Contrast-enhanced ultrasound: clinical applications in patients with atherosclerosis

Carotid stenosis - basing treatment on individual patients' needs. Optimal medical therapy alone or accompanied by stenting or endarterectomy

Though carotid artery stenosis is a known origin of stroke, risk assessment and treatment modality are not yet satisfactorily established. Guideline updates according to latest evidence are expected shortly. Current clinical weakness concerns in particular the identification of "at-risk" patients. Beside the symptomatic status and the degree of stenosis, further signs of unstable plaque on carotid and cerebral imaging should be considered. Moreover, medical and endovascular therapy are continuously improving. Randomized trials and meta-analyses have shown similar long-term results for protected carotid artery stenting and endarterectomy. However, endovascular revascularization was associated with an increased 30-day rate of minor strokes. Newly developed embolic protection devices could possibly compensate for this disadvantage. Furthermore, high-level optimal medical therapy alone is currently being evaluated comparatively. We assume that a comprehensive evaluation of plaque vulnerability, serious consideration of advanced embolic protection, and more space for optimal medical therapy alone according to latest evidence, will benefit patients with carotid stenosis.

Contrast-enhanced ultrasound with a novel nanoparticle contrast agent for clinical diagnosis in patients with non-small cell lung cancer

Non-small cell lung cancer (NSCLC) initiates in the non-small cells of the lung and is one of the most common types of human cancer. It is known for its rapid growth, easy migration, invasion and reoccurrence, and has the highest incidence rate of all types of cancer. Early detection of NSCLC is difficult to achieve and this is the primary reason for low survival rates in NSCLC. Contrast-enhanced ultrasound is the most common application for evaluating patients diagnosed with NSCLC. In the present study, a contrast-enhanced ultrasound combined with nanoparticles was performed with the aim of identifying patients with NSCLC at an early stage. The present study evaluated the effectiveness of administering a nanoparticle contrast agent through respiration in combination with enhanced ultrasound at improving image quality compared with traditional ultrasound. This maybe a novel method of detecting early-stage tumors in patients. There are numerous benefits to conducting diagnoses of NSCLC using contrast-enhanced ultrasound. It is a non-invasive imaging modality, induces little pain, has a low cost, an extensive range and produces high-resolution images. This means that it is safer and more beneficial to use in patients with NSCLC than conventional imaging examinations, including X-ray and bronchoscopy. Furthermore, the nanoscale microbubble contrast agent containing liposome-encapsulated epidermal growth factor receptor was inhaled by nebulization, which may lead to an enhanced ultrasound image. The sensitivity of contrast-enhanced ultrasound was investigated in mice with early stage NSCLC. The results indicated that ultrasound administrated with nanoscale microbubble enhanced sensitivity and improved image quality compared with simple ultrasound. Furthermore, enhanced ultrasound resulted in a reliable and sensitive assessment of tumor mass in early-stage tumors. Altogether, contrast-enhanced ultrasound facilitated the efficient detection of NSCLC in patients in situ at an early stage. This protocol improved the understanding of the pathophysiology of NSCLC and may be applied in the detection of early-stage tumors in patients suspected of having cancer.

Guided longer pulses from a diagnostic ultrasound and intraclot microbubble enhanced catheter-directed thrombolysis in vivo

The mechanism of ultrasound thrombolysis (UT) is generally attributed to cavitation. The insufficiency of microbubbles (MB) to serve as cavitation nuclei in the vessel-obstructing thrombi significantly reduces the effectiveness of UT. Taking advantage of the widely performed catheter-directed therapy (CDT), in a thrombo-embolized rabbit IVC model with a simultaneous catheter directed rt-PA thrombolysis procedure, guided moderate mechanical index longer pulses from a modified diagnostic ultrasound transducer, combined with an intraclot infusion of MB, significantly accelerated the thrombolysis process. The higher thrombolysis efficacy score and consistent elevated post-treatment plasma concentration level of D-Dimer, a product of fibrinolysis, both indicated the superiority of CDT + UT over CDT/UT alone. Pathologic examination of the treated occluded IVC segments revealed an almost complete dissolution of the thrombi treated with CDT + UT. There was no evidences of thrombo-embolism or local thrombus formation in the cardiac-pulmonary vessels. Combined with intraclot infusion of MB, guided longer pulse ultrasound from a diagnostic transducer is able to safely and significantly improve a catheter-directed thrombolysis procedure. It thus has the potential to achieve earlier clot removal, administration of a lower dosage of thrombolytic agent and, consequently, a lower incidence of thrombolysis-related side effects.

