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The aim of the present study was to investigate the imaging transfer characteristics and the luminescence efficiency (XLE) of Gd2O2S\!\!\!\!:\!\!\!\!Eu powder scintillator for use in X-ray mammography detectors. Gd2O2S\!\!\!\!:\!\!\!\!Eu emits in the red part of the visible spectrum, having very good spectral compatibility with optical sensors employed in digital imaging systems. Three Gd2O2S\!\!\!:\!\!Eu powder scintillating screens, with coating thicknesses 33.1, 46.4 and 63.1 mg/cm^2, were prepared in our laboratory. The imaging performance of these screens was assessed by experimental determination of the modulation transfer function (MTF), the noise transfer function (NTF) and the detective quantum efficiency (DQE) as well as a single index image quality parameter such as the information capacity (IC). A theoretical model, describing radiation and light transfer, was used to fit experimental MTF data. This has allowed the estimation of optical attenuation coefficients of the scintillator. In addition, a previously validated Monte Carlo code, based on the X-ray attenuation properties and on the Mie light scattering theory, was used to estimate the X-ray detection efficiency, the Swank factor and the zero frequency DQE of the Gd2O2S\!\!\!:\!\!\!Eu scintillator. Results showed that Gd2O2S\!\!:\!\!Eu exhibits high MTF and DQE values, which are comparable to those of a commercially employed Gd2O2S\!\!:\!\!Tb screen. In addition Gd2O2S\!\!:\!\!Eu shows high compatibility (effective gain) to CCDs and to recently introduced CMOS based detectors. Considering our image quality parameters and luminescence efficiency results, this material can potentially be considered for use in digital X-ray mammography detectors. [ABSTRACT FROM AUTHOR]

Fundamental imaging performance in terms of Modulation Transfer Function (MTF), Noise Power Spectrum (NPS) and Detective Quantum Efficiency (DQE) was investigated for a high resolution CMOS based imaging sensor. The device consists of a 33.91 mg/cm^2~Gd_2 O _2 S:Tb scintillator screen, placed in direct contact with a CMOS photodiode array. The CMOS photodiode array, featuring 1200\,\times\,1600 pixels with a pixel pitch of 22.5 \mu m , was used as an optical photon detector. In addition to the conventional frequency dependent parameters characterizing image quality, image information content was assessed through the application of information capacity (IC). The MTF was measured using the slanted-edge method to avoid aliasing while the Normalized NPS (NNPS) was determined by two-dimensional (2D) Fourier transforming of uniformly exposed images. Both measurements were performed under the representative radiation quality (RQA) settings, RQA-5 (70 kVp digital-radiography) and RQA-M2 (28 kVp digital-mammography) recommended by the International Electrotechnical Commission Reports 62220-1 and 62220-1-2 respectively. The DQE was assessed from the measured MTF, NPS and the direct entrance surface air-Kerma (ESAK) obtained from X-ray spectra measurement with a portable cadmium telluride (CdTe) detector. The ESAK values ranged between 11–87 \muGy for RQA-5 and 6–40 \muGy for RQA-M2. Additionally the output electrons per X-ray photon of the detector and its signal transfer characteristics were assessed via an analytical model, within the framework of the linear cascaded systems (LCS) theory. It was found that the detector response function was linear for the exposure ranges under investigation. Additionally our results showed that for the same RQA quality the output electrons per X-ray photon, as well as the measured and analytically predicted MTF, were not significantly affected by ESAK. MTF and DQE where found better compared to previously published data for other CCD and CMOS sensors, while the NNPS appeared to be comparable in the frequency range under investigation (0–10 cycles/mm). [ABSTRACT FROM AUTHOR]

This paper investigates the light emission efficiency of Lu[sup2]SiO[sup5] :Ce (LSO) powder scintillator under conditions employed in projection X-ray imaging. Although single-crystal LSO has been thoroughly studied in medical imaging energies, the efficiency of powder LSO has not been previously investigated experimentally under X-ray medical radiography conditions. For this purpose, three scintillating screens with a coating thickness of 63.4, 108.4, and 172.5 mg/cm² were prepared by sedimentation of LSO powder. Measurements of luminescence efficiency (emitted light energy flux over incident X-ray energy flux) were performed in the radiographic X-ray tube voltages range (40-140 kVp). Parameters related to X-ray detection, i.e., quantum detection efficiency, energy absorption efficiency and probability of K-fluorescence reabsorption were calculated. A theoretical model, describing radiation and light transfer, was employed to fit luminescence experimental data and to estimate values of the intrinsic conversion efficiency and of the light attenuation coefficients of the scintillating screens. The spectral compatibility of the LSO powder scintillator to varions optical detectors used in digital radiography was also determined by performing light emission spectrum measurements and by taking into account the spectral sensitivity of electronic optical detectors. Maximum values of LSO luminescence efficiency were observed within the range from 40 to 60 kVp. The 172.5 mg/cm² thick screen was found more efficient than the two thinner screens examined in our experiments. The intrinsic conversion efficiency of LSO (0.10) was found close to that of currently employed phosphors. Spectral compatibility data of LSO screens indicates that LSO may be efficiently coupled to optical detectors used in digital radiography imaging systems. [ABSTRACT FROM AUTHOR]

The degradation of X-ray image passing through thin glass substrate was experimentally investigated in term of modulation transfer function (MTF). The screen was prepared by sedimentation of the powder phosphor (Gd2O2S:Eu) on thin glass substrate with thickness 140 μm (Waldemar Knittel-GmbH). The experiment was carried out under X-ray mammographic conditions. The beam quality was 28 kV, 60 mAs, with W/Rh target/filter combination. The screen was coupled to an optical readout device including a CMOS remote RadEye HR photodiode pixel array. Results showed that there is a 40% degradation of the MTF on average, in the whole spatial frequency range, due to the glass substrate. The glass substrate has a low impact on resolution of the image at low frequencies (12% on average, up to 2.7 cy/mm) and a high impact at medium and high frequencies (70% on average). [ABSTRACT FROM AUTHOR]