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The aim of this study was to examine [Gd.sub.2][O.sub.2]S:Eu (also known as GOS:Eu) powder scintillator under X-ray mammography imaging conditions. For this purpose, three scintillator screens with coating thicknesses of 33.1, 46.4 and 63.1 mg/[cm.sup.2] were prepared in our laboratory by sedimentation of [Gd.sub.2][O.sub.2]S:Eu powder. Light emission efficiency and optical emission spectra of the screens were measured under X-ray excitation using X-ray tube voltages (22-49 kVp) employed in mammography. Spectral compatibility with various optical photon detectors (photodiodes, photocathodes, charge coupled devices, films) and intrinsic conversion efficiency value (0.12) were determined by using emission spectrum data. In addition, parameters related to X-ray detection and energy absorption efficiency were calculated. [Gd.sub.2][O.sub.2]S:Eu showed peak emission in the wavelength range 620-630 nm. The 63.1 mg/[cm.sup.2] phosphor screen appeared with the maximum light emission efficiency. Due to its reddish emission spectrum, [Gd.sub.2][O.sub.2] S:Eu showed excellent compatibility with the sensitivity of many currently used photodetectors and could be considered for application in X-ray imaging especially in various digital detectors. Index Terms--[Gd.sub.2][O.sub.2] S:Eu, luminescence efficiency, matching factor powder phosphors.

This paper investigates the light emission efficiency of [Lu.sub.2]Si[O.sub.5]: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/[cm.sup.2] 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 various 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/[cm.sup.2] 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. Index Terms--Inorganic scintillators, luminescence efficiency, LSO: Ce, powder phosphors.

LYSO:Ce and LuYAP:Ce are single crystal non-hygroscopic scintillators of high density, high light yield and short decay time, which have been successfully used in small animal PET imagers. In the present study, the luminescence emission properties of [([Lu.sub.0.9], [Y.sub.0.1]).sub.2] Si[O.sub.5]:Ce (LYSO:Ce) and ([Lu.sub.0.7], [Y.sub.0.3])Al[O.sub.3]:Ce (LuYAP:Ce) crystals were investigated for use in x-ray medical imaging. Both crystals had dimensions of 2 x 2 x 8 [mm.sup.3], with all surfaces polished. Evaluation was performed by determining the x-ray luminescence efficiency (XLE) (emitted light energy flux over incident x-ray energy flux) and the detector optical gain (DOG) (emitted light photons per incident x-ray photon) in a wide range of x-ray energies employed in mammography (22-49 kVp) and in general x-ray imaging (50-140 kVp). Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. The emission spectrum under x-ray excitation was measured using an optical grating monochromator to determine the spectral compatibility to various optical photon detectors incorporated in medical imaging detectors. Optical characteristics such as transmission and absorption spectra were investigated in addition to the scintillation properties. The light emission performance of the two scintillation materials studied was found adequately high for x-ray imaging. Index Terms--Detector optical gain, inorganic scintillators, luminescence eficiency, LuYAP:Ce, radiation detectors.

The luminescence of [(Lu, Y).sub.2]Si[O.sub.5]: Ce (LYSO:Ce) and [Gd.sub.2]Si[O.sub.5]: Ce (GSO:Ce) crystals was studied for use in tomographic medical x-ray imaging. LYSO:Ce and GSO:Ce are high density (7.1 g/[cm.sup.3] and 6.71 g/[cm.sup.3] respectively), high atomic number (71 for Lu and 64 for Gd), non-hydroscopic, and short decay time (40 ns and 60 ns respectively) scintillators. Evaluation was performed by determining: 1) the luminescence efficiency (LE) (emitted fight energy flux over incident x-ray energy flux) in x-ray energies employed in general x-ray imaging (40-140 kVp) and in mammographic x-ray imaging (22-49 kVp), 2) the fight emission spectrum, determined at various x-ray energies (22-140 kVp), and 3) the spectral compatibility to optical photon detectors, incorporated in medical imaging systems. Both scintillation materials exhibited adequately high LE in the x-ray diagnostic energy range, with LYSO:Ce's LE being distinctively higher. LYSO:Ce and GSO:Ce were found most compatible with the S-20 photocathode (0.9 for both materials) and adequately compatible to the amorphous silicon photodiode (0.74 for both materials), incorporated in many digital x-ray detectors. Index Terms--Inorganic scintillators, luminescence efficiency, LYSO:Ce, matching factor, radiation detectors.