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.

Imaging of the ulcerated carotid atherosclerotic plaque: a review of the literature

Abstract

Carotid atherosclerotic disease constitutes a major modern health problem whose diagnosis primarily relies on imaging. Grading of stenosis has been long used as the main factor for risk stratification and guiding of management. Nevertheless, increasing evidence has shown that additional plaque characteristics such as plaque composition and surface morphology play an important role in the occurrence of symptoms, justifying the term “vulnerable plaque”. Carotid plaque surface characteristics either in the form of surface irregularities or ulceration represent an important factor of vulnerability and are associated with the occurrence of neurologic symptoms. The delineation of the carotid plaque surface can be performed with virtually all imaging modalities including ultrasound, contrast-enhanced ultrasound, multi-detector computed tomography angiography, magnetic resonance angiography and the traditional reference method of angiography. These techniques have shown varying levels of diagnostic accuracy for the identification of ulcerated carotid plaques or plaque surface irregularities. As a consequence and given its high clinical significance, radiologists should be familiar with the various aspects of this entity, including its definition, classification, imaging findings on different imaging modalities and associations. The purpose of this review is to present the current literature regarding carotid plaque ulcerations and present illustrative images of ulcerated carotid plaques.

Teaching Points

• Plaque surface and ulceration represent risk factors for stroke in carotid disease.

• Characterisation of the plaque surface and ulcerations can be performed with every modality.

• US is the first-line modality for carotid disease and identification of ulcerations.

• The administration of microbubbles increases US accuracy for diagnosis of carotid ulceration.

• MDCTA and MRA are valuable for diagnosing ulceration and evaluating plaque composition.

Myocardial Contrast Agents – Safety Considerations and Clinical Efficacy in Stress Echocardiography

Transthoracic echocardiographic examination is known to be a safe, non-invasive and reproducible method, used in every day clinical practice to obtain important information about cardiac structure and function. Unfortunately, a significant proportion of studies have highlighted the considerable technically difficultly in producing diagnostic images due to a poor acoustic window and more than 33% of patients undergoing stress echocardiography have suboptimal echocardiographic images. All these limitations have led to the use of contrast agents to improve the quality of standard ultrasound examination to provide a better delineation of left ventricle endocardial borders or to obtain information that cannot be achieved by using standard echocardiography, such as assessing myocardial microcirculation and therefore perfusion. This paper sought to review the clinical efficacy and safety of ultrasound contrast agents focusing on stress echocardiography.

Molecular Imaging of Vulnerable Atherosclerotic Plaques in Animal Models

Atherosclerosis is characterized by intimal plaques of the arterial vessels that develop slowly and, in some cases, may undergo spontaneous rupture with subsequent heart attack or stroke. Currently, noninvasive diagnostic tools are inadequate to screen atherosclerotic lesions at high risk of acute complications. Therefore, the attention of the scientific community has been focused on the use of molecular imaging for identifying vulnerable plaques. Genetically engineered murine models such as ApoE^−/− and ApoE^−/−Fbn1C1039G^+/− mice have been shown to be useful for testing new probes targeting biomarkers of relevant molecular processes for the characterization of vulnerable plaques, such as vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, intercellular adhesion molecule (ICAM)-1, P-selectin, and integrins, and for the potential development of translational tools to identify high-risk patients who could benefit from early therapeutic interventions. This review summarizes the main animal models of vulnerable plaques, with an emphasis on genetically altered mice, and the state-of-the-art preclinical molecular imaging strategies.