Evaluation of CT images in the very low x-ray exposure with a photon counting detector with a CdTe semiconductor

The development of a pixilated semiconductor detector such as CdTe or CdZnTe, which is available for x-ray imaging, has been pursued by many researchers. In the case of x-ray imaging, the photon flux is very high, and thus conventional CT systems adopt energy integration detectors. On the other hand, the reduction of patient dose becomes one of the major issues in state-of-art CT systems. Thus, detectors require high sensitivity and signal to noise ratio in low flux, and we developed a new CdTe semiconductor detector with a dedicated application-specific integration circuits (ASICs) for a photon counting mode. In this paper, we compared our detector with a conventional energy integration detector by evaluating CT images reconstructed with the projection data that were acquired by each detector. Especially, we evaluated these detectors in terms of the effects on the CT images in the very low x-ray flux. The results showed that no significant differences on CT images between the two detectors were observed except for streak artifacts in the images with the energy integration detector. Our previous research confirmed that the signal to noise ratio of our detector was slightly better than that of the energy integration detector in the very low flux. The results showed that a high signal to noise ratio contributed to the reduction of artifacts in CT images with very low x-ray flux.