Defining the optimal imaging time point for fluorescence-lifetime-based tumor identification using the non-targeting near-infrared dye indocyanine green and post-processed high-dynamic-range images

Indocyanine green (ICG) is used for tumor visualization using fluorescence-intensity imaging, but false-positive signals are common. Fluorescence-lifetime-based tumor identification may overcome this limitation by measuring the time behavior of fluorescent light. However, the optimal time point for fluorescence lifetime imaging after the intravenous administration of ICG is yet to be defined. In this paper, the in vivo time course of ICG is investigated in syngeneic tumor-bearing mice using a novel macroscopic fluorescence lifetime camera. High-dynamic-range images were generated through post-processing, investigated, and subsequently applied for time-domain intensity and lifetime image analysis. The results indicate that fluorescence lifetime imaging may provide higher accuracy in tumor identification than intensity-based imaging, but the optimal imaging time point appears to require a 24-48 hour interval after intravenous injection, similar to intensity measurements. However, earlier time points might be of interest to investigate for liver and intestinal tumors.