Frequency and pressure dependent attenuation and scattering by microbubbles.

The aim of this study was to evaluate experimentally the degree of pressure dependence of attenuation and scattering by microbubbles at low acoustic pressures with an empirical nonlinear model. In addition, the pressure dependency over a range of frequencies (1 to 5 MHz) has been studied. A series of transmission and scattering measurements were made with the microbubble SonoVue, using an automated system. Results show that, within the pressure range studied, attenuation as a result of the microbubble is pressure-dependent, whereas no such dependence of scattering was detectable. The pressure dependence of attenuation for SonoVue was found to be most significant at 1.5 MHz. The scattering is shown to be the highest at the lowest insonation frequency, around 1 approximately 1.25 MHz, and then decreases with frequency.