Motion Analysis of the Carotid Artery Wall and Plaque Using B-Mode Ultrasound

Motion of the arterial wall and atheromatous plaque, especially in the longitudinal direction, has recently gained attention as a determinant of carotid atherosclerosis. Vessel wall motion, caused by blood pressure, blood flow and tethering to the surrounding tissue, may be responsible for tissue rupture and cerebrovascular symptoms. B-mode ultrasound allows non-invasive recording of arterial wall and plaque motion in two directions, namely radial and longitudinal. Temporal sequences of ultrasound images, recorded at high frame rates, can be used to quantitatively estimate movement of the arterial wall. Motion of the carotid artery wall and plaque from sequences of ultrasound images has been estimated using block matching and optical flow techniques. Block matching is based on tracking blocks of pixels, assuming that the blocks remain constant over time and motion. Optical flow relies on the estimation of the spatiotemporal change of individual pixel intensities throughout a sequence, resulting in a dense vector map where each pixel is represented by a vector corresponding to its velocity between two frames. An important issue in studies of arterial wall motion is the validation of the motion analysis techniques. Tissue-mimicking phantoms as well as computergenerated simulation images have been used to validate motion analysis algorithms. In conclusion, motion of the carotid artery wall and plaque can be quantitatively estimated from B-mode ultrasound and may represent a powerful tool to study further the mechanisms of atherosclerosis.