Decay time images of HpD fluorescence for tumor detection in mice

A system for time-gated imaging has been used to measure the spatial distribution of the fluorescence decay time in tumor-bearing mice sensitized with Hematoporphyrin Derivative. Mice were injected with five doses of the sensitizer ranging from 0.1 to 10 mg/kg body weight. Several fluorescence images of each mouse were acquired at different delays after the excitation pulses, and a matrix processing algorithm was applied to calculate the average decay time corresponding to each pixel. It was found that, for any drug dose, the decay time of the exogenous fluorescence in the tumor is always significantly longer than in normal tissues. The images created by associating a gray scale to the decay time matrix of each sample allow a reliable and precise detection of the neoplasia, even with a very low dose of the sensitizer.