Abstract
X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality in optical molecular imaging, which has attracted more attention and has been widely studied. In XLCT, the accuracy and operational efficiency of an optical transmission model play a decisive role in the rapid and accurate reconstruction of light sources. For simulation of optical transmission characteristics in XLCT, considering the limitations of the diffusion equation (DE) and the time and memory costs of simplified spherical harmonic approximation equation (SPN ), a hybrid light transport model needs to be built. DE and SPN models are first-order and higher-order approximations of RTE, respectively. Due to the discontinuity of the regions using the DE and SPN models and the inconsistencies of the system matrix dimensions constructed by the two models in the solving process, the system matrix construction of a hybrid light transmission model is a problem to be solved. We provided a new finite element mesh regrouping strategy-based hybrid light transport model for XLCT. Firstly, based on the finite element mesh regrouping strategy, two separate meshes can be obtained. Thus, for DE and SP N models, the system matrixes and source weight matrixes can be calculated separately in two respective mesh systems. Meanwhile, some parallel computation strategy can be combined with finite element mesh regrouping strategy to further save the system matrix calculation time. Then, the two system matrixes with different dimensions were coupled though repeated nodes were processed according to the hybrid boundary conditions, the two meshes were combined into a regrouping mesh, and the hybrid optical transmission model was established. In addition, the proposed method can reduce the computational memory consumption than the previously proposed hybrid light transport model achieving good balance between computational accuracy and efficiency. The forward numerical simulation results showed that the proposed method had better transmission accuracy and achieved a balance between efficiency and accuracy. The reverse simulation results showed that the proposed method had superior location accuracy, morphological recovery capability, and image contrast capability in source reconstruction. In-vivo experiments verified the practicability and effectiveness of the proposed method.
Highlights
X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality in optical molecular imaging [1,2,3,4]
Adipose, stomach, and kidneys belonged to Region1, while heart, liver, and lungs belonged to Region2 in the experiments of this paper
5.1.1 Forward Simulation Optical transmission models including diffusion equation (DE), SP3, hybrid diffusion equation–SPN method (HDSM), and mesh regrouping strategy-based hybrid light transport model (MRHM) were used for forward simulation; in the hybrid optical transmission model HDSM and MRHM, the same tissue classification was performed according to the experimental setup
Summary
X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality in optical molecular imaging [1,2,3,4]. Chen et al verified that the emission peaks in the emission luminescence spectrum of Gd2O2S:Tb3+ locate at wavelengths of 545, 585, and 620 nm, and the highest peaks locate at wavelengths of 545 nm [20]. It is consistent with the conclusion on the luminescence properties of Tb3+ doping and it corresponds to green emission [21]. Due to reduced tissue-scattering effect resulting from longer wavelength, Eu3+-based nanometer material is more commonly used as X-ray excitable nanophosphors. In the research conclusions of Zhang et al, SP3 simulation is more suitable for Eu3+ luminescence [25]
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