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A Therasonic 1030 (Electro-Medical Supplies) therapeutic ultrasound generator operating at 1 Mkiz continuous wave was used to insonate aerated water at two temperatures, 22 "C and 37 "C. Using various acoustically reflecting materials, sound fields were set up with different standing wave components. Measurements of the acoustic pressure variations on the axis of the sound fields were made using a needle hydrophone and the results were compared with photographs of the spatial distributions of the image intensified sonoluminescent light output. The near field region was used, thereby simulating the clinical situation.Sustained sonoluminescence was observed for nominal intensities of 3 W cm-*, and acoustic reflections of greater than 40%. Under these conditions, if sonoluminescence did not appear spontaneously it could always be induced by rotating the transducer. Whenever bands of maximum light output formed they correlated closely with the pressure antinodes in the standing wave pattern. Very little light was produced by travelling wave fields.

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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 counts 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-* was estimated. The density of free radicals produced under these conditions was also estimated. The effects of temperature and duty cycle were investigated. Sonoluminescence increased with temperature over the range 22-45 "C and pulsed regimens produced more sonoluminescence than continuous wave ultrasound over a significant part of the pulse height spectrum. ResumeEtude par sonoluminescence des effets de cavitation des ultrasons utilises en clinique: 2. Seuils de sonoluminescence pour u n faisceau d'ultrasons a usage therapeutique et effet de la temperature et des conditions d'utilisation.