Quantitative contrast-enhanced ultrasound of intraplaque neovascularization in patients with carotid atherosclerosis

Contrast-Enhanced Ultrasound Feasibility in Assessing Carotid Plaque Vulnerability-Narrative Review

The risk assessment for carotid atherosclerotic lesions involves not only determining the degree of stenosis but also plaque morphology and its composition. Recently, carotid contrast-enhanced ultrasound (CEUS) has gained importance for evaluating vulnerable plaques. This review explores CEUS's utility in detecting carotid plaque surface irregularities and ulcerations as well as intraplaque neovascularization and its alignment with histology. Initial indications suggest that CEUS might have the potential to anticipate cerebrovascular incidents. Nevertheless, there is a need for extensive, multicenter prospective studies that explore the relationships between CEUS observations and patient clinical outcomes in cases of carotid atherosclerotic disease.

Advances in Noninvasive Carotid Wall Imaging with Ultrasound: A Narrative Review

Carotid atherosclerosis is a major cause for stroke, with significant associated disease burden morbidity and mortality in Western societies. Diagnosis, grading and follow-up of carotid atherosclerotic disease relies on imaging, specifically ultrasound (US) as the initial modality of choice. Traditionally, the degree of carotid lumen stenosis was considered the sole risk factor to predict brain ischemia. However, modern research has shown that a variety of other imaging biomarkers, such as plaque echogenicity, surface morphology, intraplaque neovascularization and vasa vasorum contribute to the risk for rupture of carotid atheromas with subsequent cerebrovascular events. Furthermore, the majority of embolic strokes of undetermined origin are probably arteriogenic and are associated with nonstenosing atheromas. Therefore, a state-of-the-art US scan of the carotid arteries should take advantage of recent technical developments and should provide detailed information about potential thrombogenic (/) and emboligenic arterial wall features. This manuscript reviews recent advances in ultrasonographic assessment of vulnerable carotid atherosclerotic plaques and highlights the fields of future development in multiparametric arterial wall imaging, in an attempt to convey the most important take-home messages for clinicians performing carotid ultrasound.

Diagnostic Performance of Atherosclerotic Carotid Plaque Neovascularization with Contrast-Enhanced Ultrasound: A Meta-Analysis

Objectives

To evaluate the diagnostic performance of contrast-enhanced ultrasound (CEUS) for atherosclerotic carotid plaque neovascularization.

Methods

The electronic databases like PubMed, Embase, OVID, and Web of Science were used to search for the relevant studies, which are involved in the evaluation of the diagnostic parameters of QUS for atherosclerotic carotid plaque neovascularization. Review Manager 5.4 and Stata 14.0 were used to estimate the pooled diagnostic value of CEUS. Forest plots, sensitivity analysis, and Deeks' funnel plots were performed on the included studies.

Results

Ten studies eventually met the final inclusion criteria. For diagnostic performance, CUES showed that the pooled values of sensitivity, specificity, positive likelihood odds ratios, negative likelihood odds ratios, and diagnostic odds ratios were 0.83 (95% CI 0.78-0.86), 0.77 (95% CI 0.68-0.84), 3.61 (95% CI 2.59-5.03), 0.23 (95% CI 0.18-0.28), and 16.02 (95% CI 10.02-25.60), respectively. The estimate of the area under curve (AUC) was 0.85 (95% CI 0.82-0.88).

Conclusion

Our research supported that CEUS had high sensitivity and specificity in the diagnosis of atherosclerotic carotid plaque neovascularization. More high-quality prospective multicenter studies focusing on the accuracy of CEUS for carotid atherosclerotic plaque should be performed to verify our conclusions.

Advance ultrasound techniques for the assessment of plaque vulnerability in symptomatic and asymptomatic carotid stenosis: a multimodal ultrasound study

Background

Advanced carotid ultrasound techniques may be useful in characterizing plaque vulnerability, but comprehensive studies are still lacking. The aim of this study was to identify factors associated with vulnerable plaques using advanced ultrasound techniques.

Methods

This is a prospective observational study of patients with >50% internal carotid stenosis (ICA). All patients underwent conventional ultrasound, superb microvascular imaging (SMI) and shear wave elastography (SWE) examinations. Plaque size, echogenicity, stiffness and intraplaque neovascularization (IPN) were assessed and compared between symptomatic and asymptomatic groups. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic performance of SWE and SMI of the vulnerable plaques.

