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

Abstract

Abstract. The aim of the current work was to assess the resolution properties of a calcium tungstate (CaWO 4 ) screen (screen coating thickness: 50.09 mg/cm 2 , actual thickness: 167.2 μm) coupled to a high resolution complementary metal oxide semiconductor (CMOS) digital imaging sensor. A 2.7x3.6 cm 2 CaWO 4 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 CaWO 4 /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, CaWO 4 could be also considered for use in X-ray imaging devices such as charged-coupled devices (CCD) and CMOS.

Organic Cation Design of Manganese Halide Hybrids Glass toward Low‐Temperature Integrated Efficient, Scaling, and Reproducible X‐Ray Detector

“…With the paste fixation method, residual air or gaps will cause the loss of optical energy and affect the resolution, while the direct deposition method is technically challenging and expensive. [ 7,8 ] Besides, the large‐area preparation capability makes traditional scintillators uncompetitive. Therefore, the exploration and development of a new‐generation scintillator material to solve the above problems are eagerly anticipated.…”

Imaging performance of a CaWO4/CMOS sensor

“…Thus, it would be of interest to integrate a scintillating material that came to the spotlight once again, with this state-ofthe-art sensor in order to further exploit their imaging characteristics. The CaWO 4 screen was directly overlaid onto the active area of the CMOS and irradiated with a BMI General Medical Merate tube having rotating Tungsten anode and inherent filtration equivalent to 2 mm Al at 70 kV (RQA-5) X-ray beam quality and source to detector distance of 156 cm [21].…”

“…The updated IEC 62220-1-1:2015 [11,33,40] standard describes certain modifications, such as the method for the determination of the modulation transfer function (MTF) in which the final MTF can be now obtained only through averaging of the oversampled edge spread function (ESF) [33,[41][42][43]. The average of all oversampled ESFs was then fitted with a modified Fermi-Dirac distribution function as follows [11,21]:…”

“…The values of fitting parameters are a=7200, b=15, c=65500 and d=0. The fitted ESF was differentiated to obtain the line spread function (LSF) and Fourier transformed to finally obtain the MTF [21,44].…”

“…However, beyond the dominance of terbium-doped gadolinium oxysulfide, the interest for CaWO 4 has been renewed in applications such as, particle astrophysics in the quest for dark matter in the universe [15][16][17], for WIMP-nucleon elastic scattering interactions [18,19], as well as, for customs and border control [15,20]. The resolution properties of this material [21,22], along with the adequate luminescence emission efficiency, at specific Xray energies [5] could be also considered for dual energy applications [23][24][25][26][27][28]. All the aforementioned applications require efficient detectors, of high resolution, with good spectral matching between the phosphor's emission light and the sensitivity of the sensor, thus the aim of this study is to investigate further the properties of a thin layered calcium tungstate screen, coupled to a state-of-the-art NDT active pixel sensor (APS) CMOS sensor, in order to enhance the imaging capabilities of the integrated detector.…”