Fluorescence spectroscopy in tissue phantoms for improved depth resolution in tissue imaging

A way to determine the depth of an embedded fluorescent object, for example deep-lying tumors marked with a fluorescent probe, is to detect fluorescent light that has propagated through the medium at two different wavelength bands. A ratio can then be calculated between the corresponding intensities. The wavelength regions should be chosen such that there is a difference in the absorption in the medium. This spectral information could be used as a complement in other methods, for example in tomography, due to its straightforward implementation. In this study we have performed phantom measurements to determine the depth of a fluorescent object, filled with fluorophores. The transmission of yellow and red fluorescence was measured and a ratio of yellow to red fluorescence was calculated for several depths in tissue with a thickness of 2 cm. The ratio showed a clear dependence on the depth of the object.