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Atherosclerotic carotid bifurcation plaque rupture is a major cause of ischemic stroke and transient ischemic attacks. It has been proposed that mechanical forces contribute to the ultimate phenomenon of plaque rupture or ulceration. These mechanical forces are produced by blood pressure oscillations, blood flow and blood vessel movement throughout the cardiac cycle. It has been suggested that asymptomatic plaques, which do not rupture, have all of their components moving in the same direction as they are influenced by mechanical forces. Conversely, plaques that tend to rupture display uncoordinated movement throughout the cardiac cycle. Therefore, nonsynchronous motion, with different portions of a plaque moving in opposing directions, may be a factor in symptomaticity – a matter that this research aims to elucidate and a factor that may be able to predict risk.
Using standard ultrasound imaging, video loops of B-mode ultrasound images of 35 carotid bifurcation plaques were obtained (4 symptomatic and 31 asymptomatic) from patients with carotid bifurcation atherosclerosis. They were classified visually as showing concordant (n=22) or discordant motion (n=13). Concordant plaques were characterized by uniform orientation of motion throughout the cardiac cycle. Discordant plaques exhibited significant spread in motion orientation at different parts of the cardiac cycle, especially at systole. We developed real-time motion analysis software that applies Farneback’s method to estimate velocities between consecutive video frames, and can be easily utilized in conjunction with standard ultrasound imaging. For each video, we looked at the spreads of the motion orientations for different motion magnitudes.
Using these motion-spread measurements, we quantified discordant movement. Motion spread measurements were analyzed in terms of Sum of Maximum Fan Widths (SMFW), a measure derived from pixel motion vectors. A median value of 100 degrees and inter-quartile range (IQR) of (80, 110) degrees was established for the concordant plaques and 270, (230, 430) for the discordant plaques (P < 0.001).
Therefore, we have a new tool to differentiate between concordant and discordant plaques, and are one step closer to an effective, efficient diagnostic tool.