[Gd.sub.2]Si[O.sub.5] :Ce (GSO:Ce) is a high-Z, nonhygroscopic fast emitting scintillator used in detectors of positron emission tomography (PET) systems. The purpose of this study was to evaluate the luminescence efficiency of GSO:Ce scintillator under irradiation conditions employed in X-ray medical imaging, since findings may be of value in novel applications such as computed tomography breast imaging or modern fast image producing X-ray computed tomography. To this aim the absolute luminescence efficiency (emitted light flux over X-ray exposure), the spectral matching factor (compatibility to optical detectors), and the effective efficiency (the product of absolute efficiency and spectral compatibility) were determined for X-ray tube voltages ranging from 20 to 140 kV. The efficiency of GSO:Ce was found to increase with increasing X-ray tube voltage, while the GSO:Ce spectrum, peaking at 440 and 490 nm, was found compatible to most optical detectors (photodiodes, photocathodes, and charge-coupled devices). Index Terms--Inorganic scintillators, luminescence efficiency, matching factor, radiation detectors.

Bone quality is a broad term encompassing factors affecting the structural and material properties of bone. X-ray dual-energy method (XDEM) provides one way to explore bone quality in terms of bone tissue material properties. In this study a XDEM is presented for the determination of Ca/P mass ratio, parameter which appears to play an important role in bone health. The low- and high-energy intensity measurements were combined, using a nonlinear mapping function, to cancel out the soft tissue structures and generate the dual energy (DE) Ca/P mass ratio value. The total entrance-skin exposure from low- and high-energy measurements was constrained so that it is similar to diagnostic-examination levels. The DE simulated data were exported using variable Ca and PO4 thicknesses, while the tissue thickness was kept constant. The thickness of each material was fitted separately using a nonlinear least squares minimization algorithm. The functional forms of inverse functions that have been investigated are the linear, quadratic, cubic, and conic functions. The inverse- mapping functions were found to vary as analytic functions of second (conic) and third (conic) order. A nonlinear eight term rational function was selected for dual energy calibration which appeared to be capable of high fitting accuracy while requiring relative few terms. [ABSTRACT FROM AUTHOR]

The Dual energy method, using two different energies generated by an X-ray tube, has been applied in the diagnosis of osteoporosis by determining bone mass or bone density. By measuring parameters that characterize bone quality, such as the Ca/P or Hydroxyapatite/Collagen (HAp/Col) ratios, a potential bone fracture can be predicted more efficiently. The aim of this study was the optimization of dual energy X-ray spectra through the estimation of the Coefficient of Variation (CV) in HAp/Col ratio determination. The upper limit of CVHAp/Col value was set to ≤ 3%. Single and double exposure methods were used in order to obtain polyenergetic spectra. Unfiltered spectra were obtained from Boone et al (1997 Med. Phys. 24 1661-70) for Tungsten (W) anode. For the implementation of the low and high energy beams, several filters were applied to the spectra, based on their K-edges, so as to provide quasi-monochromatic beams. The optimum results, for the single exposure method, were obtained for a 120kVp spectrum with added beam filtration of 800um Ce (CVHAp/Col=1.88%). For the double exposure technique, a CVHAp/Col value of 2.23% was obtained using 40 and 120kVp with added filtration of 250um Cd and 1150um Yb, respectively. [ABSTRACT FROM AUTHOR]

