Targeted Native Molecular Fluorescence Imaging of Flat Colonic Neoplasia

Abstract

Introduction: Non-polypoid (flat) colorectal neoplasia are prevalent and easily missed during colonoscopy. Missed or unseen flat neoplasia may account for some incident cancers. The routine use of chromoendoscopy during screening colonoscopy for the detection of flat neoplasia is unlikely to be widely embraced by endoscopists. A real time objective technique for detecting and visualizing flat neoplasia is needed. Background and methods: We have previously shown that fluorescence due to tryptophan is significantly increased in cancerous cells compared to normal cells of the colon. We have developed a prototype hyperspectral camera that is sensitive for short wavelength macroscopic imaging of tissue and imaged the fluorescence from tryptophan as well as three other native fluorophores. Excitation light of 280 nm, 320 nm, 340 nm, and 440 nm were used to respectively image tryptophan, collagen, NADH, and FAD fluorescence. A series of freshly resected surgical specimens of colonic mucosa were imaged within 30 minutes of resection. The raw images were corrected for background light, flat-field, absorption and source power fluctuation. Results: Of the four native molecular targets studied, tryptophan fluorescence provided the best high contrast grayscale image of flat colonic neoplasia (see Figure 1). Conclusions: Tryptophan fluorescence, the intensity of which is greater in cancerous than in normal cells, has been macroscopically imaged in the colon for the first time. Macroscopic imaging of tryptophan fluorescence appears to be a promising method for the detection and diagnosis of flat neoplasia of the colon, without the use of topical dyes or other exogenous markers such as fluorescent antibodies. The technique can be incorporated into existing endoscopes.