Optimization and Estimation of Parameters for a Compton Camera Consisting of the DSSD Scatterer and the GAGG Absorber with the Monte Carlo Simulation

With the advent of new rare-earth-based scintillators, a variety of Compton cameras with novel features in detector material and structure have been developed for the application to either molecular imaging or gamma-ray observation with space telescopes. In this study, we investigated the performance of a Compton camera consisting of a DSSD as a scatterer and an array-type GAGG scintillator as an absorber. We mainly focused on how to optimize the performance of the Compton camera in imaging resolution as well as in efficiency and thereby determined the optimal geometrical configuration with the Monte Carlo simulation using a GEANT4 toolkit. The energy discrimination levels were set in the simulation so that the general experimental environments could be taken into account. We studied different configurations with a figure of merit accounted for efficiency and resolution as a function of the gamma-ray energy, the pixel size of the absorber, the source-to-scatterer distance, the scatterer-to-absorber distance and the scatterer-to-absorber angle in this study. The figure of merit reached its maximum when the source-to-scatterer distance was 3 cm, the scatterer-to-absorber distance was 5 cm and the scatterer-to-absorber angle, that is, the absorber with 256 pixels was located at an angle of 15° with respect to the scatterer for 356-keV gamma rays used in this study. We also investigated how the event rates for Compton scattering obtained by counting the scattering events were contributed to the reconstructed image and caused unwanted imaging artifacts for the optimal configuration. Finally, calculations were performed by using the gamma-ray tracking method with inclusion of two-fold events occurring within the absorber and showed increase in imaging efficiency by 25%.