Scattering properties of human whole blood under simple shear

To have a fundamental understanding of laser Doppler flowmetry (LDF), knowledge on the optical properties of blood under realistic circumstances is important. In most experiments that have been published, either diluted blood was used, or whole blood in such a configuration that the signal was generated by multiply scattered photons. However, it is questionable whether results of diluted blood can be extrapolated to whole blood. Also, in LDF the signal is partly generated in small vessels, where the multiple scattering regime of light scattering models is not applicable. An experimental facility has been developed that allows for the determination of the scattering cross section and the scattering phase function of thin layers of undiluted blood. The layer is formed between to flat glass plates. By rotating one of the plates, a simple shear can be imposed onto the blood. Experiments have been performed with 633 nm light on layers with a thickness between 20 and 60 micrometer. It was shown that for shear rates in the range 150-500 s^-1, the scattering coefficient has a constant value of 115 mm^-1. Also, the scattering anisotropy for single scattering g ranges from 0.95 at lower shear rates, to 0.975 at higher shear rates. The value of g increases with the shear, both in a direction parallel to and perpendicular to the shear direction.