Image Quality Assessment of a CMOS/Gd₂O₂S:Pr,Ce,F X-Ray Sensor

Abstract

The aim of the present study was to examine the image quality performance of a CMOS digital imaging optical sensor coupled to custom made gadolinium oxysulfide powder scintillators, doped with praseodymium, cerium, and fluorine (Gd 2 O 2 S:Pr,Ce,F). The screens, with coating thicknesses 35.7 and 71.2 mg/cm 2 , were prepared in our laboratory from Gd 2 O 2 S:Pr,Ce,F powder (Phosphor Technology, Ltd.) by sedimentation on silica substrates and were placed in direct contact with the optical sensor. Image quality was determined through single index (information capacity, IC) and spatial frequency dependent parameters, by assessing the Modulation Transfer Function (MTF) and the Normalized Noise Power Spectrum (NNPS). The MTF was measured using the slanted-edge method. The CMOS sensor/Gd 2 O 2 S:Pr,Ce,F screens combinations were irradiated under the RQA-5 (IEC 62220-1) beam quality. The detector response function was linear for the exposure range under investigation. Under the general radiography conditions, both Gd 2 O 2 S:Pr,Ce,F screen/CMOS combinations exhibited moderate imaging properties, in terms of IC, with previously published scintillators, such as CsI:Tl, Gd 2 O 2 S:Tb, and Gd 2 O 2 S:Eu.

Radioluminescence properties of the CdSe/ZnS Quantum Dot nanocrystals with analysis of long-memory trends

“…Hurst exponent (H) is a mathematical quantity which can detect long-range dependencies in time-series (Stodilka et al, 2009;Lawrence et al, 2012). It can estimate the temporal smoothness of time-series and can search if the related phenomenon is a temporal fractal (Petraki et al, 2013;Nikolopoulos et al, 2012Nikolopoulos et al, , 2014a2015). H-values between 0.5 < H < 1, manifest long-term positive auto-correlation between samples in the time-series.…”

“…H-values between 0.5 < H < 1, manifest long-term positive auto-correlation between samples in the time-series. This means that a high present value will be, possibly, followed by a high future value and this tendency will last for long future time-periods (persistency) (Petraki et al, 2013;Nikolopoulos et al, 2012Nikolopoulos et al, , 2014a2015). H-values between 0 < H < 0.5 indicate time-series with long-term switching between high and low values.…”

“…H-values between 0 < H < 0.5 indicate time-series with long-term switching between high and low values. Namely, a high present value will be, possibly, followed by a low future value, whereas the next future value will be high and this switching will last long, into future (anti-persistency) (Petraki et al, 2013;Nikolopoulos et al, 2012Nikolopoulos et al, , 2014a2015). H ¼ 0.5 implies completely uncorrelated time-series.…”

“…Both, the experimental and the computational techniques, offer an extensive methodology to incorporate new and innovative RMI designs, especially, in the modalities which utilise radiation sensors (Knoll, 2010). The current approaches aim to employ new fast lightemitting materials with efficient coupling to state-of-the art optical sensors (Michail, 2015). In particular, the new methods look promising to integrate novel nanophosphors with appealing characteristics, well-established Complementary Metal Oxide Semiconductors (CMOS), e.g.…”

Investigation of YAG:Ce-Based Optical Fibre Sensor for Use in Ultra-Fast External Beam Radiotherapy Dosimetry

“…Eu, La also exhibit a significant energy effect as it has a relatively high effective atomic number (Zeff), which means that the scintillating material-based sensor as a radiation dosimeter requires energy correction of the calibration to reference dosimeters. The effective atomic number of the scintillator GOS is 66.1 [15,16], whilst the Zeff of water, muscle, skin, fat and bone is 7.42, 7.42, 7.31, 5.92 and 13.8, respectively [17,18]. The radiation effect has a very strong dependence on the effective atomic number of the absorbed materials.…”