Research On The Key Technique For Near-infrared Optical Tomography Reconstruction And In Vivo Monitoring Of Thermal Coagulation Of Biological Tissue

Near-infrared optical tomography (OT) is an advanced non-invasively technology in clinic, which can be used to diagnose some diseases based on the measurement of the spatial distribution of inner biological tissue optical parameters. Both the image reconstruction technique and the diagnosis theory of diseases are under the development. The fast image reconstruction algorithm and the tumor targeting method are the most important problems, which are difficult in optical tomography system. The existing methods of OT also fail either in terms of computing-time or quality of spatial resolution. The application of OT in medical engineering has also been probed gradually. The main objective of this dissertation is to obtain a faster and real time optical parameters image reconstruction algorithm with partial biological priori anatomical information and deduce the theory model of inverse problem of OT. It is the first time in this field that we employ OT to monitor the process of tissue's thermal coagulation in vivo. The effective monitoring method is difficult problem in hyperthermia therapy, so the relationship between the optical parameters, thermal coagulation degree and temperature was deeply studied. The important results can be used in monitoring of thermal coagulation therapy.The main achievements in this dissertation are as follows:1. The forward problem of OT was solved based on photon propagation theory in high scattering turbid media. The 2-dimentional steady-state diffuse equation was deducted. The vital important process and conclusion in the solution to the diffuse equation by variational finite element method were deducted and proved in theory. The boundary condition was simplified by considering the real model. The Femlab software was used to simulate the processing of the solution to diffuse equation by finite element method, then photon intensity distribution map in non-uniform high scattering turbid media were given.2. The method for translating the inverse problem of near-infrared optical tomography system into a multi-parameter optimization algorithm was proposed. This method was not based on Jacobian matrix and could avoid the ill-conditioned problem and calculation error of Jacobian matrix. N-decimal system parted coding operator Genetic Algorithm was proposed as the optimization algorithm in above method. Simulations on some representative functions were given to validate the results and theory. The proposed method could improve the reconstruction image accuracy and speed of optical parameter of partial biological tissue.3. The hardware of near-infrared optical tomography system, which was continuous wave-intensity instrument, has been constructed. This system was noninvasive, portable, low-cost and low-power. The different models and experiments were designed to test the properties of this system.4. The relationship between the reduced scattering properties and thermal coagulation of biological tissue was studied. The relationship between inner temperature, process of thermal coagulation and optical parameters was further investigated. The relationship could provide us a possible solution to measure the inner temperature non-invasively in clinic, which confused researcher for a long time.5. A non-invasive method was proposed, which employed near-infrared optical tomography system to monitor processing of thermal coagulation by the spatial distribution of reduced scattering properties. The local reduced scattering coefficient image could be used to evaluate the processe of thermal coagulation. The experiments indicated that the change of reduced scattering coefficient results in the variety of photon energy around the boundary of tissue. Therefore employing the curves of the variety of photon energy, the coagulation processing could be also monitored.NIR OT is currently difficult and hot field in biomedical engineering. There are still lots of problems need to be solved. The ultimate goal of this dissertation, which is on partial optical parameter imaging fast reconstruction alogorithm of OT and medical application of monitoring thermal coagulation, has been accomplished basically.