Innovative Multiparametric Characterization of Carotid Plaque Vulnerability by Ultrasound

Abstract

Objective: The degree of stenosis of a carotid plaque is a well-established risk factor for ischemic stroke. Nevertheless, the risk of ipsilateral stroke in asymptomatic carotid stenosis remains low and new imaging markers are needed to better target which patients would benefit most from endarterectomy or intensive medical therapy. Ultrafast ultrasound imaging offers parameters helping at characterizing the carotid plaque by shear wave elastography and Ultrafast Doppler (UFD). We aimed at using these techniques to characterize 3 different ultrasound biomarkers: plaque stiffness heterogeneity, wall shear stress (WSS) and intraplaque micro-flows and to correlate these biomarkers with findings on computed tomography angiography (CTA) and the pathological examination.

Methods: We present the case of a multimodal evaluation of a carotid plaque using ultrasound. Elastography has been coupled to the WSS assessment and the detection of intraplaque micro-flows by UFD. The data have been compared to CTA and to the pathology examination of the tissue after carotid endarterectomy.

Results: Elastography allowed at identifying stiff areas corresponding to calcifications, as well as a soft area corresponding to an intraplaque hemorrhage. The flow evaluation with UFD showed an increase of the WSS along the plaque and identified the presence of a plaque rupture, confirmed by the pathologist.

Conclusion: Ultrafast ultrasound imaging is an innovative, easily accessible technique that provides imaging modalities on top of the conventional B-mode. Ultrafast ultrasound biomarkers such as plaque stiffness heterogeneity, WSS and intraplaque micro-flows could help to define the vulnerability of the carotid plaque in order to stratify patients that could benefit most from endarterectomy or intensive medical therapy.

Keywords: carotid plaque; elastography; plaque vulnerability; ultrafast ultrasound imaging; wall shear stress.

FIGURE 1

Layout of elastography assessment (A), B-mode ultrasound acquisition (B), computed tomography angiography (C) and gross examination (D) of the same plaque in a longitudinal axis view. The red arrow indicates the main haemorrhagic area on panel (D). It corresponds to a low stiffness (A), hypoechogenic (B) and low-density (C) area. The white arrow indicates a fibrous and calcified area on panel (D). It corresponds to a high stiffness (A), hyperechogenic (B) and high-density (C) area. Ci, internal carotid; Cc, common carotid.

FIGURE 2

Pathology examination of the carotid plaque. Gross longitudinal section (A). Presence of an intraplaque hemorrhage (surrounded by the red box) in the upper section, as seen in cross-sectional microscopic analysis (B). Identification of the rupture zone of the fibrous cap (arrow 1). At higher magnification of the blue box (D) the intraplaque hemorrhage contains numerous red blood cells with intact membranes, confirming a recent hemorrhage. The posterior part of the plaque (white box) shows surface calcifications (arrow 2) and deep calcifications (arrow 3) (C).

FIGURE 3

Ultrafast vector flow imaging. Representation of the velocities map (A). Representation of the wall shear stress (WSS) map along the carotid walls (B) and the changes over the cardiac cycle (C) at the plaque’s ascent (1), plaque’s peak (2) and plaque’s descent (3).

FIGURE 4

Ultra-sensitive Doppler imaging. B-mode picture (A) and the signed power Doppler picture (B). The plaque was manually delineated. The white arrow indicates the presence of an isolated centrifugal micro-flux originating from the lumen inside the plaque’s wall, which may correspond to a rupture zone of the fibrous cap.