Temperature rise in tissue: Continuous and pulsed ultrasound regimes

Abstract

Temperature rise in mouse testicular tissue is a linear function of incident cw ultrasound intensity (0–130 W/cm2). Small‐diameter chromel‐constantan thermocouples are used to measure the temperature rise. The absorption coefficient for this tissue (0.029 to 0.070 cm−1 intensity absorption coefficient at 1.1 MHz) provides temperature rises not exceeding 4–5°C with our focused ultrasonic irradiators. When pulse regimes are employed, the linear relationship between temperature rise and average intensity applies in limited circumstances. With spatial peak intensity less than 100 W/cm2 and burst time 100 msec or longer (1000 Hz prf) the temperature rise seems linearly related to average ultrasound intensity. For peak intensities above 100 W/cm2, average intensities below 10 W/cm2, and burst times below 100 msec, the temperature rise is essentially linearly related to peak intensity. For peak intensities below 100 W/cm2 and average intensities below 2–3 W/cm2 the temperature rise appears to be that characteristic of the continuous wave case. Preliminary data on mouse ovarian tissue indicate the same general phenomena is operative. Various experimental configurations have been uses in an attempt to demonstrate that the observed phenomena is a tissue ultrasound interaction effect and not an artifact of the tissue‐thermocouple complex.