The aim of the present study was the optimization of polyenergetic x-ray spectra for Dual energy imaging. The latter was accomplished by using various combinations of filter thicknesses and kVp. X-ray spectra were optimized by using double track x-ray tubes equipped with Molybdenum (Mo) and Rhodium (Rh), Mo and Tungsten (W), Rh and W, and a W or Rh anode combined with various K-edge filters and combinations. Filtering of energy spectra was implemented by determining the optimum combination and thicknesses of the lanthanides filters. The filtered spectra were normalized at standard exposure conditions. Best performance characteristics were obtained from the combination of Rh anode spectrum at 25kVp filtered with 100 μm Rh for low energy, and W anode spectrum at 50Vp filtered with 400 μm Ce for mammography, with mean energy values 19.57 and 30.10KeV respectively. For bone densitometry, best results were obtained from a W anode filtered spectrum at 110KVp with 900 μm Ce and mean energy values 37.78 and 85.56KeV for low and high energy respectively. [ABSTRACT FROM AUTHOR]

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]

The aim of the present work is to study the performance of scintillators currently used in PET and animal PET systems, under conditions met in radiation therapy and PET/CT imaging. The results of this study will be useful in applications where both CT and PET photons as well as megavoltage cone beam CT (MV CBCT) photons could be detected using a common detector unit. To this aim crystal samples of GSO, LSO, LYSO, LuYAP and YAP scintillators, doped with cerium (Ce3+) were examined under a wide energy range of photon energies. Evaluation was performed by determining the absolute luminescence efficiency (emitted light flux over incident X-ray exposure) in the energy range employed in X-ray CT, in Nuclear Medicine (70 keV up to 662 keV) and in radiotherapy 6 MV (approx. 2.0 MeV mean energy)-18 MV (approx. 4.5 MeV mean energy). Measurements were performed using an experimental set-up based on a photomultiplier coupled to a light integration sphere. The emission spectrum under X-ray excitation was measured, using an optical grating monochromator, to determine the spectral compatibility to optical photon detectors incorporated in medical imaging systems. Maximum absolute luminescence efficiency values were observed at 70 keV for YAP:Ce and LuYAP:Ce and at 140 keV for LSO:Ce, LYSO:Ce and GSO:Ce. Highest absolute efficiency between the scintillators examined was observed for LSO:Ce, followed by LYSO:Ce. The detector optical gain (DOG) exhibited a significant variation with the increase of energy between 70 keV to 2.0 MeV. All scintillators exhibited low compatibility when combined with GaAsP (G5645) photodetector. [ABSTRACT FROM AUTHOR]

LYSO:Ce and LuYAP:Ce are single crystal non-hygroscopic scintillators of high density, high light yield and short decay time, which have been successfully used in small animal PET imagers. In the present study, the luminescence emission properties of (Lu0.9, Y0.1)2SiO5:Ce (LYSO:Ce) and (Lu0.7, Y0.3)AlO3 :Ce (LuYAP:Ce) crystals were investigated for use in x-ray medical imaging. Both crystals had dimensions of 2 × 2 × 8 mm3, with all surfaces polished. Evaluation was performed by determining the x-ray luminescence efficiency (XLE) (emitted light energy flux over incident x-ray energy flux) and the detector optical gain (DOG) (emitted light photons per incident x-ray photon) in a wide range of x-ray energies employed in mammography (22-49 kVp) and in general x-ray imaging (50-140 kVp). Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. The emission spectrum under x-ray excitation was measured using an optical grating monochromator to determine the spectral compatibility to various optical photon detectcrs incorporated in medical imaging detectors. Optical characteristics such as transmission and absorption spectra were investigated in addition to the scintillation properties. The light emission performance of the two scintillation materials studied was found adequately high for x-ray imaging. [ABSTRACT FROM AUTHOR]

