Issue 50

N. Martini et alii, Frattura ed Integrità Strutturale, 50 (2019) 471-480; DOI: 10.3221/IGF-ESIS.50.39 471 Focused on the research activities of the Greek Society of Experimental Mechanics of Materials Imaging performance of a CaWO 4 /CMOS sensor Niki Martini, Vaia Koukou, George Fountos, Ioannis Valais, Ioannis Kandarakis, Christos Michail Radiation Physics, Materials Technology and Biomedical Imaging Laboratory, Department of Biomedical Engineering, University of West Attica, Athens 12210, Greece michail@upatras.gr , http://orcid.org/0000-0001-5863-8013 Athanasios Bakas, Eleftherios Lavdas, Konstantinos Ninos, Georgia Oikonomou, Lida Gogou Department of Biomedical Sciences, University of West Attica, Athens 12210, Greece George Panayiotakis Department of Medical Physics, Faculty of Medicine, University of Patras, 265 00 Patras, Greece A BSTRACT . The aim of this study was to investigate the modulation transfer function (MTF) and the effective gain transfer function (eGTF) of a non- destructive testing (NDT)/industrial inspection complementary metal oxide semiconductor (CMOS) sensor in conjunction with a thin calcium tungstate (CaWO 4 ) screen. Thin screen samples, with dimensions of 2.7x3.6 cm 2 and thickness of 118.9 μm, estimated from scanning electron microscopy-SEM im- ages, were extracted from an Agfa Curix universal screen and coupled to the active area of an active pixel (APS) CMOS sensor. MTF was assessed using the slanted-edge method, following the IEC 62220-1-1:2015 method. MTF values were found high across the examined spatial frequency range. eGTF was found maximum when CaWO 4 was combined with charge-coupled devices (CCD) of broadband anti-reflection (AR) coating (17.52 at 0 cycles/mm). The combi- nation of the thin CaWO 4 screen with the CMOS sensor provided very promis- ing image resolution and adequate efficiency properties, thus could be also con- sidered for use in CMOS based X-ray imaging devices, for various applications. K EYWORDS . CaWO 4 ; Phosphors; Medical imaging; APS; CMOS sensors; MTF. Citation: Martini, N., Koukou, V., Fountos, G., Valais, I., Kandarakis, I., Michail, Ch., Ba- kas, A., Lavdas, E., Ninos, K., Oikonomou, G., Gogou, L., Panayiotakis, G., Imaging perform- ance of a CaWO 4 /CMOS sensor, Frattura ed Integrità Strutturale, 50 (2019) 471-480. Received: 22.01.2019 Accepted: 22.05.2019 Published: 01.10.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION hosphor materials made of calcium tungstate (CaWO 4 ) [1,2] and zinc sulfide (ZnS) were used as radiation detectors, in the form of thin screens, for almost a century [3,4]. CaWO 4 is a low cost, very stable material, but with a decay time not ideal for applications that require high counting rate measurements (Table 1) [5]. CaWO 4 emits light in P