Vaporization phenomena for ultrasound phase-change contrast agents assessed via high-speed optical microscopy

Many studies have proposed phase-change contrast agents (PCCAs) that vaporize to form bubbles ideal for contrast and cavitation. Understanding the phenomena involved with droplet vaporization to determine possible bioeffects will have a profound impact on designing agents to be effective in desired applications. In this study, we use ultra-high-speed microscopy to explore for the first time the vaporization phenomena of decafluorobutane (DFB) droplets. Results show that DFB droplets vaporize more rapidly than reported values for perfluoropentane droplets. As a result, bubbles from nanoscale droplets reach their final size within 200 ns, and are immediately subject to compression and rarefaction from the continuing pulse. DFB microscale droplets, in contrast, vaporize over the course of several microseconds, and tend to fuse with nearby bubbles. For very short pulses, the resulting bubbles show characteristic over-expansion and resonant oscillatory settling.