Angular distribution of photons scattered on
red blood cells in suspension

Ioan Turcu, Cristian V. L. Pop, Silvia Neamtu

National Institute for Research and Development of Isotopic and Molecular Technologies, P.O. Box 700, 400293, Cluj-Napoca, Romania

Red blood cells (RBCs) scatter light mainly in the forward direction where the scattering phase function has a narrow peak. An experimental investigation was performed into the angular distribution of light scattered by blood in the small angle domain. We focus on two main aspects: the efficiency of the scattering process measured by the scattering cross-section and the angular dispersion of the scattered photons given by the anisotropy parameter.
A highly diluted suspension of RBCs, with haematocrits in the range 510-5-510-2, was illuminated with a He-Ne laser with 632.8 nm wavelength. The experiments were performed in two successive steps:
•	experimental determination of the mean scattering cross-section from the decrease of the transmitted light intensity with the increase of sample haematocrit;
•	angle-resolved measurements of the scattered light in the range of small off-axis deflections. Different samples with increasing haematocrit were investigated and the scattering anisotropy decrease quantitatively characterized.
The intensity of the transmitted collimated beam was captured by three types of photo-detectors:
•	a high resolution monochrome CCD camera
•	a photovoltaic cell
•	a UV/VIS spectrophotometer
The best device proves to be the CCD camera used for far field light detection.
The most relevant parameters that can be obtained by light scattering techniques are:
•	the anisotropy parameter (the mean cosine of scattering angle)
•	the photon mean free path (the inverse of scattering coefficient)
•	the mean scattering cross-section
The transmission and the angular distribution of scattered light were compared with the predictions of the effective phase function model and the single scattering parameters are obtained by fitting the experimental data.

References

1.	M. Hammer, A.N. Yaroslavsky, D. Schweitzer, A scattering phase function for blood with physiological haematocrit, Physics in Medicine and Biology, 46, N65-N69, 2001.
2.	C.V.L. Pop, C. Vamos, I. Turcu, Numerical simulation of speckled light scattered by red blood cells in suspensions, 4th European Biophysics Congress, Alicante, Spain, July 5-9, 2003.
3.	I. Turcu, Effective Phase Function for light scattered by disperse systems – the small angle approximation, Journal of Optics A: Pure and Applied Optics 6 537-543, 2004.