Artifact analysis of a far-field coded-aperture gamma camera extended to partially coded field-of-view

Purpose Coded-aperture gamma cameras play an important role for homeland security nowadays.They have limitedfield-of-view(FOV)which is a critical parameter for many applications.The FOV can be potentially increased by extending it to the penumbra area(partially coded FOV).Methods In this study,we analyzed this artifact phenomenon based on simulating a commercial coded-aperture gamma camera.The camera uses a modified uniformly redundant array(MURA)mask with a basic pattern of rank 11.Its opening angle of the basic pattern to the detector center is 26.36◦which is the commonly used non-artifact FOV(NAFOV).In some applications,the radiation source is a far-field single-point source.Thus,we extend its FOV to 40◦by including a part of the partially coded area,which is a trade-off between the FOV and image quality.Analytical calculations and simulation studies were carried out.The system matrix was calculated using the Sidden’s algorithm.The maximum likelihood expectation maximization(MLEM)reconstruction method was employed.Projections and reconstruction results of the point source at different positions were compared.The second moment of inertia was used as thefigure of merit.Results Results show that projections have periodic similarity with a period of NAFOV,and reconstructions also have periodic artifacts,i.e.,fromθtoθ+NAFOV.Artifacts are the most serious at the edge of the NAFOV.The upper and lower artifacts are more serious than the left and right artifacts due to the difference between the horizontal centerline(tungsten)and vertical centerline(holes expect the center unit)of the mask.Conclusions For a point source with high activity,artifacts can be reduced by increasing the iteration number of the MLEM reconstruction.Even at the edge of NAFOV,the point source can be possibly reconstructed thanks to the large size of the position sensitive detector(PSD)used.The noise will significantly increase artifacts,which may lead to error locate the point source with low activity at some specific positions.

CLSTM-KF reconstruction method for a low-activity moving radiation source localization and tracking with a coded-aperture gamma camera

Background Accurate localization of a low-activity moving radiation source plays an important role in nuclear security and safety.The coded-aperture gamma camera is generally applied to detect a radiation source,but its reconstruction methods may have some limitations when the radiation source is motional and weak.Purpose The purpose of this paper is to improve the quality of the reconstruction images and the localization accuracy when detecting a low-activity moving radiation source with a gamma camera.Method The CLSTM-KF method consists of the CLSTM network and the Kalman filter.The CLSTM network is applied to improve the CNR of reconstruction images by making an adaptive superposition for sequential reconstruction images decoded by the correlation analysis method.After the CLSTM network,a series of sequential positions would be filtered by the Kalman filter.Results By comparing with the traditional methods of the gamma camera,the CLSTM-KF method performs well in improving both the CNR of reconstruction images and the localization accuracy.Moreover,the computation time of the CLSTM-KF method can also meet the application requirements.Conclusion In summary,the CLSTM-KF method provides a better choice than the traditional methods in locating and tracking a low-activity moving radiation source.