Investigation of dual-energy X-ray photon counting using a cadmium telluride detector and two comparators and its application to photon-count energy subtraction

Abstract

To obtain two tomograms with two different photon energy ranges simultaneously, we have performed dual-energy X-ray photon counting using a cadmium telluride (CdTe) detector, two comparators, two frequency–voltage converters (FVCs), and an analog digital converter (ADC). X-ray photons are detected using the CdTe detector with an energy resolution of 1% at 122 keV, and the event pulses from a shaping amplifier are sent to two comparators simultaneously to regulate two thresholds of photon energy. The logical pulses from a comparator are sent to an FVC consisting of two integrators, a microcomputer, and a voltage–voltage amplifier. The smoothed outputs from the two FVCs are input to the ADC to carry out dual-energy imaging. To observe contrast variations with changes in threshold energy, we performed energy-dispersive computed tomography utilizing the dual-energy photon counting at a tube voltage of 70 kV and a current of 25 µA. Two tomograms were obtained simultaneously at two energy ranges of 20.0–70.0 keV and 33.2–70.0 keV. The photon-count subtraction was carried out using photon energies ranging from 20.0 to 33.2 keV. The maximum count rate was 5.4 kilocounts per second with energies of 20.0–70.0 keV, and the exposure time for tomography was 10 min.