An experimental investigation of streaming in pulsed diagnostic ultrasound beams.

Streaming is shown to occur in water in the focused beams produced by a number of medical pulse-echo devices. The use of hot film anemometry to measure the streaming velocity is described and velocities measured in water using commercial equipment are quoted. The highest velocities occur in pulsed Doppler mode with a maximum velocity of 14 cm s-1 being observed. An experimental set-up was used to investigate the parameters affecting streaming and it was found that the harmonic content of the pulse waveform had a major effect on the streaming velocity. The time taken for a stream to become established at the focus of the acoustic beams studied was typically approximately 0.5 s.