Ultrasound contrast agent behavior near the fragmentation threshold

Understanding the fragmentation process of ultrasound contrast agents is important in therapeutic ultrasound applications (such as ultrasound-enhanced drug delivery), as well as in certain imaging applications (such as "flash echo" imaging. In the fragmentation of Optison/sup TM/ microbubbles, our observations suggest that there are two pressure thresholds, a threshold which leads to shell rupture and the production of smaller daughter bubbles, and another one leading to the onset of sustained inertial cavitation activity. Between the shell-disruption threshold and sustained IC threshold is a region where intermittent inertial cavitation activity was detected. The acoustic signature of the intermittent region, the pressure level for the various thresholds, and the strength of the subsequent cavitation activity are all highly dependent on the acoustic pulse parameters.