Ischemic stroke from thromboembolic sources is linked to carotid artery atherosclerotic disease with a trend toward medical management in asymptomatic patients. Extent of disease is currently diagnosed by noninvasive imaging techniques that measure luminal stenosis, but it has been suggested that a better biomarker for determining risk of future thromboembolic events is plaque morphology and composition. Specifically, plaques that are composed of mechanically-soft lipid/necrotic regions covered by thin fibrous caps are the most vulnerable to rupture. An ultrasound technique that noninvasively interrogates the mechanical properties of soft tissue, called acoustic radiation force impulse (ARFI) imaging, has been developed as a new modality for atherosclerotic plaque characterization using phantoms and atherosclerotic pigs, but the technique has yet to be validated in vivo in humans. In this preliminary study, in vivo ARFI imaging is presented in a case-study format from four patients undergoing clinically-indicated carotid endarterectomy and compared to histology. In two type Va plaques, characterized by lipid/necrotic cores covered by fibrous caps, mean ARFI displacements in focal regions were high relative to the surrounding plaque material, suggesting soft features covered by stiffer layers within the plaques. In two type Vb plaques, characterized by heavy calcification, mean ARFI peak displacements were low relative to the surrounding plaque and arterial wall, suggesting stiff tissue. This pilot study demonstrates the feasibility and challenges of transcutaneous ARFI for characterizing the material and structural composition of carotid atherosclerotic plaques via mechanical properties, in humans, in vivo.

Objective Stroke is commonly caused by thromboembolic events originating from ruptured carotid plaque with vulnerable composition. The purpose of this study was to assess the performance of Acoustic Radiation Force Impulse (ARFI) imaging, a noninvasive ultrasound elasticity imaging method, for delineating the composition of human carotid plaque in vivo with histological validation. Methods Carotid ARFI images were captured prior to surgery in twenty-five patients undergoing clinically indicated carotid endarterectomy (CEA). The surgical specimens were histologically processed with sectioning matched to the ultrasound-imaging plane. Three radiologists, blinded to histology, evaluated parametric images of ARFI-induced peak displacement (PD) to identify plaque features such as necrotic core (NC), intraplaque hemorrhage (IPH), collagen (COL), calcium (CAL), and fibrous cap (FC) thickness. Reader performance was measured against the histological standard using receiver operating characteristic (ROC) curve analysis, linear regression, Spearman correlation (ρ), and Bland-Altman analysis. Results ARFI PD was two-to-four-times larger in regions of NC and IPH relative to regions of COL or CAL. Readers detected soft plaque features (NC/IPH) with median area under the curve (AUC) of 0.887 (range: 0.867 – 0.924) and stiff plaque features (COL/CAL) with median AUC of 0.859 (range: 0.771 – 0.929). Two of the three readers’ FC thickness measurements correlated with histology (reader 1: R2 = 0.64, ρ = 0.81; reader 2: R2 = 0.89, ρ = 0.75). Conclusions This study suggests that ARFI is capable of distinguishing soft from stiff atherosclerotic plaque components and delineating FC thickness.

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Thoracic aortic aneurysm with fistulization into the trachea or the esophagus is usually a lethal complication. An unusual case of combined aortotracheal and aortoesophageal fistulae is presented here. The patient had a successful outcome after resection of the aneurysm with tracheal repair and esophageal resection. A review of literature on this subject is also included in this manuscript.