Purpose Accurate localization of radioactive materials is critical to nuclear safety and nuclear security.A coded aperture imaging system provides a visualization solution.However,the correlation method has poor recon...Purpose Accurate localization of radioactive materials is critical to nuclear safety and nuclear security.A coded aperture imaging system provides a visualization solution.However,the correlation method has poor reconstruction performance for sources with low counts and for extended sources.Methods In this study,a Monte Carlo optimization-based MLEM algorithm(MC-MLEM)is proposed.The system matrix was obtained by accurate Monte Carlo simulation,so the physical effects such as mask penetration that affect the imaging process were taken into account in the MLEM algorithm.In the simulation process,the normalization of the system matrix was realized by controlling the source at different position of the source plane to have the same activity and emission angle.Results The experimental results showed that compared with the correlation method,the MC-MLEM algorithm could improve the signal-to-noise ratio and angular resolution and locate the source position quickly and accurately under low count conditions.Furthermore,the MC-MLEM algorithm could reconstruct the shape of the extended source and the expected activity ratio of cold-hot sources with large activity differences.Conclusion The MC-MLEM algorithm improved the imaging results and enhanced the reconstruction performance.展开更多
Purpose Coded aperture imaging was a widely used imaging method for radiation sources.However,the traditional gamma camera based on two-dimensional projection information for coded aperture imaging ignored the influen...Purpose Coded aperture imaging was a widely used imaging method for radiation sources.However,the traditional gamma camera based on two-dimensional projection information for coded aperture imaging ignored the influence of the interaction depth of particles and detectors on the projection information,which reduced the imaging quality of the camera to some extent.Therefore,a method of correcting the coded gamma camera based on the interaction depth of particles and detectors is proposed to improve the location accuracy of detectors.Methods The camera developed in this work uses a 7×7 YSO crystal array coupled with two 7×7 Si-PM arrays.The crystal is evenly divided into 11 parts in the depth direction,with a voxel size of 3×3×3 mm3.The coded mask is a 13×13 array,which is a mosaic of two cycles of 7×7 modified uniformly redundant array mask.The depth resolution of the detector is obtained via the subsurface laser engraving dual-end readout method.After obtaining the three-dimensional position information of the interaction point the projection information obtained by the detector is layered,and the image is reconstructed.According to the spatial position information of the detector and the coded mask,the corresponding field of view of each layer of the detector is calculated,and the reconstructed image of each layer is amplified and superimposed according to the ratio of the field of view to obtain the reconstructed image combined with the depth information.Results and conclusion According to Monte Carlo simulation and radiation source imaging experiment results,this method can effectively improve the positioning ability of the detector.For the experimental scenario mentioned in the paper,the location accuracy can be improved by up to 1.54°.展开更多
基金supported by the National Natural Science Foundation of China(No.11905229).
文摘Purpose Accurate localization of radioactive materials is critical to nuclear safety and nuclear security.A coded aperture imaging system provides a visualization solution.However,the correlation method has poor reconstruction performance for sources with low counts and for extended sources.Methods In this study,a Monte Carlo optimization-based MLEM algorithm(MC-MLEM)is proposed.The system matrix was obtained by accurate Monte Carlo simulation,so the physical effects such as mask penetration that affect the imaging process were taken into account in the MLEM algorithm.In the simulation process,the normalization of the system matrix was realized by controlling the source at different position of the source plane to have the same activity and emission angle.Results The experimental results showed that compared with the correlation method,the MC-MLEM algorithm could improve the signal-to-noise ratio and angular resolution and locate the source position quickly and accurately under low count conditions.Furthermore,the MC-MLEM algorithm could reconstruct the shape of the extended source and the expected activity ratio of cold-hot sources with large activity differences.Conclusion The MC-MLEM algorithm improved the imaging results and enhanced the reconstruction performance.
基金supported by the National Natural Science Foundation of China under Grant Nos.12005234 and 12105307.
文摘Purpose Coded aperture imaging was a widely used imaging method for radiation sources.However,the traditional gamma camera based on two-dimensional projection information for coded aperture imaging ignored the influence of the interaction depth of particles and detectors on the projection information,which reduced the imaging quality of the camera to some extent.Therefore,a method of correcting the coded gamma camera based on the interaction depth of particles and detectors is proposed to improve the location accuracy of detectors.Methods The camera developed in this work uses a 7×7 YSO crystal array coupled with two 7×7 Si-PM arrays.The crystal is evenly divided into 11 parts in the depth direction,with a voxel size of 3×3×3 mm3.The coded mask is a 13×13 array,which is a mosaic of two cycles of 7×7 modified uniformly redundant array mask.The depth resolution of the detector is obtained via the subsurface laser engraving dual-end readout method.After obtaining the three-dimensional position information of the interaction point the projection information obtained by the detector is layered,and the image is reconstructed.According to the spatial position information of the detector and the coded mask,the corresponding field of view of each layer of the detector is calculated,and the reconstructed image of each layer is amplified and superimposed according to the ratio of the field of view to obtain the reconstructed image combined with the depth information.Results and conclusion According to Monte Carlo simulation and radiation source imaging experiment results,this method can effectively improve the positioning ability of the detector.For the experimental scenario mentioned in the paper,the location accuracy can be improved by up to 1.54°.
