title: Intracellular growth of nanoscale perfluorocarbon droplets for enhanced ultrasound-induced phase-change conversion.
abstract: Perfluorocarbon (PFC) nanodroplets (NDs) have been proposed as phase-change contrast agents for ultrasound imaging. Since the ultrasound energy required to convert PFC droplets to microbubbles is inversely related to size, the conversion of PFC NDs at clinically-relevant pressures is challenging. We propose that if PFC NDs can accumulate in a close-packed configuration and grow in size in situ, phase-change conversion can occur at lower ultrasound pressures compared with isolated NDs. In this article, we show that PFC NDs can be designed to grow in size after loading in cells, from 0.26 ± 0.09 μm to 1.7 ± 0.6 μm after 2 h. This growth allowed for a substantial decrease in the ultrasound conversion threshold (to 1.4 MPa and 4.8 MPa at 1 MHz and 18 MHz, respectively), whereas non-coalesced NDs in cells and NDs alone were not converted up to the maximum applied pressure (2.1 MPa and 6.3 MPa at 1 MHz and 18 MHz, respectively). These results indicate that PFC NDs with conversion pressures too high for diagnostically feasible conversion can be used as phase-change agents if they can be induced to grow in size in situ.
authors.affiliation: Sunnybrook Research Institute, Toronto, ON, Canada.
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Martin
authors.forename: Minseok
authors.initials: M
authors.lastname: Seo
authors.forename: Ross
authors.initials: R
authors.lastname: Williams
authors.forename: Grace
authors.initials: G
authors.lastname: Belayneh
authors.forename: F Stuart
authors.initials: FS
authors.lastname: Foster
authors.forename: Naomi
authors.initials: N
authors.lastname: Matsuura
mesh_terms: D000818:Animals; D002460:Cell Line; D003287:Contrast Media / Q000138:chemical synthesis*; D005466:Fluorocarbons / Q000138:chemical synthesis*; D008264:Macrophages / Q000737:chemistry* / Q000000981:diagnostic imaging*; D051379:Mice; D049329:Nanostructures / Q000737:chemistry*; D014463:Ultrasonography
chemical_list: D003287:Contrast Media; D005466:Fluorocarbons; C078626:perflexane