Publications (2)2.89 Total impact
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Article: Evaluation of the Red Emitting Powder Scintillator for Use in Indirect X-Ray Digital Mammography Detectors
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ABSTRACT: The aim of the present study was to investigate the imaging transfer characteristics and the luminescence efficiency (XLE) of Gd<sub>2</sub>O<sub>2</sub>S:Eu powder scintillator for use in X-ray mammography detectors. Gd<sub>2</sub>O<sub>2</sub>S:Eu emits in the red part of the visible spectrum, having very good spectral compatibility with optical sensors employed in digital imaging systems. Three Gd<sub>2</sub>O<sub>2</sub>S:Eu powder scintillating screens, with coating thicknesses 33.1, 46.4 and 63.1 mg/cm<sup>2</sup> , 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 Gd<sub>2</sub>O<sub>2</sub>S:Eu scintillator. Results showed that Gd<sub>2</sub>O<sub>2</sub>S:Eu exhibits high MTF and DQE values, which are comparable to those of a commercially employed Gd<sub>2</sub>O<sub>2</sub>S:Tb screen. In addition Gd<sub>2</sub>O<sub>2</sub>S: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.IEEE Transactions on Nuclear Science 11/2011; · 1.45 Impact Factor -
Article: Experimental and Theoretical Evaluation of a High Resolution CMOS Based Detector Under X-Ray Imaging Conditions
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ABSTRACT: 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<sup>2</sup> Gd<sub>2</sub>O<sub>2</sub>S:Tb scintillator screen, placed in direct contact with a CMOS photodiode array. The CMOS photodiode array, featuring 1200×1600 pixels with a pixel pitch of 22.5 μm, 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 μGy for RQA-5 and 6-40 μGy 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 prev- - iously 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).IEEE Transactions on Nuclear Science 03/2011; · 1.45 Impact Factor
