Purpose Robotic CTs can achieve customized trajectory scanning with x-ray tube and detector held by flexible robotic arms rather than fixed rails or gantry.However,the motion errors of the robotic arms cannot be negle...Purpose Robotic CTs can achieve customized trajectory scanning with x-ray tube and detector held by flexible robotic arms rather than fixed rails or gantry.However,the motion errors of the robotic arms cannot be neglected.Hence,the reconstruction method of Robotic CTs should be suitable for arbitrary trajectory and should take motion errors into full consideration.Method In this paper,we present an iterative reconstruction method for robotic CT systems.Unlike the analytical algorithms,such as FDK,this method makes no assumption about the scan trajectory.The projection and backprojection operations are modeled by 3D distance-driven algorithm using the coordinates of x-ray source and detector center fed back from the robotic arm’s positioning system directly.Both numerical simulations and practical experiments are conducted to verify the effectiveness of this method in arbitrary trajectory reconstruction and motion errors correction for robotic CT systems.Results For our non-circular and non-planar trajectory scan,this proposed method could easily handle the reconstruction and obtain a result comparable to reference.In addition,for 0.1%motion errors,using the proposed method could improve the reconstruction quality,and the RMSE could be reduced by 30%.Conclusions This iterative reconstruction method is suitable for arbitrary trajectory scans and can decrease the degradation of image quality caused by motion errors of robotic arm.展开更多
In eight quadrants,the positive and negative signs of tensor components describing physical properties of biaxial crystals have been given.The distributions of the physical properties described with different order te...In eight quadrants,the positive and negative signs of tensor components describing physical properties of biaxial crystals have been given.The distributions of the physical properties described with different order tensors and their space symmetries have been discussed.These results show that the distributions of effective physical constants are symmetrical in the eight quadrants for the orthorhombic system,but there are two and four kinds of distributions for monoclinic and triclinic systems respectively.Thence,to avoid ambiguities and difficulties in characterizing and applying properties of biaxial crystals,we suggest that the really positive directions of the coordinate axes should be defined before the measurements of their physical properties and their device applications.展开更多
The anisotropic physical property is the most noteworthy feature of crystals.In this paper,the subscript change method is used to analyze the sign changes of different tensors describing physical properties in uniaxia...The anisotropic physical property is the most noteworthy feature of crystals.In this paper,the subscript change method is used to analyze the sign changes of different tensors describing physical properties in uniaxial crystals.The distribution of some physical properties in special point groups exhibits non-symmetry in eight quadrants,which should attract the attention of crystal research.The difference between the crystallographic and physical coordinate systems and the lack of crystal symmetry operations are considered to be the origins of the non-symmetry.To avoid ambiguities and difficulties in characterizing and applying crystal physical properties,eight quadrants in space should be clarified.Hence,we proposed the use of piezoelectric properties to define the positive direction of the optical coordinate axis prior to the research and applications of optical properties.展开更多
基金National Natural Science Foundation of China(NSFC)(No.11975250).
文摘Purpose Robotic CTs can achieve customized trajectory scanning with x-ray tube and detector held by flexible robotic arms rather than fixed rails or gantry.However,the motion errors of the robotic arms cannot be neglected.Hence,the reconstruction method of Robotic CTs should be suitable for arbitrary trajectory and should take motion errors into full consideration.Method In this paper,we present an iterative reconstruction method for robotic CT systems.Unlike the analytical algorithms,such as FDK,this method makes no assumption about the scan trajectory.The projection and backprojection operations are modeled by 3D distance-driven algorithm using the coordinates of x-ray source and detector center fed back from the robotic arm’s positioning system directly.Both numerical simulations and practical experiments are conducted to verify the effectiveness of this method in arbitrary trajectory reconstruction and motion errors correction for robotic CT systems.Results For our non-circular and non-planar trajectory scan,this proposed method could easily handle the reconstruction and obtain a result comparable to reference.In addition,for 0.1%motion errors,using the proposed method could improve the reconstruction quality,and the RMSE could be reduced by 30%.Conclusions This iterative reconstruction method is suitable for arbitrary trajectory scans and can decrease the degradation of image quality caused by motion errors of robotic arm.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB1102201)the 111 Project 2.0(Grant No.BP2018013)+3 种基金the National Natural Science Foundation of China(Grant Nos.51772170,51572155,and 11504389)the Shandong Provincial Key R&D Program,China(Grant No.2018CXGC0411)the Young Scholars Program(Grant No.2018WLJH67)the Fundamental Research Founds of Shandong University(Grant No.2017JC044)。
文摘In eight quadrants,the positive and negative signs of tensor components describing physical properties of biaxial crystals have been given.The distributions of the physical properties described with different order tensors and their space symmetries have been discussed.These results show that the distributions of effective physical constants are symmetrical in the eight quadrants for the orthorhombic system,but there are two and four kinds of distributions for monoclinic and triclinic systems respectively.Thence,to avoid ambiguities and difficulties in characterizing and applying properties of biaxial crystals,we suggest that the really positive directions of the coordinate axes should be defined before the measurements of their physical properties and their device applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51772170,51572155,and 11504389)the National Key Research and Development Program of China(Grant No.2016YFB1102201)the Young Scholars Program(Grant No.2018WLJH67).
文摘The anisotropic physical property is the most noteworthy feature of crystals.In this paper,the subscript change method is used to analyze the sign changes of different tensors describing physical properties in uniaxial crystals.The distribution of some physical properties in special point groups exhibits non-symmetry in eight quadrants,which should attract the attention of crystal research.The difference between the crystallographic and physical coordinate systems and the lack of crystal symmetry operations are considered to be the origins of the non-symmetry.To avoid ambiguities and difficulties in characterizing and applying crystal physical properties,eight quadrants in space should be clarified.Hence,we proposed the use of piezoelectric properties to define the positive direction of the optical coordinate axis prior to the research and applications of optical properties.
