Fabrication and characterization of pixelated Gd2O2S:Tb scintillator screens for digital X-ray imaging applications (original) (raw)
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Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2011
We have synthesized europium-doped gadolinium oxide (Gd 2 O 3 :Eu) scintillators by a precipitation method with advantages of simple process and low-temperature calcinations for high resolution X-ray imaging detectors. The powders with about 15-30 nm particle sizes were obtained by subsequent calcinations of the precursor at a different temperature of 600-800 1C for 10 h. The wavelength of the main emission peak was about 610 nm and as temperature increased, light intensity of the scintillator increased in the X-ray luminescence case. Imaging performance such as X-ray linearity and spatial resolution of both commercial bulk and nanocrystalline-Gd 2 O 3 :Eu scintillator screens was measured and compared with the X-ray imaging system after coupling these to a CCD image sensor.
Investigation of Scintillation Screens for X-Ray Imaging
Key Engineering Materials, 2006
Terbium-doped gadolinium oxysulfide (Gd 2 O 2 S:Tb) phosphor screen is the most popular X-ray converter in diagnostic radiology. We have investigated the fundamental imaging performance of Gd 2 O 2 S:Tb screens in terms of X-ray sensitivity and MTF (modulation-transfer function). The measurements were performed for a wide range of coverages (34-135 mg/cm 2) by using a conventional film radiographic method. In addition, CsI:Tl having columnar structure was also investigated.
Journal of Instrumentation, 2013
The aim of this paper is the evaluation of an alternative, low cost solution for the gamma detector in planar imaging. It is based on a powder scintillator, well established in X-ray imaging, and could be further exploited in simultaneous bimodal imaging systems. For this purpose, we have examined the performance of Gd 2 O 2 S:Pr powder scintillator, in the form of thick granular screens easily produced in the laboratory by commercially available Gd 2 O 2 S:Pr powder. The screen was coupled to a round position sensitive photomultiplier tube (R3292 PSPMT). The system's evaluation was performed in photon counting mode under 99m Tc excitation. In all measurements, a general purpose hexagonal parallel collimator was used. Different samples of screens with coating thickness varying from 0.1 g/cm 2 to 1.2 g/cm 2 were tested. The 0.6 g/cm 2 screen, corresponding to ∼2 mm actual thickness, was found most efficient under 140 keV irradiation. The system's performance with the proposed screen is reported with the modulation transfer function. Moreover sensitivity, spatial and energy resolution as well as the uniformity response using phantoms were measured. The performance of the proposed screen was compared with two CsI:Tl pixellated crystal arrays with 2×2×3 mm 3 and 3×3×5 mm 3 pixel size. A spatial resolution, of 3 mm FWHM, for a 99m Tc line source, was achieved at zero source to collimator distance. In addition, the Gd 2 O 2 S:Pr screen showed a slower degradation of the spatial resolution with increasing source to collimator distance e.g at 20 cm, the Gd 2 O 2 S:Pr screen showed aq spatial resolution of 8.4 mm while the spatial resolution of the pixellated crystals was 15 mm. Taking into account its easy production, its flexibility due to powder form, the very low cost and the good spatial resolution properties of the proposed alternative detector, powder scintillators could potentially be used for the construction of flexible detector geometries, such as ring type or gamma probes or as a low cost
High spatial resolution scintillator screens coupled to CCD detectors for X-ray imaging applications
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1994
New generations of X-ray imaging detectors are being developed for X-ray diffraction studies using both conventional sources and synchrotron beam lines. In many cases, these detectors utilise a scintillator screen to convert the X-ray photon energy into scintillation light. However, the spatial resolution is limited due to the diffusion of light that occurs within the scintillator layer. Results are presented for a scintillation screen that improves the spatial resolution through the use of a specially prepared fibre optic surface where the clad glass has been selectively etched away to leave the protruding columns of core glass. When evaporated onto this surface, the scintillator grows as extensions of these pillars forming discrete columns which individually act as light guides for the scintillation light. A calculation of the system DQE is presented and used to predict the performance to 8 keV X-rays. A Monte Carlo simulation of the X-ray interaction in CsI is also used to evaluate the system DQE above the K shell absorption edges (33 and 37 keV) and therefore determine the useful energy range of the scintillator.
IEEE Transactions on Nuclear Science, 2011
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/cm2 , 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.
