Experimental and theoretical studies on acoustic droplet vaporization

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Phase shift nanodroplets are better alternatives to microbubbles due to their enhanced stability and smaller size distribution. These nanodroplets undergo phase transition from liquid to highly echogenic gaseous state under acoustic excitation through a process termed acoustic droplet vaporization (ADV). In this study, we synthesized lipid-coated perfluoropentane (PFP)-filled nanodroplets via sonication and mechanical agitation methods. We investigated the ADV threshold of these nanodroplets as a function of acoustic parameters such as excitation frequency and pulse repetition period (PRP). Experiments were performed at frequencies 2.25, 5, and 10 MHz. The acoustic signature of droplet vaporization was observed to be a broadband signal at all the studied frequencies. The ADV threshold was studied by increasing the excitation pressure in steps of 200 kPa. The ADV threshold at 2.25 and 5 MHz was found to be 1.8 and 2.2 MPa, respectively. The scattered response from droplets were studied at different PRPs of...