N. Kalyvas

Technological Educational Institute of Athens, Athínai, Attica, Greece

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Publications (24)31.12 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of the present study was to experimentally evaluate the imaging characteristics of the Lu2O3:Eu nanophosphor thin screen coupled to a high resolution CMOS sensor under radiographic conditions. Parameters such as the Modulation Transfer Function (MTF), the Normalized Noise Power Spectrum (NNPS) and the Detective Quantum Efficiency (DQE) were investigated at 70 kVp under three exposure levels (20 mAs, 63 mAs and 90 mAs). Since Lu2O3:Eu emits light in the red wavelength range, the imaging characteristics of a 33.3 mg/cm2 Gd2O2S:Eu conventional phosphor screen were also evaluated for comparison purposes. The Lu2O3:Eu nanophosphor powder was produced by the combustion synthesis, using urea as fuel. A scintillating screen of 30.2 mg/cm2 was prepared by sedimentation of the nanophosphor powder on a fused silica substrate. The CMOS/Lu2O3:Eu detector`s imaging characteristics were evaluated using an experimental method proposed by the International Electrotechnical Commission (IEC) guidelines. It was found that the CMOS/Lu2O3:Eu nanophosphor system has higher MTF values compared to the CMOS/Gd2O2S:Eu sensor/screen combination in the whole frequency range examined. For low frequencies (0 to 2 cycles/mm) NNPS values of the CMOS/Gd2O2S:Eu system were found 90% higher compared to the NNPS values of the CMOS/Lu2O3:Eu nanophosphor system, whereas from medium to high frequencies (2 to 13 cycles/mm) were found 40% higher. In contrast with the CMOS/ Gd2O2S:Eu system, CMOS/Lu2O3:Eu nanophosphor system appears to retain high DQE values in the whole frequency range examined. Our results indicate that Lu2O3:Eu nanophosphor is a promising scintillator for further research in digital X-ray radiography.
    SPIE Medical Imaging; 03/2014
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    ABSTRACT: Objectives. In this work, a simple technique to assess the image quality characteristics of the postprocessed image is developed and an easy to use figure of image quality (FIQ) is introduced. This FIQ characterizes images in terms of resolution and noise. In addition information capacity, defined within the context of Shannon's information theory, was used as an overall image quality index. Materials and Methods. A digital mammographic image was postprocessed with three digital filters. Resolution and noise were calculated via the Modulation Transfer Function (MTF), the coefficient of variation, and the figure of image quality. In addition, frequency dependent parameters such as the noise power spectrum (NPS) and noise equivalent quanta (NEQ) were estimated and used to assess information capacity. Results. FIQs for the "raw image" data and the image processed with the "sharpen edges" filter were found 907.3 and 1906.1, correspondingly. The information capacity values were 60.86 × 10(3) and 78.96 × 10(3) bits/mm(2). Conclusion. It was found that, after the application of the postprocessing techniques (even commercial nondedicated software) on the raw digital mammograms, MTF, NPS, and NEQ are improved for medium to high spatial frequencies leading to resolving smaller structures in the final image.
    BioMed Research International 01/2014; 2014:634856. · 2.71 Impact Factor
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    ABSTRACT: 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.
    Radiation Measurements. 01/2014;
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    ABSTRACT: Nanocrystallic europium-activated lutetium oxide (Lu2O3:Eu) is a strong candidate for use in digital medical imaging applications, due to its spectroscopic and structural properties. The aim of the present study was to investigate the imaging and efficiency properties of a 33.3 mg/cm2 Lu2O3:Eu scintillating screen coupled to a high resolution RadEye HR CMOS photodetector under radiographic imaging conditions. Since Lu2O3:Eu emits light in the red wavelength range, the light emission efficiency and the imaging performance were compared with results for a Gd2O2S:Eu phosphor screen. Parameters such as the Absolute Efficiency (AE), the X-ray Luminescence Efficiency (XLE), and the Detector Quantum Gain (DQG), were investigated. The imaging characteristics of Lu2O3:Eu nanophosphor screen were investigated in terms of the Modulation Transfer Function (MTF), the Normalized Noise Power Spectrum (NNPS) and the Detective Quantum Efficiency (DQE). It was found that Lu2O3:Eu nanophosphor has higher AE and XLE by a factor of 1.32 and 1.37 on average, respectively, in the whole radiographic energy range in comparison with the Gd2O2S:Eu screen. DQG was also found higher in the energy range from 50 kVp to 100 kVp and comparable thereafter. The imaging quality of Lu2O3:Eu nanophosphor coupled to the CMOS sensor was found to outmatch in any aspect in comparison with the Gd2O2S:Eu screen. These results indicate that Lu2O3:Eu nanophosphor could be considered for further research in order to be used in medical imaging applications.
