The color of cancer

Optical spectroscopic techniques examine different types of light–tissue interactions and provide biochemical and morphological information that can be used to characterize changes that take place as tissues become diseased. Tissue is a turbid medium with significant levels of scattering and absorption. To understand the origins of the spectroscopic signals emitted from tissue, it is necessary to use models that take into account the manner in which tissue components interact with light. Using such model-based methods, we extract quantitative information related to different tissue parameters that change with progression to cancer. Specifically, we combine information from simultaneously measured fluorescence and reflectance spectra using a model based on Monte Carlo simulations of light propagation in tissue to remove distortions introduced in the fluorescence spectra by tissue scattering and absorption. We can then extract in a quantitative way differences in the biochemical composition of healthy and pre-cancerous tissues. Tissue reflectance spectra are analyzed using a diffusion-theory-based model to describe changes in the corresponding scattering and absorption properties of normal and diseased sites. Information on the spectra of light singly backscattered from tissues is extracted and analyzed to detect changes in the size and refractive index of cell nuclei. The combined use of intrinsic fluorescence, diffuse reflectance and light scattering spectroscopy yields complementary information which can be used to detect pre-cancers.