title: Effect of filling gases on the backscatter from contrast microbubbles: theory and in vivo measurements.
abstract: Two surfactant-based contrast agents, ST44 and ST68, were produced according to US Patent # 5,352,436 and filled with either air, C4F10 (perfluorobutane) or SF6 (sulfur hexaflouride). Ten rabbits received i.v. injections of each agent/gas combination with 5 repetitions of each dose (range: 0.005-0.13 mL/kg). A custom-made 10-MHz cuff transducer was placed around the surgically exposed distal aorta and audio Doppler signals were acquired in vivo. Quantitative in vivo dose responses were calculated off-line using spectral power analysis and compared to a theoretical model of microbubble dissolution and enhancement. For qualitative comparisons, 10 rabbits were imaged pre- and postcontrast administration (dose: 0.1 mL/kg) in gray-scale and colour. All agent/gas combinations produced marked Doppler enhancement with air bubbles enhancing least of all (p < 0.0001) and ST68-SF6 best of all (maximum: 27.6 +/- 2.04 dB; p < 0.012). There were no significant differences between other agent/gas combinations (0.30 < p < 0.70). Theoretical enhancement was within 1 order of magnitude of the experimental observations (i.e., deviations of up to 10 dB). The duration of contrast enhancement was 1-2 min for air-filled bubbles, 3-5 min for SF6-filled bubbles and more than 7 min for C4F10-filled bubbles. In conclusion, ST68-SF6 microbubbles produced most in vivo enhancement of the agent/gas combinations studied. Theory matched the measurements within an order of magnitude.
authors.affiliation: Department of Radiology, Thomas Jefferson University, Philadelphia, PA 19107, USA. forsberg@esther.rad.tju.edu
authors.forename: F
authors.initials: F
authors.lastname: Forsberg
authors.forename: R
authors.initials: R
authors.lastname: Basude
authors.forename: J B
authors.initials: JB
authors.lastname: Liu
authors.forename: J
authors.initials: J
authors.lastname: Alessandro
authors.forename: W T
authors.initials: WT
authors.lastname: Shi
authors.forename: N M
authors.initials: NM
authors.lastname: Rawool
authors.forename: B B
authors.initials: BB
authors.lastname: Goldberg
authors.forename: M A
authors.initials: MA
authors.lastname: Wheatley
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D005466:Fluorocarbons; D005740:Gases; D007275:Injections, Intravenous; D007668:Kidney / Q000000981:diagnostic imaging; D008863:Microspheres; D019047:Phantoms, Imaging; D011817:Rabbits; D013459:Sulfur Hexafluoride; D013501:Surface-Active Agents; D014465:Ultrasonics; D018615:Ultrasonography, Doppler, Color
chemical_list: D003287:Contrast Media; D005466:Fluorocarbons; D005740:Gases; D013501:Surface-Active Agents; C108042:perfluorobutane; D013459:Sulfur Hexafluoride