Time lapse observation of phase change nano droplet after vaporization stimulated by ultrasound

Abstract

Small enough to permeate through tumor blood vessel, and can be detect by ultrasound, phase change nano droplet (PCND) have been studied as contrast agents and therapeutic sensitizer for career. To investigate performance for these purpose, we investigated physical behavior of PCND, especially a lifetime of microbubbles generated by ultrasound stimulation. To investigate bubble’s behavior after phase change, we observed a time-lapse change of bubbles population with following method. Focused transducer with a frequency of 3.3 MHz was placed in a water bath of 37 degrees. At the focal point, polyacrylamide gel including PCND was placed. Focused hydrophone was placed perpendicularly to the direction of ultrasound propagation. Two kind of ultrasound pulse wave was used; phase change pulse at the beginning and observation pulse at every 500 μs. The amplitude of scattering signal (SS) reflects the sum of scattering cross-section of bubbles. The time lapse observation of PCND after phase change showed two kinds of behavior, quick and slow decay of scattering signal from the bubbles. The unique increase of SS from the phase-changed bubbles in the monitoring phase was observed. We improved the experimental setup to measure bubble’s population properly from various directions using 1-D array transducer and will present the result.