Cothren et al., Gastrointestinal Endoscopy Vol 44, No. 2, 1996

Detection of dysplasia at colonoscopy using laser-induced fluorescence: a blinded study

- Methods: Fluorescence spectra were collected from normal mucosa and colonic polyps during colonoscopy using 370 nm excitation. Tissue was classified as normal, hyperplastic, or adenomatous by histologic examination. Preliminary data was used to devise an algorithm to differentiate tissue type based on probability distributions of the fluorescence intensity at 460 nm and the ratio of the intensity at 680 nm to that at 600 nm. The algorithm was then tested in a blinded fashion.

- Previously published studies have employed a variety of wavelengths in the ultraviolet range. Kapadia et al. distinguished excised adenomatous polyps from normal mucosa using 325 nm excitation light produced by a helium-cadmium (HeCd) laser and step-wise multivariate linear regression analysis. Marchesini et al. used 410 nm excitation light from a conventional spectrofluorimeter to discriminate dysplastic from nondysplastic colonic biopsy specimens.

(Kapadia CR, Cutruzzola FW, O'Brien KM, Stetz ML, Enriquez R, Deckelbaum LI. Laser-induced fluorescence spectroscopy of
human colonic mucosa: detection of adenomateus transformation. Gastroenterology 1990;99:150-7.)

(Marchesini R, Brambilla M, Pignoli E, et al. Light-induced fluorescence spectroscopy of adenomas, adenocarcinomas and nonneoplastic mucosa in human colon. I. In vitro measurements. J Photochem Photobiol B 1992;14:219-30.)

- We have systematically studied the fluorescence spectra of excised colon tissue excited by ultraviolet and visible wavelengths of light using a spectrofluorimeter to generate fluorescence excitation-emission matrices. The results of these preliminary observations identified excitation light of wavelengths near 330 nm, 370 nm, and 430 nm as optimal for the discrimination of normal and dysplastic colon tissue.

- Fluorescence spectra from normal mucosa, a hyperplastic polyp, and an adenomatous polyp from a typical patient are shown in Figure 2A. Each fluorescence spectrum exhibits a strong emission peak near 460 nm and only weak fluorescence at wavelengths greater than 600 nm. Generally, the peak fluorescence intensity of normal mucosa at 460 nm was greater than that of adenomatous polyps, with hyperplastic polyps intermediate in intensity.

- Previous studies by our group demonstrated that excitation wavelengths throughout the near-ultraviolet range are potentially suitable for the detection of colonic dysplasia. However, our excitation and emission spectral data indicated that 370 nm excitation light provides more specific information than shorter ultraviolet excitation wavelengths. In particular, shorter wavelengths were found to be less likely to excite fluorescence observed at 680 nm.