An improved method for energy calibration of photon counting X-ray detectors

Photon counting X-ray detectors with energy discrimination capabilities can discriminate the energy of incident X-ray photon, thereby spectral imaging is possible with them. Energy calibration is a process to find a linear mapping function between the amplitudes of electric pulses and their corresponding photon energy. For practical and efficient energy calibration, the X-ray tube voltage can be used as a reference. However, as the exposure time increases, the threshold giving 50 % of OFF pixels also increases without converging to a point. To reduce calibration errors due to this non-convergent behavior, we present an improved method for energy calibration with applying it to two commercial photon counting X-ray detectors, i.e., a CdTe Medipix2 detector and a CdTe Pixirad2 detector with PFXIE-II read-out ASIC. With the improved mapping function estimated by the improved method, we can better identify the iodine component in a phantom consisting of iodine and other components.