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Title: Monte Carlo study on the imaging performance of powder Lu{sub 2}SiO{sub 5}:Ce phosphor screens under x-ray excitation: Comparison with Gd{sub 2}O{sub 2}S:Tb screens

Abstract

Lu{sub 2}SiO{sub 5}: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 Gd{sub 2}O{sub 2}S:Tb (GOS) phosphor material. The relative luminescence efficiency of LSO phosphor was found inferior to that of GOS. This is due tomore » the lower intrinsic conversion efficiency of LSO (0.08 instead of 0.15 of GOS) and the relatively high light extinction coefficient m{sub ext} of this phosphor (0.239 {mu}m{sup -1} instead of 0.218 {mu}m{sup -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/cm{sup 2}, 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.« less

Authors:
; ; ; ;  [1];  [2];  [2]
  1. Department of Medical Physics, Faculty of Medicine, University of Patras, 265 00 Patras (Greece)
  2. (Greece)
Publication Date:
OSTI Identifier:
20951303
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 5; Other Information: DOI: 10.1118/1.2724065; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BIOMEDICAL RADIOGRAPHY; COMPUTERIZED SIMULATION; IMAGES; LUMINESCENCE; MAMMARY GLANDS; MONTE CARLO METHOD; NOISE; PHOSPHORS; POSITRON COMPUTED TOMOGRAPHY; QUANTUM EFFICIENCY; SOLID SCINTILLATION DETECTORS; SPATIAL RESOLUTION

