Laser-induced fluorescence spectroscopy at endoscopy: tissue optics, Monte Carlo modeling, and in vivo measurements

Abstract

The optical properties (absorption coefficient, scattering coefficient and the anisotropic factor of scattering) and fluorescence characteristics of normal and abnormal bronchial tissue were measured in vitro. After adding additional blood optical properties to in vitro optical properties of tissue, the in vivo bronchial fluorescence was simulated and analyzed by Monte Carlo modeling. The Monte Carlo simulation results showed that with an appropriate illumination and fluorescence collection geometry, the distortion of in vivo fluorescence spectra of tissue caused by variations of optical properties at different wavelengths could be much reduced. Based on these results, a spectrofluorometry system was developed for the collection of in vivo laser-induced fluorescence spectra of tissue during endoscopy. In comparing the in vivo fluorescence spectral shape of bronchial tissue collected by this system with the intrinsic one obtained in vitro, we found no obvious distortion in the in vivo spectra. This was completely consistent with the analysis of Monte Carlo modeling. The in vivo measurement results demonstrated that significant differences in fluorescence intensity between normal and diseased bronchial tissue (dysplasia, carcinoma in situ) can be used to differentiate them from each other. Also, changes in fluorescence intensity are more robust for detecting abnormal tissues than the differences in spectral characteristics.