title: Nonspherical oscillations of ultrasound contrast agent microbubbles.
abstract: The occurrence of nonspherical oscillations (or surface modes) of coated microbubbles, used as ultrasound contrast agents in medical imaging, is investigated using ultra-high-speed optical imaging. Optical tweezers designed to micromanipulate single bubbles in 3-D are used to trap the bubbles far from any boundary, enabling a controlled study of the nonspherical oscillations of free-floating bubbles. Nonspherical oscillations appear as a parametric instability and display subharmonic behavior: they oscillate at half the forcing frequency, which was fixed at 1.7 MHz in this study. Surface modes are shown to preferentially develop for a bubble radius near the resonance of radial oscillations. In the studied range of acoustic pressures, the growth of surface modes saturates at a level far below bubble breakage. With the definition of a single, dimensionless deformation parameter, the amplitude of nonspherical deformation is quantified as a function of the bubble radius (between 1.5 and 5 microm) and of the acoustic pressure (up to 200 kPa).
authors.affiliation: Physics of Fluids Group, Department of Science and Technology, University of Twente, Enschede, The Netherlands. benjamin.dollet@univ-rennes1.fr
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dollet
authors.forename: Sander M
authors.initials: SM
authors.lastname: van der Meer
authors.forename: Valeria
authors.initials: V
authors.lastname: Garbin
authors.forename: Nico
authors.initials: N
authors.lastname: de Jong
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse
authors.forename: Michel
authors.initials: M
authors.lastname: Versluis
mesh_terms: D003287:Contrast Media; D007089:Image Enhancement; D045423:Microbubbles; D010743:Phospholipids; D011312:Pressure; D012212:Rheology; D012542:Scattering, Radiation; D013499:Surface Properties; D014464:Ultrasonic Therapy / Q000379:methods*
chemical_list: D003287:Contrast Media; D010743:Phospholipids