Optimization of hardware-based photon rejecter to separate electronic noise in the photon counting detector

The cadmium telluride (CdTe)-based photon-counting detector is limited in capability under a high x-ray flux. A photon rejecter composed of aluminum, for example, can reduce this limitation by modulating the incident number of photons. In addition to this function, the optimal photon rejecter can separates electronic noise. The aim of this work was to optimize the photon rejecter for high quality image acquisition by removing electronic noise from the actual pulse signal. We acquired data with various types of photon rejecter materials composed of aluminum (Al) and iodine at three different tube voltages (50, 70 and 90 kVp). A phantom composed of high atomic number materials was imaged to evaluate the efficiency of the photon rejecter. Photon rejecters composed of 1-mm Al, 10-mm Al, and a combination of 10-mm Al and iodine provided optimum capability at 50, 70 and 90 kVp, respectively. Each optimal combination of photon rejecter material and voltage effectively separated electronic noise from the actual pulse signal and gave highest contrast for materials on the image. These optimized types of photon rejecter can effectively discriminate electronic noise and improve image quality according to the different tube voltages.