Abstract
During in vivo fluorescence and absorption spectroscopy, light is usually delivered to the tissue surface by an optical fiber and collected either by the same fiber or another at some distance from the source. Because of absorption and scattering, the response of such a system to a local change in the absorption coefficient or the fluorescence quantum yield will depend on the position of this perturbation. Proper interpretation of spectra obtained from inhomogeneous media requires knowledge of this spatial dependence. In this paper we describe a model based on diffusion theory which permits calculation of this dependence in three dimensions. Since the propagation of excitation and emitted light are separately considered, both absorption and fluorescence spectroscopy can be studied. The model can also be applied to time-resolved or frequency-domain absorption spectroscopy by use of the time-dependent diffusion equation. Experimental tests of the model have been performed for cw fluorescence spectroscopy by moving a small fluorescent target in a tissue-simulating medium and recording the signal as a function of position. These results are presented with predictions of the model for various irradiation/collection geometries and a range of tissue optical properties.
© 1991 Optical Society of America
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