Ultrasound phase velocities in SonoVue™ as a function of pressure and bubble concentration

This work investigates the effects of insonating pressure on ultrasound phase velocity in the SonoVue^TM microbubble suspension. Ultrasound transmission measurements were carried out using a single element transducer and calibrated needle hydrophone, for a range of SonoVue^TM concentrations from 50 to 800μl/l. Phase velocity was calculated using an established method based on the phase difference between pulses transmitted through the contrast agent and reference pulses for a range of insonating pressures from 13 to 128 kPa. Phase velocity was shown to be dependent on frequency, insonating pressure and SonoVue^TM concentration. The relationship between pressure and phase velocity was found to be approximately linear, with the pressure-velocity gradient increasing with concentration. These results may have significant implications for contrast-enhanced ultrasonography, for example in understanding artifact generation and quantitative applications such as estimating local bubble concentration.