Results

The final analysis included 123 patients (78.9% male; mean age, 66±8 years), 65 were enrolled in the symptomatic group, and 58 were enrolled in the asymptomatic group. The mean elasticity was 78.1±25.4 kPa for asymptomatic and 51.5±18.3 kPa for symptomatic plaques. Symptomatic plaques showed higher visual IPN grades on SMI than asymptomatic plaques (P<0.001). Multivariate regression analysis showed that plaque stiffness (PS) (OR 0.95, 95% CI, 0.919-0.974) and IPN level (OR 4.17, 95% CI, 2.008-8.664) were independently associated with symptomatic plaques. The combination of the two factors had a preferable accuracy to discriminate symptomatic plaques (AUC 0.89, 95% CI, 0.827-0.944).

Conclusions

Advanced carotid ultrasound techniques can identify plaque characteristics that are associated with ischemic events and may be potentially indicative of plaque vulnerability. These factors may ultimately be used in the clinical management of carotid stenosis.

Contrast imaging ultrasound for the detection and characterization of carotid vulnerable plaque

Not only the degree of luminal narrowing but also the plaque morphology and composition play an important role in risk stratification of carotid atherosclerotic lesions. During the last few years, carotid contrast-enhanced ultrasound (CEUS) has emerged as a valuable imaging tool to assess such vulnerable carotid plaques. This review article discussed the use of CEUS for the detection of carotid plaque irregularities and ulcerations as well as the quantification of intraplaque neovascularization and its correlation with histology and inflammatory biomarkers. Apart from evaluating for markers of vulnerable carotid plaques, CEUS enhancement is directly associated with past cerebrovascular events. More importantly, preliminary evidence has shown that CEUS could be used to predict future cerebrovascular and cardiovascular events. Despite the progress in CEUS imaging for carotid atherosclerotic disease, past studies still suffer from the retrospective nature, small sample size, and a lack of matched, well controlled prospective studies. In the future, large multi-center prospective studies addressing the relationship between CEUS findings and patient clinical outcomes in carotid atherosclerotic disease are warranted.

Ultrasonography of vulnerable atherosclerotic plaque in the carotid arteries: B-mode imaging

The most common type of stroke, i.e. ischemic stroke, is a great challenge for contemporary medicine as it poses both diagnostic and therapeutic difficulties. Atherosclerosis, which is rapidly beginning to affect more and more social groups, is the main cause of cerebrovascular accidents. Atherosclerosis is currently defined as a generalized, dynamic and heterogeneous inflammatory and immune process affecting arterial walls. Atherosclerotic plaque is the emanation of this disease. As the paradigm of the diagnosis of atherosclerosis has changed, it has become crucial to properly identify plaque instability within the carotid arteries by evaluating parameters and phenomena that signify a developing cascade of complications, eventually leading to stroke. Irrespective of the ultrasound technique employed, proper morphological evaluation of atherosclerotic plaque, involving observation of its echogenicity, i.e. subjective analysis of its structure, with the classification to Gray-Weale–Nicolaides types as well as assessment of the integrity of its surface, makes it possible to roughly evaluate plaque morphology and thereby its stability. This enables treatment planning and therapy monitoring. This evaluation should be a prelude to further diagnostic work-up, which involves non-invasive examinations that enable unambiguous assessment of plaque stability. These examinations include contrast-enhanced ultrasound to assess progression or recession of inflammation, which presents as plaque neovascularization, or shear wave elastography to objectively define tissue stiffness, and thereby its mineralization.

Contrast-enhanced ultrasonography for assessing neovascularization of carotid atherosclerotic plaque

