Double-Layered CZT Compton Imager

In this paper, we propose a double-layered cadmium zinc telluride Compton camera using the weighted list-mode maximum likelihood expectation maximization (MLEM) method. We performed a Monte Carlo simulation of the performance. The detection system comprised two detector arrays arranged in parallel. Each array consisted of 6 \times 6 crystals with a 7.5 mm pixel pitch. The dimension of a single crystal was 6 \times 6 \times 15 mm. For Compton imaging, the ¹³⁷Cs activity was set to 78 kBq and the acquisition time was set to 2 hours. By applying the weighted MLEM method, the events with small angular uncertainty were more emphasized than those with large angular uncertainty. Each angular uncertainty was calculated based on the energy and geometry uncertainties of each event. We compared the traditional list-mode MLEM and the weighted list-mode MLEM for single and double detector arrays. The results showed that the combination of a double-layered imager with the weighted MLEM method represented the best image performance compared to other combinations. The sources at the offset positions were also simulated to estimate the directional dependency of the camera system.