Laufer, Jan; (2000) Photothermal determination of tissue optical coefficients using an optical fibre sensor. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is concerned with the development of an optical fibre sensor for the photothermal determination of the optical coefficients of tissue. The detection of differences in tissue optical properties might be used for the diagnosis of cancers and other tissue pathologies. The sensor consists of a thin transparent polymer film mounted at the distal end of an optical fibre. The film acts as a Fabry-Perot interferometer. The absorption of short, low energy laser pulses transmitted through the film and into the tissue generates thermal as well as acoustic transients, which propagate into the film and modulate its thickness. The changes in the optical thickness of the film are detected interferometrically. The temporal and amplitude characteristics of the detected photoacoustic and photothermal signals are determined by the optical, acoustic, thermal and spatial properties of the tissue. The interpretation of photothermal signals may allow the diagnosis of tissue pathologies. Photothermal signals detected using the optical fibre sensor were used in conjunction with a numerical model and model-based parameter estimation to determine the optical properties of tissue phantoms. The optical fibre sensor was found to be applicable to the determination of optical coefficients from the photothermal signal provided the thermal coefficients of the target were known with high certainty. The analysis of the parameter sensitivity revealed that the optical fibre sensor in its present configuration is more sensitive to the thermal coefficients than the optical coefficients of the target. Pulsed photothermal radiometry was found to have higher sensitivity to the optical coefficients than has the optical fibre sensor in its present form. However, modifications to the configuration of the sensor can produce a performance matching that of pulsed photothermal radiometry.

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