First Sentence

"To use the fluorescence lifetime as a contrast parameter for microscopy instead of the fluorescent intensity has a number of advantages: (i) The fluorescence lifetime of a probe molecule often differs considerably from that of the background radiation or autofluorescence, providing an opportunity to suppress the contributions of the latter to the total signal; (ii) Fluorescence lifetime imaging provides an alternative to the technique of ratio imaging based on wavelength differences which is used for e.g. the imaging of ion concentrations in biological samples."