P1F-5 Simultaneous Optical and Acoustical Observation of Microbubbles Behaviour

This paper reports on the investigation of the behaviour of single microbubbles under ultrasound excitation, based on simultaneous acoustical and optical observations covering long time intervals (up to 4 minutes). Bubbles from an ultrasound contrast agent (SonoVuereg, Bracco, Geneva) were contained in a small, optically and acoustically transparent tube. The population was diluted until a single bubble was contained within the acoustical focus of an ultrasound transducer irradiating 3 MHz, 210 kPa pulses at 250Hz repetition frequency. Both amplitude and phase information were extracted from the backscattered echo signal. Optical recordings and off-line processing of the images allowed for measuring the resting bubble diameter and displacement. A simulator was used to predict the bubble radial motion and the consequent signal intensity backscattered in the conditions used in the experiments. During experiments, bubbles having a diameter up to 8 mum deflate with a rate depending on the actual diameter. In all cases, when the diameter approached the resonant dimension, the deflation process accelerate. The backscattered signal showed peak amplitudes and phase changes emphasizing the bubble resonant stage during deflation. Other experiments made at 2, 3 and 4 MHz with pressures in the range of 140-900 kPa have yielded similar observations