The limitations inherent to angiography served as a technological springboard for the development of other devices in search of better visualization, quantification, and identification of the coronary vasculature and assessment of the efficacy of subsequent clinical therapeutics. Intravascular ultrasound (IVUS) was invented and introduced to clinical practice in the late 1980s as an invasive intravascular imaging device. As a front-runner in this field, IVUS has greatly contributed to the investigation of the pathophysiology of coronary artery disease in symptomatic patients and to the guidance of percutaneous coronary interventions (PCI).
Since the early 2000s, optical coherence tomography (OCT), which was first introduced in the ophthalmology field, has been applied to human intravascular imaging. Apart from these intravascular imaging systems, spectroscopy has also begun to gather attention as a device to determine plaque components. Spectroscopy provides adjunctive information when used with IVUS, though current clinical applications are limited to the detection of cholesterol within the vessel wall.
This chapter will provide information related to concrete usage and tips of adjunctive intravascular imaging devices as well as to review evidence and rationale for use as a procedural guide in the cardiac interventional setting.
After the first initial clinical experience by Yock et al. in 1988,1 IVUS has become established as an adjunctive diagnostic device as well as an essential research tool in the cardiac catheterization laboratory. Moreover, its development and findings have been a driving force in the expansion of the intravascular diagnostic field. With a miniaturized ultrasound probe equipped at a tip of an IVUS catheter, a high-frequency ultrasound beam ranging from 20 to 45 megahertz (MHz) is transmitted radially from the probe to a vessel wall and its reflection sound waves are reconstructed to depict a cross-sectional image. The higher frequency ultrasound beam (shorter wave length) than those utilized in noninvasive echocardiography (2-5 MHz, longer wave length) potentiates its high resolution to visualize vessel and intravascular structures, which leads to its low radial penetration of 4 to 8 mm from the IVUS catheter. To improve the resolution of IVUS images, adoption of ultrasound with higher frequency (55-60 MHz) than conventional IVUS is currently underway; this will possibly lead to better interpretation of gray-scale IVUS imaging by improving tissue and plaque differentiation.
There are several intermediate resolution/penetration ultrasound catheter devices for peripheral (15-20 MHz) or intracardiac (intracardiac echocardiography [ICE], 5-10 MHz) uses, specifically developed to guide catheter-based treatments of peripheral vessels and structural heart disease, or catheter ablation. Detailed descriptions of ICE can be found elsewhere in this textbook (see Chapter 13).
Imaging Systems and Image Acquisition Procedure
IVUS imaging systems consist of 3 components: an imaging catheter, a console for imaging reconstruction/display/recording/analysis, and a catheter interface unit with motorized transducer pullback capability. Specifically, 2 types of imaging acquisition processes are applied to commercially available IVUS catheters: ...