Quantitative spectrophotometry on scattering media

Performing spectrophotometry upon a scattering medium is not trivial as the relationship between the absorption of the medium and its attenuation of light is non-linear. Within this thesis the form of this relationship is investigated, with a view to enabling improvements over current spectrophotometric methods. First, an expression is derived that describes the relationship, both in terms of the absorption coefficient of the medium and the modulation frequency of light used to probe the sample. The expression takes the form of a power series in terms of the absorption coefficient and the modulation frequency, with the coefficients being scaled cumulants of the distribution of photon flight times, which is the temporal point spread function. Approximate expressions for the cumulants of the temporal point spread function are then calculated for various medium geometries based upon expresions for the tempora1 point spread function derived using photon diffusion theory. These expressions allow for trends in the relationship between the scattering coefficient of the medium and the cumulants to be assessed. A number of method .. for performing quantitative spectrophotometry are then described that are based upon the expressions derived. The effectiveness of the proposed methods is assessed by applying the methods to results from Monte Carlo simulations of a tissue phantom. The above methods assume that the absorbers present in a medium are evenly distributed. A method by which spectrophotometry can be performed when this is not the case is then described , assuming the properties of only a single region of this heterogeneous medium is of interest. Finally, a, review of previous spectrophotometric methods is given, relating the methods and assumptions which are made to the theory described in the thesis. A comparison between the methods described in the thesis and those reviewed show that the novel methods described can give an improvement in accuracy when used to determine the concentrations of known absorbers present with in a scattering medium.EThOS - Electronic Theses Online ServiceGBUnited Kingdo