Basic study on detection of outer boundary of arterial wall using its longitudinal motion

The longitudinal motion of the arterial wall can be observed in a B-mode image obtained by recent ultrasonic diagnostic equipment. In this study, the longitudinal displacement was quantitatively estimated by the block matching of RF echoes using cross correlation. However, the estimated longitudinal displacement is discrete depending on the spacing between two ultrasound beams of about 0.1 mm. Such an accuracy is not sufficient for tracking the region of interest (ROI) in the arterial wall. Therefore, the spacing of 0.1 mm is reduced using the interpolation of measured RF echoes to improve the tracking of the ROI in the displacement estimation. In this study, the optimum parameter in the interpolation was investigated. The spatial distribution of longitudinal displacements along the arterial radial direction was estimated using the optimum parameter. There were significant differences between the longitudinal displacements in the arterial wall and those in the region considered to be tissue outside the arterial wall. These results show the possibility of using this method to identify the outer boundary of the adventitia, which has not been achieved by conventional ultrasonic imaging.