Acoustic detection of microbubble destruction in gaseous contrast agents

Abstract

The destruction of microbubbles from ultrasound contrast agents has recently received much attention because the disintegration can be used to create new imaging modalities and may produce adverse bioeffects as well. Both passive and active acoustic detection techniques were employed in our experiments to investigate the collective and individual behaviors of contrast microbubbles at different insonification levels. With the passive technique, the oscillation and destruction of microbubbles were studied by characterizing the waveforms of scattered acoustic signals and analyzing the harmonic and noise contents in the spectra of the signals. It was observed that discrete subharmonics and superharmonics (up to the 20th order) were generated at low acoustic pressures. When the bubble destruction occurred at high acoustic pressures, the noise level in the spectra was raised and the discrete harmonic structure in the higher frequency domain reduced to broadband noise. The noise spectrum in the higher frequency range was found to broaden as the acoustic pressure increased. A modified ACD (acoustic cavitation detector) with improved spatial resolution was utilized to study the disintegration process of an individual microbubble. The comparison of results from passive and active detections will be presented.