Fluorescence lifetime and depth estimation of a tumor site for functional imaging purposes

Cancerous cells have irregular environmental conditions, such as temperature and pH, which distinguish them from their surroundings. Fluorescence lifetime imaging using near-IR (NIR) fluorescent probes, whose lifetime value is sensitive to pH and temperature, enables the estimation of these values, and provides functional information about the tumor. The lifetime value, extracted from the time-resolved intensity decay curve, combines the photon time delays, caused by the photon time of flight, and the intrinsic lifetime in which we are interested. In this study, we present a model, based on the diffusion approximation of the radiation transport equation, for extracting both the depth of an NIR fluorescent probe, and its intrinsic lifetime value, from a fluorescence time decay curve. The model was validated for different inclusion depths, fluorescent lifetime values, and scattering coefficients using a time-resolved Monte Carlo simulation. Our reported results are the first step toward performing functional imaging using fluorescence lifetime in vivo measurements.