Citation Formats

Liaparinos, Panagiotis F., Kandarakis, Ioannis S., Cavouras, Dionisis A., Delis, Harry B., Panayiotakis, George S., Department of Medical Instruments Technology, Technological Educational Institute, 122 10 Athens, and Department of Medical Physics, Faculty of Medicine, University of Patras, 265 00 Patras. Monte Carlo study on the imaging performance of powder Lu{sub 2}SiO{sub 5}:Ce phosphor screens under x-ray excitation: Comparison with Gd{sub 2}O{sub 2}S:Tb screens. United States: N. p., 2007. Web. doi:10.1118/1.2724065.
Liaparinos, Panagiotis F., Kandarakis, Ioannis S., Cavouras, Dionisis A., Delis, Harry B., Panayiotakis, George S., Department of Medical Instruments Technology, Technological Educational Institute, 122 10 Athens, & Department of Medical Physics, Faculty of Medicine, University of Patras, 265 00 Patras. Monte Carlo study on the imaging performance of powder Lu{sub 2}SiO{sub 5}:Ce phosphor screens under x-ray excitation: Comparison with Gd{sub 2}O{sub 2}S:Tb screens. United States. doi:10.1118/1.2724065.
Liaparinos, Panagiotis F., Kandarakis, Ioannis S., Cavouras, Dionisis A., Delis, Harry B., Panayiotakis, George S., Department of Medical Instruments Technology, Technological Educational Institute, 122 10 Athens, and Department of Medical Physics, Faculty of Medicine, University of Patras, 265 00 Patras. Tue . "Monte Carlo study on the imaging performance of powder Lu{sub 2}SiO{sub 5}:Ce phosphor screens under x-ray excitation: Comparison with Gd{sub 2}O{sub 2}S:Tb screens". United States. doi:10.1118/1.2724065.
@article{osti_20951303,
title = {Monte Carlo study on the imaging performance of powder Lu{sub 2}SiO{sub 5}:Ce phosphor screens under x-ray excitation: Comparison with Gd{sub 2}O{sub 2}S:Tb screens},
author = {Liaparinos, Panagiotis F. and Kandarakis, Ioannis S. and Cavouras, Dionisis A. and Delis, Harry B. and Panayiotakis, George S. and Department of Medical Instruments Technology, Technological Educational Institute, 122 10 Athens and Department of Medical Physics, Faculty of Medicine, University of Patras, 265 00 Patras},
abstractNote = {Lu{sub 2}SiO{sub 5}: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 Gd{sub 2}O{sub 2}S: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 m{sub ext} of this phosphor (0.239 {mu}m{sup -1} instead of 0.218 {mu}m{sup -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/cm{sup 2}, 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.},
doi = {10.1118/1.2724065},
journal = {Medical Physics},
number = 5,
volume = 34,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • In medical mammographic imaging systems, one type of detector configuration, often referred to as indirect detectors, is based on a scintillator layer (phosphor screen) that converts the x-ray radiation into optical signal. The indirect detector performance may be optimized either by improving the structural parameters of the screen or by employing new phosphor materials with improved physical characteristics (e.g., x-ray absorption efficiency, intrinsic conversion efficiency, emitted light spectrum). Lu{sub 2}O{sub 3}:Eu is a relatively new phosphor material that exhibits improved scintillating properties indicating a promising material for mammographic applications. In this article, a custom validated Monte Carlo program was usedmore » in order to examine the performance of compact Lu{sub 2}O{sub 3}:Eu powdered phosphor screens under diagnostic mammography conditions (x-ray spectra: 28 kV Mo, 0.030 mm Mo and 32 kV W, 0.050 mm Rh). Lu{sub 2}O{sub 3}:Eu screens of coating weight in the range between 20 and 40 mg/cm{sup 2} were examined. The Monte Carlo code was based on a model using Mie-scattering theory for the description of light propagation within the phosphor. The overall performance of Lu{sub 2}O{sub 3}:Eu powdered phosphor screens was investigated in terms of the (i) quantum detection efficiency, (ii) luminescence efficiency, (iii) compatibility with optical sensors, (iv) modulation transfer function, (v) the Swank factor, and (vi) zero-frequency detective quantum efficiency. Results were compared to the traditional rare-earth Gd{sub 2}O{sub 2}S:Tb phosphor material. The increased packing density and therefore the light extinction properties of Lu{sub 2}O{sub 3}:Eu phosphor were found to improve the x-ray absorption (approximately up to 21% and 16% at 40 mg/cm{sup 2} for Mo and W x-ray spectra, respectively), the spatial resolution (approximately 2.6 and 2.4 cycles/mm at 40 mg/cm{sup 2} for Mo and W x-ray spectra, respectively), as well as the zero-frequency detective quantum efficiency (approximately up to 8% and 18% at 20 mg/cm{sup 2} for Mo and W x-ray spectra, respectively) of the screens in comparison to the Gd{sub 2}O{sub 2}S:Tb screens. Data obtained by the simulations indicate that certain optical properties of Lu{sub 2}O{sub 3}:Eu make this material a promising phosphor which, under appropriate conditions, could be considered for use in x-ray mammography imagers.« less
  • Purpose: To evaluate Gd{sub 2}O{sub 2}S:Eu powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. Gd{sub 2}O{sub 2}S:Eu is nonhygroscopic, emitting red light with decay time close to that of Gd{sub 2}O{sub 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{sup 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)more » 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{sub 2}O{sub 2}S:Eu scintillators. Results: Gd{sub 2}O{sub 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{sub 2}O{sub 2}S:Tb and CsI:Tl screens. MTF estimated by the Monte Carlo code was found very close to the experimental MTF values. Gd{sub 2}O{sub 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{sub 2}O{sub 2}S:Eu is an efficient phosphor potentially well suited to radiography and especially to some digital detectors sensitive to red light.« less
  • The preparation of cerium-substituted barium lutetium borate, Ba2Lu5B5O17:Ce3+, is achieved using high temperature solid state synthesis. This compound crystallizes in the Ba2Y5B5O17-type structure and shows an efficient blue emission (λmax = 447 nm) when excited by UV-light (λex = 340 nm) with a photoluminescent quantum yield near 90%, a fast luminescence decay time (<40 ns), and a thermal quenching temperature of 452 K. Further, preparing a solid solution following Ba2(Y1–xLux)5B5O17:Ce3+ (x = 0, 0.25, 0.50, 0.75, 1) confirms that all compounds are isostructural and follow Vegard’s law. Substituting Y3+ for Lu3+ yields a nearly constant emission spectrum that blue-shifts bymore » only 9 nm and has a consistent luminescence lifetime across the range prepared. The photoluminescent quantum yield (PLQY) and thermal quenching (T50) of the solid solution, however, are dramatically impacted by the composition, with the PLQY decreasing to ≈70% and the T50 dropping 49 K going from x = 1 to x = 0. These significant changes in the optical properties likely stem from enhanced structural rigidity as the larger, more polarizable Y3+ is substituted for the smaller, harder Lu3+ cation. These results highlight the importance of optimizing chemical bonding to improve a phosphor’s optical properties.« less
  • In the recent successful improvement of scintillation efficiency in Lu{sub 3}Al{sub 5}O{sub 12}:Ce driven by Ga{sup 3+} and Gd{sup 3+} admixture, the “band-gap engineering” and energy level positioning have been considered the valid strategies so far. This study revealed that this improvement was also associated with the cerium valence instability along with the changes of chemical composition. By utilizing X-ray absorption near edge spectroscopy technique, tuning the Ce{sup 3+}/Ce{sup 4+} ratio by Ga{sup 3+} admixture was evidenced, while it was kept nearly stable with the Gd{sup 3+} admixture. Ce valence instability and Ce{sup 3+}/Ce{sup 4+} ratio in multicomponent garnets canmore » be driven by the energy separation between 4f ground state of Ce{sup 3+} and Fermi level.« less
  • In the context of research on U/minor actinides for nuclear fuel reprocessing in the transmutation process, developments are first studied with surrogates containing uranium and lanthanides to facilitate testing. The tests consist of precipitating and calcining a hydrazinium uranium/cerium oxalate. The structure of this oxalate had not been previously determined, but was necessary to validate the physicochemical mechanisms involved. The present study, firstly demonstrates the structural similarity of the U/Ce oxalate phase (N{sub 2}H{sub 5},H){sub 2.9}U{sub 1.1}Ce{sub 0.9}(C{sub 2}O{sub 4}){sub 5}·10H{sub 2}O, synthesized using a vortex precipitator for continuous synthesis of actinide oxalates, with previously known oxalates, crystallizing in P6{submore » 3}/mmc symmetry, obtained by more classical methods. This fast precipitation process induces massive nucleation of fine powders. Their structural and microstructural determination confirms that the raw and dried phases belong to the same structural family as (NH{sub 4}){sub 2}U{sub 2}(C{sub 2}O{sub 4}){sub 5}·0.7H{sub 2}O whose structure was described by Chapelet-Arab in P6{sub 3}/mmc symmetry, using single crystal data. However, they present an extended disorder inside the tunnels of the structure, even after drying at 100 °C, between water and hydrazinium ions. This disorder is directly related to the fast vortex method. This structure determination can be used as a basis for further semi-quantitative analysis on the U/minor actinides products formed under various experimental conditions. - Highlights: • Uranium cerium oxalate precipitate characterization by X-ray powder diffraction. • Morphology characterization by SEM analysis. • Structure determination by unit cell Rietveld refinement.« less