25 research outputs found
Luminescence and Structural Characterization of Gd2O2S Scintillators Doped with Tb3+, Ce3+, Pr3+ and F for Imaging Applications
none14siRadiodiagnostic technologies are powerful tools for preventing diseases and monitoring the condition of patients. Medicine and sectors such as industry and research all use this inspection methodology. This field demands innovative and more sophisticated systems and materials for improving resolution and sensitivity, leading to a faster, reliable, and safe diagnosis. In this study, a large characterization of gadolinium oxysulfide (Gd2O2S) scintillator screens for imaging applications has been carried out. Seven scintillator samples were doped with praseodymium (Pr3+), terbium (Tb3+) activators and co-doped with praseodymium, cerium, and fluorine (Gd2O2S:Pr,Ce,F). The sample screens were prepared in the laboratory in the form of high packing density screens, following the methodology used in screen sample preparation in infrared spectroscopy and luminescence. Parameters such as quantum detection efficiency (QDE), energy absorption efficiency (EAE), and absolute luminescence efficiency (ALE) were evaluated. In parallel, a structural characterization was performed, via XRD and SEM analysis, for quality control purposes as well as for correlation with optical properties. Spatial resolution properties were experimentally evaluated via the Modulation Transfer Function. Results were compared with published data about Gd2O2S:Pr,Ce,F screens produced with a standard method of a sedimentation technique. In particular, the ALE rose with the X-ray tube voltage up to 100 kVp, while among the different dopants, Gd2O2S:Pr exhibited the highest ALE value. When comparing screens with different thicknesses, a linear trend for the ALE value was not observed; the highest ALE value was measured for the 0.57 mm thick Gd2O2S:Pr,Ce,F sample, while the best MTF values were found in the thinner Gd2O2S:Pr,Ce,F screen with 0.38 mm thickness.De Martinis, Alessia; Montalto, Luigi; Scalise, Lorenzo; Rinaldi, Daniele; Mengucci, Paolo; Michail, Christos; Fountos, George; Martini, Nicki; Koukou, Vaia; Valais, Ioannis; Bakas, Athanasios; Fountzoula, Christine; Kandarakis, Ioannis; David, StratosDe Martinis, Alessia; Montalto, Luigi; Scalise, Lorenzo; Rinaldi, Daniele; Mengucci, Paolo; Michail, Christos; Fountos, George; Martini, Nicki; Koukou, Vaia; Valais, Ioannis; Bakas, Athanasios; Fountzoula, Christine; Kandarakis, Ioannis; David, Strato
Imaging performance of a CaWO4/CMOS sensor
The aim of this study was to investigate the modulation transfer function (MTF) and the effective gain transfer function (eGTF) of a non-destructive testing (NDT)/industrial inspection complementary metal oxide semiconductor (CMOS) sensor in conjunction with a thin calcium tungstate (CaWO4) screen. Thin screen samples, with dimensions of 2.7x3.6 cm2 and thickness of 118.9 μm, estimated from scanning electron microscopy-SEM images, were extracted from an Agfa Curix universal screen and coupled to the active area of an active pixel (APS) CMOS sensor. MTF was assessed using the slanted-edge method, following the IEC 62220-1-1:2015 method. MTF values were found high across the examined spatial frequency range. eGTF was found maximum when CaWO4 was combined with charge-coupled devices (CCD) of broadband anti-reflection (AR) coating (17.52 at 0 cycles/mm). The combination of the thin CaWO4 screen with the CMOS sensor provided very promising image resolution and adequate efficiency properties, thus could be also considered for use in CMOS based X-ray imaging devices, for various applications
Phosphors and Scintillators in Biomedical Imaging
Medical imaging instrumentation is mostly based on the use of luminescent materials coupled to optical sensors. These materials are employed in the form of granular screens, structured crystals, single transparent crystals, ceramics, etc. Storage phosphors are also incorporated in particular X-ray imaging systems. The physical properties of these materials should match the criteria required by the detective systems employed in morphological and functional biomedical imaging. The systems are analyzed based on theoretical frameworks emanating from the linear cascaded systems theory as well as the signal detection theory. Optical diffusion has been studied by different methodological approaches, such as experimental measurements and analytical modeling, including geometrical optics and Monte Carlo simulation. Analysis of detector imaging performance is based on image quality metrics, such as the luminescence emission efficiency (LE), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). Scintillators and phosphors may present total energy conversion on the order of 0.001–0.013 with corresponding DQE in the range of 0.1–0.6. Thus, the signal-to-noise ratio, which is crucial for medical diagnosis, shows clearly higher values than those of the energy conversion
Comparative study using Monte Carlo methods of the radiation detection efficiency of LSO, LuAP, GSO and YAP scintillators for use in positron emission imaging (PET)
The radiation detection efficiency of four scintillators employed, or
designed to be employed, in positron emission imaging (PET) was
evaluated as a function of the crystal thickness by applying Monte Carlo
Methods. The scintillators studied were the LuSiO5 (LSO), LuAlO3 (LuAP),
Gd2SiO5 (GSO) and the YAlO3 (YAP). Crystal thicknesses ranged from 0 to
50 mm. The study was performed via a previously generated photon
transport Monte Carlo code. All photon track and energy histories were
recorded and the energy transferred or absorbed in the scintillator
medium was calculated together with the energy redistributed and
retransported as secondary characteristic fluorescence radiation.
