Fluorescence endoscopic imaging system for detection of colonic adenomas

Abstract

Background/Aims: Autofluorescence spectra have been collected from colonic mucosa with optical fiber contact probes. This technique was found to be sensitive to the biochemical and microarchitectural differences between normal and pre-malignant tissue. It is desired to extend this method to wide area surveillance using endoscopically-collected fluorescence images. Methods: An analytic model was developed to determine the number of photons collected endoscopically in terms of system parameters. This model was used to design a prototype fluorescence imaging instrument. Excitation light at 3 51 and 364 nm was delivered through an optical fiber at a power of 300 mW. Fluorescence images over the spectral bandwidth from 400 to 700 nm were collected from colonic mucosa in 33 ms frames . . fluorescence images were collected in vitro from colectomy specimens from patients with familial adenomatous polyposis and in vivo from patients undergoing routine colonoscopy. Each raw image was corrected for differences in distance and instrument light collection efficiency by normalizing to a spatially averaged image. Intensity thresholding was then used to identify diseased regions of mucosa. Results: For the in vitro studies, a sensitivity of 90% and a specificity of 92% were achieved with the threshold set to 75% of the average normal intensity. The average fluorescence intensity from normal mucosa was found to be greater than that from the adenomas by a factor of 2.2 ± 0.6. For the in vivo images, a sensitivity of 86% for adenomas and a specificity of 100% for hyperplastic polyps were achieved at a threshold of 75%. On average, the ratio between the fluorescence intensity of normal mucosa and that from adenomas was 2.0 ± 0.6 and that from hyperplastics was 1.1 ±. 0.2. The diseased regions on fluorescence were best localized when the colonoscope was directed at normal incidence to the mucosa. At higher angles there were greater effects of artifacts from shadows. Conclusions: Autofluorescence images of colonic mucosa can be collected endoscopically in vitro and in vivo. With image processing techniques, dysplasia can be detected and localized with high sensitivity and specificity. These results demonstrate the potential of this method to direct biopsy site selection.