Light transport in superficial tissues

We have developed and validated analytic and computational radiative transport models to address both forward and inverse problems of light transport applicable on millimeter length scales for homogeneous and heterogeneous tissues. Such models are demonstrated to provide an accurate description for optical properties and spatial scales relevant for epithelial tissues, and thus aid in the development of optical methods to monitor structural and physiological changes associated with epithelial cancer.; Specifically, we have developed a delta-P1 approximation to the radiative transport equation, which is capable of describing accurate light distributions for spatial scales where the light field exhibits highly asymmetric distribution. This new optical model is validated for steady-state and intensity-modulated sources using experimental and simulated measurements, respectively. In addition, we design and employ a multi-step nonlinear optimization to determine the optical properties of homogeneous infinite medium from spatially-resolved irradiance measurements. The novelty of this method is the ability to extract the single scattering asymmetry, which provides a morphologic measure of the microscopic scatterers within the medium. However, this analytic method is currently somewhat limited to modeling simple homogeneous media. Epithelial tissues are typically composed of two or more layers of different morphology bearing different optical properties. To handle this situation, we develop an inversion algorithm based on perturbation Monte Carlo. This algorithm is capable of accurately modeling light transport within heterogeneous tissue structures such as layered epithelial tissues. We validate this algorithm computationally and experimentally using an optical tissue model that mimics optical structure of cervical tissues.