Towards the enhancement of medical imaging with non-destructive testing (NDT) CMOS sensors. Evaluation following IEC 62220-1-1:2015 international standard

Abstract

The aim of the current work was to investigate the modulation transfer function (MTF) of a non-destructive testing (NDT)/ industrial inspection CMOS sensor in conjunction with a calcium tungstate (CaWO4) thin screen, following both the IEC 62220-1:2003 and IEC 62220-1-1:2015 methods. Thin screen samples, with dimensions of 2.7x3.6 cm2 and mean coating thickness of 36.26 mg/cm2 (actual thickness: 118.9 μm estimated from scanning electron microscopy-SEM images) were extracted from an Agfa Curix universal screen and were manually coupled to the active area of a high resolution, active pixel (APS), complementary metal oxide semiconductor (CMOS) sensor. Experiments were performed using the RQA-5 beam quality, as described in the IEC series. Modulation transfer function was assessed using the slanted-edge method. The final MTF, following IEC 62220-1-1:2015 was obtained through averaging the oversampled edge spread function (ESF), using a custom-made software developed in our laboratory. MTF values were found with close agreement in the low and medium spatial frequency ranges, for both methods. Thereafter, MTFs calculated following the 62220-1:2003 protocol, were found overestimated for spatial frequencies higher than 5.7 cycles/mm. The combination of the thin calcium tungstate screen and the CMOS sensor provided very promising image resolution properties and thus could be also considered for use in CMOS based X-ray imaging devices, for various applications.