The effect of light losses in double integrating spheres on optical properties estimation

Abstract

The double integrating sphere setup (DIS) measures diffuse reflectance, diffuse transmittance and collimated transmittance, from which the optical properties of tissue (the absorption coefficient /spl mu//sub a/, the scattering coefficient /spl mu//sub s/ and the anisotropy of scattering g) are estimated. The effect of light losses in the DIS and optical thickness on optical properties estimation by the inverse adding doubling algorithm (IAD) and uniqueness of measurement have been investigated using a Monte Carlo method. Results were obtained for optical properties in turbid tissues (0.80/spl les/albedo/spl les/0.99, 0.80/spl les/anisotropy/spl les/ 0.99, 1.5/spl les/optical thickness/spl les/7.5) sandwiched between glass slides. At optical thickness=6.0 the loss of light through the glass slides is ranging from 13%/spl plusmn/0.5% (at albedo=0.80) to 15%/spl plusmn/0.5% (at albedo=0.98) of the incident power. The loss of light at the exit port in the transmittance sphere is increasing up to 50% of the incident power at highly forward scattering. These losses result in a dependency on optical thickness of the optical properties estimation by the IAD algorithm. Furthermore, because of these losses, the DIS setup measurement is found to be fundamentally nonunique, when simultaneously measuring the diffuse reflectance, diffuse transmittance and collimated transmittance.