Coronary artery tissue characterization with standard grey-scale IVUS image

the imaging of atherosclerosis in patients. Intravascular ultrasound (IVUS) has evolved as a valuable adjunct to angiography, providing insights that are significantly altering conventional paradigms in diagnosis and therapy. IVUS translates the strength (amplitude) of reflected ultrasonic transmissions at the tip of an intravascular catheter equipped with a tiny transducer into gray-scale pixels, which are then combined to create circumferential images representing the anatomical structure of the coronary arteries. Angiography allows evaluation only of the geometry of the unobstructed part of lumen; it cannot provide information on the structure of the coronary artery wall, which is essential to understand the processes leading to plaque progression or regression. IVUS can provide the necessary structural information in situ and the development and refinement of IVUS have provided a powerful in vivo method to assess plaque morphology. The “grey scale” IVUS offers clinicians the ability to detect luminal borders, plaque volumes and calcium deposits within the coronary artery. Extensive research has been conducted on IVUS image analysis for determining plaque composition and compared the ultrasound appearance of plaques to histology. Lipid-laden lesions appear hypoechoic, fibromuscular lesions generate low-intensity echoes, and fibrous or calcified tissues are relatively echogenic. Fibrous plaques are generally thought of as advanced lesions that contain dense fibrous tissue, elastin fibers, and proteoglycans. Calcium obstructs ultrasound penetration, obscuring the underlying vessel wall as acoustic shadowing. The angle subtended by the calcified arc can be used to quantify the severity of calcification. 8) Coronary artery tissue characterization with standard grey-scale IVUS image 1. Normal coronary artery IVUS has the capability to distinguish between muscular (i.e. coronary arteries, external iliac and femoral arteries) and elastic arteries like the aorta and pulmonary arteries. IVUS is capable of discovering intimal thickening, if it exceeds 150 to 200 mm. The intimal thickening increase with age, with average values of 60 mm from 1 to 5 years, 220 mm at 30 and 250 mm at 40 years, which leads to a typical three-layer (intima, media and adventitia) appearance of the coronary arteries (Fig. 1, A). The lumen-intima border and the media-external elastica lamina region can be imaged in great detail, while the external elastica laminaadventitia border is almost newer to distinguish. 10) 2. Plaque calcification Calcification of the coronary arteries is a well-recognized occurrence in the atherosclerotic process and usually signifies complex plaque formation. The deposition of calcium may occur after plaque rupture or thrombosis and is thought to represent a more “mature” point in the natural history of the atherosclerotic lesion. Calcification is easily identified by IVUS because of its high echogenicity. Calcified regions are defined as bright signals (brighter than the reference adventitia) with distal shadowing of underlying tissue (Fig. 1, B). Arcs of calcification can be easily identified on IVUS images, and the location within the atheroma may be characterized as either superficial or deep. 3. Fibrous plaque The fibrous plaque is generally an advanced lesion that contains dense fibrous tissue, collagen and elastic fibers, proteoglycans, and necrotic debris with or without calcification. Dense fibrous plaque, often with small regions of early calcification (Fig. 1, C), may be relatively “senescent,” causing stable anginal symptoms that can readily be treated with medical therapy, catheter-based intervention, or possible bypass surgery. Similar to calcified regions of plaque, dense fibrous plaque components are generally bet-