An aging study of the signal and noise characteristics in large-area CMOS detectors

摘要

For a detector consisting of a phosphor screen and a photodiode array made by complementary metal-oxide-semiconductor (CMOS) process, we have experimentally re-investigated the long-term stability of the signal and noise characteristics as a function of the accumulated dose at the entrance surface of the detector in addition to the previous study [IEEE Trans. Nucl. Sci. 56(3) 1121 (2009)]. The irradiation and analysis were more systematically performed. We report the aging effect in image quality in terms of dark pixel signal, dynamic range, modulation-transfer function (MTF), and noise-power spectrum (NPS). Unlike the previous study, the electronic noise was dominantly increased with the total dose and the other statistical and structural noise sources were nearly independent on the cumulative dose. Similarly, the increase of dark pixel signal and the related noise gradually reduces the dynamic range as the total dose increases. While MTF was almost insensitive to the total dose, degradation in NPS was observed. Therefore, preprocessing without properly updated offset and gain images would underestimate the detective quantum efficiency when performing quality control of a detector in the field. Restoration of degraded dark signals due to aging is demonstrated by annealing the aged detector with thermal activation energy. This study provides a motivation that the periodic monitoring of the image-quality degradation is of great importance for the long-term and healthy use of digital x-ray imaging detectors.