Study of absorption and scattering properties of tissues

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To investigate the scattering properties of blood, goniophotometric measurement system was developed. The scattering diagram of diluted blood was measured and compared the results with the Mie theory, and estimated the optical parameters.The experimental method is as follows. A cylindrical quarts tube of 9mm in diameter was used as a sample cell. The cell was set in a water bath, and illuminated through an optical window by polarized and collimated laser beam from a laser diode.The scattered light from the sample was collected by an optical fiber hold by the arm of the goniometer, and detected light was transformed to electric signal by an abalanche photodiode. The wavelength of laser beam was 805 nm.Suspensions of spherical acrylic particles with known optical parameters were used as the reference. The Refractive index of sphere was 1.49. Two type of spheres with 1.5 and 5.0 in diameter were used. The differential scattering cross section scattering (scattered power per unit volume per unit incident light intensity) were theoretically calculated for the each reference sample by using Mie theory.By dividing the measured scattered power from the reference sample (0.00245%) by the differential scattering cross section obtained from the theoretical calculation, the instrument factor was determined.Fresh human blood were diluted with a physiological saline to hold single scattering status. Goniophotometric measurements of scattered light from blood samples (Hematocrit 0.025%, 0.011%, 0.0058%, 0.0028%) were carried out, and then those measured results were interpreted to the differential scattering cross sections of blood by using the instrument factor.From the measurement, it ca be seen that anisotropic parameter of diluted blood is around 0.99, and Scattering coefficient per 1% volume fraction of red blood cells in single scattering status is about 7 (mm^<-1>).