Optical Droplet Vaporization of Micron-sized Perfluorocarbon Droplets and their Photoacoustic Detection
2011
An acoustic and photoacoustic characterization of micron-sized perfluorocarbon (PFC) droplets is presented. PFC
droplets are currently being investigated as acoustic and photoacoustic contrast agents and as cancer therapy agents.
Pulse echo measurements at 375 MHz were used to determine the diameter, ranging from 3.2 to 6.5 μm, and the sound
velocity, ranging from 311 to 406 m/s of nine droplets. An average sound velocity of 379 ± 18 m/s was calculated for
droplets larger than the ultrasound beam width of 4.0 μm. Optical droplet vaporization, where vaporization of a single
droplet occurred upon laser irradiation of sufficient intensity, was verified using pulse echo acoustic methods. The
ultrasonic backscatter amplitude, acoustic impedance and attenuation increased after vaporization, consistent with a
phase change from a liquid to gas core. Photoacoustic measurements were used to compare the spectra of three droplets
ranging in diameter from 3.0 to 6.2 μm to a theoretical model. Good agreement in the spectral features was observed
over the bandwidth of the 375 MHz transducer.
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