Acoustic generation of intra-arterial contrast boluses

Microbubbles generated by ultrasonic cavitation in vivo might be useable as flow indicators in some situations instead of injectable contrast agents. Knowledge of those vascular microbubble-generating ultrasonic fields which produce from negligible up to significant damage will help improve guidelines for more effective, safer diagnostic and therapeutic ultrasound. Microbubble boluses have been generated by a 1.8-MHz, focused sound field in the in vivo canine abdominal aorta. Spatial peak acoustic intensities of 19,000 W cm-2 generated microbubble boluses when exposure was longer than 12 ms, whereas intensities greater than 4300 W cm-2 generated a bolus when exposure was for 250 ms. The onset time of these boluses (less than one cardiac cycle) is unachievable with intravenous contrast injection. With optimized waveforms and focusing, acoustic bolus generation may prove to be an effective, minimally invasive method for fast performance of certain selective angiography.