Non-uniform oscillations of deflating bubbles - a pilot study

Phospholipids-coated Ultrasound Contrast Agents (UCA) may deflate or dissolve because of stress resulting from US-induced oscillations. In this work we investigate the behavior of isolated UCA during prolonged US excitation. An isolated UCA bubble was placed in a thin capillary tube and its oscillations were recorded using the Brandaris-128 camera while it was excited with hundreds of US pulses at low mechanical index. The results show that UCA undergo an irreversiblenon destructive deflation process. Such deflation seems to occur in discrete steps rather than as a continuous process; furthermore, the oscillation of the bubble changes during deflation: both symmetric and asymmetric oscillations occur at various stages of the deflation process. Strongly asymmetric oscillations, such as compression-only and expansion-only, were also observed: notably, expansion-only is associated with a quick size reduction, whereas compression-only mostly occurs when the bubble size does not change. These preliminary results indicate that bubble deflation might be resulting from at least two distinct phenomena, namely gas loss and material shed from the shell.