engleski

Acoustic streaming in liquids induced by ultrasound

Acoustic streaming generated by diagnostic ultrasound field is an important area for study for safety reasons. The radiation forces which allow acoustic power to be measured also can cause movement of the liquid medium in the direction of wave propagation called acoustic streaming. The generation mechanism is explained using radiation - pressure gradient due to absorption of ultrasound in the propagation process. The velocity of this acoustically induced flow depends on several parameters, such as sound intensity, sound beam radius, and three liquid properties: viscosity, absorption and speed of sound. Additionally, the harmonic content of the pulse waveform had a major effect on the streaming velocity. Streaming in vivo has been noted during clinical scanning using commercial diagnostic scanners. As the use of ultrasound increases, with the introduction of new techniques, and with increased in acoustic pressures, intensities and powers used in diagnostic ultrasound, raise the possibility that streaming can be induced in liquids within the body. If cells are not free to move but fixed they may experience shear viscous forces due to nearby streaming fluid flow. It is not known yet what is the stress threshold for permanent cell displacement in weakly bounded tissues such as those in the embryo. The possible bioeffects need to be investigated. In diagnostic ultrasound the magnitude of streaming is assumed to be small in vivo and the bioeffects have been considered insignificant. Nevertheless it demonstrates the presence of radiation forces which deserve to be included within an overall discussion of ultrasound safety.

ultrasound; acoustic streaming; liquids

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