Histology Validation of Optical Coherence Tomography Images

Abstract

Optical coherence tomography (OCT) can reliably visualize the microstructure (i.e., 10–50 μm) of normal and atherosclerotic arteries. Typically, the media of the coronary artery appears as a lower signal intensity band relative to that of the intima and adventitia, providing a three-layered appearance (bright–dark–bright). In OCT images, fibrous plaques exhibit homogeneous, signal-rich (highly backscattering) regions; lipid-rich plaques exhibit signal-poor regions (lipid pools) with poorly defined borders and overlying signal-rich bands (corresponding to fibrous caps); and fibrocalcific plaques exhibit signal-poor regions with sharply delineated upper and/or lower borders. Studies have also assessed the ability of OCT to detect vulnerable plaque. A thin fibrous cap of vulnerable plaque, commonly named thin-cap fibroatheroma (TCFA), has a fibrous cap thickness of <65 μm. Although the ability of OCT to characterize a lipid pool containing necrotic core needs to be clarified in future histologic studies, OCT could visualize thin (<65 μm) fibrous cap overlying the necrotic core and thus detect TCFA. Infiltration of macrophages within the fibrous cap is another characteristic of vulnerable plaque. In OCT images, macrophage accumulation is seen as signal-rich, confluent punctuate regions that exceed the intensity of background speckle noise. The unique capabilities of OCT as an investigational tool for high-risk lesions will serve the cardiology community well, as it advances us toward a better understanding of atherosclerotic plaque. This information will improve our ability to more precisely treat our patients, both acutely and in the long term.