ABSTRACT

Biological tissues are highly scattering, turbid media. This makes it difficult to predict the light pathways in tissue and renders optical imaging inside the tissue a challenging task. Figure 3.1 schematically shows the different pathways when a beam of light shines on a transparent medium, such as a piece of glass, versus a turbid medium, such as a tissue slab. For the glass piece, its optical properties can be completely described by the refractive index n and the absorption coefficient µa. Light transport and pathways can be easily predicted by geometry optics. For the tissue slab, due to scattering two more optical parameters, the scattering coefficient µs and the scattering anisotropy g are added to its optical properties description. Light transport and pathways become difficult to predict due to multiple scattering. Also shown are the fluorescence escape process that is complicated by multiple scattering as well.