In vivo characterization of atherosclerotic plaque of human carotid arteries with histopathological correlation using ARFI ultrasound

Atherosclerotic plaque characterization with acoustic radiation force impulse (ARFI) imaging has recently been developed using phantoms and atherosclerotic pigs, but has yet to be validated in vivo in humans. We present initial results from an ongoing clinical trial investigating in vivo ARFI imaging of human carotid plaque with spatially-matched histopathology. Patients undergoing clinically-indicated carotid endarterectomy (CEA) were recruited from UNC Hospitals and imaged with ARFI prior to surgery. After surgery, the extracted specimen was sectioned according to noted arterial geometry for spatial registration to the ultrasound imaging plane and processed histologically. In two symptomatic patients, plaques were composed of a mixture of small and large necrotic cores, mild intra-plaque hemorrhage, and fibrosis. Mean ARFI peak displacements were observed to be two to three times higher in regions corresponding to either necrotic core or intra-plaque hemorrhage compared to regions of dense fibrosis or calcification. In an asymptomatic patient with predominantly calcified plaque, mean ARFI peak displacements were small (~1-2 μm) suggesting stiff tissue. The results of this study indicate that areas of relatively large displacement by ARFI imaging correlate with lipid/necrotic cores and/or inflammation, which may confer an increased chance of plaque rupture and future ischemic event. This work demonstrates the feasibility of transcutaneous ARFI for characterizing the material and structural composition of carotid atherosclerotic plaques via mechanical properties, in humans, in vivo.