title: High-frequency dynamics of ultrasound contrast agents.
abstract: Ultrasound contrast agents enhance echoes from the microvasculature and enable the visualization of flow in smaller vessels. Here, we optically and acoustically investigate microbubble oscillation and echoes following insonation with a 10 MHz center frequency pulse. A high-speed camera system with a temporal resolution of 10 ns, which provides two-dimensional (2-D) frame images and streak images, is used in optical experiments. Two confocally aligned transducers, transmitting at 10 MHz and receiving at 5 MHz, are used in acoustical experiments in order to detect subharmonic components. Results of a numerical evaluation of the modified Rayleigh-Plesset equation are used to predict the dynamics of a microbubble and are compared to results of in vitro experiments. From the optical observations of a single microbubble, nonlinear oscillation, destruction, and radiation force are observed. The maximum bubble expansion, resulting from insonation with a 20-cycle, 10-MHz linear chirp with a peak negative pressure of 3.5 MPa, has been evaluated. For an initial diameter ranging from 1.5 to 5 microm, a maximum diameter less than 8 microm is produced during insonation. Optical and acoustical experiments provide insight into the mechanisms of destruction, including fragmentation and active diffusion. High-frequency pulse transmission may provide the opportunity to detect contrast echoes resulting from a single pulse, may be robust in the presence of tissue motion, and may provide the opportunity to incorporate high-frequency ultrasound into destruction-replenishment techniques.
authors.affiliation: UC Davis, Davis, CA 95616, USA. ywsun@ucdavis.edu
authors.forename: Yang
authors.initials: Y
authors.lastname: Sun
authors.forename: Dustin E
authors.initials: DE
authors.lastname: Kruse
authors.forename: Paul A
authors.initials: PA
authors.lastname: Dayton
authors.forename: Katherine W
authors.initials: KW
authors.lastname: Ferrara
mesh_terms: D003287:Contrast Media / Q000737:chemistry* / Q000528:radiation effects*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D045423:Microbubbles; D010316:Particle Size; D011846:Radio Waves; D013010:Sonication; D013314:Stress, Mechanical; D014463:Ultrasonography / Q000379:methods*; D014732:Vibration
chemical_list: D003287:Contrast Media