Effect of acoustic streaming on ultrasonic heating.

It was found in in vitro experiments performed on tissue phantoms that acoustic streaming in low attenuating fluid may dramatically reduce the temperature rise generated by ultrasound at the surface of bone, if the ultrasound path contains a low-attenuating-fluid/thin-soft-tissue/bone structure. The temperature rise at the surface of bone generated by a 3.5 MHz focused ultrasound beam of 180 mW source acoustic power and an average acoustic intensity at the focus of 5.8 W/cm2 was measured to be only 18% of the value predicted by an existing model, when the bone was in contact with the low attenuating fluid. When a bone surface that is covered by 1 mm thick soft tissue is exposed to the same ultrasound beam, the measured temperature rise at the tissue-bone surface is only 60% of the calculated value.