Impact of the fiber-optic faceplate on the imaging performance of a CMOS X-ray detector

Abstract Complementary metal-oxide-semiconductor (CMOS) active-pixel detectors are widely used in various imaging applications owing to their faster operation with lower noise and higher sensitivity than their conventional amorphous silicon-based counterparts. However, CMOS detectors are vulnerable to radiation damage owing to their crystalline structures. They also suffer from ghosting artifacts and gradual reduction of dynamic range along with their lifetime. Most CMOS detectors employ a fiber-optic faceplate (FOP) between the X-ray converter and CMOS active-pixel array to mitigate the radiation effect and increase longevity. In this study, we investigated the effect of an additional FOP layer on the imaging performance of a CMOS detector, including the modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). For X-ray energies ranging from 40 to 70 kV, we measured the large-area signal-transfer functions, MTFs, and NPSs and calculated the corresponding DQEs. The FOP degraded the MTF performance over the entire spatial frequency, but improved the NPS performance with increasing spatial frequency. Consequently, the FOP layer enhanced the DQE performance for the given energy ranges. The measured results are discussed in detail using a theoretical cascaded-systems model.