Modeling of spectral changes for depth localization of fluorescent inclusion.

We have performed modeling of fluorescence signals from inclusions inside turbid media to investigate the influence of a limited fluorescence contrast and how accurately the depth can be determined by using the spectral information. The depth was determined by forming a ratio of simulated fluorescence intensities at two wavelengths. The results show that it is important to consider the background autofluorescence in determining the depth of a fluorescent inclusion. It is also necessary to know the optical properties of the tissue to obtain the depth. A 20% error in absorption or scattering coefficients yields an error in the determined depth of approximately 2-3 mm (relative error of 10-15%) in a 20 mm thick tissue slab.