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George Fountos

Bio: George Fountos is an academic researcher from University of the West. The author has contributed to research in topics: Scintillator & Luminescence. The author has an hindex of 20, co-authored 122 publications receiving 1202 citations. Previous affiliations of George Fountos include Technological Educational Institute of Athens & American Hotel & Lodging Educational Institute.


Papers
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Journal ArticleDOI
TL;DR: 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 and it was found that the detector response function was linear for the exposure ranges under investigation.
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/cm2 Gd2O2S: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 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).

68 citations

Journal ArticleDOI
TL;DR: The Ca/P ratio of the radius was significantly lower in patients with postmenopausal osteoporosis than in premenopausal controls.

55 citations

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated Gd 2 O 2 S : Eu powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography.
Abstract: Purpose: To evaluate Gd 2 O 2 S : Eu powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. Gd 2 O 2 S : Eu is nonhygroscopic, emitting red light with decay time close to that of Gd 2 O 2 S : Tb . Methods: The light intensity emitted per unit of x-ray exposure rate (absolute luminescence efficiency) was measured for laboratory prepared screens with coating thicknesses of 33.1, 46.4, 63.1, 78.3, and 139.8 mg / cm 2 and tube voltages ranging from 50 to 140 kVp. Parameters related to image quality such as the modulation transfer function(MTF) and the detective quantum efficiency (DQE) were also experimentally examined. In addition, a previously validated Monte Carlo code was used to estimate intrinsic x-ray absorption and optical properties, as well as the MTF and the Swank factor ( I ) of the Gd 2 O 2 S : Eu scintillators. Results: Gd 2 O 2 S : Eu light intensity was found higher than that of single CsI:Tl crystal for tube voltages up to 100 kVp. The MTF and the DQE were found to be comparable with those of Gd 2 O 2 S : Tb and CsI:Tl screens. MTF estimated by the Monte Carlo code was found very close to the experimental MTF values. Gd 2 O 2 S : Eu showed peak emission in the wavelength range 620–630 nm. Its emission spectrum was excellently matched to various optical detectors (photodiodes, photocathodes, CCDs, and CMOS) employed in flat panel detectors. Conclusions: Gd 2 O 2 S : Eu is an efficient phosphor potentially well suited to radiography and especially to some digital detectors sensitive to red light.

54 citations

Journal ArticleDOI
TL;DR: A new method for assessing the Ca/P ratio of bone in vivo using gamma-ray photon absorptiometry, using two radiation sources and a germanium detector, and the effect of collagen and fat on the measurements was investigated.
Abstract: We describe a new method for assessing the Ca/P ratio of bone in vivo using γ-ray photon absorptiometry. The theoretical approach of the method and the estimation of the variance are presented. Two radiation sources, Gd-153 (100 keV), and I-125 (27.5 keV), and a germaniumdetector were used to determine this ratio. Measurements were made on bone phantoms with different Ca/P ratios; also, the ratio was measured on lamb and sheep tibias, rabbit tibias, and human fingers. Since the accuracy of the method is affected by the amount of fat and collagen in the measurement field, the effect of collagen and fat on the measurements also was investigated. In all cases, the precision of the method, expressed as the coefficient of variation (CV): 100× standard deviation/mean , was near to the theoretical one, ranging from 1.8% to 3.2%. For human fingers, the CV was 3.2%, a value near to the theoretical 2.9% with a dose to the skin ranging from 0.044 to 0.066 mGy, depending on the width of the finger.

49 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the imaging and efficiency properties of a 33.3 millimeter Europium-activated lutetium oxide (Lu 2 O 3 :Eu) scintillating screen coupled with a high resolution RadEye HR CMOS photodetector under radiographic imaging conditions.

40 citations


Cited by
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01 Jan 2016
TL;DR: The the essential physics of medical imaging is universally compatible with any devices to read, and is available in the digital library an online access to it is set as public so you can get it instantly.
Abstract: Thank you very much for reading the essential physics of medical imaging. As you may know, people have search hundreds times for their chosen novels like this the essential physics of medical imaging, but end up in harmful downloads. Rather than enjoying a good book with a cup of tea in the afternoon, instead they juggled with some infectious virus inside their laptop. the essential physics of medical imaging is available in our digital library an online access to it is set as public so you can get it instantly. Our digital library saves in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Merely said, the the essential physics of medical imaging is universally compatible with any devices to read.

632 citations

Journal ArticleDOI
09 Feb 2018
TL;DR: Topics include positive hysteresis, the co-doping of non-luminescent ions, the introduction of an aimed impurity phase, the excitation density effect and the complementary relationship between scintillators and storage phosphors.
Abstract: Scintillation materials and detectors that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspection, are reviewed. The fundamental physics understood today is explained, and common scintillators and scintillation detectors are introduced. The properties explained here are light yield, energy non-proportionality, emission wavelength, energy resolution, decay time, effective atomic number and timing resolution. For further understanding, the emission mechanisms of scintillator materials are also introduced. Furthermore, unresolved problems in scintillation phenomenon are considered, and my recent interpretations are discussed. These topics include positive hysteresis, the co-doping of non-luminescent ions, the introduction of an aimed impurity phase, the excitation density effect and the complementary relationship between scintillators and storage phosphors.

245 citations

Journal Article
TL;DR: In this article, the authors describe how suitably doped semiconductor scintillators could provide a combination of high light output, short decay time, and linearity of response that approach fundamental limits.

242 citations

Journal ArticleDOI
TL;DR: This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material.
Abstract: Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

188 citations