Effect of filling gases on the backscatter from contrast microbubbles: Theory and in vivo measurements

Two surfactant-based contrast agents, ST44 and ST68, were produced accordin g to US Patent # 5,352,436 and filled with either air, C4F10 (perfluorobuta ne) or SF6 (sulfur hexaflouride), Ten rabbits received IV injections of eac h 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 surgical ly exposed distal aorta and audio Doppler signals were acquired in vivo. Qu antitative in vivo dose responses were calculated off-line using spectral p ower analysis and compared to a theoretical model of microbubble dissolutio n 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 b ubbles enhancing least of all (p < 0.0001) and ST68-SF6 best of all (maximu m: 27.6 +/- 2.04 dB; p < 0.012), There were no significant differences betw een other agent/gas combinations (0.30 < p < 0.70), Theoretical enhancement was within 1 order of magnitude of the experimental observations (i.e., de viations 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 mos t in vivo enhancement of the agent/gas combinations studied. Theory matched the measurements within an order of magnitude. (C) 1999 World Federation f or Ultrasound in Medicine & Biology.