Determination of focal field strength in ultrasound hyperthermia

The lack of noninvasive thermometry systems capable of determining three-dimensional temperature distributions is a major problem in all types of hyperthermia treatment. A study of estimation of the temperature distribution around tumors for focused ultrasound hyperthermia systems was performed. The difference-frequency wavefield formed by focusing a 100% amplitude-modulated 925-kHz acoustic wave carrier with a 25-kHz modulating signal in a water medium was analyzed. Related phase and amplitude measurements of this field were performed. These measurements are used to determine the mean size of the focus and the intensity of acoustic energy at the focus, which yields an estimate for the temperature distribution in the focal volume.<>