Survival of single microbubbles insonated in solution and in narrow tubes

To optimise the use of contrast agents clinically, it is necessary to have a thorough understanding of their behaviour. We have assessed the acoustic response of biSphere¿ microbubbles in both free and 200 ¿m rigid tube environments. An experimental system utilising a Philips research scanner Sonos 5500, previously described, has been used for the assessment of the acoustic response of microbubble contrast agent in solution. More recently a version of this system which enabled the investigation of the acoustic response of single microbubbles in tubes from 200¿m to 12¿m diameter has been TM designed. BiSphere microbubbles were insonated with 7 identical consecutive pulses, at 1ms intervals, using a 6-cycle, 1.6MHz ultrasound pulse for peak negative acoustic pressures ranging 160-1000 kPa. The tubes used for the data described below were 200¿m cellulose tubes with a gravity feed inducing the flow. TM For biSphere , data for 800 single bubbles in tubes and 800 free single bubbles has been analysed by decomposing the calibrated backscattered RF signal into fundamental and harmonic components. The fundamental RMS backscatter from free microbubbles was generally higher than from tubed microbubbles. For rigid shelled biSphere microbubbles, more destruction was observed in tubed microbubbles than in free. The presence of the tube is not thought to have a significant effect on the incident acoustic field. The behaviour of free and microbubbles in 200¿m tubes is not identical and this should be addressed theoretically. Future work will collect data from a range of tube diameters to determine microbubble behaviour at the range of vessel diameters encountered in vivo.