Tissue autofluorescence has been widely used for diagnostics purposes. However, in the field of fluorescence imaging and tomography, the tissue autofluorescence has always been a nuisance, contributing with nothing but noise to the acquired data. One of the approaches employed by the the Biophotonics Group is to use a new kind of fluorophores, known as Upconverting Nanocrystals, to suppress the effects of the endogenous tissue autofluorescence.