Detecting spatially resolved inertial cavitation with a diagnostic ultrasound system

The onset and presence of inertial cavitation in high-intensity focused ultrasound (HIFU) therapy has been identified as an important indicator of energy deposition for therapy planning. A common technique for detecting inertial cavitation is passive cavitation detection, where broadband noise emissions indicative of inertially driven bubbles collapses are detected using a fixed focus transducer. This technique is suboptimal for clinical applications, because most passive cavitation detector (PCD) transducers are tightly focused and thus afford limited spatial coverage of the HIFU focal region. Here, we report on efforts to use a diagnostic ultrasound system as a PCD by operating in passive mode and filtering out the main HIFU frequencies. This approach allows for spatially resolved detection of inertial cavitation throughout the focal region while being insensitive to scattering from voids or bubbles. [Work supported by the Dept. of the Army and the Center for Subsurface Sensing and Imaging Systems.]