Stable cavitation in ultrasound image-guided high intensity focused ultrasound therapy

Abstract

Microbubble activity is significantly involved in both diagnostic and therapeutic aspects of ultrasound image-guided HIFU therapy. Ultrasound interrogation techniques (A-, B-, M-mode, Doppler, harmonic and contrast imaging, and passive and active cavitation detection) were integrated with HIFU. Our results using HIFU devices of 1–5 MHz, and focal, derated intensities of 1,000–10,000 W/cm2, show the formation of microbubbles (about 100 bubbles/mm3, 5–100 microns in size) at the HIFU focus. Boiling, stable, and inertial acoustic cavitation activities were detected during therapy. The presence of bubbles allows the observation of the treatment spot as bright hyperechoic regions in ultrasound images, providing an effective method for guidance and monitoring of therapy. The stable cavitation of microbubbles may provide a mechanism for enhanced HIFU energy delivery, as well as induction of biological responses for stimulation and regulation of specific physiological events such as coagulum and thrombus formation for hemostasis applications, apoptotic activity in treating tumor margins, and stimulation of immune response. Stable cavitation of extrinsic bubbles (contrast agents) is used in detection and localization of internal occult bleeding, using harmonic imaging. There appears to be benefits in utilizing stable cavitation in both diagnostic and therapeutic objectives of ultrasound image-guided HIFU. Funding: DoD, NIH, NSBRI.