Time-course Characterization of High-intensity Focused Ultrasound Exposure Using B-mode Ultrasound Imaging

High-Intensity Focused Ultrasound (HIFU) is an emerging non-invasive surgical technique. HIFU systems are generally designed to deliver a fixed amount of energy to tissue, but because the tissue thermal response is variable across patients and tissue type, this approach can often lead to underdosing or overdosing. In order to improve the dosing precision in HIFU we are investigating real time monitoring of the energy deposition process through high-frequency diagnostic ultrasound imaging. Ultimately the development of monitoring techniques will allow real-time adjustment of energy to obtain optimal treatment. We present results from an exploratory study into the transient response of HIFU exposure in phantoms and animal tissue. The transient response observed in the B-mode ultrasound images is due to a combination of the thermal-acoustic lens effect, thermal expansion of the medium and cavitation. These preliminary experiments will inform the development of new image analysis techniques for determining dosage received in tissue during HIFU exposure.