparable (27% vs 31%, p = 0.677). No association was found between the carotid intima-media thickness and coronary artery disease. An association was found between the presence of carotid plaque and coronary artery disease in the patients with FH and the controls. The absence of carotid plaque, observed in 5 patients (7%) with FH, excluded the presence of obstructive coronary artery disease. In conclusion, the patients with FH had a high prevalence of carotid plaque and a significantly greater median coronary calcium score than did the controls. A correlation was found between carotid plaque and coronary artery disease in patients with FH; however, the presence of carotid plaque and carotid plaque burden are not reliable indicators of obstructive coronary artery disease.

Assessment of subclinical atherosclerosis using contrast-enhanced ultrasound.

AIMS: The sensitivity of standard carotid ultrasound and colour Doppler for the detection of subclinical atherosclerotic plaques is suboptimal. The aim of this study is to assess whether contrast-enhanced ultrasound (CEUS) added to standard carotid ultrasound improves the detection of subclinical atherosclerosis. METHODS AND RESULTS: Carotid intima-media thickness (CIMT) measurement, standard carotid ultrasound including colour Doppler imaging, and CEUS were performed in 100 asymptomatic patients with one or more risk factors for atherosclerosis. CEUS was performed using intravenous administration of SonoVue™ contrast agent (Bracco S.p.A., Milan, Italy). CIMT, standard ultrasound, colour Doppler, and CEUS were reviewed by two independent observers. Standard ultrasound, colour Doppler, and CEUS were scored for the presence of atherosclerotic plaques. Subclinical atherosclerosis was diagnosed if patients had a CIMT above their age-corrected threshold value or if atherosclerotic plaques were present on standard carotid ultrasound clips or CEUS clips. McNemar's test was performed to compare between groups. Twenty-one patients (21%) had a thickened CIMT value and were considered to have subclinical atherosclerosis. Standard carotid ultrasound including colour Doppler demonstrated atherosclerotic plaques in 77 patients (77%). The addition of CEUS to the standard ultrasound protocol demonstrated atherosclerotic plaques in 88 patients (88%). The incorporation of CEUS into the standard carotid ultrasound protocol resulted in a significantly improved detection of patients with subclinical atherosclerosis (P < 0.01). CONCLUSION: CEUS has an incremental value for the detection of subclinical atherosclerosis in the carotid arteries. Atherosclerotic plaques which were only detected with CEUS and not with standard carotid ultrasound and colour Doppler imaging were predominantly hypoechoic.

Usefulness of contrast-enhanced ultrasound for detection of carotid plaque ulceration in patients with symptomatic carotid atherosclerosis.

Previous data have indicated that carotid plaque ulceration is a strong predictor of cerebrovascular events. Standard ultrasound and color Doppler ultrasound (CDUS) scans have poor diagnostic accuracy for the detection of carotid plaque ulceration. The aim of the present prospective study was to assess the value of contrast-enhanced ultrasound (CEUS) scans for the detection of carotid plaque ulceration. The Institutional Ethics Committee approved the study protocol, and all patients provided informed consent. The patients had symptomatic stenosis of the internal carotid artery and underwent carotid computed tomographic angiography as part of their clinical evaluation. All patients underwent a CDUS examination in conjunction with CEUS. Carotid plaque ulceration was defined as the presence of ≥1 disruptions in the plaque-lumen border ≥1 × 1 mm. Carotid computed tomographic angiography was used as reference technique. The study population consisted of 20 patients (mean age 64 ± 9 years, 80% men), and 39 carotid arteries were included in the present analysis. Computed tomographic angiography demonstrated that the plaque surface was smooth in 15 (38%), irregular in 7 (18%) and ulcerated in 17 (44%) carotid arteries. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CDUS for the detection of ulceration was 29%, 73%, 54%, 46%, and 57%, respectively. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CEUS for the detection of ulceration was 88%, 59%, 72%, 63%, and 87%, respectively. CEUS had superior sensitivity and diagnostic accuracy for the assessment of carotid plaque ulceration compared with CDUS. CEUS improved the intrareader and inter-reader variability for the assessment of carotid plaque ulceration compared with CDUS. In conclusion, CEUS could be an additional method for the detection of carotid plaque ulceration. The role of CDUS for the assessment of carotid plaque ulceration seems limited.

Estimating 3D lumen centerlines of carotid arteries in free-hand acquisition ultrasound.

PURPOSE: The purpose of this paper is to present a methodology to estimate the carotid artery lumen centerlines in ultrasound (US) images obtained in a free-hand examination. Challenging aspects here are speckle noise in US images, artifacts, and the lack of contrast in the direction orthogonal to the US beam direction. METHOD: An algorithm based on a rough lumen segmentation obtained by robust ellipse fitting was developed to deal with these conditions and estimate the lumen center in 2D B-mode scans. In a free-hand sweep examination, continuous image acquisitions are performed through time when the radiologist moves the probe on the patient's neck. The result is a series of images that show 2D cross-sections of the carotid's morphology. A tracking sensor (Flock of Birds) was attached to the probe and both were connected to a PC executing the Stradwin software, which relates spatial information to the acquisition data of the US probe. The spatial information was combined with the 2D lumen center estimates to provide a centerline in 3D. For validation, 19 carotid scans from 15 different patients were scanned, their centerlines calculated by the algorithm and compared with results acquired by manual annotations. RESULTS: The average Euclidean distance between both among all the examinations was 0.82  mm. For each examination, the percentage of these Euclidean distances below 2  mm was calculated; the average over all examinations was 92%. CONCLUSION: Automated 3D estimation of carotid artery lumen centerlines in free-hand real-time ultrasound is feasible and can be performed with high accuracy. The algorithm is robust enough to keep the centerlines inside the vessel, even in the absence of contrast in parts of the vessel wall.

