Improvement of double photon emission Compton imaging using angular and polarization correlations in cascade photons

Abstract

A Compton camera is a gamma ray imaging system that produces images by superposing Compton cones calculated from Compton kinematics. However, the reconstructed images exhibit a high background. In this study, the angular correlation and polarization correlation were used to decrease the background. 111In, which emits 171 keV and 245 keV cascade gamma rays, was imaged using Compton camera modules in the ring structure. The 3D list-mode ordered subset expectation maximization method was used to reconstruct the images. Probability modeling of events reflecting angular and polarization correlations was applied to the image-reconstruction algorithm. The results were compared with those of a typical Compton camera method using only 245 keV Compton cones. The sensitivity of the proposed method was 1.03% of that of the typical method. However, compared to the typical method, the application of angular and polarization correlations improved the signal-to-background ratio. The proposed method is expected to be useful in capturing low-background images wherein a ring-type Compton camera and cascade photon-emitting nuclides can be used.