Computer-assisted fluorescence identification of colon cancer in rats

Hematoporphyrin derivative (HPD) fluorescence is highly sensitive in identifying colon cancers in the rat. Its specificity, however, is compromised by HPD accumulation in lymphoid follicles. We developed a computer-assisted method to distinguish lymphoid from malignant tissue using HPD fluorescence. Colon cancer was induced in rats by weekly injections of 1,2-dimethylhydrazine. Twenty-four hours after intravenous HPD injection, the animals were sacrificed and the colonic surface was illuminated with a blue light (340-410 nm). Computer images were examined for characteristic patterns of fluorescence at 632 nm. The ratio of fluorescence intensity between lesions and adjacent background areas was also determined. The fluorescent areas were then coded and examined histologically. Eighty-one lesions (21 cancers, 60 lymphoid follicles) were identified. Only two lesions (one cancer, one lymphoid follicle) were incorrectly identified using computer images (concordance rate = 98%). The lesion:background fluorescence ratio was higher in malignant tissue than lymphoid follicles, but significant overlap was seen. These results indicate that computer-enhanced images of HPD fluorescence can distinguish malignant from lymphoid tissue in the rat colon and may have a potential role in the diagnosis of colon cancer.