Doppler measurement of acoustic streaming

To characterize acoustic streaming caused by pulsed ultrasonic beams we used Doppler signal processing to measure streaming velocity under a variety of conditions in-vitro using blood and water. We found velocities as high as 5 mm/s in blood at the diagnostic power levels used in 20 MHz catheter velocimetry. In general, streaming decreases with distance as a function of absorption, increases with applied acoustic power, and decreases with increased viscosity. The time constant to a step change in power is 80 ms in blood and 200 ms in water. We conclude that streaming is measurable in pulsed Doppler beams, that it could produce artifacts or unintended effects, and that it could have important practical applications.