Ultrasound Contrast Agent Microbubble Shell Rupture

I will be speaking on ways to determine the fragmentation pressure threshold of ultrasound contrast agent microbubbles which has significant applications for contrast imaging, development of therapeutic agents and evaluation of potential bioeffects. Using a passive cavitation detector, this work evaluates fragmentation thresholds based on acoustic emissions from single encapsulated gas-filled microbubbles. Sinusoidal ultrasound pulses were transmitted into weak solutions of OptisonTM at different center frequencies (0.9, 2.8 and 4.6 MHz), pulse durations (3, 5 and 7 cycles of the center frequencies), and peak rarefactional pressure levels (0.07 to 5.39 MPa). Pulse repetition frequency was 10 Hz. Signals detected with a 13-MHz center-frequency transducer revealed post-excitation acoustic emissions (between 1 and 5 µs after the excitation) with broadband spectral content. The observed acoustic emissions were consistent with the acoustic signature that would be anticipated from inertial collapse followed by “rebounds” when a microbubble ruptures and thus generates daughter/free bubbles that grow and collapse. The peak rarefactional pressure threshold for detection of these emissions increased with frequency (e.g. 0.53, 0.87 and 0.99 MPa for 0.9, 2.8 and 4.6 MHz, respectively; 5-cycle pulse duration) and decreased with pulse duration. The emissions identified in this work were separated from the excitation in time and spectral content, and provide a novel determination of microbubble shell rupture.

Azzdine Y. Ammi is currently a Research Assistant Professor at OHSU in the Cardiovascular Medicine Division. He received his Ph.D in Acoustical Physics (Dissertation: Detection and modeling of ultrasound contrast agent shell rupture) (2006), from the University Pierre et Marie Curie, Paris VI, France. He received his Master of Science in Acoustical Physics, (2002) at the University Denis Diderot, Paris VII, France. He received his Bachelor of Science in Applied Physics, (2001) at the University Denis Diderot, Paris VII, France which included an academic year (third) at the University of York, England (European ERASMUS Program).