A study of the absorption and scattering factors of light in whole blood.

Abstract

The oxygen saturation of blood, the cardiac output and the nature of pathological conditions in the heart and larger vessels can be determined by photometry using whole blood. Under certain conditions a phenomenological theory which describes the propagation of light in an absorbing and scattering medium, such as whole blood, is possible. In a non-coherent and isotropic scattering medium with a one-dimensional geometry and illuminated by a Lambertian light source the theory of Kubelka and Munk is valid. This theory can be considered as a special case of a photon diffusion theory, which was suggested by Longini and Zdrojkowski, which can also serve to solve three-dimensional problems. In this paper the theory of Kubelka and Munk is reviewed in as far as it is concerned. It is shown that the absorption factor for diffused light in a diffusing medium is twice that of a collimated beam in a clear solution having the same concentration of the absorbing agent. Furthermore, it is pointed out that the scattering factor ρ depends on the haemoglobin concentrationC according to ρ=aC exp (—bC). Shockley showed that the absorption and scattering factors can be related to the parameters of the diffusion model i.e. photon lifetime and diffusion constant. The data thus provided can be used to apply the diffusion theory to the study and design of an oximeter having a three dimensional structure.