Acoustic signal characterization of phase change nanodroplets in tissue-mimicking phantom gels

To apply superheated perfluorocarbon nanodroplets to tumor diagnosis and treatment, acoustic signals formed upon the vaporization of droplets in tissue-mimicking phantoms were measured with 3MHz ultrasound. A characteristic impulse wave was associated with phase change induction with 100 cycles of ultrasound at a 9MPa peak negative pressure, observed as an intensity change in B-mode imaging. In addition, the subsequent impulse waves were observed only from the phase change induction in gels. Therefore, these subsequent impulse waves were suggested to be characteristic features of the vaporization of superheated nanodroplets at rigid boundaries. Furthermore, such impulse waves reflect the properties of surrounding environments such as elasticity and viscosity in the gel. The findings of this study would lead to a novel microscale tissue characterization method applicable to local sites.