Studies of acoustic streaming in biological fluids with an ultrasound Doppler technique.

Acoustic streaming generated by diagnostic ultrasound fields is an important area for study both for safety reasons and because of its potential application as a diagnostic tool. A method of investigating streaming in biological fluids is reported. A number of fluids were insonated using a 3.5 MHz weakly focused single element transducer which was driven in pulsed mode. Streaming was detected in each fluid using an 8 MHz continuous wave Doppler system. The maximum streaming velocity was obtained by spectral analysis of the Doppler signal. Using this system longitudinal streaming profiles were measured. At an acoustic power of 150 mW the maximum streaming velocities detected were: 9.3 cm s-1 in water, 6.8 cm s-1 in 4.5% human serum albumin (HSA) solution and 4.9 cm s-1 in blood, when transmission was through a water path of approximately 10 cm into a 3 cm sample of fluid. When measurements were made in the biological fluids alone, without a water path, the maximum streaming velocities were reduced.