Studies of the cavitational effects of clinical ultrasound by sonoluminescence: 2. Thresholds for sonoluminescence from a therapeutic ultrasound beam and the effect of temperature and duty cycle

For pt.1 see ibid., vol.33, no.11, p.1239-48 (1988). Sonoluminescence, produced when a therapeutic ultrasound generator operating at 1 MHz was used to insonate a tank of water, was detected using a photomultiplier tube and analysed using pulse height analysis. Spectra of the number of counter per second were obtained for the complete range of observed pulse heights, under exposure conditions similar to those used in clinical practice. Water containing different concentrations of dissolved gases and an agar solution were investigated during the course of the experiments. Measurements were made to establish a threshold for sonoluminescence and the total sonoluminescent light output from tap water insonated with continuous wave ultrasound at 1 W cm -2 was estimated. The density of free radicals produced under these conditions was also estimated. The effects of temperature and duty cycle were investigated over the range 22-45 degrees C and pulsed regimens produced more sonoluminescence than continuous wave ultrasound over a significant part of the pulse height spectrum.