    Journal of Luminescence. 01/2014; 151:229–234.
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    ABSTRACT: Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (nC) giving the percentage of the X-ray photon power converted to optical photon power. nC is considered a constant value for X-ray energies in the order of keV although a non proportional behavior has been reported. In this work an analytical model, has been utilized to single crystals scintillators GSO:Ce, LSO:Ce and LYSO:Ce to examine whether the intrinsic conversion efficiency shows non proportional behavior under X-ray excitation. DOG was theoretically calculated as a function of the incident X-ray spectrum, the X-ray absorption efficiency, the energy of the produced optical photons and the light transmission efficiency. The theoretical DOG values were compared with experimental data obtained by irradiating the crystals with X-rays at tube voltages from 50 to 140 kV and by measuring the light energy flux emitted from the irradiated screen. An initial value for nC (calculated from literature data) was assumed for the X-ray tube voltage of 50 kV. For higher X-ray tube voltages the optical photon propagation phenomena was assumed constant and any deviations between experimental and theoretical data were associated with changes in the intrinsic conversion efficiency. The experimental errors were below 7% for each experimental setup. The behavior of nC values for LSO:Ce and LYSO:Ce were found very similar, i.e., ranging with values from 0.089 at 50 kV to 0.015 at 140 kV, while for GSO:Ce, nC demonstrated a peak at 80 kV.
    Optics and Spectroscopy 01/2014; 116(5):743-747. · 0.56 Impact Factor
  • Journal of Luminescence 12/2013; · 2.14 Impact Factor
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    ABSTRACT: PurposeThe purpose of this study was to provide an analysis of imaging performance in digital mammography, using indirect detector instrumentation, by combining the Linear Cascaded Systems (LCS) theory and the Signal Detection Theory (SDT). Observer performance was assessed, by examining frequently employed detectors, consisting of phosphor-based X-ray converters (granular Gd2O2S:Tb and structural CsI:Tl), coupled with the recently introduced complementary metal-oxide-semiconductor (CMOS) sensor. By applying combinations of various irradiation conditions (filter-target and exposure levels at 28 kV) on imaging detectors, our study aimed to find the optimum system set-up for digital mammography. For this purpose, the signal to noise transfer properties of the medical imaging detectors were examined for breast carcinoma detectability.Methods An analytical model was applied to calculate X-ray interactions within software breast phantoms and detective media. Modeling involved: (a) three X-ray spectra used in digital mammography: 28 kV Mo/Mo (Mo: 0.030 mm), 28 kV Rh/Rh (Rh: 0.025 mm) and 28 kV W/Rh (Rh: 0.060 mm) at different entrance surface air kerma (ESAK) of 3 mGy and 5 mGy, (b) a 5 cm thick Perspex software phantom incorporating a small Ca lesion of varying size (0.1–1 cm), and (c) two 200 μm thick phosphor-based X-ray converters (Gd2O2S:Tb, CsI:Tl), coupled to a CMOS based detector of 22.5 μm pixel size.ResultsBest (lowest) contrast threshold (CT) values were obtained with the combination: (i) W/Rh target-filter, (ii) 5 mGy (ESAK), and (iii) CsI:Tl-CMOS detector. For lesion diameter 0.5 cm the CT was found improved, in comparison to other anode/filter combinations, approximately 42% than Rh/Rh and 55% than Mo/Mo, for small sized carcinoma (0.1 cm) and approximately 50% than Rh/Rh and 125% than Mo/Mo, for big sized carcinoma (1 cm), considering 5 mGy X-ray beam. By decreasing lesion diameter and thickness, a limiting CT (100%) was occurred for size values less than 0.2 cm.ConclusionCT was found to be affected by the selection of target/filter and exposure combination. It was found that the optimum thickness of CsI:Tl was approximately 190 μm and for Gd2O2S:Tb 120 μm for the studied energy and ESAK range.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2013; 697:87–98. · 1.14 Impact Factor
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    ABSTRACT: This paper reports a theoretical model of the optical gain of single-crystal scintillators of Nuclear Imaging. The model described the generation, propagation and escape of scintillation light as function of thickness and absorbed gamma ray energy. The latter was calculated via Monte Carlo methods at various crystal depths. The energies of 140 keV, 364 keV and 512 keV were investigated. The adopted thickness and energy values cover the range utilized in nuclear medicine imaging. For the semi-empirical approach, theoretical results were compared to experimental data for photon energies of 140 keV and 364 keV and the model's optical parameters were determined by the trial and error method. The results rendered the calculation of the optimum crystal thickness per investigated gamma ray energy. The presented results could be useful in designing nuclear medicine imaging systems.
