Spatial and temporal distribution patterns of photosensitizers or their photoproducts is an important observation when attempting to understand the cellular and molecular effects of a particular photochemotherapeutic compound on cells and tissues. While fluorescence microscopy can be readily used to determine the spatial distribution of specific fluorophores within cells, certain limitations arise with this commonly used technique. These limitations include spectral overlap between probes and the fluorophore of interest, endogenous autofluorescence of various intracellular components, and artifactual signals derived from exogenous dyes, all of which interfere with the fluorescent signals emitted from the molecules of interest in a study. The most significant artifactual fluorescent signals given off by intracellular molecules include fluorescence emitted from certain aromatic amino acids, collagen, elastin, pyridoxine, nicotinamide adenine dinucleotides, flavins, and several different porphyrins. In addition to these obstacles, the intercellular environment may influence some fluorophores when macroscopic analysis of tissues is performed. Different fluorophores have different photodynamic activities, photobleaching characteristics, emission wavelength maxima and bandwidths, and fluorescence quantum yields, all of which may lead to a shift in a particular emission signal by a certain fluorophore in a given tissue environment.