Atherosclerosis and atheroma plaque rupture: imaging modalities in the visualization of vasa vasorum and atherosclerotic plaques

Abstract

Invasive angiography has been widely accepted as the gold standard to diagnose cardiovascular pathologies. Despite its superior resolution of demonstrating atherosclerotic plaque in terms of degree of lumen stenosis, the morphological assessment for the plaque is insufficient for the analysis of plaque components, and therefore, unable to predict the risk status or vulnerability of atherosclerotic plaque. There is an increased body of evidence to show that the vasa vasorum play an important role in the initiation, progression, and complications of atherosclerotic plaque leading to major adverse cardiac events. This paper provides an overview of the evidence-based reviews of various imaging modalities with regard to their potential value for comprehensive characterization of the composition, burden, and neovascularization of atherosclerotic plaque.

Figure 1

Volume-rendered micro-CT imaging of a coronary plaque and vasa vasorum. Volume-rendered 3D micro-CT image of a right coronary artery showing the main coronary lumen in red; noncalcified and calcified plaque areas are indicated by the arrows (noncalcified plaque is transparent). Vasa vasorum (VV) are shown in light blue (VV externa) or red (VV interna, directly originating from the main lumen). Reprint with permission from [23].

Figure 2

Vasa vasorum blood volume on contrast-enhanced ultrasound imaging. Examples of maximum intensity projection images 2 s after the destructive pulse sequence are shown for femoral arteries 2 weeks after injection of either saline (a) or whole blood (b), illustrating a greater vasa vasorum (VV) density (arrows) in the latter. (c) Example of pixel intensity threshold analysis for the blood-injected vessel whereby pixels within the region of interest that enhance beyond threshold intensity are displayed in red-orange color scale and those that do not are displayed in blue. (d) Mean (± standard error of the mean) area of enhancement on pixel intensity threshold analysis, an index of functional VV blood density. Data for contralateral noninjected control vessels were similar between treatment cohorts and are grouped. *P < 0.05 versus control contralateral artery; ^† P < 0.05 versus both contralateral and saline-injected arteries (corrected for multiple comparisons). Reprint with permission from [41].

Figure 3

Depiction of qualitative representation of enhancement. Unprocessed images are displayed (a) before, (b) during, and (c) after injection of microbubbles. Corresponding processed images are displayed in (d)–(f). Enhancement is graded from minimal (blue) to maximal (red). Values are a percentage of the maximum grey level intensity difference (255). Arrows indicate points of intense, stable enhancement at the media-adventitia border. Diffuse points of enhancement are present nearby. Reprint with permission from [53].

Figure 4

Representative OCT images of coronary plaque with microchannels. (a), (b) Two consecutive cross-sectional OCT images. Eccentric lipid-rich plaque (L) was imaged. Two microchannels (arrow) were located in thickened intima at shoulder region of plaque. (c) Proximal site adjacent to plaque imaged in Figures (a) and (b). Two microchannels (arrow) were located in thickened intima at 7-o'clock position. Intracoronary thrombus (arrowhead) was also visualized. (d) Minimum lumen area site. Lipid-rich plaque was visualized. (e) Lipid-rich plaque covered by thin fibrous cap (50 μm) imaged and found to be thin cap fibroatheroma. Reprint with permission from [69].

Figure 5

Vasa vasorum images in a 63-year-old man with hypertension. Adventitial transfer constant was 0.129 min⁻¹ before therapy and 0.099 min⁻¹ after 1-year treatment. There was subtle gradation of color in adventitial zone (arrows). Reprint with permission from [91].