Effects of beam steering angle and excitation frequency on blood flow imaging with plane wave imaging

The vector Doppler method was developed to overcome the limitations of conventional methods, which can only estimate axial velocities. Because the vector Doppler method uses steered beams, the excitation frequency is set lower than the resonance frequency of the transducer elements to prevent the generation of grating lobes. Although lowering the steering angle is another solution, a larger steering angle span leads to a more accurate estimation of velocity vectors. We have developed a method for estimating the steering angle from the received echo signals, which might enable an accurate estimation of velocity vectors even with small steering angles. In this study, the effects of steering angle and excitation frequency were investigated by numerical simulation and in vivo measurement of the carotid artery. The results showed that similar accuracies were obtained at high (6.94 MHz) and low (4.8 MHz) frequencies, and that better visualization of weak echoes from blood cells was achieved at 6.94 MHz.