Quantitative analysis of ultrasound contrast flow behavior in carotid plaque neovasculature.

Intraplaque neovascularization is considered as an important indication for plaque vulnerability. We propose a semiautomatic algorithm for quantification of neovasculature, thus, enabling assessment of plaque vulnerability. The algorithm detects and tracks contrast spots using multidimensional dynamic programming. Classification of contrast tracks into blood vessels and artifacts was performed. The results were compared with manual tracking, visual classification and maximal intensity projection. In 28 plaques, 97% of the contrast spots were detected. In 89% of the objects, the automatic tracking determined the contrast motion with an average distance of less than 0.5 mm from the manual marking. Furthermore, 75% were correctly classified into artifacts and vessels. The automated neovascularization grading agreed within 1 grade with visual analysis in 91% of the cases, which was comparable to the interobserver variability of visual grading. These results show that the method can successfully quantify features that are linked to vulnerability of the carotid plaque.

Far-wall pseudoenhancement during contrast-enhanced ultrasound of the carotid arteries: clinical description and in vitro reproduction.

The present study describes the presence of pseudoenhancement during contrast-enhanced ultrasound (CEUS) imaging of human carotid arteries and the reproduction of this pseudoenhancement in vitro. Seventy patients underwent bilateral CEUS examination of the carotid arteries using a Philips iU22 ultrasound system equipped with a L9-3 ultrasound probe and SonoVue microbubble contrast. During CEUS of the carotid arteries, we identified enhancement in close proximity to the far wall, parallel to the main lumen. The location of this enhancement does not correlate to the anatomical location of a parallel vessel. To corroborate the hypothesis that this is a pseudoenhancement artifact, the enhancement was recreated in a tissue-mimicking material phantom, using the same ultrasound system, settings and contrast agent as the patient study. The phantom study showed that pseudoenhancement may be present during vascular CEUS and that the degree of pseudoenhancement is influenced by the size and concentration of the microbubbles. During vascular CEUS, identification of the artifact is important to prevent misinterpretation of enhancement in and near the far wall.

Noninvasive imaging of the vulnerable atherosclerotic plaque.

Atherosclerosis is an inflammatory disease, complicated by progressively increasing atherosclerotic plaques that eventually may rupture. Plaque rupture is a major cause of cardiovascular events, such as unstable angina, myocardial infarction, and stroke. A number of noninvasive imaging techniques have been developed to evaluate the vascular wall in an attempt to identify so-called vulnerable atherosclerotic plaques that are prone to rupture. The purpose of the present review is to systematically investigate the accuracy of noninvasive imaging techniques in the identification of plaque components and morphologic characteristics associated with plaque vulnerability, assessing their clinical and diagnostic value.

Prognostic significance of QRS duration in patients with suspected coronary artery disease referred for noninvasive evaluation of myocardial ischemia.

The purpose of this study was to evaluate the prognostic significance of QRS duration in patients with suspected coronary artery disease (CAD) referred for noninvasive evaluation of myocardial ischemia by dobutamine stress echocardiography. QRS duration is a prognostic marker in patients with previous myocardial infarction and/or heart failure. The relation between QRS duration and outcome of patients without known heart disease has not been evaluated. A total of 1,227 patients (707 men, mean age 61 +/- 14 years) with suspected CAD underwent dobutamine stress echocardiography for evaluation of myocardial ischemia. Patients were followed to determine predictors of cardiac events and to assess the incremental significance of QRS duration compared to clinical and dobutamine stress echocardiographic data. During a mean follow-up of 4.2 +/- 2.4 years, 280 patients (23%) died (129 cardiac deaths), and 60 (5%) had a nonfatal infarction. Annualized cardiac death rates were 2.0% in patients with QRS duration <120 ms and 4.4% in patients with QRS duration >or=120 ms, respectively (p <0.0001). Annualized event rates for cardiac death/nonfatal infarction were 2.8% in patients with QRS duration <120 ms and 4.8% in patients with QRS duration >or=120 ms (p = 0.0001). Multivariate models identified age, male gender, smoking, QRS duration >or=120 ms, and an abnormal dobutamine stress echocardiogram as independent predictors of cardiac death and the combined end point cardiac death/nonfatal infarction. In conclusion, QRS duration is an independent predictor of cardiac death and cardiac death/nonfatal infarction in patients with suspected CAD. This risk is persistent after adjustment for clinical variables, left ventricular function, and myocardial ischemia.