Date of Award

1996

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Supervisor

Dr. Michael S. Patterson

Abstract

The goal of this work was to develop and study the use of a diagnostic in vivo tissue spectroscopy system based upon frequency-domain light measurements. Intensity-modulated light which is incident upon a scattering sample creates waves of light intensity which propagate through the medium in a manner which is dependent upon the scattering and absorption characteristics of the tissue. Detection of these waves at a point on the surface of the sample can be used to non-invasively estimate the scattering and absorption coefficients. Recovering these optical interaction parameters requires the use of a suitable model of light propagation in tissue, for which diffusion theory has been shown to work. The technical development of this system and the theoretical modelling are examined in this study. Some physiologically important chromophores can be detected within tissue using the spectral discrimination provided by a wavelength tunable source or detector. The quantification of chromophores can be used in dosimetry for therapeutic laser treatments or for diagnostic laser applications such as measuring hemoglobin oxygen saturation.

In addition to reflectance measurements, diffuse fluorescence can be detected from a scattering medium such as tissue if there is an active fluorescent molecule present. The theoretical modeling for diffuse fluorescence signals was developed and experimentally tested in a tissue-simulating phantom. There was excellent agreement between the theoretical model and the experimental tests with a fluorophore in a scattering emulsion. This work suggests that measurements of fluorescence lifetime or quantum yield can be made on a homogeneous tissue volume by deconvolution of the effects of multiple scattering.

Preliminary work was done on an optical tomography algorithm using measurements of phase and intensity at multiple points on a tissue surface to reconstruct images of the optical properties of the interior. Tomographic imaging is routinely done with x-rays for diagnostic imaging and recent developments suggest that a similar form of imaging can be accomplished with light, albeit with much poorer resolution and contrast. Frequency-domain measurements can provide a method for diffuse optical imaging through relatively thin tissue volumes (i.e., thickness less than approximately 10 cm). The theoretical development of a tomographic imaging system is examined in the final section of this thesis and tested with data from a tissue simulating phantom. The potential medical applications of such a system range from tissue oxygenation imaging to detection of cancerous regions within soft tissue.

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