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Date of Award

9-1996

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Supervisor

Douglas R. Wyman

Abstract

Interstitial Laser Photocoagulation (ILP) is a minimally invasive cancer treatment technique whereby optical energy from an implanted optical fiber is used to destroy small, solid tumours. In this work, an optical diffusion approximation and heat transfer equations were used to develop dynamic models of interstitial laser heating. Modifications in the thermophysical and optical properties due to tissue coagulation (T ≥ 60°C) and vaporization of tissue water (T ≥ 100°C) were incorporated into the physical description. In addition, the effect of different blood perfusion approximations on temperature distributions for an in vivo liver model was explored. The calculational results presented indicate the necessity to include dynamic modifications in the tissue biophysical and blood perfusion properties in future parametric investigations of the potential of ILP in various tissues. A quasi-linear model of tissue charring during single fiber ILP was derived. The increase in optical absorption at the fiber tip due to the browning/charring process was modelled as a linear continuous shift in energy deposition from a point optical source to a point heat source. The tissue charring temperature was estimated by placing experimentally measured charring dimensions on calculated temperature profiles. The potential for combining online thermometry with dynamic thermal modelling to reconstruct complete tissue temperature distributions during ILP was also investigated. Features of an on-line temperature reconstruction system have been identified and the physical and technical limitations explored.

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