Various parameters were calculated e.g. the fraction of the incident
photon energy absorbed, transmitted or redistributed as fluorescence
radiation, the scatter to primary ratio, the photon and energy
distribution within each scintillator block etc. As being most
significant, the fraction of the incident photon energy absorbed was
found to increase with increasing crystal thickness tending to form a
plateau above the 30 mm thickness. For LSO, LuAP, GSO and YAP
scintillators, respectively, this fraction had the value of 44.8, 36.9
and 45.7% at the 10mm thickness and 96.4, 93.2 and 96.9% at the 50mm
thickness. Within the plateau area approximately (57-59)%, (59-63)%,
(52-63)% and (58-61)% of this fraction was due to scattered and
reabsorbed radiation for the LSO, GSO, YAP and LuAP scintillators,
respectively. In all cases, a negligible fraction (< 0.1%) of the
absorbed energy was found to escape the crystal as fluorescence
radiation. (c) 2006 Elsevier B.V. All rights reserved
Absolute Luminescence Efficiency of Europium-Doped Calcium Fluoride (CaF<sub>2</sub>:Eu) Single Crystals under X-ray Excitation
The absolute luminescence efficiency (AE) of a calcium fluoride (CaF2:Eu) single crystal doped with europium was studied using X-ray energies met in general radiography. A CaF2:Eu single crystal with dimensions of 10 × 10 × 10 mm3 was irradiated by X-rays. The emission light photon intensity of the CaF2:Eu sample was evaluated by measuring AE within the X-ray range from 50 to 130 kV. The results of this work were compared with data obtained under similar conditions for the commercially employed medical imaging modalities, Bi4Ge3O12 and Lu2SiO5:Ce single crystals. The compatibility of the light emitted by the CaF2:Eu crystal, with the sensitivity of optical sensors, was also examined. The AE of the 10 × 10 × 10 mm3 CaF2:Eu crystal peaked in the range from 70 to 90 kV (22.22 efficiency units; E.U). The light emitted from CaF2:Eu is compatible with photocathodes, charge coupled devices (CCD), and silicon photomultipliers, which are used as radiation sensors in medical imaging systems. Considering the AE results in the examined energies, as well as the spectral compatibility with various photodetectors, a CaF2:Eu single crystal could be considered for radiographic applications, including the detection of charged particles and soft gamma rays
H-1 MRS and MRSI: analysis of acquisition parameters and improvement of various clinical applications.
MRS and MRSI are valuable tools for diagnosis and staging of several
pathologies, much before become detectable by other imaging methods.
Combined with other imaging techniques in an advancing modality like MRI
offer the ability to estimate accurately the overall condition of the
examined tissue. MRS and MRSI could be potentially suited for repeated
monitoring since it entails no exposure to ionizing radiation.
Incorporation of these tools in clinical practice is, however, limited
due to the considerable amount of user intervention. In this study
various acquisition parameters and their effect in spectrum quality are
investigated. A series of experiments were conducted, using a
manufacturer’s spectroscopy phantom, to assess the quality of various
spectroscopic imaging techniques. The effectiveness of the available
water and lipid suppression techniques and their compatibility with
other parameters were also investigated. The stability of the equipment,
the appearance of artifacts and the reproducibility of the results were
also examined to obtain conclusions for the interaction of acquisition
parameters. All the data were processed with jMRUI 2.2 to analyze
various aspects of the measurements, quantify parameters such as signal
to noise ratio (SNR) and full width at half maximum (FWHM) and extract
useful conclusions for the function of these methods. The experience
acquired from the conducted experiments was applied in improvement of
clinical applications (prostate, brain and muscle examinations) by
significantly improving the spectrum quality, SNR (up to 75%), spatial
resolution and in most cases reducing exam times (up to 60%)