Real-time visualization of instantaneous frequency from bubble cavitation using color Doppler ultrasound imaging

Time-resolved observations of acoustic cavitation emission signals are important in understanding bubble cavitation dynamics and monitoring sonoporation efficiencies of ultrasound-assisted drug delivery systems. Previous methods using back propagation of such signals measure frequencies with high time resolutions but require post-processing. We propose a method using color Doppler ultrasound to obtain instantaneous frequencies of these signals from the phase differences with an external reference signal. Standard color Doppler processing is applied to both emissions and reference signals to enable real-time observations of bubble cavitation generated by high-intensity ultrasound wave irradiation. A sinusoidal wave signal was used to confirm the accuracy of our method with an estimation error of 8.59%. Experiments were performed using Sonazoid suspensions of two different concentrations. With a sound pressure of 1.0 MPa for the ultrasound wave, the type of bubble cavitation that is dominant is different before and after irradiation of about ten pulses.