| Optical molecular imaging is an important branch of molecular imaging. It uses optical probes to label specific molecules in organisms. The distribution and variation of the molecular probes can be detected by the outside imaging system, and as a result the organisms would be imaged and analyzed quantitatively and qualitatively in the cell or molecular level. With the development of nanophosphors and optical molecular imaging, a dual-modality imaging system that merges x-ray and optical imaging—X-ray luminescence computed tomography has attracted widespread attention.When excited with x-rays, the nanophosphors can emit visible or near infrared(NIR) luminescence which can be measured by sensitive photon detectors and then be reconstructed. The x-rays passed through the imaging object can be collected by x-ray detector as x-ray projection which would be reconstructed. The XLCT images can be obtained by the fusion of the reconstructed optical and CT images. Compared with other optical molecular imaging modalities, XLCT has several advantages. First, the use of x-ray excitation can eliminate the autofluorescence and the background fluorescence in optical imaging which helps to improve the imaging resolution. Second, XLCT imaging is able to provide more depth localization and resolution due to the good penetrating quality and the selective excitation of X-rays. Further, both the anatomical images with high resolutions and the functional images with sensitive information can be achieved. What's more, the development of nanoparticles also promotes the extensive application prospect of XLCT especially in small animal molecular imaging.Due to the high imaging efficiency and being easy to implement, cone beam XLCT has been developing rapidly since 2013. Since then cone beam XLCT has been the mainstream in the study of XLCT. Cone beam XLCT consists of X-ray source, X-ray detector, rotation stage and optical camera. The cone beam XLCT study has established the imaging model and reconstruction framework, and has made progress on simulation and single target imaging. The imaging efficiency have been greatly improved. However, the imaging precision of cone beam XLCT is not high. Focusing on this question, this thesis carries out researches aiming at:(1) The establishment of cone beam XLCT systemAiming at the study of cone beam XLCT reconstruction algorithm and improving the imaging precision, we have established the cone beam XLCT system which combined the Micro-CT system and the optical imaging system. Firstly, to decrease the influence of incorrect geometry, we have taken a geometric correction on the cone beam XLCT system. The geometric position of all the components of XLCT system has been certified and the accurate geometric parameters have been obtained. Then the hybrid CT/optical modality was registered to complete the establishment of cone beam XLCT system. Finally, a XLCT software platform which combines data sampling, projection simulation and data reconstruction has been developed.(2) The solution of cone beam XLCT imaging modelBased on the cone beam XLCT imaging model, the simulation of the forward problem with finite element method and the inverse problem reconstructed with optimisation and Tikhonov regularization method have been established. The validity of the simulation has been proved by simulation and reconstruction results.(3) The scatter correction of cone beam XLCTX-ray scatters not only result in artifacts in CT reconstructed images but also decrease the imaging precision of XLCT. In this paper, the scatter distribution in a homogeneous phantom has been studied through Monte-Carlo simulation. Based on the simulation results, a scatter correction method has been proposed using an attenuation plate. The physical phantom experiment demonstrated that the reconstruction error has been reduced by the proposed method.(4) The principle component analysis based dual-target imaging of XLCTTo resolve the distribution of drugs in different organs is an important issue in optical molecular imaging. However, the resolution of cone beam XLCT is low because of the ill-posed problem and the scatter of light in tissue. In the in vivo imaging, different organs often accumulate drugs of different concentrations. We have firstly demonstrated the different luminescent efficiency of nanophosphors with different concentrations under a variety of X-ray voltages through physical experiments and induced the principle component analysis method to deal with the optical reconstructed data. The results showed that the distributions of nanophosphors in adjacent tubes with different concentrations has been resolved.In conclusion, aiming at the study of cone beam XLCT system and simulation system, this paper has mainly achieved the finite element simulation of cone beam XLCT which has been verified by simulation and physical phantoms. In addition, the high precision imaging method has been proposed considering the X-ray scatter and multi-target imaging. The proposed methods have improved the imaging precision of cone beam XLCT. |
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