「画像診断の進歩」循環器画像診断の進歩―冠動脈の画像診断法を中心に―

Abstract

Cardiovascular imaging can be divided into 2 groups: non-invasive imaging, such as echocardiography, multi-slice CT, and MRI, and invasive imaging, such as coronary angiography (CAG), intravascular ultrasound (IVUS), coronary angioscopy and optical coherence tomography (OCT). Although CAG has been widely used to diagnose ischemic heart disease, there are limitations to its utility, because CAG reveals only the lumen of coronary arteries. IVUS directly visualizes three-dimensional coronary vessels and precisely measures the plaque area, lumen area, and vessel area, as well as plaque volume, lumen volume and vessel volume. Recently, novel IVUS images have been generated using radiofrequency analysis of ultrasound signals to evaluate the tissue characteristics of the plaque components. Coronary angioscopy is another method to visualize plaque surface and evaluate yellow plaques and various kinds of thrombi. There are numerous yellow plaques in addition to culprit lesion in patients with previous myocardial infarction, and these findings are helpful in the management of coronary risk factors. This modality is also useful to evaluate neointimal coverage after stent implantation, because neointimal coverage after application of a drug-eluting stent is usually delayed compared to that with a bare metal stent. OCT provides very high-resolution images. Because the axial resolution is 10 μm, OCT is able to measure the precise thickness of the fibrous cap above the lipid core within the plaque. The information obtained based on the findings of these images is very useful to applying optimal antiplatelet therapy to patients after stent implantation as secondary prevention during long-term statin treatment.