title: Characterization of submicron phase-change perfluorocarbon droplets for extravascular ultrasound imaging of cancer.
abstract: Because many tumors possess blood vessels permeable to particles with diameters of 200 nm, it is possible that submicron perfluorocarbon droplets could constitute a novel extravascular ultrasound contrast agent capable of selectively enhancing tumors. Under exposure to bursts of ultrasound of sufficient rarefactional pressure, droplets can undergo vaporization to form echogenic microbubbles. In this study, phase-change thresholds of 220-nm-diameter droplets composed of perfluoropentane were studied in polyacrylamide gel phantoms maintained at temperatures of 21-37°C, exposed to high-pressure bursts of ultrasound with frequencies ranging from 5-15 MHz and durations of 1 μs to 1 ms. The thresholds were found to depend inversely and significantly (p < 0.001) on ultrasound frequency, pulse duration, and droplet temperature, ranging from 9.4 ± 0.8 MPa at 29°C for a 1-μs burst at 5 MHz to 3.2 ± 0.5 MPa at 37°C for a 1-ms burst at 15 MHz. The diameters of microbubbles formed from droplets decreased significantly as phantom stiffness increased (p < 0.0001), and were independent of pulse duration, although substantially more droplets were converted to microbubbles for 1-ms pulse durations compared with briefer exposures. In vivo experiments in a mouse tumor model demonstrated that intravenously injected droplets can be converted into highly echogenic microbubbles 1 h after administration.
authors: Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada M4N 3M5. williams@sri.utoronto.ca
authors: Ross
authors: R
authors: Williams
authors: Cameron
authors: C
authors: Wright
authors: Emmanuel
authors: E
authors: Cherin
authors: Nikita
authors: N
authors: Reznik
authors: Mike
authors: M
authors: Lee
authors: Ivan
authors: I
authors: Gorelikov
authors: F Stuart
authors: FS
authors: Foster
authors: Naomi
authors: N
authors: Matsuura
authors: Peter N
authors: PN
authors: Burns
mesh_terms: D000180:Acrylic Resins; D000704:Analysis of Variance; D000818:Animals; D003287:Contrast Media / Q000737:chemistry*; D004195:Disease Models, Animal; D005466:Fluorocarbons / Q000737:chemistry*; D051379:Mice; D045423:Microbubbles; D009369:Neoplasms / Q000000981:diagnostic imaging*; D010316:Particle Size; D019047:Phantoms, Imaging; D014463:Ultrasonography; D010420:Pentanes
chemical_list: D000180:Acrylic Resins; D003287:Contrast Media; D005466:Fluorocarbons; C016680:polyacrylamide gels; C008806:perfluoropentane; D010420:Pentanes