Acoustic droplet vaporization for enhancement of thermal therapies.

Abstract

Vaporization of superheated microdroplets of perfluorocarbon can be triggered by transcutaneous ultrasound for the local production of gas bubbles. Acoustic droplet vaporization (ADV) was performed in the canine renal artery or segmental artery for blood flow control by capillary occlusion to accelerate rf ablation exclusively in the target vascular bed and for future trapping of released drugs. Occlusions of 82% were obtained for >20 min in the two best exteriorized canine kidneys with intracardiac droplet injections. Intravenous injection studies avoided induced cardiac arrhythmias. In four of the six IV studies, mean achieved renal artery flow reduction was 75% for 3 min. Perfusion by colored microspheres showed larger regional reductions in some cases. Droplets that administered IV or intra-arterially were vaporized by transcutaneous ultrasound in five studies with 3.5–5.5-cm tissue paths to produce increased kidney cortex echogenicity, but not substantial occlusion. Improved occlusion is expected by enhanced bubble coalescence and creation of a narrower droplet size distribution at diameters close to the transpulmonary limit. Achieved ADV bubble concentrations also appear adequate for enhancement of HIFU therapy by reflection of acoustic energy exiting the focus, increasing absorption exclusively therein, and revealing targeted tissues. [Work supported in part by NIH Grants R01-EB000281 and S10-RR022425.]