Optimization of focal position of ultrasonic beam in measurement of small change in arterial wall thickness

We have previously developed a method for measurement of a small change in thickness of the arterial wall during a single cardiac cycle [H. Kanai, M. Sato, Y. Koiwa and N. Chubachi: IEEE Trans. UFFC 43 (1996) 791]. The result ant change in thickness is shown to be useful for the in vitro assessment o f the regional elasticity of the arterial wall. Although the accuracy of th e measurement of the change in thickness is found to be within 1 mum, it is affected by the interference of ultrasonic pulses. In this study, we simul ate the propagation of ultrasonic pulses transmitted and received by a line ar probe. In the simulation experiments, the ultrasonic pulses generated by a computer are reflected by a tube, which has a small change in wall thick ness of 10 mum. The optimum focal position of the ultrasonic beam is determ ined by evaluating the root-mean-square (rms) error in the measured change in thickness.