Influence of the emission-reception geometry in laser-induced fluorescence spectra from turbid media

Routine clinical detection of precancerous lesions by laser-induced autofluorescence was recently demonstrated in several medical fields. This technique is based on the analysis of complex spectra with overlapping broad structures. However, in biological tissues, scattering and absorption are wavelength dependent, and the observed fluorescence signals are distorted when the illumination and detection geometry varies, making comparison of results from different groups difficult. We study this phenomenon experimentally in human tissue in a simple experiment: A fiber is used for the excitation and an identical fiber is used for reception of the signal; both fibers are maintained in contact with the tissue. We study the distortion of the spectra as a function of the distance between the two fibers. For correction of the spectra we show that it is possible to use a fast and accurate ab initio Monte Carlo simulation when the spectral variations of the optical properties of the medium are known. The main advantage of this simulation is its applicability even for complex boundary conditions or when the sample consists of several layers. (C) 1998 Optical Society of America.