Peter Burns PhD, Presenter: Nothing to Disclose

Nico DeJong PhD, Abstract Co-Author: Nothing to Disclose

Peter Bevan MS, Abstract Co-Author: Nothing to Disclose

Ayache Bouakaz PhD, Abstract Co-Author: Nothing to Disclose

Raffi Karshafian MS, Abstract Co-Author: Nothing to Disclose

Glenn Tickner PhD, Abstract Co-Author: Nothing to Disclose

Bubble disruption remains the basis of the most sensitive method for detecting perfusion with contrast agents, and is an essential component of hemodynamic quantitation. To date, understanding the disruption behaviour of bubbles has been limited to acoustic studies and underdetermined mathematical models. Here we combine high speed optical imaging and multipulse acoustic detection of similar bubbles to help elucidate mechanisms.

Four experimental air/polymer agents (Point Biomedical, San Carlos CA) with differing shell thicknesses were studied at 2MHz at pressures up to –2MPa. Acoustic studies: Bubbles were flowed through a chamber and exposed to a calibrated disruption pulse flanked by a sequence of eight very low MI detection pulses. Echoes were collected by a second transducer at –1, 1, 10, 20, 30, 50, 100, 200ms after disruption. Optical studies: The Erasmus University Brandaris camera was used to image the same bubble preparations flowing in a fiber under similar disruption pulses. 128 consecutive images were recorded at a framerate of 10-18 million/sec.

At low MI, these bubbles behave as low elasticity, linear scatterers. Optically, hardly any oscillations are seen. At high MI, a disruption threshold is seen, increasing with shell thickness. Optically, bubbles “break” immediately upon arrival of the 1st US cycle, releasing gas. Following disruption, a transient increase in scattered power is measured corresponding to gas escaping and forming new, probably free bubbles that oscillate vigorously during subsequent cycles. The subsequent decay rate is independent of shell thickness and seen to correspond to gas diffusion.

These experiments present preliminary, independent correlation between the acoustic and optical response of microbubbles following disruption. The disruption echo comes not from the agents, but from the free gas released after shell fracture. Whereas the shell thickness determines disruption threshold, gas diffusion determines echo decay time, which is shortest for air. These measurements will help optimise clinical imaging methods to detect disrupting bubbles and provide a method to assess new bubbles, including ones designed for drug release.

P.B.,N.D.: Research Grant from Point BiomedicalG.T.: Works for Point Biomedical

Burns, P, DeJong, N, Bevan, P, Bouakaz, A, Karshafian, R, Tickner, G, Looking at and Listening to Breaking Bubbles: A Correlative Optical/Acoustic Study of Experimental Polymer/Air Agents.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4416636.html