Four-dimensional ultrasonographic characterization of plaque surface motion in patients with symptomatic and asymptomatic carotid artery stenosis

Background and Purpose-In vitro studies of atherosclerotic plaque fracture mechanics suggest that analysis of local variations in surface deformabilit y may provide information on relative vulnerability to plaque fissuring or rupture. We investigated plaque surface deformations in patients with sympt omatic and asymptomatic carotid artery disease using 4-dimensional ultrason ography and techniques for measuring optical flow. Methods-Four-dimensional ultrasound examinations of carotid artery plaques were performed in 23 asymptomatic and 22 symptomatic patients with 50% to 9 0% stenosis of the internal carotid artery. Plaque surface motion during 1 cardiac cycle was computed with a hierarchical model-based motion estimator . Results were compared with plaque echogenicity and surface structure. Resul ts-Of the 45 patients examined, plaque surface motion estimates were obtain ed for 18 asymptomatic and 13 symptomatic patients. There were no significa nt differences in echogenicity or surface structure of asymptomatic and sym ptomatic plaques (P>0.05). Results of motion estimation showed that asympto matic plaques had surface motion vectors of equal orientation and magnitude to those of the internal carotid artery, whereas symptomatic plaques demon strated evidence of inherent plaque movement. There was no significant diff erence in maximal plaque velocity between symptomatic and asymptomatic plaq ues (P<0.14). Maximal discrepant surface velocity (MDSV) in symptomatic pla ques was 3.85+/-1.26 mm/s (mean+/-SD), which was significantly higher (P<0. 001) than MDSV of asymptomatic plaques with 0.58+/-0.42 mm/s (mean+/-SD). Conclusions-MDSV of carotid artery plaques is significantly different in as ymptomatic and symptomatic disease. Further studies are warranted to determ ine whether plaque surface motion patterns can identify vulnerable plaques in patients with carotid artery stenosis.