Characterization of submicron phase-change perfluorocarbon droplets for extravascular ultrasound imaging of cancer.

Abstract Because many tumors possess blood vessels permeable to particles with diameters of 200 nm, it is possible that submicron perfluorocarbon droplets could constitute a novel extravascular ultrasound contrast agent capable of selectively enhancing tumors. Under exposure to bursts of ultrasound of sufficient rarefactional pressure, droplets can undergo vaporization to form echogenic microbubbles. In this study, phase-change thresholds of 220-nm–diameter droplets composed of perfluoropentane were studied in polyacrylamide gel phantoms maintained at temperatures of 21–37°C, exposed to high-pressure bursts of ultrasound with frequencies ranging from 5–15 MHz and durations of 1 μs to 1 ms. The thresholds were found to depend inversely and significantly ( p p In vivo experiments in a mouse tumor model demonstrated that intravenously injected droplets can be converted into highly echogenic microbubbles 1 h after administration.