Carotid plaque characterization with ARFI imaging: Blinded reader study

Stroke is commonly caused by thromboembolic events originating from vulnerable atherosclerotic plaque in the carotid vasculature. The purpose of this study was to evaluate the ability of acoustic radiation force impulse (ARFI) imaging, a noninvasive elastography imaging technique, to assess the composition of carotid artery plaques using histologic examination as the gold standard. Twenty-five patients undergoing carotid endarterectomy (CEA) were enrolled and imaged with ARFI. After surgery, extracted specimens were histologically processed and matched to the ultrasound imaging plane. Parametric 2D ARFI images of peak displacement (PD) were evaluated by three radiologists blinded to the histology result. Receiver operating characteristic (ROC) curve analysis was performed, and area under the ROC curve (AUC) was taken as a metric of performance for detecting plaque features such as necrotic core (NC), intraplaque hemorrhage (IPH), collagen (COL), and calcium (CAL). Additionally, linear regression was performed on fibrous cap (FC) thickness measurements. Areas of plaque with NC and IPH were observed to have substantially increased ARFI PD (2× to 4×) compared to areas of plaque with COL or CAL. Median AUC for detecting soft plaque features (NC/IPH) was 0.887 (range: 0.867 - 0.924) and stiff plaque features (COL/CAL) was 0.859 (range: 0.771 - 0.929). FC thickness measured by two of the three radiologists matched closely with histology (reader 1: R² = 0.64; reader 2: R² = 0.89). This study suggests that ARFI is capable of distinguishing soft from stiff compositional elements of atherosclerotic plaques and may be relevant to improving plaque risk assessment.