Simulation results of a dual aperture gamma ray imager

We report on a hybrid radiation imaging system that combines the advantages of a multi-aperture mechanical collimator with electronic-collimation. The combination offers both efficiency and good angular resolution, and is unique since a single gamma ray can contribute information to both modalities simultaneously. The mechanically collimated camera is most effective for imaging lower energy photons while electronic collimation uncouples spatial resolution from efficiency for higher energies. Our proposed Dual Aperture Gamma Imager (DAGI) combines a high-resolution URA coded aperture with a Compton scatter camera to provide a broader range of energy response suitable for a wider range of industrial applications (50keV-2MeV). The primary detector is a large area LaCl₃:Ce scintillator coupled directly to a Hammamatsu PSPMT, chosen to provide portability, efficiency and energy resolution. A pixellated CsI(Na)/PSPMT combination serves as the secondary absorption detector. Point and ring shaped radiation sources (140, 364, 662 and 1275 keV) are simulated. The results show that DAGI can cover a broad energy range of radiation and the combined dual collimation image, using the maximum likelihood method for image reconstruction, yields better images than either a mechanical or electronic image at intermediate energies. The sensitivity loss of the Compton imager due to the introduction of the mechanical collimator is discussed.