Goals
The primary goal of this dissertation is to permit accurate estimates of the
light distributions in tissue during laser irradiation. This goal has two separate
but related tasks:
- 1.
- Develop an exact solution to calculate light fluences
- 2.
- Develop methods to measure the optical properties of a tissue.
The first task is dealt with in the chapters 2 and 3 according to the
method of solution. These are
- Develop a Monte Carlo model for 3D problems
- Develop an adding-doubling model for 1D slab problems
The Monte Carlo method is the currently the only way to calculate fluence for
finite width beams with index mismatching and anisotropic scattering. Chapter 3
discusses the adding-doubling method. This method is very accurate and
much faster than the Monte-Carlo method. Unfortunately, the adding-doubling
method is restricted to one dimension. Consequently, the Monte Carlo and the
adding-doubling methods are complementary accurate techniques useful in
different contexts.
Related to the first goal, but mainly useful for the second goal is the
delta-Eddington approximation. This approximation is an improvement on the diffusion
approximation. The delta-Eddington approximation is very fast and can be used
in iterative procedures to determine the optical properties of tissues. Goals
related to the delta-Eddington approximation are
- Develop a delta-Eddington model for fast, approximate solutions
- Determine accuracy of delta-Eddington approximation
Chapter 4 is devoted to these two subgoals. The Monte Carlo and adding-
doubling methods are used to evaluate the delta-Eddington approximation.
The measurement of optical properties falls into two categories. The first
one concerns the measurement of the phase function
- Give a method for measuring the phase function of tissue
- Determine accuracy of the method
- Make measurements on human dermis
The method for measuring the phase function is based on the single scattering
approximation. The range of optical thicknesses over which this technique is
applicable is evaluated using the adding-doubling method as ``truth.'' In Chapter
5 the method is outlined, the accuracy of the method is checked, and results for
human dermal samples are reported.
In Chapter 6 a method for measuring the optical properties with a
spectrophotometer is discussed.
- Present the inverse iterative method
- Determine errors in the inverse method
- Make measurements on human dermis
The iterative method is outlined in Chapter 6, as well as the limits of its
applicability, and experimental results for human dermis.
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