Light propagation in tissue during fluorescence spectroscopy with single-fiber probes

• Published in: IEEE journal of selected topics in quantum electronics Vol. 7; no. 6; pp. 1004 - 1012
• Main Authors: Pfefer, T.J., Schomacker, K.T., Ediger, M.N., Nishioka, N.S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2001; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Apertures; Computer simulation; Design engineering; Excitation; Fiber optics; Fluorescence; Laser applications; Light; Light propagation; Mathematical models; Monte Carlo methods; Numerical aperture; Optical design; Optical devices; Optical fibers; Optical propagation; Photons; Probes; Propagation; Signal design; Spectroscopic analysis; Spectroscopy; Spectrum analysis; Stimulated emission; Tissue
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/2944.983306

Fluorescence spectroscopy systems designed for clinical use commonly employ fiberoptic probes to deliver excitation light to a tissue site and collect remitted fluorescence. Although a wide variety of probes have been implemented, there is little known about the influence of probe design on light propagation and the origin of detected signals. In this study, we examined the effect of optical fiber diameter, probe-tissue spacing and numerical aperture on light propagation during fluorescence spectroscopy with a single-fiber probe. A Monte Carlo model was used to simulate light transport in tissue. Two distinct sets of excitation-emission wavelength pairs were studied (337/450 nm and 400/630 nm). Simulation results indicated that increasing fiber diameter or fiber-tissue spacing increased the mean excitation-emission photon pair pathlength and produced a transition from high selectivity for superficial fluorophores to a more homogeneous probing with depth. Increasing numerical aperture caused an increase in signal intensity, but axial emission profiles and pathlengths were not significantly affected for numerical aperture values less than 0.8. Tissue optics mechanisms and implications for probe design are discussed. This study indicates that single-fiber probe parameters can strongly affect fluorescence detection and should be considered in the design of optical diagnostic devices.