title: Low-amplitude non-linear volume vibrations of single microbubbles measured with an "acoustical camera".
abstract: Contrast-enhanced ultrasound imaging is based on the detection of non-linear vibrational responses of a contrast agent after its intravenous administration. Improving contrast-enhanced images requires an accurate understanding of the vibrational response to ultrasound of the lipid-coated gas microbubbles that constitute most ultrasound contrast agents. Variations in the volume of microbubbles provide the most efficient radiation of ultrasound and, therefore, are the most important bubble vibrations for medical diagnostic ultrasound imaging. We developed an "acoustical camera" that measures the dynamic volume change of individual microbubbles when excited by a pressure wave. In the work described here, the technique was applied to the characterization of low-amplitude non-linear behaviors of BR14 microbubbles (Bracco Research, Geneva, Switzerland). The amplitude dependence of the resonance frequency and the damping, the prevalence of efficient subharmonic and ultraharmonic vibrations and the amplitude dependence of the response at the fundamental frequency and at the second harmonic frequency were investigated. Because of the large number of measurements, we provide a statistical characterization of the low-amplitude non-linear properties of the contrast agent.
authors.affiliation: Biomedical Engineering, ThoraxCenter, Erasmus Medical Center, Rotterdam, The Netherlands. Electronic address: renaud_gu@yahoo.fr.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Renaud
authors.affiliation: Biomedical Engineering, ThoraxCenter, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: Johan G
authors.initials: JG
authors.lastname: Bosch
authors.affiliation: Biomedical Engineering, ThoraxCenter, Erasmus Medical Center, Rotterdam, The Netherlands; Acoustical Wavefield Imaging Research Group, Delft University of Technology, Delft, The Netherlands.
authors.forename: Antonius F W
authors.initials: AF
authors.lastname: Van Der Steen
authors.affiliation: Biomedical Engineering, ThoraxCenter, Erasmus Medical Center, Rotterdam, The Netherlands; Acoustical Wavefield Imaging Research Group, Delft University of Technology, Delft, The Netherlands.
authors.forename: Nico
authors.initials: N
authors.lastname: De Jong
mesh_terms: D000162:Acoustics / Q000295:instrumentation*; D004867:Equipment Design; D005466:Fluorocarbons / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D045423:Microbubbles; D010743:Phospholipids / Q000737:chemistry*; D012815:Signal Processing, Computer-Assisted; D014463:Ultrasonography / Q000295:instrumentation*; D014732:Vibration
chemical_list: C471302:BR14 contrast agent; D005466:Fluorocarbons; D008081:Liposomes; D010743:Phospholipids
keywords: Contrast-enhanced ultrasound imaging; Lipid-coated gas microbubble; Non-linear acoustics; Non-linear scattering; Subharmonic emission; Ultrasound spectroscopy