    Journal of Instrumentation 11/2012; 7(11):P11021. · 1.66 Impact Factor
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    ABSTRACT: A theoretical model based on Linear Cascaded Systems (LCS) theory was developed in order to study the noise properties of a commercially available high resolution CMOS sensor (RadEye CMOS). The parameters studied were the Normalized Noise Power Spectrum (NNPS) and the Noise Transfer Function (NTF). The modeling was applied to digital mammography conditions. It considered the physical properties of the scintillator incorporated into RadEye CMOS as well as the probability of X-ray absorption directly in the photoreceptor. Furthermore it took into account the pixel pitch and the thickness of the photoreceptor. The model was compared with experimental results obtained from literature. The NTF curves were I good agreement with the experimentally determined. NNPS curves deviations were attributed to the effect of the digitization procedure as well as the non-linear behavior of CMOS detector.
    01/2011;
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    ABSTRACT: To evaluate Gd2O2S:Eu powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. Gd2O2S:Eu is nonhygroscopic, emitting red light with decay time close to that of Gd2O2S:Tb. 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/cm2 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 Gd2O2S:Eu scintillators. Gd2O2S:Eu light intensity was found higher than that of single CsI:T1 crystal for tube voltages up to 100 kVp. The MTF and the DQE were found to be comparable with those of Gd2O2S:Tb and CsI:T1 screens. MTF estimated by the Monte Carlo code was found very close to the experimental MTF values. Gd2O2S: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. Gd2O2S:Eu is an efficient phosphor potentially well suited to radiography and especially to some digital detectors sensitive to red light.
    Medical Physics 07/2010; 37(7):3694-703. · 2.91 Impact Factor
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    ABSTRACT: The 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 latter consists of a 33.91 mg/cm2 Gd2O2S:Tb scintillator screen, placed in direct contact with a CMOS photodiode array, featuring up to 1200×1600 pixels with a pixel pitch of 22.5 um. The MTF was measured using a slanted-edge method to avoid aliasing while the NNPS was determined by two-dimensional (2D) Fourier Transforming of uniformly exposed images. Both measurements were performed under the representative radiation quality settings, RQA-5 (70kVp Digital-Radiography) and RQA-M2 (28kVp Digital-Mammography) recommended by the IEC Reports 62220-1 and 62220-1-2 respectively. The DQE was assessed from the measured MTF and NPS. The ESAK values ranged between 11-87uGy for RQA-M2 and between 6-40uGy for RQA-5. Additionally the output efficiency 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 dose ranges under investigation. Additionally our results showed that for the same RQA quality the output efficiency as well as the measured and analytically predicted MTF, were not significantly affected by ESAK. This could be of importance if further reducing X-ray exposures without image quality degradation is required. MTF and DQE retains high values in the whole spatial frequency range, while NNPS appeared with essentially white noise.
    Imaging Systems and Techniques (IST), 2010 IEEE International Conference on; 01/2010
  • Medical Physics 01/2010; 37. · 2.91 Impact Factor
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    ABSTRACT: The dominant powder scintillator in most medical imaging modalities for decades has been Gd2O2S:Tb due to the very good intrinsic properties and overall efficiency. Apart from Gd2O2S:Tb, there are alternative powder phosphor scintillators such as Lu2SiO5:Ce and Gd2O2S:Eu that have been suggested for use in various medical imaging modalities. Gd2O2S:Eu emits red light and can be combined mainly with digital mammography detectors such as CCDs. Lu2SiO5:Ce emits blue light and can be combined with blue sensitivity films, photocathodes and some photodiodes. For the purposes of the present study, two scintillating screens, one from Lu2SiO5:Ce and the other from Gd2O2S:Eu powders, were prepared using the method of sedimentation. The screen coating thicknesses were 25.0 and 33.1 mg cm−2 respectively. The screens were investigated by evaluating the following parameters: the output signal, the modulation transfer function, the noise equivalent passband, the informational efficiency, the quantum detection efficiency and the zero-frequency detective quantum efficiency. Furthermore, the spectral compatibility of those materials with various optical detectors was determined. Results were compared to published data for the commercially employed 'Kodak Min-R film-screen system', based on a 31.7 mg cm−2 thick Gd2O2S:Tb phosphor. For Gd2O2S:Eu, MTF data were found comparable to those of Gd2O2S:Tb, while the MTF of Lu2SiO5:Ce was even higher resulting in better spatial resolution and image sharpness properties. On the other hand, Gd2O2S:Eu was found to exhibit higher output signal and zero-frequency detective quantum efficiency than Lu2SiO5:Ce.
