title: Wave scattering from encapsulated microbubbles subject to high-frequency ultrasound: contribution of higher-order scattering modes.
abstract: The theoretical understanding of encapsulated microbubble response to high-frequency ultrasound (HFUS) excitation is still limited although some novel experimental HFUS contrast imaging techniques have been well developed. In this paper, the higher-order modal (HOM) contributions to the scattered field are studied for such microbubbles driven by 1-100 MHz ultrasound. An exact solution of all small-amplitude vibrational modes of a single encapsulated microbubble in water is given by the wave scattering theory (WST) method and compared to results obtained from Church's Rayleigh-Plesset-like model for the small-amplitude radial oscillation of a microbubble in an incompressible fluid. From numerical results, we show that the HOM field contribution is significant for scattering properties from individual Nycomed microbubbles with normalized frequency > or = 0.2. It is also shown that the multiple scattering is strengthened for monodispersed Definity microbubbles of 3 microm radius at frequencies >40 MHz. However, comparisons between the authors' analyses and known experimental data for polydispersed Definity microbubbles indicate that the HOM contributions are insignificant in attenuation estimation at frequencies <50 MHz. In conclusion, the WST model analysis suggests that HOM scattering is an important consideration for single bubbles but may be less critical in the modeling of polydispersed Definity bubbles at high frequencies.
authors.affiliation: Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309-0427, USA.
authors.forename: Jiusheng
authors.initials: J
authors.lastname: Chen
authors.forename: Kendall S
authors.initials: KS
authors.lastname: Hunter
authors.forename: Robin
authors.initials: R
authors.lastname: Shandas
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D045423:Microbubbles; D008962:Models, Theoretical; D014465:Ultrasonics