Proof of concept experiments on an novel ultrasonic diagnostic and therapeutic agent, phase change nano droplet (PCND), were performed. It was found using gel phantoms that PCND works as a cavitation accelerator only when ultrasound pulses which trigger the phase change of PCND from liquid to gas are exposed in advance. Another kind of nano droplet that cannot change its phase to a gas does not work even in the presence of the trigger. The cavitation induction with the aid of PCND was significant in B-mode echography as a brightness enhancement. Such a brightness change was also observed in in vivo experiments on tumor baring mice in the presence of systemically administered PCNDs and triggering pulses. Moreover, damages in tumor tissues were confirmed at the site of the brightness change. The lack of either a PCND or a phase change ultrasound did not induce any brightness change, suggesting the same mechanism as a gel phantom works in living tissues. Our results are promising for use in a noble ultrasound therapy system with high selectivity and safety while improving the throughput of current ultrasound tumor treatment systems.
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