Transverse flow imaging based on photoacoustic Doppler bandwidth broadening.

We propose a new method to measure transverse flow velocity based on photoacoustic Doppler bandwidth broadening, which is determined by the geometry of the probe-beam and the velocity of the transverse flow. By exploiting pulsed laser excitation and raster motor scanning, three-dimensional structure and flow velocity can be imaged simultaneously. In addition, the flow direction can be determined with bidirectional scanning. In a flowing suspension of red-dyed microspheres (diameter: 6 microm), transverse flow speeds ranging from 0 to 2.5 mms as well as flow direction were measured. A cross-sectional flow image was also obtained with the tube laid in a zigzag pattern.