Characterization of coronary atherosclerosis by intravascular imaging modalities

Abstract

Coronary artery disease (CAD) is highly prevalent in Western countries and is associated with morbidity, mortality, and a significant economic burden. Despite the development of anti-atherosclerotic medical therapies, many patients still continue to suffer from coronary events. This residual risk indicates the need for better risk stratification and additional therapies to achieve more reductions in cardiovascular risk. Recent advances in imaging modalities have contributed to visualizing atherosclerotic plaques and defining lesion characteristics in vivo. This innovation has been applied to refining revascularization procedure, assessment of anti-atherosclerotic drug efficacy and the detection of high-risk plaques. As such, intravascular imaging plays an important role in further improvement of cardiovascular outcomes in patients with CAD. The current article reviews available intravascular imaging modalities with regard to its method, advantage and disadvantage.

Keywords: Atherosclerosis; imaging; plaque.

Figure 1

Plaque phenotypes on gray-scale IVUS. (A) Attenuated plaque: attenuation (asterisk) is observed between 3 to 9 o’clock; (B) echolucent plaque: arrow head indicates echolucent zone in the plaque; (C) calcified nodule: calcified nodule (asterisk) is observed as protrusion of calcified plaque with irregular luminal surface; (D) spotty calcification: arrow indicates small deposit of calcium in the plaque; (E) multiple layer appearance: double arrow heads indicate different layer of the plaque. IVUS, intravascular ultrasound.

Figure 2

Virtual histology intravascular ultrasound (VH-IVUS) derived classification of plaques. (A) Pathological intimal thickening (PIT); (B) thin-cap fibroatheroma (TCFA); (C) thick-cap fibroatheroma (ThCFA); (D) fibrotic plaque; (E) fibrocalcific plaque. VH-IVUS, virtual histology intravascular ultrasound. Reproduce from: Garcia et al. Eur Heart J 2010;3:2456-69. (43).

Figure 3

Images of plaque phenotype on IB-IVUS. Upper panels show grayscale IVUS images while lower panels show corresponding IB-IVUS images. (A) Fibrous plaque; grayscale IVUS shows high echogenic plaque between 12 to 8 o’clock. IB-IVUS image shows that most of plaque is classified into fibrous tissue (green and yellow); (B) lipid-rich plaque: graysclae IVUS image shows attenuated plaque between 6 to 12 o’clock. IB-IVUS image shows that most of plaque is classified into lipid-rich tissue (blue); (C) calcification: grayscale IVUS shows superficial entire-circumference of calcification. Corresponding IB-IVUS image indicates the presence of superficial calcification (red). IB-IVUS, integrated backscatter intravascular ultrasound. IVUS, intravascular ultrasound.

Figure 4

Images of plaque phenotype on OCT. (A) Fibrous plaque: fibrous plaque (asterisk) is imaged as a high backscattering and homogeneous region; (B) lipid-rich plaque: lipid-rich plaque (asterisk) is imaged as a signal-poor region with a poorly delineated borders; (C) fibrocalcific plaque: calcification (arrow head) is imaged by OCT from 12 to 3 o’clock, as well-delineated, signal-poor region; (D) fibrous cap: a fibrous cap (double arrow) is imaged as a signal-rich homogeneous region overlying a lipid core; (E) macrophage: macrophages (arrow heads) are imaged as signal-rich linear regions accompanied by high attenuation; (F) microchannel: microchannels (arrow heads) are imaged as signal poor voids observed in multiple contiguous frames; (G) cholesterol crystal: cholesterol crystal (arrows) is imaged by OCT as linear, high-backscattering structures within the plaque. OCT, optical coherence tomography.

Figure 5

Lipid core plaque in the right coronary artery detected by NIRS-IVUS. (A) Angiography showed stenosis in the mid-right coronary artery. Automated pullback was performed from mid (red arrow head) to proximal right coronary artery (blue arrow head); (B) IVUS image shows plaque between 9 to 4 o’clock. The ring around the IVUS image represents the NIRS values. High probability of lipid core plaque is displayed as yellow and low probability as red. At this lesion, NIRS indicated no lipid core plaque; (C) the cross sectional IVUS image shows with superficial calcification and resultant shadowing in the mid-right coronary artery. NIRS showed nearly circumferential lipid core plaque; (D) this figure shows “chemogram” of the right coronary artery between red arrow head and blue arrow head. (B’) Corresponds to Figure 5B lesion, while (C’) corresponds Figure 5C lesion. NIRS, near infrared spectroscopy; IVUS, intravascular ultrasound.

Figure 6

Classification of plaques by the yellowness of plaques on angioscopy image. Coronary plaques are classified by angioscopy according to the yellowness as follows: grade 0 = white; grade 1 = light yellow; grade 2 = yellow; grade 3 = intensive yellow.