Virtual histology

Angiography has for decades been the gold standard to assess the morphology and severity of atherosclerotic lesions in the coronary tree. Nevertheless, quantitative angiographic measurements can be deceptive, since this technique only allows the assessment of the shape of the lumen.1 Indeed, coronary angiography as a standard for the assessment of coronary artery disease has two major limitations: first, visual assessment of stenosis severity has high intraobserver and interobserver variabilities; secondly, there is a clear discrepancy between the appearance of the opacified vascular lumen and the actual degree of atherosclerosis. The common finding of mild diffuse disease that involves the whole length of the opacified coronary tree, without a remnant diseasefree reference segment, makes the lumen appear as if it was an atherosclerosis-free area. Although quantitative coronary assessment (QCA) has reduced the visual error, it is known that at the site identified by QCA as the proximal boundary of the lesion, there may exist a 50% area stenosis when such a segment is analyzed by intravascular ultrasound (IVUS).2 Thus, IVUS is the gold standard for evaluation of coronary plaque, lumen, and vessel dimensions; it provides an accurate, reproducible, real-time, tomographic assessment of the vessel wall.3-5 However, although visual interpretation of gray-scale IVUS can characterize plaque composition, particularly calcification, it cannot reliably differentiate lipid-rich from fibrous plaque.4 In contrast, IVUS radiofrequency (RF) data analysis (IVUS virtual histology or IVUSVH) can accurately characterize four tissue types in atherosclerotic plaques.