Quantitative acoustic characterization of a new surfactant-based ultrasound contrast agent

The acoustic properties of a new ultrasound contrast agent, ST68, have been investigated, ST68 is a sonicated mixture of nonionic surfactants (Span-type and Tween-type) consisting of stabilized microbubbles with a mean diameter of 3.8 mu m and a concentration of 7.1 x 10(8) bubbles/mL. A pulsatile Bow system was used to acquire data in vitro. The acoustic properties of ST68, as a function of time, frequency and dose, were calculated. Enhancement changed nonlinearly with contrast agent dose; maximum was 13.1 dB +/- 1.0 dB for a dose of 0.30 mu L/mL of suspending medium. Attenuation reached approximately 11 dB/cm for dosages above 0.27 mu L/mL and for frequencies between 2.5 and 6.0 MHz. In vivo, IV injections of ST68 were given to 4 rabbits (doses from 0.01 to 0.23 mL/kg). A clear increase in Bow signal intensity was observed for 1 to 2 min. An in vivo dose-response curve was calculated from audio Doppler signals obtained with a 10-MHz cuff transducer placed around the distal aorta. Maximum enhancement was 18.3 dB +/- 3.13 dB for a 0.13 mL/kg dose. Moreover, ST68 appears to follow a simple relationship between in vivo enhancement and dose. In conclusion, ST68 is capable of producing marked vascular enhancement. Its acoustic properties have been characterized in vitro and in vivo. (C) 1997 World Federation for Ultrasound in Medicine & Biology.