Hybrid Light Transport Model And The Corresponding Three-dimensional Optical Imaging

With the advantage of high sensitivity, high specificity, simple operation, optical imaging has been widely applied in the field of gene expression, tumor diagnosis, and drug development. Because of the ability of monitoring the lesion at the cell or molecular level, three-dimensional optical imaging has a great potential in the early diagnosis of gastric cancer. However, the void region existed in the stomach must be considered and overcome. Previous studies have shown that void region would have a great influence on the light transport and the corresponding 3D optical imaging.For the void problem, an accurate light transport model and the corresponding reconstruction algorithm are the foundation for the diagnosis of gastric cancer. The main works are to establish an accurate and high efficient light transport model, which are summarized as follows:1. Because of the blurring of the previous classification criterion of the biological tissue, the unreasonable evaluation of the performance and the applicability of the third-order simplified spherical harmonics approximation (SP3) and the diffusion approximation (DA), a new classification criterion based on the absolute value of the optical coefficient rather than based on the ratio of the reduced scattering to the absorption parameter was proposed. In the proposed classification criterion, biological tissues were sorted into four categories:the high-scattering-high-absorption (HSHA), high-scattering-low-absorption (HSLA), low-scattering-high-absorption (LAHA), low-scattering-low-absorption (LALA), by which tissues were characterized with both scattering and absorption. Based on the defined classification criterion, the performance and the applicability of SP3 and DA were investigated with a series of simulation experiments. Experiments have demonstrated that the proposed classification criterion was more suitable for depicting the applicability and the performance of SP3 and DA than those of traditional.2. For the void problem, a hybrid radiosity-diffusion method(HRDM) was utilized to quantitatively investigate the influence of the void region on light transport in turbid medium. We also extend the application of the HRDM into the animal model. Our investigation results suggested that the influence of the void region could be neglected when the size of the void region less than a certain range, otherwise it must be considered. Result obtained by HRDM-based reconstruction method also demonstrated that void region would have a great influence on 3D optical imaging.3. Because of the HRDM method only validated in the high scattering region coupled with void region, a hybrid SPN-radiosity light transport model (HSRM) and the corresponding 3D optical imaging method were proposed to overcome this limitation. In the HSRM, SPN was utilized to model the light transport in scattering region, the radioisty theory was used to depict the light transport in void region. Then, the different two light transport models were coupled together by a newly constructed boundary condition. The accuracy of the proposed HSRM was firstly verified by simulation and physical experiments. Then, simulation experiments demonstrated that the HSRM has a better performance than HRDM. Lastly, the HSRM-based reconstruction has a better performance than HRDM-based one.4. In order to balance the accuracy and the high efficiency, an adaptively alternative light transport model and the corresponding 3D optical imaging were proposed. The concept of adaptively alternative was established based on the principle of optimality. In the framework of the adaptively alternative light transport model, the first step is to classify tissues into different categories, and then select suitable light transport models to describe light propagation in different categories of tissues. By constructing boundary conditions at the boundary of different tissues, these different light transport models were coupled together into the adaptively alternative light transport model. Simulation experiments have demonstrated that the adaptively alternative light transport model could performed with a good balance between the accuracy and the efficiency. The longitudinal and quantitative monitoring of gastric cancer experiment has demonstrated that 3D optical imaging based on the adaptively alternative light transport model has the ability and the potential for accurately and efficiently reconstructing the location and the power of the lesion.