Lu2SiO5:Ce (LSO) scintillator is a relatively new luminescent material which has been successfully applied in positron emission tomography systems. Since it has been recently commercially available in powder form, it could be of value to investigate its performance for use in x-ray projection imaging as both physical and scintillating properties indicate a promising material for such applications. In the present study, a custom and validated Monte Carlo simulation code was used in order to examine the performance of LSO, under diagnostic radiology (mammography and general radiography) conditions. The Monte Carlo code was based on a model using Mie scattering theory for the description of light attenuation. Imaging characteristics, related to image brightness, spatial resolution and noise of LSO screens were predicted using only physical parameters of the phosphor. The overall performance of LSO powder phosphor screens was investigated in terms of the: (i) quantum detection efficiency (ii) emitted K-characteristic radiation (iii) luminescence efficiency (iv) modulation transfer function (v) Swank factor and (vi) zero-frequency detective quantum efficiency [DQE(0)]. Results were compared to the traditional rare-earth Gd2O2S:Tb (GOS) phosphor material. The relative luminescence efficiency of LSO phosphor was found inferior to that of GOS. This is due to the lower intrinsic conversion efficiency of LSO (0.08 instead of 0.15 of GOS) and the relatively high light extinction coefficient mext of this phosphor (0.239 μm-1 instead of 0.218 μm-1 for GOS). However, the property of increased light extinction combined with the rather sharp angular distribution of scattered light photons (anisotropy factor g=0.624 for LSO instead of 0.494 for GOS) reduce lateral light spreading and improve spatial resolution. In addition, LSO screens were found to exhibit better x-ray absorption as well as higher signal to noise transfer properties in the energy range from 18 keV up to 50.2 keV (e.g. DQE(0)=0.62 at 18 keV and for 34 mg/cm2, instead of 0.58 for GOS). The results indicate that certain optical properties of LSO (optical extinction coefficient, scattering anisotropy factor) combined with the relatively high x-ray coefficients, make this material a promising phosphor which, under appropriate conditions, could be considered for use in x-ray projection imaging detectors. [ABSTRACT FROM AUTHOR]

The luminescence of (Lu, Y)2 SiO5 : Ce (LYSO:Ce) and Gd2 SiO5 : Ce (GSO:Ce) crystals was studied for use in tomographic medical x-ray imaging. LYSO:Ce and GSO:Ce are high density (7.1 g/cm3 and 6.71 g/cm3 respectively), high atomic number (71 for Lu and 64 for Gd), non-hydroscopic, and short decay time (40 ns and 60 ns respectively) scintillators. Evaluation was performed by determining: 1) the luminescence efficiency (LE) (emitted light energy flux over incident x-ray energy flux) in x-ray energies employed in general x-ray imaging (40-140 kVp) and in mammographic x-ray imaging (22-49 kVp), 2) the light emission spectrum, determined at various x-ray energies (22-140 kVp), and 3) the spectral compatibility to optical photon detectors, incorporated in medical imaging systems. Both scintillation materials exhibited adequately high LE in the x-ray diagnostic energy range, with LYSO:Ce's LE being distinctively higher. LYSO:Ce and GSO:Ce were found most compatible with the S-20 photocathode (0.9 for both materials) and adequately compatible to the amorphous silicon photodiode (0.74 for both materials), incorporated in many digital x-ray detectors. [ABSTRACT FROM AUTHOR]

Gd2SiO5 :Ce (GSO:Ce) is a high-Z, nonhygroscopic fast emitting scintillator used in detectors of positron emission tomography (PET) systems. The purpose of this study was to evaluate the luminescence efficiency of GSO:Ce scintillator under irradiation conditions employed in X-ray medical imaging, since findings may be of value in novel applications such as computed tomography breast imaging or modern fast image producing X-ray computed tomography. To this aim the absolute luminescence efficiency (emitted light flux over X-ray exposure), the spectral matching factor (compatibility to optical detectors), and the effective efficiency (the product of absolute efficiency and spectral compatibility) were determined for X-ray tube voltages ranging from 20 to 140 kV. The efficiency of GSO:Ce was found to increase with increasing X-ray tube voltage, while the GSO:Ce spectrum, peaking at 440 and 490 nm, was found compatible to most optical detectors (photodiodes, photocathodes, and charge-coupled devices). [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]