Intravascular Ultrasound

Abstract

Intravascular ultrasound (IVUS) is a valuable adjunct to angiography, providing new insights in the diagnosis of and therapy for coronary disease. Angiography depicts only a 2D silhouette of the lumen, whereas IVUS allows tomographic assessment of lumen area, plaque size, distribution, and composition. The safety of IVUS is well documented, and the assessment of luminal dimensions represents an important application of this modality. Comparative studies show the greatest disparities between angiography and ultrasound after mechanical interventions. In young subjects, normal intimal thickness is typically approximately 0.15 mm. With IVUS, lipid-laden lesions appear hypoechoic, fibromuscular lesions generate low-intensity echoes, and fibrous or calcified tissues are echogenic. Calcium obscures the underlying wall (acoustic shadowing). The extent and severity of disease by angiography and ultrasound are frequently discrepant. Arterial remodeling refers to changes in vascular dimensions during the development of atherosclerosis. At diseased sites, the external elastic membrane may actually shrink in size, contributing to luminal stenosis. The interpretation of IVUS relies on simple visual inspection of acoustic reflections to determine plaque composition. However, different tissue components may look quite similar, and artifacts may adversely affect ultrasound images. IVUS commonly detects occult disease in angiographically "normal" sites. In ambiguous lesions, ultrasound permits lesion quantification, particularly for left main coronary disease. IVUS has emerged as the optimal method for the detection of transplant vasculopathy. An important potential application of ultrasound is the identification of atheromas at risk of rupture. The mechanisms of action of interventional devices have been elucidated using IVUS, and ultrasound is used by some operators to select the most suitable interventional device. IVUS-derived residual plaque burden is the most useful predictor of clinical outcome. In restenosis after balloon angioplasty, negative remodeling is a major mechanism of late lumen loss. IVUS is not routinely used for stent optimization, and there is no consensus regarding optimal procedural end points. Ultrasound has proven useful in evaluating brachytherapy. New and emerging applications for IVUS are continuing to evolve, particularly in atherosclerosis regression-progression trials.

Use of Ultrasound for Non-Invasive Assessment of Flow-Mediated Dilation

“…Although atherosclerosis is commonly described as the presence of plaques that obstruct the lumen of the conduit arteries, endothelial dysfunction precedes plaque formation [14][15][16] . Reduced endothelial responses can be observed early in the course of atherogenesis, preceding angiographic or ultrasonic evidence of atherosclerotic plaque 13) .…”

Development of a catheter for combined intravascular ultrasound and photoacoustic imaging

“…7 For example, the ultrasoundbased technique-intravascular ultrasound ͑IVUS͒ imaging-can be used to image the atherosclerotic plaques in arteries. [8][9][10] This minimally invasive catheter-based approach is suitable to detect unrecognized disease, lesions of uncertain severity ͑40%-75% stenosis͒, and risk of stratification of atherosclerotic lesions in interventional practice. [10][11][12] The two clinically approved IVUS imaging systems are based on catheter with either mechanically scanned single-element transducer operating at up to 40 MHz or electronically scanned 64 element array transducer operating in the 20 MHz range.…”

Detection of inflamed atherosclerotic lesions with diadenosine-5′,5‴- P 1 , P 4 -tetraphosphate (Ap 4 A) and positron-emission tomography

“…Molecular imaging probes and techniques based on intravascular MRI, computed tomography (CT), ultrasound, and optical coherence tomography have been proposed for accurate identification of atherosclerotic plaque, plaque formation, and vul- Abbreviations: AppCHClppA, P 2 ,P 3 -monochloromethylene diadenosine-5Ј,5ٞ-P 1 ,P 4 -tetraphosphate; Ap4A, diadenosine-5Ј,5ٞ-P 1 ,P 4 (3,(14)(15)(16)(17)(18)(19)(20)(21)(22). A limited number of reports describe noninvasive visualization of atherosclerotic lesions.…”