title: Surface modes and acoustic scattering of microspheres and ultrasound contrast agents.
abstract: Surface modes of spherical objects subject to ultrasound excitation have been recently proposed to explain experimental measurements of scattering from microspheres and ultrasound contrast agents (UCAs). In this work, the relationship between surface modes and resonance frequencies of microspheres and UCAs is investigated. A finite-element model, built upon the fundamentals of wave propagation and structural mechanics, was introduced and validated against analytical solutions (error <5%). Numerical results showed the existence of a systematic relationship between resonance frequencies and surface modes of a 30 μm microsphere driven at 1-70 MHz. On the contrary, for a 100 nm shelled, 4 μm diameter UCA, no clear relationship between the resonance frequencies and the surface modes was found in the frequency range examined. Instead, the UCA exhibited a collection of complex oscillations, which appear to be a combination of various surface modes and displacements. A study of the effects of varying the shell properties on the backscatter showed the presence of peaks in the backscatter of thick-shelled UCAs, which are not predicted by previous models. In summary, this work presents a systematic effort to examine scattering and surface modes from ultrasound contrast agents using finite-element models.
authors.affiliation: Department of Electrical and Computer Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario, M5B 2K3, Canada. ofalou@ryerson.ca
authors.forename: Omar
authors.initials: O
authors.lastname: Falou
authors.forename: Amin
authors.initials: A
authors.lastname: Jafari Sojahrood
authors.forename: J Carl
authors.initials: JC
authors.lastname: Kumaradas
authors.forename: Michael C
authors.initials: MC
authors.lastname: Kolios
mesh_terms: D003198:Computer Simulation; D003287:Contrast Media / Q000737:chemistry*; D055119:Elastic Modulus; D020342:Finite Element Analysis; D008863:Microspheres; D008962:Models, Theoretical; D009716:Numerical Analysis, Computer-Assisted; D011137:Polystyrenes / Q000737:chemistry*; D011312:Pressure; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D013016:Sound; D013499:Surface Properties; D013997:Time Factors; D014465:Ultrasonics / Q000379:methods; D014463:Ultrasonography; D014732:Vibration
chemical_list: D003287:Contrast Media; D011137:Polystyrenes