Resolution Properties of a Calcium Tungstate (CaWO₄) Screen Coupled to a CMOS Imaging Detector

The aim of the current work was to assess the resolution properties of a calcium tungstate (CaWO₄) screen (screen coating thickness: 50.09 mg/cm², actual thickness: 167.2 μm) coupled to a high resolution complementary metal oxide semiconductor (CMOS) digital imaging sensor. A 2.7x3.6 cm² CaWO₄ sample was extracted from an Agfa Curix universal screen and was coupled directly with the active area of the active pixel sensor (APS) CMOS sensor. Experiments were performed following the new IEC 62220-1-1:2015 International Standard, using an RQA-5 beam quality. Resolution was assessed in terms of the Modulation Transfer Function (MTF), using the slanted-edge method. The CaWO₄/CMOS detector configuration was found with linear response, in the exposure range under investigation. The final MTF was obtained through averaging the oversampled edge spread function (ESF), using a custom-made software developed by our team, according to the IEC 62220-1-1:2015. Considering the renewed interest in calcium tungstate for various applications, along with the resolution results of this work, CaWO₄ could be also considered for use in X-ray imaging devices such as charged-coupled devices (CCD) and CMOS.