Autofluorescence and Photofrin-induced fluorescence imaging and spectroscopy in an animal model of oral cancer

Developments in the fluorescence detection of cancer aim either to distinguish tissue autofluorescence from that of injected fluorophores or to exploit differences in autofluorescent spectra of normal versus transforming, premalignant and malignant tissue. This study evaluates the utility of autofluorescence and Photofrin-induced fluorescence imaging and spectroscopy to distinguish tissue transformation associated with early malignant change in the oral cavity. The model of tissue transformation used was that induced by the carcinogen DMBA in the hamster buccal cheek pouch. Fluorescence spectra were obtained using a high-sensitivity fiber optic spectrometer, while imaging was performed using a Multispectral Fluorescence Guidance (MFG) system designed for use in intraoperative fluorescence imaging during photodynamic therapy. The results demonstrate that Photofrin fluorescence can be used to predict the pathologic state of tissue, the fluorescence intensity being directly proportional to the degree of malignant transformation. Autofluorescence detection measured two parameters that are altered by transformation stage: the red/green fluorescence ratio and the total fluorescence intensity. The most striking feature was the change in the latter in malignant tissue. The MFG imaging device performed as well as spectroscopy: the sensitivity and specificity for the imaging system were 65% and 90% for autofluorescence and 87% and 85% with Photofrin. This indicates that either the autofluorescence intensity index of the tissue or the Photofrin-induced fluorescence may provide a good parameter for the "first approximation" characterization of the tissue.