Optical Diffusion in Blood

Light is absorbed and scattered by whole blood. At very low hematocrit values scattering is small, but for hematocrit ¿0.05 light patterns in blood indicate that scattered photons obey the diffusion equations. Diffusion theory predicts the circular light patterns observed in normal whole blood. Transmittance measurements by small fiberoptic probes in a blood medium give data which are in good agreement with diffusion theory. Values of the diffusion penetration depth ¿d are obtained from the data, which give a quantitative measure of light penetration into blood.