Research On Diagnosis Of Gastrointestinal Carcinoma Using Laser-Induced Autofluorescence

Cancer is regarded as one of the biggest threat to human health. Early detection is critical for cancer treatment. The traditional symptom-based diagnostic methods, in most cases, fail to detect cancers in early phases. The methods based on biochemical and morphological information are becoming more and more important for early cancer detection. Among them, autofluorescence has shown great potential to distinguish early carcinoma from normal tissue without invasion.Based on the earlier work of our group, we set up an apparatus for early tumor detection based on the autofluorescence properties of the gastrointestinal tissues, developed a complete detection method for gastrointestinal cancers, and evolved a theoretical model for transportation of autofluorescence in human gastrointestinal tissues. This thesis consists of three parts:1. High performance detection system for early gastrointestinal cancer using laser-induced autofluorescence (LIAF).Using combined technologies of laser, opto-electronics and computer, a pulsed laser source(energy: 20μJ / mm~2, frequency: 1Hz) suitable for clinical trial is obtained from Nd:YAG laser pumped Ti:Sapphire laser. The laser is used to induce autofluorescence of human gastrointestinal tissues. A highly sensitive detection apparatus is used to collect the autofluorescence which has poor intensity. After systematically optimization, the instrument has been calibrated and validated, and has shown high sensitivity, resolution and wavelength accuracy, which is suitable for the studies of the LIAF of human gastrointestinal tissue.2. Detection and Analysis of the LIAF spectra of normal gastrointestinal tissue and carcinoma.Various wavelengths have been used to test 35 pairs of cancerous and normal gastric samples using Laser-Induced Autofluorescence (LIAF) method, and the optimal excitation wavelength with λ of 360 nm for differentiation cancer and normal tissue has been obtained. The remitted spectra of cancerous and normal gastric samples are carefully compared, and the bands at wavelength range of are chosen as the characteristic bands for cancerous tissues. At last, the maximum curvature of fitting curve of LIAF spectrum within the range of 425 nm to 475 nm is used as the criteria todistinguish gastrointestinal tumor from normal tissue with both sensitivity andspecificity up to 96.7 .3. Model Set up and utilization of the theoretical model of fluorescence transportation.A theoretical model is set up for fluorescence transportation in human two-layer gastrointestinal tissues by Monte-Carlo simulation. The model has been successfully used to analyze the effects of tissue shape, dimension, and boundary conditions on remitted fluorescence. The modeling study has shown that the characteristic fluorescence from carcinoma varies little regardless of the thickness of mucosa. The two-layer tissue model also allows us to reconstruct the LIAF spectra of gastrointestinal tissues.In conclusion, according to the characteristic of cross-subject of our study, this paper presented a set of relative complete detecting and analyzing method for early gastrointestinal cancer, as well as a fluorescent spectroscopy system with high quality has been developed. Some corresponding theoretical researches in the field of tissue biology are developed firstly in China. In a word, we have achieved some innovations and breakthroughs both in experiments and corresponding theories.