<title>Imaging of tumors by time-delayed laser-induced fluorescence</title>

Abstract

A technique to improve signal-to-background ratio in fluorescence images of superficially growing tumors marked with photosensitizers is described. Time-delayed detection of fluorescence following pulsed-laser excitation allows suppression of the autofluorescence background falling into the fluorescence band of the photosensitizer. This technique exploits the longer fluorescence-decay times of porphyrin-based photosensitizers compared to average decay times of tissue autofluorescence. The feasibility of time-delayed fluorescence imaging of tumors has been demonstrated in vitro. From time-delayed fluorescence spectra the authors infer that the ratio between photosensitizer signal and autofluorescence background can be improved by about one order of magnitude.