Powder phosphor materials consist of a variety of grain sizes glued together in a binder material forming a specific grain size distribution (GSD). Within these materials, light is produced through ...fluorescence mechanisms and thereafter travel until its emission from the phosphor layer. Between the stage of production and the stage of emission, light propagation is significantly affected by the light ray interactions with grains. The present study investigates the effect of different GSDs since the distributed sized grains influence the light ray trajectories and may cause different optical emission profiles of a certain phosphor material chemical compound. Light beam interactions with grains were modeled though LIGHTAWE Monte Carlo simulation tool and the optical emission performance was assessed in terms of the amount and distribution of light emitted. Three regions of investigation were selected based on the particularities of the optical parameters (light extinction coefficient, anisotropy factor) variation with grain size. Representative mean values of grain size of those regions were chosen to be 500 nm, 1000 nm and 7000 nm and two GSD configurations (Gaussian of different standard deviations) were examined for each value, separately. Results showed differences on light emission properties between phosphor layers of mean grain sizes and layers of distributed sized grains. The difference was found to be: (a) apparent in the submicron scale (e.g., 500 nm), approximately up to 1.1%, (b) negligible in the micron scale (e.g., 7000 nm), and (c) noticeable at the limit of both scales (e.g., 1000 nm), approximately up to 2.7%. However, the estimated differences were not found to be important by changing the range of grain sizes. The range of the optical parameters
,
with respect to region of grain sizes considered
,
was found to be the “key parameters” for constructing layers of suitable light performance (amount and distribution) per case of investigation and application.
Calcifications are products of mineralization whose presence is usually associated with pathological conditions. The minerals mostly seen in several diseases are calcium oxalate (CaC
O
), calcium ...carbonate (CaCO
) and hydroxyapatite (HAp). Up to date, there is no in vivo method that could discriminate between minerals. To this aim, a dual energy x-ray method was developed in the present study. An analytical model was implemented for the determination of the Calcium/Phosphorus mass ratio (Formula: see text). The simulation was carried out using monoenergetic and polyenergetic x-rays and various calcification thicknesses (100-1000 Formula: see text) and types (CaC
O
, CaCO
, HAp). The experimental evaluation of the method was performed using the optimized irradiation conditions obtained from the simulation study. X-ray tubes, combined with energy dispersive and energy integrating (imaging) detectors, were used for the determination of the Formula: see text in phantoms of different mineral types and thicknesses. Based on the results of the experimental procedure, statistical significant difference was observed between the different types of minerals when calcification thicknesses were 300 Formula: see text or higher.
•Α 36.26 mg/cm2 CaWO4 screen was examined under radiographic X-ray energies.•Comparisons with a custom-made PMMA/Gd2O2S:Tb (30.8 mg/cm2) composite film screen were performed.•CaWO4 LE was found ...maximum at 50 kVp (2.34 E.U), whereas Gd2O2S:Tb was (2.67 E.U).•The emission spectrum is excellent matched with photocathodes and silicon photomultipliers.
The aim of the present study was to investigate the absolute luminescence efficiency (AE) of a CaWO4 screen, under X-ray irradiation and to compare it with a custom made PMMA/Gd2O2S:Tb composite film screen. The emitted light was evaluated by performing measurements of the AE under X-ray exposure conditions, with tube voltages ranging from 50 to 125 kV. The spectral compatibility of the CaWO4 screen, with various existing optical detectors, was investigated after emission spectra measurements. AE was found maximum at 50 kVp (2.34 Efficiency Units-E.U) which was slightly lower than the corresponding “gold standard” Gd2O2S:Tb (2.67 E.U), at the same X-ray energy. The emission spectrum of CaWO4 is excellent matched with the spectral sensitivities of photocathodes and silicon photomultipliers often employed in radiation detectors, and with good matching with amorphous silicon photodiodes. Considering the adequate luminescence efficiency values and the spectral compatibility with various photodetectors, CaWO4 could be also considered for use in X-ray imaging devices such as charged-coupled devices (CCD) and complementary metal oxide semiconductors (CMOS).
The aim of the present study was to investigate the absolute luminescence efficiency of gadolinium oxysulfide powder scintillators, doped with praseodymium, cerium and fluorine (Gd2O2S:Pr,Ce,F). ...Gd2O2S:Pr,Ce,F is a non-hygroscopic material, emitting green light with short decay time. For the purposes of this study, two scintillating screens with coating thicknesses 35.7 and 71.2 mg/cm2, were prepared in our laboratory from Gd2O2S:Pr,Ce,F powder (Phosphor Technology, Ltd) by sedimentation on silica substrates. The light emitted by the phosphors under investigation was evaluated by performing measurements of the absolute efficiency under X-ray exposure conditions with tube voltages ranging from 50 to 130 kV. Results were compared with previously published data for Gd2O2S:Eu screens. The spectral compatibility of Gd2O2S:Pr,Ce,F with various existing optical detectors, was investigated after emission spectra measurements. Particle size and morphology parameters of the Gd2O2S:Pr,Ce,F powder phosphor were verified via scanning electron microscope (SEM) micrographs. Absolute efficiency was found to maximize at 60 kVp for the 71.2 mg/cm2 and at 90 kVp for the 35.7 mg/cm2 Gd2O2S:Pr,Ce,F screens. Absolute efficiency of the 71.2 mg/cm2 Gd2O2S:Pr,Ce,F screen was higher in the whole X-ray tube voltage range showing potential interest for non-CT medical imaging (i.e. dental radiology) or industrial digital radiography.
