Measurement of shear wave propagation speed by estimation of two-dimensional wavenumbers using phase of particle velocity

Measurement of shear wave propagation speed in biological tissue is useful for evaluation of tissue stiffness. At present, there is a method using a shear wave generated by an ultrasonic push pulse, whose intensity is relatively higher than that used for B-mode imaging. However, this method poses a risk of tissue injury caused by cavitation. Therefore, a safer assessment method for shear wave propagation speed is required. In this paper, we propose a new method using shear waves generated by heartbeat pulses. Shear wave propagation speed is obtained by estimating wavenumbers in two dimensions using the phase of particle velocity. In basic experiments, different shear wave propagation speeds were obtained from two agar phantoms, whose stiffnesses were altered by changing the concentration of agar. In an in vivo experiment, the estimated shear wave propagation speed in a healthy liver was similar to those reported in the literature. These results show that the proposed method would be useful for safer estimation of shear wave propagation speed.