Increasing evidence suggests that inflammation may contribute to the process of carcinogenesis. This is the basis of several clinical trials evaluating potential chemopreventive drugs. These trials require quantitative assessments of inflammation, which, for the oral epithelium, are traditionally provided by histopathological evaluation. To reduce patient discomfort and morbidity of tissue biopsy procedures, we develop a noninvasive alternative using diffuse reflectance spectroscopy to measure epithelial thickness as an index of tissue inflammation. Although any optical system has the potential for probing near-surface structures, traditional methods of accounting for scattering of photons are generally invalid for typical epithelial thicknesses. We develop a single-scattering theory that is valid for typical epithelial thicknesses. The theory accurately predicts a distinctive feature that can be used to quantify epithelial thickness given intensity measurements with sources at two different angles relative to the tissue surface. This differential measure approach has acute sensitivity to small, layer-related changes in scattering coefficients. To assess the capability of our method to quantify epithelial thickness, detailed Monte Carlo simulations and measurements on phantom models of a two-layered structure are performed. The results show that the intensity ratio maximum feature can be used to quantify epithelial thickness with an error less than 30% despite fourfold changes in scattering coefficients and 10-fold changes in absorption coefficients. An initial study using a simple two-source, four-detector probe on patients shows that the technique has promise. We believe that this new method will perform well on patients with diverse tissue optical characteristics and therefore be of practical clinical value for quantifying epithelial thickness in vivo.
For individuals with cancer risk factors, reducing tissue inflammation may reduce the risk of developing cancer. This is the basis of several clinical trials evaluating potential chemoprevention drugs. These trials require quantitative assessments of inflammation which, for the oral epithelium, are traditionally provided by punch biopsies. To reduce patient discomfort and morbidity, we have developed a non-invasive alternative using diffuse reflectance spectroscopy. Though any optical system has the potential for probing near-surface structures, traditional methods of accounting for scattering of photons are generally invalid for typical epithelial thicknesses. We have previously developed a theory that is valid in this regime and validated it with Monte Carlo simulations. We use a differential measure with acute sensitivity to small changes in layer scattering coefficients. To assess the capability of the approach to quantify epithelial
thickness, detailed Monte Carlo simulations and measurements on phantom models of a two layered structure have been performed. Preliminary results from this work show that our key feature varies less than 20 percent despite four-fold changes in scattering coefficients and ten-fold changes in absorption coefficients. This indicates that the method will be of practical clinical value for quantifying epithelial thickness in vivo.
Recent studies suggest that inflammatory cell products may contribute to the evolution of particular cancers leading to new chemoprevention trials exploring the benefit of anti-inflammatory drugs such as aspirin and related products. As part of a prospective trial evaluating this anti-inflammatory strategy for oral cancer, we evaluated a non-invasive optical system to determine if we could use an indirect measure of oral inflammation, mucosal thickness, as a monitoring parameter to evaluate the effectiveness of anti-inflammatory drug therapy. Diffuse reflectance spectroscopy has the potential for probing near-surface structures, however, traditional methods for accounting for scattering of photons are generally invalid for typical epithelial thicknesses. Monte Carlo simulations have shown that, with proper scaling, a simple photon model may be used to predict photon behavior under these conditions. A differential measure, which is very sensitive to small changes, has been shown to have the potential to quantify epithelial thickness. A simple prototype device has been brought from desk, to bench and bedside in a rapid manner to fill a need for a non-invasive measure of oral inflammation. From the theory, a simple feature has been identified that corresponds to patient oral inflammation. Preliminary results from this work are presented and indicate that further development of the approach to enable quantification of epithelial thickness in vivo is warranted.
Intrinsic and exogenous fluorescent molecules may be used as specific markers of disease processes, or metabolic status. A variety of fluorescent markers have been successfully used for transparent tissue, in-vitro studies, and in cases where the markers are located close to the tissue surface. For example, given fluorescence lifetime measurements of a fluorophore such as bis(carboxylic acid) dye, the known relationship of pH on its lifetime may be used to determine the pH of tissue at the fluorophore's location. For fluorophore depths greater than approximately one millimeter in normal tissue, such as might be encountered in in vivo studies, multiple scattering makes it impossible to make direct measurements of characteristics such as fluorophore lifetime. In a multiple scattering environment, the collected intensity depends heavily on the scattering and absorption coefficients of the tissue at both the excitation and emission frequencies. Thus, to obtain values for specific fluorophore characteristics such as the lifetime, a theoretical description of the complex photon paths is required. We have applied Random-walk theory to successfully model photon migration in turbid medias such as tissue. We show how time-resolve intensity measurements may be used to determine fluorophore location and lifetime even when the fluorophore site is located many mean photon scattering lengths from the emitter and detector.
We have developed a random walk model that uses time-dependent contrast functions to quantify the crosssection and the diffusion and absorption coefficients of an optically abnormal target from time-of-flight (TOF) data obtained in time-resolved transillumination experiments1. To substantiate our methodology we have used two different sets of data. The first set of data, provided by colleagues at University College London, are TOF measurements obtained using a solid phantom whose thickness (55mm), optical properties (absorption, ?a=0.006mm-1, transport corrected scattering, ?sc'=0.7mm-1), and characteristics of its abnormal target (size=5mm, optical properties twice those of the background) are close to those of a human breast. The second set of data, provided by colleagues at Politecnico di Milan, are TOF measurements on a 50mm thick phantom (?a=0.01mm-1, ?sc'= 1mm-1) in which two 10mm abnormal targets (one abnormally scattering, ?sc'=2mm-1; one abnormally absorbing and scattering, ?a =0.04mm-1, ?sc'=2mm-1), are embedded. None of these data includes very short path photons whose measurements are clinically impractical. Using our time-dependent contrast functions, we were able to estimate the size and optical properties of the targets with an error margin of 3-25%.
Fluorescence lifetime imaging is a useful tool for quantifying site-dependent environmental conditions in tissue. Fluorophores exist with known lifetime dependencies on factors such as concentrations of O2 and other specific molecules, as well as on temperature and pH. Extracting fluorophore lifetime for deeply embedded sites in turbid media such as tissue is made difficult by the multiple scattering of photons traveling through tissue. This scattering introduces photon arrival delays that have similar characteristics to the delays resulting from the excitation and subsequent emission of photons by fluorophores. Random walk theory (RWT) provides a framework in which the two sources of diffusion-like delays can be separated so that the part due to fluorescent lifetime can be quantified. We derive a closed-form solution that predicts time-resolved photon arrivals from a deeply embedded fluorophore site. The solution requires that an average absorption coefficient be used. However, it is shown that this assumption introduces only a small error. This RWT-derived solution is also shown to be valid for a range of geometries in which the fluorophore site is embedded at least 10 mean scattering lengths and in which the fluorophore lifetime is less than 1 ns.
Blood vessels overlying one another at distinct depths (and hence appearing to intersect) in the sclera of the eye can be distinguished reliably from those that in fact do branch within the same depth, using only the information contained in a single photograph of the conjunctiva. That conclusion arises from extension of earlier work that qualitatively inferred relative depth of vessels. The current research was motivated by the need to quantify such inferences in terms of their sensitivities and robustness. A physics first principles model forms the basis for selection of features that capture blood vessel depth information. Features extracted from the image are shown to be useful in that effort; their utility is verified with phantoms that mimic the behavior of the conjunctiva and sclera. Because no special preparations are needed, the method works as well on archived images as on newly-acquired ones, and thus can be used in retrospective studies of images of the eye and other diffuse media.