Tumor detection in HpD-sensitized mice with fluorescence lifetime imaging

Three time-delayed fluorescence images were used to calculate the spatial distribution of the fluorescence decay time (fluorescence lifetime image) in tumor-bearing mice sensitized with Hematoporphyrin Derivative (HpD). This allowed us to observe that the drug has a significantly longer fluorescence lifetime when it is incorporated in neoplastic tissues with respect to healthy surrounding ones. The imaging technique can be applied noninvasively in vivo in real time. Its diagnostic potential was tested on two murine tumor models (MS-2 fibrosarcoma and L1210 leukemia) after sensitization with low doses of HpD (1 and 0.1 mg/kg body weight). In all the experimental conditions considered, the tumor could be easily identified in the lifetime images. Images were acquired also after removal of the skin overlying the tumor mass. Removal of the skin led to higher values of the lifetime contrast and allowed an even easier tumor localization.