A new large area scintillator screen for X-ray imaging
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
We report on the development of a new, large area, powdered scintillator screen based on Lu 2 O 3 (Eu). As reported earlier, the transparent ceramic form of this material has a very high density of 9.4 g/cm 3 , a high light output comparable to that of CsI(Tl), and emits in a narrow spectral band centered at about 610 nm. Research into fabrication of this ceramic scintillator in a large area format is currently underway, however the process is not yet practical for large scale production. Here we have explored fabrication of large area screens using precursor powders from which the ceramics are fabricated. To date we have produced up to 16 · 16 cm 2 area screens with thickness in the range of 18 mg/ cm 2 . This paper outlines the screen fabrication technique and presents its imaging performance in comparison with a commercial Gd 2 O 2 S:Tb (GOS) screen.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2009
Pixelated-scintillator films used for X-ray image sensors were developed and tested. The air gap between scintillator pixels reduces the transport of visible light photons generated by X-rays into the neighboring pixels so it will maximize the overall spatial resolution as well as the light collection efficiency of an X-ray imager. For further improvement, the inter-pixel gaps and surface are filled and coated with a reflective or a lower refractive material than an CsI(Tl) scintillator. The scintillator films of 30-40 mm thickness were made with thallium-doped CsI by the conventional physical vapour deposition process on glass substrates with a photo resist layer patterned by UV lithography. In this work, the effects on light collection efficiency and spatial resolution of the pixelated-scintillator films before and after reflective coating were evaluated using a CCD sensor and X-rays within the medical diagnostic energy range.
Performance studies of a monolithic scintillator-CMOS image sensor for X-ray application
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2008
We proposed the direct deposition of CsI(Tl) scintillator layer with pixelated structure on a CMOS image sensor (CIS) in order to improve the spatial resolution. CMOS sensors developed for test have a 128×128 photodiode array with 50 μm pixel pitch and integrated readout-electronics including a 10 bit pipe-lined ADC. CsI(Tl) layer has thickness of 50 μm. The modulation transfer function, the noise power spectrum, and the detective quantum efficiency of pixelated and non-pixelated CsI(Tl) X-ray image sensors (XIS) were estimated with a 50 kVp X-ray beam. At 10% of modulation transfer function (MTF), the spatial resolution of pixelated and non-pixleated XIS are about 8 and 6 lp/mm, respectively. It implies that pixelation enhances the spatial resolution by reducing the lateral light diffusion. Though the NPS of pixelated XIS was slightly higher than the non-pixelated XIS, its detective quantum efficiency (DQE) values were much better than non-pixelated XIS especially at high spatial frequencies.
The British journal of radiology, 1998
The scintillator effective luminescence efficiency, which may be defined in terms of the scintillator's X-ray luminescence efficiency and the scintillator-photodetector spectral matching and geometrical configuration, was studied for various X-ray imaging applications. Four scintillator materials Gd2O2S:Tb, Y2O2S:Tb, ZnSCdS:Ag and CsI:Na were used to prepare test screens. They were evaluated in relation to various photodetectors used in X-ray imaging, such as radiographic films, photocathodes, and photodiodes. Effective luminescence efficiency was determined for a range of X-ray tube voltages (50-140 kVp) by measuring the light flux emitted per unit of incident exposure rate and the spectra of the light emitted by the four scintillators. Scintillator-photodetector combinations resulting in higher image brightness level were determined for different X-ray imaging systems. Findings indicate that CsI:Na is very efficient with orthochromatic radiographic films, Gd2O2S:Tb could be us...
Journal of the Optical Society of Korea, 2014
Columnar-structured cesium iodide (CsI) scintillators doped with thallium (Tl) are frequently used as x-ray converters in medical and industrial imaging. In this study we investigated the imaging characteristics of CsI:Tl films with various reflective layers-aluminum (Al), chromium (Cr), and titanium dioxide (TiO 2) powder-coated on glass substrates. We used two effusion-cell sources in a thermal evaporator system to fabricate CsI:Tl films on substrates. The scintillators were observed via scanning electron microscopy (SEM), and scintillation characteristics were evaluated on the basis of the emission spectrum, light output, light response to x-ray dose, modulation transfer function (MTF), and x-ray images. Compared to control films without a reflective layer, CsI:Tl films with reflective layers showed better sensitivity and light collection efficiency, and the film with a TiO 2 reflective layer showed the best properties.