Frequency dependence of the vaporization threshold of sonosensitive perfluorocarbon droplets varying their liquid core and size

Abstract

Phase shift liquid perfluorocarbon (PFC) droplets vaporizable by ultrasound have received increasing attention for therapeutic and diagnostic applications. The ultrasound activation pressure required for the phase change of these droplets into echogenic microbubbles is termed acoustic droplet vaporization (ADV). This study systematically investigates the effect of frequency of excitation¾2.25 MHz, 10 MHz and 15 MHz¾on ADV and inertial cavitation (IC) thresholds of a suspension of PFC droplets by varying the physical properties of the liquid droplets (size and boiling point) in a tubeless setup. We prepared lipid-coated droplets with three different liquid cores, perfluoropentane (PFP), perfluorohexane (PFH) and perfluorooctyle bromide (PFOB), of two different size ranges ¾ one with diameter smaller than 3 I¼m and the other with diameter larger than 10 I¼m. We found that the ADV threshold increases with frequency for the most volatile PFC liquid, PFP, for both large and small size droplets. While for the s...