A fast spectroscopic system for superficial and local determination of the absorption and scattering properties of tissue (480 to 950 nm) is described. The probe can be used in the working channel of an endoscope. The scattering properties include the reduced scattering coefficient and a parameter of the phase function called gamma, which depends on its first two moments. The inverse problem algorithm is based on the fit of absolute reflectance measurements to cubic B-spline functions derived from the interpolation of a set of Monte Carlo simulations. The algorithm's robustness was tested with simulations altered with various amounts of noise. The method was also assessed on tissue phantoms of known optical properties. Finally, clinical measurements performed endoscopically in vivo in the stomach of human subjects are presented. The absorption and scattering properties were found to be significantly different in the antrum and in the fundus and are correlated with histopathologic observations. The method and the instrument show promise for noninvasive tissue diagnostics of various epithelia.
Histological analysis, which is used to detect and diagnose most tissue alterations, requires an invasive biopsy procedure and a time-consuming tissue treatment, which limit its efficiency in providing rapid, cost-effective diagnosis and hinder the longitudinal study of tissue alteration. To address these limitations, we have developed a novel procedure, using the features of elastic-scattering spectroscopy, for a real-time, non-invasive analysis of tissues. We have tested whether this approach can detect in vivo changes in mouse skin induced by a single exposure to either complete Freund's adjuvant or 12-O-tetradecanoylphorbol-13-acetate, two drugs known to induce discrete alterations of epidermis and dermis, without obvious changes on the skin surface. Here we report that the evaluation of localized absorption and reduced scattering coefficients permitted the detection of changes in skin regions that showed histological alterations, but not in regions which failed to be modified by the drugs. Results show that the optical in vivo analysis of small regions has sufficient specificity and sensitivity to detect minimal alterations of superficial tissues. In view of the prominent involvement of mucosal alterations in most human diseases, including carcinomas, the method provides a useful complement to standard biopsy, notably for the in vivo screening of early in situ epithelial alterations.
The results show that, in a normal clinical setting, the optical in vivo analysis provided by our system detects alterations typical of gastritis, and allow for their graded scoring with a specificity and sensitivity that compare well with those of standard histology, while avoiding the invasiveness of the latter procedure. The method is adaptable to the screening of other types of lesions and mucosae and, hence, should prove useful in improving available diagnostic approaches.
An optical tissue diagnosis technique, often called "optical biopsy", has been developed, It is based on the simultaneous determination of the optical properties of tissues such as the reduced scattering coefficient µ s ' and the absorption coefficient µ a . These data are obtained by applying a small diameter probe (ø 2mm) on tissues, through the working channel of usual endoscopes. The simultaneous determination of µ a and µ s ' with a local probe was made possible by the consideration of the first two moments of the phase function and a proven model of light propagation in tissues at propagation length comparable to the scattering mean free path. Non-invasive measurements of the optical coefficients of superficial tissues have been obtained in vivo at different wavelength
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