•Two Gd2O2S:Pr,Ce,F screens (35.7 & 71.2 mg/cm2) were prepared by sedimentation.•Peak absolute efficiency was obtained for the 71.2 mg/cm2 screen at 60 kVp.•Gd2O2S:Pr,Ce,F showed very good spectral compatibility with CMOS and CCD sensors.
The purpose of the present study was to assess the information content of structured CsI:Tl scintillating screens, specially treated to be compatible to a CMOS digital imaging optical sensor, in ...terms of the information capacity (IC), based on Shannon's mathematical communication theory. IC was assessed after the experimental determination of the Modulation Transfer Function (MTF) and the Normalized Noise Power Spectrum (NNPS) in the mammography and general radiography energy range. The CMOS sensor was coupled to three columnar CsI:Tl scintillator screens obtained from the same manufacturer with thicknesses of 130, 140 and 170 μm respectively, which were placed in direct contact with the optical sensor. The MTF was measured using the slanted-edge method while NNPS was determined by 2D Fourier transforming of uniformly exposed images. Both parameters were assessed by irradiation under the mammographic W/Rh (130, 140 and 170 μm CsI screens) and the RQA-5 (140 and 170 μm CsI screens) (IEC 62220-1) beam qualities. The detector response function was linear for the exposure range under investigation. At 70 kVp, under the RQA-5 conditions IC values were found to range between 2229 and 2340 bits/mm2. At 28 kVp the corresponding IC values were found to range between 2262 and 2968 bits/mm2. The information content of CsI:Tl scintillating screens in combination to the high resolution CMOS sensor, investigated in the present study, where found optimized for use in digital mammography imaging systems.
•Three structured CsI:Tl screens (130,140 & 170 um) were coupled to a CMOS sensor.•MTF of the CsI/CMOS was higher than GOS:Tb and CsI based digital imaging systems.•IC of CsI:Tl/CMOS was found optimized for use in digital mammography systems.
Due to the increased radiation pollution in the environment as a result of the often nuclear accidents taking place around the world, the need for efficient, reliable, smart and handheld radiation ...measurement systems has been born especially in daily routine. In this study it is evaluated the angular response of two crystal non-pixelated Gd3Al2Ga3O12:Ce (GAGG:Ce) scintillators with dimensions at 10x10x10mm3 & 10x10x20mm3 under 137Cs isotope emitting at 662 keV coupled to a 4x4 discrete silicon photomultiplier array (SiPM). A symmetric resistive voltage division matrix was applied reducing the array 16 outputs to 4 analog position signals which digitized by a 4 Channel 12 bit 250 MS/s desktop waveform digitizer. The number of the evaluated angles set at 5 (0°, 45°, 90°, 135°, 180°) and a variety of measured values are presented (energy resolution, sensitivity, figure of merit etc). The encouraging results such as energy resolution about 9% and figure of merit equal to 4.11 for 10x10x10mm3 and 4.43 for 10x10x20mm3 crystal, prove that this system could build up to a compact radiation sensor for integration into mobile applications.
Cerium (Ce) ion doped scintillators are of high interest in Medical Imaging systems and radiation monitoring devices, due to their very fast response and very good emission characteristics. In this ...study, a series of measurements regarding the energy resolution, photofraction, sensitivity, as well as the figure of merit, of Gd3Al2Ga3O12:Ce (GAGG:Ce) scintillator crystals, is presented. All GAGG:Ce crystals have a surface area of 3x3 mm2 with varying thicknesses, from 4 up to 20 mm (4, 5, 6, 8, 10, 15 and 20 mm). These crystals were exposed to γ radiation, using two different radioactive sources: 137Cs (0.662 MeV) and 60Co (1.173 MeV and 1.332 MeV). Each crystal was measured individually and was optically coupled to a KETEK PM3350 SiPM, an optical sensor with high gain, suitable to operate in room temperature. The digitization of the pulses was accomplished using CAEN DT5720 desktop digitizer and its corresponding digital pulse processing (DPP) firmware. Each measurement was performed in a light-tight box and had duration of 30 min. The best energy resolution value was measured for the GAGG:Ce crystal with dimensions 3x3x15mm3, equal to 3.9% at 1.332 MeV. Results were evaluated and compared to previous published data.
The purpose of the present study was to assess the information content of a high resolution active pixel CMOS imaging sensor coupled to Gd2O2S:Eu phosphor screens in terms of single index image ...quality metrics such as the information capacity (IC) and the noise equivalent passband (Ne).
