Acoustic Response of Microbubbles Derived from Phase-Change Nanodroplet

Abstract

An in vitro feasibility test for a novel ultrasound therapy using a type of superheated perfluorocarbon droplet, phase-change nanodroplet (PCND), was performed in gel phantoms with the goal of high selectivity and low invasiveness. Measurements of broadband signal emission revealed that a triggering ultrasound pulse (peak negative pressure of 2.4 MPa) reduces the pressure threshold for cavitation induced by a subsequent ultrasound exposure at an order of magnitude from 2.4 to 0.2 MPa. The maximum allowed interval between the two ultrasound exposures for inducing cavitation with 100- and 1,000-cycle triggering ultrasound was about 100 and 500 ms, respectively. The echo signal increases induced by the triggering ultrasound with 100- and 1000-cycles were enhanced and suppressed by the subsequent ultrasound exposure, respectively. This different behavior seemed to be due to the presence of enlarged free bubbles, which should be avoided for the localization of therapeutic effects.

Phase-shift perfluorocarbon agents enhance high intensity focused ultrasound thermal delivery with reduced near-field heating

“…In response to the limitations inherent in the use of microbubbles and micron-sized droplets, efforts are now focused on nano-sized agents with the development of several techniques to synthesize stable liquid PFC nanodroplets (Kawabata et al, 2010;Rapoport et al, 2010;Zhang and Porter, 2010;Reznik et al, 2011;Sheeran et al, 2011a;Singh et al, 2012). When designed appropriately, PFC nanodroplets can be phase-shifted to gaseous microbubbles by the application of sufficient acoustic energy .…”

Phase-Change Contrast Agents for Imaging and Therapy

“…Two recent studies have demonstrated that the time-dependent spectral content of evolving bubbles resulting from vaporized PCCAs may have significantly different spectral information than MCAs [72, 135], which could lead to further contrast-specific imaging techniques.…”

Biomedical photoacoustics beyond thermal expansion using triggered nanodroplet vaporization for contrast-enhanced imaging

“…Owing to their highly scattering acoustic properties and nonlinear interactions with incident ultrasound, microbubbles are used in many clinical applications, including assessment of coronary artery disease, hyperlipidaemia, angiogenesis, inflammation and tumour formation. Microbubbles can also be used to assess therapeutic strategies and to facilitate delivery and release of therapeutic agents based on physical interactions of microbubbles with ultrasound [14][15][16] . Furthermore, current research is focused on adapting the microbubbles, through surface modifications, cargo encapsulation or attachment, and other modifications, to allow for additional therapeutic applications [17][18][19][20][21][22][23][24] .…”