Neovascularization of a carotid atherosclerotic plaque (AP) is associated with an increased risk of stroke. Contrast-enhanced ultrasonography (CEUS) is a widely used method for imaging intraplaque neovascularization in vivo. Unfortunately, there are no standardized guidelines for CEUS interpretation. The aim of this study was to identify the most reliable method for CEUS-based assessment of AP neovascularization. Seventy-eight AP were removed during carotid endarterectomy in 73 patients, of whom 5 had AP on both sides, and examined morphologically. All patients underwent preoperative duplex scanning and CEUS; Sonovue was used as a contrast agent. AP neovascularization was assessed on a 4-grade visual scale and with 3 different quantitative methods using QLAB software. On the visual scale (method 1), poorly (37%) and moderately (51%) vascularized plaques were the most common. Quantitative analysis (data were presented as Me (Q1; Q3)) revealed that the number of blood vessels per 1 cm2 of the plaque (method 2) was 16 (10; 26), the ratio of the total vessel area to the plaque area (method 3) was 6% (3; 9), and AP ROI (method 4) was 2.6 dB (1.8; 4.1). Significant correlations were demonstrated between the results produced by method 2 and method 3 (р < 0.0001), method 3 and method 2 (p = 0.0006), and between pathomorphological findings and the results produced by methods 1–3, especially method 2 (p < 0.004). AP ROI brightness did not correlate with other results. The presence of hyperechoic components (calcifications) in AP dramatically reduced the reliability of US-based intraplaque neovascularization assessment. The most accurate CEUS-based quantitative method for assessing intraplaque neovascularization is estimation of blood vessel number per 1 cm2 of the plaque.

Multiparametric ultrasound evaluation with CEUS and shear wave elastography for carotid plaque risk stratification

PURPOSE

To assess the diagnostic effectiveness of Multiparametric ultrasound (MPUS), which includes color Doppler ultrasound (CDUS), CEUS and Shear wave elastography (SWE), for evaluating carotid plaque as compared with CT-angiography (CTA) and histology.

MATERIALS AND METHODS

Forty-three consecutive patients scheduled to undergo carotid endarterectomy underwent MPUS. Then, after periods ranging from 2 days to 2 weeks, all underwent CTA. Each plaque was classified by means of dedicated scores for CEUS and SWE as compared with CTA features. At surgery, each plaque was removed in a single fragment to facilitate histological analysis, which evaluated 4 features: extension of the lipid core, thickness of the fibrous cap, inflammatory infiltrate (CD68 + and CD3 + markers) and the presence of intraplaque microvessels. For the CEUS, SWE and CTA, the following values for identifying plaque vulnerability were evaluated: sensitivity, specificity, accuracy, negative predictive value (NPV), positive predictive value (PPV) and Area under the curve (AUC). Cohen's kappa was used to evaluate the concordance between measurements in the different imaging methods. A p < 0.05 was considered statistically significant.

RESULTS

At histology, 31 out of 43 plaques were identified as vulnerable because of the presence of at least one of the following criteria: fibrous cap < 200 μm, lipid core, intraplaque hemorrhage, inflammatory infiltrate or intraplaque neovascularization. CTA showed a sensitivity of 87.1%, a specificity of 100%, a PPV of 100%, an NPV of 75% and an AUC of 93.5%. SWE showed a sensitivity of 87.1%, a specificity of 66.7%, a PPV of 87.1%, an NPV of 66.7% and an AUC of 76.9%. CEUS showed a sensitivity of 87.1%, a specificity of 58.3%, a PPV of 84.4%, an NPV of 63.6% and an AUC of 72.7%.

CONCLUSIONS

Multiparametric ultrasound is an effective modality to obtain comprehensive information on carotid plaques. Further studies are needed to determine whether it can be considered a diagnostic standard.

Contrast-enhanced ultrasound of the carotid system: a review of the current literature

Carotid disease is a major current health problem accounting for a significant part of stroke patients. Ultrasound with colour Doppler and spectral analysis is the primary imaging technique used for screening and diagnostic evaluation of the extracranial part of carotid arteries offering identification and grading of carotid disease. However, inherent limitations of this technique include flow-related artefacts like Doppler angle dependence and aliasing artefact which may sometimes hinder complete assessment of a stenotic part of the vessel, potentially failing to address clinically significant differential diagnosis issues. The intravenous use of microbubbles as an US contrast agent has been introduced for the supplementation of conventional technique. The value of contrast-enhanced ultrasound (CEUS) has been investigated in the evaluation of carotid disease leading to promising results. CEUS provides improved flow visualization free of artefacts and detailed plaque surface delineation, thus being able to accurately grade stenosis, identify carotid plaque ulcerations, differentiate occlusion from highly stenotic plaques and identify carotid dissection. Furthermore, microbubbles can be used to identify and grade intraplaque neovascularization, carotid wall inflammation in patients with arteritis, follow-up patients after carotid intervention and assist interventional procedures reducing the need for nephrotoxic contrast agents. The purpose of this review is to present and discuss the current literature regarding the various uses of CEUS in carotid arteries.