    Measurement Science and Technology 09/2009; 20(10):104008. · 1.44 Impact Factor
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    ABSTRACT: The aim of this study was to develop a theoretical model to examine emission features of single-crystal scintillators, used in medical imaging detectors, under X-ray excitation. For this purpose, the number of optical photons that were produced inside the crystal and escaped to the output was modeled for variant X-ray tube voltages in the energy range of Computed Tomography and for different thicknesses of the crystalline material. The theoretical model that was used to estimate the optimum dimensions and the radiation conditions of the crystal, was validated against experimental data obtained by a single-crystal scintillator irradiated by X-rays. For implementation a Gd2SiO5:Ce crystal was used. Theoretical and experimental results will be useful in designing Hybrid Tomographic imaging systems based on a common gamma-ray and X-ray detector (PET/CT or SPECT/CT).
    Journal of Instrumentation 06/2009; 4(06):P06016. · 1.66 Impact Factor
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    ABSTRACT: A Digital x-ray mammography is a modern method for the early detection of breast cancer. The quality of a mammography image depends on various factors, the detector structure and performance being of primary importance. The aim of this work was to develop an analytical model simulating the imaging performance of a new commercially available digital mammography detector. This was achieved within the framework of the linear cascaded systems (LCS) theory. System analysis has allowed the estimation of important image quality metrics such as the Mod-ulation Transfer Function (MTF), the Noise Power Spectrum (NPS) and the Detective Quantum Efficiency (DQE). The detector was an indirect detection system consisting of a large area, 100µm thick, CsI:TI scintillator coupled to an active matrix array of amorphous silicon (a-Si:H) photo-diodes combined with thin film transistors (TFT). Pixel size was 100µm, while the active pixel dimension was 70µm. MTF and DQE data were calculated for air kerma conditions of 25, 53, 67 µGy using a 28 kVp Mo-Mo x-ray spectrum. The theoretical results were compared with published experimental data. The deviation between the theoretical and experimental MTF curves was less than 4%, while the DQE differences were found at an acceptable level. The model was also used to estimate system's capability to detect low contrast objects in the breast. It was estimated that, in the breast gland, low contrast structures larger than 1.4mm can be adequately identified by the above system. KEYWORDS: X-ray detectors, X-ray mammography and scinto-and MRI-mammography, Simu-lation methods and programs 1 Corresponding author.
    Journal of Instrumentation 06/2009; 4. · 1.66 Impact Factor
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    ABSTRACT: Breast cancer is one of the most frequently diagnosed cancers among women. Several techniques have been developed to help in the early detection of breast cancer such as conventional and digital x-ray mammography, positron and single-photon emission mammography, etc. A key advantage in digital mammography is that images can be manipulated as simple computer image files. Thus non-dedicated commercially available image manipulation software can be employed to process and store the images. The image processing tools of the Photoshop (CS 2) software usually incorporate digital filters which may be used to reduce image noise, enhance contrast and increase spatial resolution. However, improving an image quality parameter may result in degradation of another. The aim of this work was to investigate the influence of three sharpening filters, named hereafter sharpen, sharpen more and sharpen edges on image resolution and noise. Image resolution was assessed by means of the Modulation Transfer Function (MTF).In conclusion it was found that the correct use of commercial non-dedicated software on digital mammograms may improve some aspects of image quality.
