Carotid plaque imaging and the risk of atherosclerotic cardiovascular disease

Abstract

Carotid artery plaque is a measure of atherosclerosis and is associated with future risk of atherosclerotic cardiovascular disease (ASCVD), which encompasses coronary, cerebrovascular, and peripheral arterial diseases. With advanced imaging techniques, computerized tomography (CT) and magnetic resonance imaging (MRI) have shown their potential superiority to routine ultrasound to detect features of carotid plaque vulnerability, such as intraplaque hemorrhage (IPH), lipid-rich necrotic core (LRNC), fibrous cap (FC), and calcification. The correlation between imaging features and histological changes of carotid plaques has been investigated. Imaging of carotid features has been used to predict the risk of cardiovascular events. Other techniques such as nuclear imaging and intra-vascular ultrasound (IVUS) have also been proposed to better understand the vulnerable carotid plaque features. In this article, we review the studies of imaging specific carotid plaque components and their correlation with risk scores.

Keywords: Radiology; atherosclerotic cardiovascular disease (ASCVD); carotid plaque; risk score.

Figure 1

Imaging features of plaque vulnerability. Six features of carotid plaque vulnerability are shown in columns, and images were obtained by CT (upper row), MRI on a 3 Tesla scanner (middle row), and ultrasound (lower row). On ultrasound images, red colour indicates orthograde flow and blue colour shows retrograde flow. In the first column (intraplaque haemorrhage) and second column (LRNC), the arrow points to the feature detected. In the third column (neovascularisation), the arrows and green circles in the pre-contrast and post-contrast CT images (upper row) show how Hounsfield units increase after administration of contrast material. Similarly, in the MRI panel (middle row), after gadolinium contrast, the plaque (arrow) shows a significant increase in signal intensity because of enhancement of the plaque. The ultrasound images (lower row) show significant enhancement in the plaque (arrow) because of the presence of microbubble. Early phase is after 30 s and delayed phase is after 120 s. In the fourth column (carotid plaque thickness), the arrows indicate the plaque and the red dotted lines show the thickness of the plaque. The green dotted line in the ultrasound image represents the outer lumen of the plaque. In the fifth column (surface morphology), the arrows in all images show the ulcer. In the ultrasound images, the two panels show the difference in sensitivity using conventional B-mode colour Doppler and microbubble injection. In this case, the ulcer is visible only with the microbubble technique. The sixth column shows carotid plaque volume analysis and tissue segmentation. The red line shows the inner boundaries of the carotid plaque wall; the yellow line shows the outer boundary of the carotid plaque wall; the green colour represents the fatty component; the blue colour indicates the mixed component. CT, computerized tomography; MRI, magnetic resonance imaging; IPH, intraplaque haemorrhage; LRNC, lipid-rich necrotic core. T1 SE FAT SAT, T1 spin-echo fat saturation MRI sequence. [request copyright permission from Saba et al. (18)].

Figure 2

Imaging feature of IPH. Carotid ultrasound shows carotid plaque with significant ICA stenosis, and a hypoechoic are (A, arrowhead) which could represent either LRNC or IPH. Gadolinium-enhanced MRI confirms the left ICA stenosis (B, arrowhead). Within the plaque, hypersignal can be detected on the source, pre-contrast T1WIs for the MRA, which suggests IPH (C,D, arrowhead). IPH, intraplaque hemorrhage; ICA, internal carotid artery; LRNC, lipid-rich necrotic core; MRI, magnetic resonance imaging.

Figure 3

Semi-automatic segmentation and analysis of carotid plaques on CTA. Semi-automatic segmentation of the left carotid plaque in axial plane indicates the lumen (red), matrix (blue), LRNC (green), and CALC (yellow) (A). Cross-sectional representations of carotid plaque in coronal plane (B). CTA, computed tomography angiography; LRNC, lipid-rich necrotic core; CALC, calcification.