Non-invasive blood flow measurement methods such as ultrasound Doppler and laser Doppler face challenges, including difficulty in measuring low flow velocities and limitations to the skin surface. To address these issues, we focus on the photoacoustic effect, which has the potential to overcome the limitations of both methods, aiming to measure blood flow velocity in small vessels at moderate depths. In this study, we applied the pulsed wave Doppler method to estimate displacement and compared the results with those obtained using the time-delay method. In the experiment, particles were introduced into a flow pass and moved, and the estimated flow velocity was calculated from the phase difference of the signals. The experimental results showed that the time-delay method closely matched the theoretical values, whereas the pulsed wave Doppler method tended to underestimate the flow velocity. This underestimation is considered to be caused by an overestimation of the photoacoustic frequency in the pulsed wave Doppler method, suggesting that improvements in frequency determination are necessary．
Tsuboi et al. (Wed,) studied this question.