    Journal of Instrumentation 05/2009; 4(05):P05018. · 1.66 Impact Factor
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    ABSTRACT: The aim of the present study was to measure the imaging transfer characteristics and the luminescence efficiency (XLE) of a Lu2SiO5:Ce (LSO:Ce) powder scintillator for use in X-ray mammography detectors. An LSO:Ce powder scintillating screen, with a coating thickness of 25mg/cm2, was prepared in our laboratory. The imaging performance of the screen was assessed by experimental determination of the modulation transfer function (MTF) and the detective quantum efficiency (DQE) as well as single index image quality parameters such as noise equivalent pass band (Ne) and informational efficiency (n I). A theoretical model, describing radiation and light transfer, was fitted to experimental MTF values in order to estimate optical properties of the scintillator. Screen irradiation was performed under exposure conditions employed in mammographic applications (27 kVp, 63 mAs). MTF was determined by the square wave response function (SWRF) method. Results showed that LSO:Ce exhibits high MTF and DQE values, which are comparable to those of the commercially used Gd2O2S:Tb. Considering our image quality parameters and luminescence efficiency results as well as the fast response of the LSO:Ce scintillator screen (40 ns), this material can be considered for use in X-ray mammographic detectors.
    Applied Physics B 03/2009; 95(1):131-139. · 1.78 Impact Factor
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    ABSTRACT: Phosphor materials are used in medical X-ray imaging combined with various pho-todetectors suitable for conventional and digital radiography and fluoroscopy. A prerequisite for these combinations is good optical spectral matching, which results in patient dose minimiza-tion. In the present work, a recently introduced factor, named OGTE, which accounts for optical gain signal-to-noise ratio transfer efficiency, is utilized for the evaluation of various phosphor-photodetector combinations. The optical photon spectrum of the phosphor materials studied was either determined experimentally, or obtained from literature. These phosphors were examined in conjunction with various photodetectors, which may be suitable for digital imaging. The corre-sponding optical response functions of the photodetectors were obtained from literature. It was found that there are numerous combinations exhibiting OGTE values above 0.80, which contribute to patient dose minimization.
    Journal of Instrumentation 01/2009; 4. · 1.66 Impact Factor
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    ABSTRACT: The aim of this study was to examine Gd<sub>2</sub>O<sub>2</sub>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</sup> were prepared in our laboratory by sedimentation of Gd<sub>2</sub>O<sub>2</sub>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</sub>O<sub>2</sub>S:Eu showed peak emission in the wavelength range 620-630 nm. The 63.1 mg/cm<sup>2</sup> phosphor screen appeared with the maximum light emission efficiency. Due to its reddish emission spectrum, Gd<sub>2</sub>O<sub>2</sub>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.
    IEEE Transactions on Nuclear Science 01/2009; · 1.22 Impact Factor
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    ABSTRACT: The dominant powder scintillator in most medical imaging modalities for decades is Gd<sub>2</sub>O<sub>2</sub>S:Tb due to the very good intrinsic properties and overall efficiency. Except Gd<sub>2</sub>O<sub>2</sub>S:Tb there are alternative powder phosphor scintillators like Lu<sub>2</sub>SiO<sub>5</sub>:Ce and Gd<sub>2</sub>O<sub>2</sub>S:Eu that has been suggested for use in various medical imaging modalities. Gd<sub>2</sub>O<sub>2</sub>S:Eu emits red light and can be combined mainly with digital detectors like CCDs and wavelength selective detectors. Lu<sub>2</sub>SiO<sub>5</sub>:Ce emits blue light and can be combined with blue sensitivity films, photocathodes and some photodiodes. For the purpose of this study two Lu<sub>2</sub>SiO<sub>5</sub>:Ce and Gd<sub>2</sub>O<sub>2</sub>S:Eu powder phosphor scintillators with screen coating thicknesses of 25 and 33 mg/cm<sup>2</sup> respectively, were prepared by the method of sedimentation in our laboratory. The output efficiency of the phosphor screens were evaluated with respect to incident exposure rate and the spatial frequency dependent Modulation Transfer Function (MTF). Furthermore the spectral compatibility of those materials with various detectors was evaluated. Results were compared to published data for the commercially employed dasiaKodak Min-R film-screen systempsila, based on a 31.7 mg/cm<sup>2</sup> thick Gd<sub>2</sub>O<sub>2</sub>S:Tb phosphor. For Gd<sub>2</sub>O<sub>2</sub>S:Eu, MTF data were found comparable to those of Gd<sub>2</sub>O<sub>2</sub>S:Tb, while the MTF of Lu<sub>2</sub>SiO<sub>5</sub>:Ce was even higher. The different spectral compatibility of these phosphors could be interesting for application based on red and blue sensitive optical sensors respectively.
    Imaging Systems and Techniques, 2008. IST 2008. IEEE International Workshop on; 10/2008