title: Pressure-dependent attenuation and scattering of phospholipid-coated microbubbles at low acoustic pressures.
abstract: Previous optical studies have shown threshold behavior of single-contrast agent microbubbles. Below the acoustic pressure threshold, phospholipid-coated microbubbles with sizes <5.0 mum in diameter oscillate significantly less than above the threshold pressure. Previous studies also revealed an acoustic pressure-dependent attenuation of ultrasound by microbubble contrast agents. In this study, we investigated whether pressure-dependent acoustic behavior may be explained by threshold behavior. For this purpose, pressure-dependent attenuation and scattering of a phospholipid-coated contrast agent were measured. Transmit frequencies between 1.5 and 6.0 MHz and acoustic pressures between 5 and 200 kPa were applied. Unlike the galactose-based contrast agent Levovist, the phospholipid-coated contrast agent BR14 showed a pressure-dependent attenuation. In addition, it was found that filtered suspensions with only microbubbles <3.0 mum in diameter show more pressure-dependent attenuation behavior than native suspensions of phospholipid-coated microbubbles. For the scattering measurements conducted at 3.0 MHz, the native suspension did not show any pressure-dependent behavior. However, the filtered suspension responded highly nonlinearly. Between 30 and 150 kPa, 16 dB additional scattered power was obtained. We concluded that threshold behavior of phospholipid-coated microbubbles results in pressure-dependent attenuation and scattering.
authors.affiliation: Department of Biomedical Engineering, Thoraxcenter, Erasmus MC, Rotterdam, The Netherlands. m.emmer@erasmusmc.nl
authors.forename: Marcia
authors.initials: M
authors.lastname: Emmer
authors.forename: Hendrik J
authors.initials: HJ
authors.lastname: Vos
authors.forename: David E
authors.initials: DE
authors.lastname: Goertz
authors.forename: Annemieke
authors.initials: A
authors.lastname: van Wamel
authors.forename: Michel
authors.initials: M
authors.lastname: Versluis
authors.forename: Nico
authors.initials: N
authors.lastname: de Jong
mesh_terms: D000162:Acoustics; D005466:Fluorocarbons; D006801:Humans; D045423:Microbubbles; D010743:Phospholipids; D011312:Pressure; D012542:Scattering, Radiation; D014465:Ultrasonics
chemical_list: C471302:BR14 contrast agent; D005466:Fluorocarbons; D010743:Phospholipids