Radiation Effects on Digital Radiography

In the moment of any given imaging task and thus over the lifetime of a detector, the deposition of certain amount of radiation dose in an electronic pixel element is inevitable. This radiation effect can give rise to a change of the pixel-element characteristics such as the leakage current of a photodiode and the threshold voltage of thin-film transistors (TFTs) [1], and which may consequently result in the degradation of image quality of imaging detectors. While a large amount of effort has been invested in the evaluation of performance degradation of the pixel element devices themselves due to the radiation damage, there has been no sufficient attention paid to the evaluation of imagequality degradation although that is an important issue regarding the quality control and assurance of detectors and thus their lifetime. In this study, we have studied radiation effects on the image quality of a photodiode array detector made by complementary metal-oxide-semiconductor (CMOS) process in conjunction with a phosphor screen. We report the observation of an image-quality degradation by assessing MTF (modulation-transfer function), NPS (noise-power spectrum) and DQE (detective quantum efficiency) with respect to the total ionizing dose at the detector entrance.