Validating a Model of Colon Colouration Using an Evolution Strategy with Adaptive Approximations

The colour of colon tissue, which depends on the tissue structure, its optical properties, and the quantities of the pigments present in it, can be predicted by a physics-based model of colouration. The model, created by analysing light interaction with the tissue, is aimed at correlating the histology of the colon and its colours. This could be of a great diagnostic value, as the development of tissue abnormalities and malignancies is characterised by the rearrangement of underlying histology. Once developed, the model has to be validated for correctness. The validation has been implemented as an optimisation problem, and evolutionary techniques have been applied to solve it. An adaptive approximate optimisation method has been developed and applied in order to speed up the computationally expensive optimisation process. This works by iteratively improving a surrogate model based on an approximate physical theory of light propagation (Kubelka Munk). Good fittings, obtained under the histologically plausible values of model parameters, are presented. The performances of the new method were compared to that of a simple Evolution Strategy which uses an accurate, but expensive, Monte Carlo method. The new method is general and can be applied with any surrogate model for optimisation.