2 Principles

The ultrasonic beam scans I (= 46 in this study) positions of tissue, e.g., along the longitudinal direction of the artery. As shown in Figure 1, with respect to each beam position i (= 1, 2, ..., I), RF pulses are transmitted with a time interval T from an ultrasonic probe, and the echo reflected by the arterial wall is received by the same probe. By referring to a B-mode or M-mode image constructed by the received RF echoes at each beam position, the depths, x₁(0) and x_MT(0) (corresponding to the distances from the probe), of the lumen-intima and media-adventitia boundaries of the posterior wall are manually assigned in the initial frame, where M_T is the number of sampled points between these assigned boundaries.