Evaluating optical properties of isolated biological scatterers from confocal and low-coherence images

In biomedical optics applications, the scattering of light by biological tissue is typically mimicked by embedding microparticles such as polystyrene microspheres or TiO₂ within a non-scattering matrix. Such particles are well structured and give rise to uniform optical scattering properties. However, typical biological scatterers are seldom well-organized nor uniformly sized. In this work, we sought to characterize the scattering properties from particles common to many tissues such as collagen fibers, cells, and lipids. These purified particles were suspended and sandwiched between 2 glass cover slips to form disposable phantoms. The phantoms were imaged by optical coherence tomography and reflectance-mode confocal microscopy. From the images, the attenuation and reflectivity of the sample were evaluated by fitting the depth-dependent signal from specified regions of the image to a theoretical model. The fitted attenuation and reflectivity were used to deduce a distribution of local values of the scattering coefficient and anisotropy factor for each phantom. The measured optical properties at the 2 wavelengths differed in ways that can be explained by Mie theory, suggesting that despite their complex structure, typical biological scatterers exhibit some regularity that can potentially be characterized quantitatively.