Understanding the pulse-to-pulse evolution of microbubble clouds using light scattering

Measurements of the dynamical response of ultrasound contrast agents to diagnostic and therapeutic ultrasound pulses have been accomplished with light scattering. Light-scattering can be used to resolve the instantaneous motion of single microbubbles and provide information about the bubble evolution over many acoustic cycles. We applied this same technique to monitor the evolution of clouds of Optison microbubbles subjected to pulsed ultrasound from a diagnostic ultrasound system. Bubble oscillations were measured by focusing a 30-mW laser beam through the suspension. At low MI settings, bubble oscillations were relatively linear. In some cases, we observed an increase in the background light scatter amplitude, suggesting that bubble coalescence or gas diffusion occurred. At higher MI settings, the motion was nonlinear. Bubble fragmentation could be observed as the background light scattered signal decreased significantly from pulse to pulse.