Quantitative frequency-domain fluorescence spectroscopy in tissues and tissue-like media
Cerussi, Albert Edward
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https://hdl.handle.net/2142/30876
Description
Title
Quantitative frequency-domain fluorescence spectroscopy in tissues and tissue-like media
Author(s)
Cerussi, Albert Edward
Issue Date
1999
Doctoral Committee Chair(s)
Gratton, E.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
fluorescence spectroscopy
somatic cell count
Language
en
Abstract
In the never-ending quest for improved medical technology at lower cost, modern near-infrared optical spectroscopy offers the possibility of inexpensive technology for
quantitative and non-invasive diagnoses. Hemoglobin is the dominant chromophore in
the 700-900 nm spectral region and as such it allows for the optical assessment of
hemoglobin concentration and tissue oxygenation by absorption spectroscopy. However, there are many other important physiologically relevant compounds or physiological states that cannot be effectively sensed via optical methods because of poor optical contrast. In such cases, contrast enhancements are required.
Fluorescence spectroscopy is an attractive component of optical tissue spectroscopy. Exogenous fluorophores, as well as some endogenous ones, may furnish the desperately needed sensitivity and specificity that is lacking in near-infrared optical tissue spectroscopy. The main focus of this thesis was to investigate the generation and
propagation of fluorescence photons inside tissues and tissue-like media (i.e., scattering dominated media). The standard concepts of fluorescence spectroscopy have been incorporated into a diffusion-based picture that is sometimes referred to as photon migration. The novelty of this work lies in the successful quantitative recovery of fluorescence lifetimes, absolute fluorescence quantum yields, fluorophore concentrations, emission spectra, and both scattering and absorption coefficients at the emission wavelength from a tissue-like medium. All of these parameters are sensitive to the fluorophore local environment and hence are indicators of the tissue's physiological state.
One application demonstrating the capabilities of frequency-domain lifetime
spectroscopy in tissue-like media is a study of the binding of ethidium bromide to bovine
leukocytes in fresh milk. Ethidium bromide is a fluorescent dye that is commonly used to
label DNA, and hence visualize chromosomes in cells. The lifetime of ethidium bromide
increases by an order of magnitude upon binding to DNA. In this thesis, I demonstrated that the fluorescence photon migration model is capable of accurately determining the somatic cell count (SCC) in a milk sample. Although meant as a demonstration of fluorescence tissue spectroscopy, this specific problem has important implications for the dairy industry's warfare against subclinical mastitis (i.e., mammary gland inflammation),
since the SCC is often used as an indication of bovine infection.
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