Carotid Plaque Motion

One feature of carotid plaques which has received little attention is plaque motion, i.e. translational plaque movements coincident with those of arterial walls, plaque rotations and local, plaque-specific deformations. Experimental work has suggested that analysis of plaque motion may provide new insights into plaque modeling as well as into mechanisms of plaque rupture with subsequent embolism. Observations on the relative positions of fiduciary markers placed along plaque specimens during pressure loading, for example, have demonstrated that, prior to plaque fissuring, the markers display asymmetrical movement. It is thought that such plaque surface movement may be attributable to deformations resulting from crack propagation of multiple local internal tears in the plaque. Identification of local variations in surface deformability may therefore provide information on relative vulnerability to plaque fissuring or rupture.

An approach for studying plaque surface deformations has been recently reported.72 This technique uses four-dimensional (4D) ultrasonography to acquire temporal three-dimensional ultrasound data on carotid artery plaques. The ultrasound data are then analyzed with motion detection algorithms to determine apparent velocity fields, also known as optical flow, of the plaque surface. Using this method, differences in plaque motion patterns between patients with symptomatic and asymptomatic carotid artery disease have been character-ized.72 Asymptomatic plaques showed a homogeneous orientation and magnitude of computed velocity vectors, corresponding to a global pattern of arterial motion without evidence of inherent plaque movement. Analysis of symptomatic plaques, however, demonstrated consistent evidence for plaque deformation, irrespective of arterial wall movements (Fig. 50.1). Whether analysis of plaque motion in patients with carotid artery stenosis may

Figure 50.1 Results of plaque surface motion estimation between two digitized frame volumes of a symptomatic carotid artery plaque in systole at 80 ms and 120 ms following the ECG R-wave. Grey-scale coding of motion vectors on the plaque surface represents the magnitude of computed velocities. The vectors have been magnified (3x) for better visualization. The plaque shows a characteristic discrepant motion pattern (fast arrows at the center of the plaque) with a maximal discrepant surface velocity of 7.1 mm/s.

Figure 50.1 Results of plaque surface motion estimation between two digitized frame volumes of a symptomatic carotid artery plaque in systole at 80 ms and 120 ms following the ECG R-wave. Grey-scale coding of motion vectors on the plaque surface represents the magnitude of computed velocities. The vectors have been magnified (3x) for better visualization. The plaque shows a characteristic discrepant motion pattern (fast arrows at the center of the plaque) with a maximal discrepant surface velocity of 7.1 mm/s.

allow detection of motion patterns specific to patients with an increased risk for plaque complications must be addressed in new prospective studies.

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