Session 2 Transmission Measurements of Albunex Attenuation and Phase Velocity at Concentrations Approaching In Vivo Doses Max Adams, PhD t, Jon N. Marsh, MSc 2, Chris S. Hall, MSc 2, Joel Mobley, MSc 2, Michael S. Hughes, PhD 1, James G. Miller, PhD 2, Gary H. Brandenburger, DSc 1 T he godl of this work was to contribute to the body of experimental knowledge concerning s0nogmphic contrast agents and to extend the range of in vitro measurements toward concentrations more typically used clinically in patients. Through-transmission attenuation measurements of Albunex (blolecular Biosystems, San Diego, CA) were made in vitro at con- centrati0ns approaching in vivo doses. The results of experiments done at high concentrations of Albunex were compared with predictions from an independent scattering model for encapsulated bubbles. blodels for encapsulated gas-filled bubbles in a liquid, as described in published reports by de Jong and Hoff [1], Church [2], and Bleeker et al. 13], predict a peak in scattering intensity and attenuation due to bubble reso- nance. These models correspond well to observed measurements in dilute concentrations of Albunex. Clinical doses of Albunex, however, may reach considerably higher concentrations than those used in previously reported broadband through-transmission attenuation measurements. It is unclear whether predictions of independent scattering models will still correspond to observed results for such high concentrations of Albunex, as certain model assumptions may no longer apply. For instance, the average bubble separation distance may no longer be much greater than the average bub- ble size, hence, the bubble suspension may no longer behave as an ensem- ble of independent scatterers. The approach used in this study was to determine broadband through-transmission signal loss for successively higher concentrations of Albunex and to determine whether the model predictions would still apply. MATERIALS AND METHODS Albunex presents special challenges that must be addressed when mak- ing measurements. First, measurements must be made rapidly because Albunex microspheres tend to deteriorate over time when removed from the vial. Second, the Albunex suspension must be mixed thoroughly and continuously during measurement to ensure a random, homogeneous spa- tial distribution of microspheres. Finally, the power emitted by the insonify- From 1Mallinckrodt Medical,Inc.,St. Louis,MO;and 2Laboratory for Ultrasonics,Washington Univer- sity PhysicsDepartment, St. Louis, MO. Address reprint requests to M. Adams, PhD, Mallinckrodt Medical, Inc., 675 McDonneZlBlvd., RO. Box 5840, St. Louis, MO 63134. Acad Radio11996 ;3 :$182-$184 9 1996, Association of University Radiologists $182