Thresholds for tissue ablation by focused ultrasound

Thresholds are reported for the production of in vivo focal ultrasonic tissue ablation, in rat kidneys, for single-shot irradiation at 1 MHz and 2.25 MHz with time durations ranging from 10 ms to 1 s. Several investigators have studied ultrasonic dosages for tissue damage, whereas here thresholds are given to produce total tissue ablation. It is shown that with short bursts, at the thresholds for tissue ablation, lesions as well as cavities surrounded by a small ring of coagulating necrosis which always appears at the focus of the sound wave are produced. However, when the intensity is increased, the lesions are more diffuse and do not necessarily appear at the focus, but at random positions. Sometimes for the highest intensities no lesion is present, suggesting that cavities form in the coupling medium