The CMOS sensor was coupled to two Gd2O2S:Eu scintillator screens with coating thicknesses of 33.3 and 65.1mg/cm2. IC and Ne were obtained by means of experimentally determined parameters such as the modulation transfer function (MTF), the detective quantum efficiency (DQE) and the noise equivalent quanta (NEQ). Measurements were performed using the standard IEC-RQA5 radiation beam quality (70kVp) and a W/Rh beam quality (28kVp).
It was found that the detector response function was linear for the exposure ranges under investigation. At 70kVp, under the RQA 5 conditions IC values were found to range between 1730 and 1851bits/mm2 and Ne values were found between 2.28 and 2.52mm−1. At 28kVp the corresponding IC values were found to range between 2535 and 2747bits/mm2, while the Ne values were found between 5.91 and 7.09mm−1.
IC and Ne of the red emitting phosphor/CMOS sensor combination were found with high values suggesting an acceptable imaging performance in terms of information content and sharpness, for X-ray digital imaging.
•Gd2O2S:Eu/CMOS combination has comparable image quality parameters to Gd2O2S:Tb/CMOS.•Information capacity was found with high values suggesting an acceptable imaging performance.•Red emitting phosphors coupled to silicon based optical sensors could be used in developing efficient imaging detectors.
The aim of the present study was to investigate the luminescence efficiency (XLE) of gadolinium aluminum perovskite (GdAlO3:Ce) powder scintillator. This powder phosphor, also known as GAP:Ce ...scintillator, is a non-hygroscopic material, emitting blue light with short decay time. For the purposes of this study, five scintillating screens with coating thicknesses, 14.7, 31.0, 53.7, 67.2 and 121.1mg/cm2, were prepared in our laboratory from GdAlO3:Ce powder (Phosphor Technology, Ltd) by sedimentation on silica substrates. The light emitted by the phosphors under investigation was evaluated by performing measurements of the absolute luminescence efficiency (AE), X-ray luminescence efficiency and detector quantum gain (DQG) under X-ray exposure conditions with tube voltages ranging from 50 to 140kV. The quantum detection efficiency (QDE) and energy absorption efficiency (EAE) were also evaluated. The spectral compatibility of GdAlO3:Ce, with various existing optical detectors, was investigated after emission spectra measurements. A theoretical model, describing radiation and light transfer, was used to fit experimental AE data. This has allowed the estimation of optical attenuation coefficients of the scintillator. GdAlO3:Ce exhibited higher QDE and EAE values, compared to aluminium perovskite (YAlO3:Ce) but lower absolute efficiency values. Absolute efficiency was found to increase with increasing X-ray tube voltage, although for values higher than 120kVp a decrease was observed.
•The X-ray quantum detection efficiency and energy absorption efficiency of GdAlO3:Ce powder scintillators were found higher than currently employed materials (aluminum perovskite-YAlO3:Ce) for detection of X-rays.•The peak absolute luminescence efficiency was obtained for the 67.2mg/cm2 screen at X-ray tube voltages from 100 to 120kVp.•The absolute luminescence efficiency is lower, compared to YAlO3:Ce, within the energy range under consideration.•The emission spectrum of GdAlO3:Ce screen showed good spectral compatibility with currently used detectors (mainly analogue).
Phosphor materials are widely used in X-ray medical imaging detector applications, coupled with suitable photoreceptors. Upon the most demanding imaging modality is X-ray mammography, since the best ...defense against breast cancer is its early detection. A material suitable as a mammographic detector should efficiently absorb X-ray photons and transform them to optical photons, so as to minimize breast dose. The aim of the present study was to investigate the X-ray absorption efficiency and the absolute efficiency (AE), defined as the output optical photon power divided by the incident exposure, of Gd2O2S:Pr powder scintillator. For the purposes of this study, three scintillating screens with coating thicknesses, 34.1, 46.0 and 81.5mg/cm2 respectively, were prepared in our laboratory from Gd2O2S:Pr powder (Phosphor Technology, Ltd.) by sedimentation on silica substrates. The quantum detection efficiency (QDE), the energy absorption efficiency (EAE), the spectral matching factor and the absolute efficiency (AE) were evaluated for X-ray mammographic conditions. Furthermore theoretical models were utilized to investigate the optical photon transmission properties through the phosphor mass. Gd2O2S:Pr presented high X-ray absorption properties and good spectral compatibility with several photoreceptors. It may be utilized for X-ray mammographic imaging if it is put in conjunction with a sensitive photoreceptor, so as to enhance Gd2O2S:Pr light emission properties.
•Gd2O2S:Pr phosphor evaluated for mammography detectors.•The X-ray absorption efficiency was found high.•Spectral matching compatibility found for several photoreceptors.•X-ray absolute efficiency measured smaller than other phosphors.•Optical diffusion length and the light transmission per layer was theoretically calculated.
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