Colorectal Tissue Optical Model Theory And Methods Of Research,

The detection and localization of tumors at their early stage is extremely crucial for treatment of cancer, and then to markedly prolong the life of the patients. Laser spectroscopy is a promising technique in detecting and localizing human tumor tissues. Compared to routine diagnosing methods used in clinic, this technique is fast, noninvasive, quantitative and can be used in vivo. In this dissertation, the main principles, mechanisms and methods for building optical model of the colorectal tissues are studied in detail. This research is mainly funded by the National Key Research Project of the Tenth-Five-Year-Project titled "Research on autofluorescence diagnosing system for early colorectal cancer detection at endoscopy ". The main contents of this dissertation include:1. The diffusion approximation-a useful tool in tissue optical diagnosing is analyzed using the transportation theory of laser in human tissues, and a novel analytical model with three parameters is proposed. Based on this model, a new iteration procedure is devised to inversely calculate the optical parameters of tissues, with the data from Monte Carlo simulations.2. The excitation, emission and propagation of tissue fluorescence are described with an analytical model. By employing Monte Carlo method and a multi-layer model of the colorectal tissue, the autofluorescence emission of colorectal tissue is simulated. It's demonstrated that more than 95 percent of fluorescence is emitted from mucosa and submucosa with ultraviolet excitation.3. The interplay of absorption and scattering can substantially distort the measured fluorescence. In order to extract the intrinsic fluorescence from measured fluorescence, a novel algorithm is given by measuring spectrum of diffuse reflectance. When measured under the same geometry, intrinsic fluorescence can be recovered from measured fluorescence together with diffuse reflectance. More accurate information may be provided with the recovered intrinsic fluorescence.4. An easy-to-use fluorescence measurement system is developed with high sensitivity and high signal-to-noise ratio. Lots of in vivo and in vitro measurements made with this system clearly show the main differences of fluorescence spectra between normal and cancerous tissues are the position of peak and the intensity of peak.