Origins of Tissue Optical Properties in the UVA, Visible, and NIR Regions

This paper describes the relationship between the ultrastructure of biological tissues and the observed macroscopic optical scattering properties. A summary of the tissue absorption spectrum is also presented. The scattering of soft tissues (liver, prostate, etc.) and fibrous tissues such as dermis are considered. The scattering of soft tissues is attribued to membranous structures and modeled as Mie scattering from spheres in the 0.2-2-μm diameter range, where membrane lipids occupy about 1-20% of the cellular volume and the refractive index mismatch is 1.46/1.35. The scattering of dermis is modeled as scattering from collagen fiber bundles in the 2.8-μm diameter range occupying 21% of the dermal volume and the refractive index mismatch is 1.38/1.35. The effects of a component of small-scale particle scattering in the Rayleigh limit is also considered. The models are compared with tissue values from the literature for the reduced scattering coefficient, μs(1-g), and the anisotropy, g. The models roughly match the absolute value and wavelength dependence of scattering in the 300-1100 nm wavelength range.