Riley, Jason; (2005) Modelling of light propagation in mixed diffusing and non-diffusing domains. Doctoral thesis , UCL (University College London).

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Abstract

The aim of this research has been to produce a new model for light transport, which handles diffusing and non-scattering domains simultaneously. The drive for this research comes from a field within medical imaging called Optical Tomography. Optical Tomography uses the behaviour of infra-red light passing through tissue to identify its optical parameters, from which clinical measures such as blood volume and oxygenation can be derived. A common model for light transport in Optical Tomography is the Diffusion Approximation to the Radiative Transfer Equation, which is appropriate for diffusing media. However in certain tissues such as the Cerebro-Spinal Fluid, this approximation breaks down, due to the non-scattering effect of this fluid. One alternative to this has been to use a full transport model throughout the domain, however this is computationally expensive. We will introduce a novel 3D model for handling light transport in diffusing domains containing non-scattering spaces. We show a hybridisation of methods from optical and neutron transport theory with further methods taken from computer graphics. We illustrate the validity of the model by comparison with numerical and physical models and use this to show how the clear regions in the head will effect neo-natal imaging. We will show the model we develop to be as accurate as more expensive full transport models for diffusing domains with non-scattering spaces. We use this to illustrate the effects such non-scattering inclusions have on the problem of Optical Tomography of the neo-natal head.

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