An SPECT system dedicated to small animal imaging shall be of a millimeter spatial resolution or even better.This study was aimed at achieving 0.5-mm spatial resolution for a small animal SPECT system at low cost.It w...An SPECT system dedicated to small animal imaging shall be of a millimeter spatial resolution or even better.This study was aimed at achieving 0.5-mm spatial resolution for a small animal SPECT system at low cost.It was developed from a single-head clinical SPECT scanner,with a seven-pinhole collimator and a four-degree-offreedom motion control stage.Several key techniques were developed,including high-resolution image reconstruction algorithm,high accuracy geometrical calibration method,and optimized system matrix derivation scheme.The system matrix was derived from Monte-Carlo simulation and de-noised by fitting each point spread function to a two dimensional Gaussian function.Experiments of point source and ultra micro hot rod phantom were conducted.With a spatial resolution of 0.5-0.6 mm,this system provides a practical way for low-cost high-resolution animal imaging on a clinic SPECT system.展开更多
In conventional PET systems,the parallax error degrades image resolution and causes image distortion.To remedy this,a PET ring diameter has to be much larger than the required size of field of view(FOV),and therefore ...In conventional PET systems,the parallax error degrades image resolution and causes image distortion.To remedy this,a PET ring diameter has to be much larger than the required size of field of view(FOV),and therefore the cost goes up.Measurement of depth-of-interaction(DOI)information is effective to reduce the parallax error and improve the image quality.This study is aimed at developing a practical method to incorporate DOI information in PET sinogram generation and image reconstruction processes and evaluate its efficacy through Monte Carlo simulation.An animal PET system with 30-mm long LSO crystals and 2-mm DOI measurement accuracy was simulated and list-mode PET data were collected.A sinogram generation method was proposed to bin each coincidence event to the correct LOR location according to both incident crystal indices and DOI positions of the two annihilation photons.The sinograms were reconstructed with an iterative OSMAPEM(ordered subset maximum a posteriori expectation maximization)algorithm.Two phantoms(a rod source phantom and a Derenzo phantom)were simulated,and the benefits of DOI were investigated in terms of reconstructed source diameter(FWHM)and source positioning accuracy.The results demonstrate that the proposed method works well to incorporate DOI information in data processing,which not only overcomes the image distortion problem but also significantly improves image resolution and resolution uniformity and results in satisfactory image quality.展开更多
To achieve a maximum compression of system matrix in positron emission tomography (PET) image reconstruction, we proposed a polygonal image pixel division strategy in accordance with rotationally symmetric PET geometr...To achieve a maximum compression of system matrix in positron emission tomography (PET) image reconstruction, we proposed a polygonal image pixel division strategy in accordance with rotationally symmetric PET geometry. Geometrical definition and indexing rule for polygonal pixels were established. Image conversion from polygonal pixel structure to conventional rectangular pixel structure was implemented using a conversion matrix. A set of test images were analytically defined in polygonal pixel structure, converted to conventional rectangular pixel based images, and correctly displayed which verified the correctness of the image definition, conversion description and conversion of polygonal pixel structure. A compressed system matrix for PET image recon was generated by tap model and tested by forward-projecting three different distributions of radioactive sources to the sinogram domain and comparing them with theoretical predictions. On a practical small animal PET scanner, a compress ratio of 12.6:1 of the system matrix size was achieved with the polygonal pixel structure, comparing with the conventional rectangular pixel based tap-mode one. OS-EM iterative image reconstruction algorithms with the polygonal and conventional Cartesian pixel grid were developed. A hot rod phantom was detected and reconstructed based on these two grids with reasonable time cost. Image resolution of reconstructed images was both 1.35 mm. We conclude that it is feasible to reconstruct and display images in a polygonal image pixel structure based on a compressed system matrix in PET image reconstruction.展开更多
为提高冲击地压矿井支护立柱防冲性能,设计缓冲吸能装置与3种填充材料,采用理论分析和试验研究方法,研究装置及3种填充材料吸能防冲特性,结果表明:缓冲吸能装置可实现柱径100 mm时初承力为90 k N的预期目标;3种填充材料均有良好的缓冲...为提高冲击地压矿井支护立柱防冲性能,设计缓冲吸能装置与3种填充材料,采用理论分析和试验研究方法,研究装置及3种填充材料吸能防冲特性,结果表明:缓冲吸能装置可实现柱径100 mm时初承力为90 k N的预期目标;3种填充材料均有良好的缓冲和吸能作用,钢板和钢管夹芯材料的各项性能指标均优于泡沫材料,且总吸能多、载荷波动系数小,缓冲作用时间长;2种夹芯材料的载荷峰值都高于泡沫材料,分别提高了5 k N和3 k N;钢管夹芯材料的总吸收能量比泡沫材料和钢板夹芯材料的强度分别高出33.7%和9.1%,而比吸能比其他2种填充材料的对应指标分别提高了9.6%和7.3%;2种夹芯材料的峰值载荷、平均压溃载荷、载荷波动系数接近,钢管夹芯材料的总吸收能量和比吸能都高于钢板夹芯材料,而钢板夹芯材料比钢管夹芯材料的卸载能力强。吸能缓冲装置与填充材料组成的刚-柔耦合支护体系可有效增强立柱抗冲击能力,在一定程度上降低冲击地压事故造成的各种损失。展开更多
基金Supported by Specialized Research Fund for the Doctoral Program of Higher Education(SRFDP200800031071)National Natural Science Foundation of China (No.10975086)the National High Technology Research and Development Program of China(No.2006AA020802)
文摘An SPECT system dedicated to small animal imaging shall be of a millimeter spatial resolution or even better.This study was aimed at achieving 0.5-mm spatial resolution for a small animal SPECT system at low cost.It was developed from a single-head clinical SPECT scanner,with a seven-pinhole collimator and a four-degree-offreedom motion control stage.Several key techniques were developed,including high-resolution image reconstruction algorithm,high accuracy geometrical calibration method,and optimized system matrix derivation scheme.The system matrix was derived from Monte-Carlo simulation and de-noised by fitting each point spread function to a two dimensional Gaussian function.Experiments of point source and ultra micro hot rod phantom were conducted.With a spatial resolution of 0.5-0.6 mm,this system provides a practical way for low-cost high-resolution animal imaging on a clinic SPECT system.
