Effects of Fiber-optic Plates on Image Quality of CMOS X-ray Detectors

Radiation damage and its effects on image quality of Complementary metal-oxide-semiconductor (CMOS) devices have also been reported by previous studies. In this regard, most CMOS sensor manufacturers usually employ a fiber-optic plate (FOP) bonded to the CMOS photodiode array. In this configuration, the FOP layer absorbs un-attenuated x-ray photons through an overlaid scintillator; otherwise the un-attenuated photons might be absorbed within the CMOS photodiode array directly. Therefore, it is important to select an optimal thickness of an FOP layer for the long-term use of CMOS sensors providing high-quality images. By comparing the image qualities of the CMOS detector measured without and with FOP, the effects of FOP on the imaging system have been investigated for various x-ray spectra. Measurements showed that the FOP degraded the x-ray sensitivity and resolving power, whereas it enhanced noise properties by absorbing un-attenuated x-ray photons. As a result, the use of FOP enhances the DQE performance which mainly governs x-ray image quality. However, for a low exposure imaging, the use of FOP may not be appropriate because it reduces the light photon transmittance by ∼55% which implies that the image quality could be easily affected by additional electronics noise rather than quantum noise. In this regard, the use of FOP may be more appropriate for industrial applications in which irradiation condition is harsh