Spatial control of gas bubbles and their effects on acoustic fields.

Because microbubbles can enhance therapy, such as by cavitation or by thermal means, treatment could be confined with localization of microbubbles. This spatial control can be achieved by the vaporization of liquid-filled droplets present throughout the medium in a process known as acoustic droplet vaporization (ADV). Bubbles in the form of an orthogonal plane or "wall" can thus be created and can scatter ultrasound to enhance the proximal acoustic field while shielding distal tissues. To investigate the possible effects of a preexistent bubble wall, tissue-mimicking polyacrylamide gels embedded with perfluorocarbon droplets were insonified under various conditions. The preliminary results presented in this paper show that a bubble wall can successfully cause proximal ADV at approximately half the transmitted pressures that are required without the use of a bubble wall, while also serving as a viable shield against ADV and potential damage in distal areas. The results seen here in a gel medium are promising and suggest further development in vivo is needed.