基金Supported by Specialized Research Fund of the Doctoral Program of Higher Education(SRFDP 200800031071 )National Natural Science Foundation of China (No.10975086)National High Technology Research and Development Program("863"Program) of China(No.2006AA020802)
文摘In conventional PET systems,the parallax error degrades image resolution and causes image distortion.To remedy this,a PET ring diameter has to be much larger than the required size of field of view(FOV),and therefore the cost goes up.Measurement of depth-of-interaction(DOI)information is effective to reduce the parallax error and improve the image quality.This study is aimed at developing a practical method to incorporate DOI information in PET sinogram generation and image reconstruction processes and evaluate its efficacy through Monte Carlo simulation.An animal PET system with 30-mm long LSO crystals and 2-mm DOI measurement accuracy was simulated and list-mode PET data were collected.A sinogram generation method was proposed to bin each coincidence event to the correct LOR location according to both incident crystal indices and DOI positions of the two annihilation photons.The sinograms were reconstructed with an iterative OSMAPEM(ordered subset maximum a posteriori expectation maximization)algorithm.Two phantoms(a rod source phantom and a Derenzo phantom)were simulated,and the benefits of DOI were investigated in terms of reconstructed source diameter(FWHM)and source positioning accuracy.The results demonstrate that the proposed method works well to incorporate DOI information in data processing,which not only overcomes the image distortion problem but also significantly improves image resolution and resolution uniformity and results in satisfactory image quality.
基金Supported by Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry and National Natural Science Foundation of China(No.10975086)
文摘To achieve a maximum compression of system matrix in positron emission tomography (PET) image reconstruction, we proposed a polygonal image pixel division strategy in accordance with rotationally symmetric PET geometry. Geometrical definition and indexing rule for polygonal pixels were established. Image conversion from polygonal pixel structure to conventional rectangular pixel structure was implemented using a conversion matrix. A set of test images were analytically defined in polygonal pixel structure, converted to conventional rectangular pixel based images, and correctly displayed which verified the correctness of the image definition, conversion description and conversion of polygonal pixel structure. A compressed system matrix for PET image recon was generated by tap model and tested by forward-projecting three different distributions of radioactive sources to the sinogram domain and comparing them with theoretical predictions. On a practical small animal PET scanner, a compress ratio of 12.6:1 of the system matrix size was achieved with the polygonal pixel structure, comparing with the conventional rectangular pixel based tap-mode one. OS-EM iterative image reconstruction algorithms with the polygonal and conventional Cartesian pixel grid were developed. A hot rod phantom was detected and reconstructed based on these two grids with reasonable time cost. Image resolution of reconstructed images was both 1.35 mm. We conclude that it is feasible to reconstruct and display images in a polygonal image pixel structure based on a compressed system matrix in PET image reconstruction.
文摘为提高冲击地压矿井支护立柱防冲性能,设计缓冲吸能装置与3种填充材料,采用理论分析和试验研究方法,研究装置及3种填充材料吸能防冲特性,结果表明:缓冲吸能装置可实现柱径100 mm时初承力为90 k N的预期目标;3种填充材料均有良好的缓冲和吸能作用,钢板和钢管夹芯材料的各项性能指标均优于泡沫材料,且总吸能多、载荷波动系数小,缓冲作用时间长;2种夹芯材料的载荷峰值都高于泡沫材料,分别提高了5 k N和3 k N;钢管夹芯材料的总吸收能量比泡沫材料和钢板夹芯材料的强度分别高出33.7%和9.1%,而比吸能比其他2种填充材料的对应指标分别提高了9.6%和7.3%;2种夹芯材料的峰值载荷、平均压溃载荷、载荷波动系数接近,钢管夹芯材料的总吸收能量和比吸能都高于钢板夹芯材料,而钢板夹芯材料比钢管夹芯材料的卸载能力强。吸能缓冲装置与填充材料组成的刚-柔耦合支护体系可有效增强立柱抗冲击能力,在一定程度上降低冲击地压事故造成的各种损失。