Motion Compensated Ultrasound Imaging Allows Thermometry and Image Guided Drug Delivery Monitoring from Echogenic Liposomes

Ultrasound imaging is widely used both for cancer diagnosis and to assess therapeutic success, but due to its weak tissue contrast and the short half-life of commercially available contrast agents, it is currently not practical for assessing motion compensated contrast-enhanced tumor imaging, or for determining time-resolved absolute tumor temperature while simultaneously reporting on drug delivery. The objectives of this study were to: 1) develop echogenic heat sensitive liposomes (E-LTSL) and non-thermosensitive liposomes (E-NTSL) to enhance half-life of contrast agents, and 2) measure motion compensated temperature induced state changes in acoustic impedance and Laplace pressure of liposomes to monitor temperature and doxorubicin (Dox) delivery to tumors. LTSL and NTSL containing Dox were co-loaded with an US contrast agent (perfluoropentane, PFP) using a one-step sonoporation method to create E-LTSL and E-NTSL. To determine temperature induced intensity variation with respect to the state change of E-LTSL and E-NTSL in mouse colon tumors, cine acquisition of 20 frames/second for about 20 min (or until wash out) at temperatures of 42°C, 39.5°C, and 37°C was performed. A rigid rotation and translation was applied to each of the "key frames" to adjust for any gross motion that arose due to motion of the animal or the transducer. To evaluate the correlation between ultrasound (US) intensity variation and Dox release at various temperatures, treatment (5 mg Dox/kg) was administered via a tail vein once tumors reached a size of 300-400 mm(3), and mean intensity within regions of interest (ROIs) defined for each sample was computed over the collected frames and normalized in the range of [0,1]. When the motion compensation technique was applied, a > 2-fold drop in standard deviation in mean image intensity of tumor was observed, enabling a more robust estimation of temporal variations in tumor temperatures for 15-20 min. due to state change of E-LTSL and E-NTSL. Consequently, a marked increase in peak intensity at 42°C compared to 37°C that corresponded with enhanced Dox delivery from E-LTSL in tumors was obtained. Our results suggest that echogenic liposomes provide a predictable change in tumor vascular contrast with temperature, and this property could be applicable to nanomonitoring of drug delivery in real time.

Contrast-enhanced ultrasound: clinical applications in patients with atherosclerosis

Contrast-enhanced ultrasound (CEUS) is increasingly being used to evaluate patients with known or suspected atherosclerosis. The administration of a microbubble contrast agent in conjunction with ultrasound results in an improved image quality and provides information that cannot be assessed with standard B-mode ultrasound. CEUS is a high-resolution, noninvasive imaging modality, which is safe and may benefit patients with coronary, carotid, or aortic atherosclerosis. CEUS allows a reliable assessment of endocardial borders, left ventricular function, intracardiac thrombus and myocardial perfusion. CEUS results in an improved detection of carotid atherosclerosis, and allows assessment of high-risk plaque characteristics including intraplaque vascularization, and ulceration. CEUS provides real-time bedside information in patients with a suspected or known abdominal aortic aneurysm or aortic dissection. The absence of ionizing radiation and safety of the contrast agent allow repetitive imaging which is particularly useful in the follow-up of patients after endovascular aneurysm repair. New developments in CEUS-based molecular imaging will improve the understanding of the pathophysiology of atherosclerosis and may in the future allow to image and directly treat cardiovascular diseases (theragnostic CEUS). Familiarity with the strengths and limitations of CEUS may have a major impact on the management of patients with atherosclerosis.

Contrast-enhanced ultrasonography of the carotids

Contrast-enhanced ultrasonography of the carotids has recently emerged as a complementary examination to conventional carotid Doppler ultrasonography. It is an examination providing improved visualization of the vascular lumen, more accurate and detailed delineation of the vascular wall, and identification of atherosclerotic plaques. Moreover, contrast-enhanced ultrasonography has specific advantages over conventional ultrasonography and plays an important role in the diagnosis of the vulnerable carotid plaque, as it can identify intraplaque neovascularization and carotid plaque ulceration. Given the specific advantages and improved imaging of the carotids provided by this method, radiologists should be familiar with it. This pictorial essay illustrates the advantages of this technique and discusses its value in the imaging of carotid arteries.