Continuous Monitoring of Pulsed HIFU Beams Using Dual-mode Ultrasound Array Systems

We have previously described several DMUA prototypes with therapeutic and imaging capabilities suited for image-guided surgery. A fully real-time system capable of intermittent therapy/imaging operation to allow for high frame rate imaging during therapeutic has been developed. This approach allows for real-time characterization of echoes from the target region at the focal spot within milliseconds of the initiation of the therapeutic pHIFU beam. For example, at intensity levels of similar to 8000 W/cm(2) at 1.15 MHz, analysis of echo data pre- and post-beamforming shows spotty transient activity from within the pHIFU focus, indicative of cavitation. Ex vivo tissue samples were exposed to pHIFU beams of durations < 300 ms at intensity levels in the range of 2500 - 8000 W/cm(2) with interruptions to analyze echo data at frame rates from 100 to 2000 fps. Examination of treated tissue samples shows correspondence between the transient echoes and the nature of the induced lesion (when present). Coupled with the DMUA system's ability to refocus the pHIFU beam at > 1000 updates per second, this approach offers the physician a unique capability of modulating the exposure with millisecond resolution. Examples of monitoring and control of single- and multiple-focus DMUA patterns will be presented and discussed.