Temperature Measurements in Tissue-Mimicking Material during HIFU Exposure

Abstract

Cavitation in high intensity focused ultrasound (HIFU) procedures can yield unpredictable results, particularly when the same location is targeted for more than several seconds. To study this effect, temperature rise was measured in tissue mimicking material (TMM) during HIFU exposures. A 50 um thin wire thermocouple (TC) was embedded in the center of a hydrogel‐based TMM that was previously developed for HIFU applications. HIFU at 825 kHz was focused at the TC junction. Thirty second HIFU exposures of increasing pressure from 1–7 MPa were applied and the temperature rise and decay during and after sonication were recorded. B‐mode imaging was used to monitor any cavitation activity during sonication. If cavitation was noted during the sonication, the sonication was repeated at the same pressure level two more times at 20 minute intervals in order to characterize the repeatability given that cavitation had occurred. The cavitation threshold of the TMM was determined to be approximately 3 MPa at 825 kHz. Temperature traces obtained at various pressure levels demonstrated a wide range of heating profiles in the TMM due to the occurrence of cavitation.