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

BODY COMPOSITION STUDIES USING Γ-RAY BEAM

THE AIM OF THE PRESENT WORK IS TO DEVELOP A NEW METHOD FOR ASSESSING THE BONE CA/P RATIO IN VIVO USING Γ-RAY PHOTON ABSORPTIOMETRY. IS BEEN PRESENTING BRIEFLY THE BONE TISSUE COMPOSITION, AND THE VARIETY OF NON-INVASIVE TECHNIQUES THAT HAS BEEN DEVELOPED FOR BONE COMPOSITION STUDIES. USING TWO ENERGIES OF Γ-RADIATION AND IMMERSION OF THE MEASURING AREA INSIDE THE WATER A REPRODUCTIBILITY OF 1-3% CAN BE ACHIEVED MAKING THE METHOD ABLE FOR LONGITUDINAL STUDIESAND CLINICAL PRACTICE. A PHOTOTYPE WAS CONSTRUCTED IN ORDER TO MEASURE THE CA/P RATIO IN HUMAN FINGERS IN VIVO, ANIMAL BONES AND PHANTOMS. THE ACCURACY OF THE METHOD MEASURING BIOLOGICAL APATITE PHANTOMS WITH DIFFERENT CA/P RATIO WAS RANGING FROM 4-8% MAINLY BECAUSE THE CHEMICALS WASN'T SIMULATING VERY WELL THE BIOLOGICAL APATITES THAT WE USE IN THE THEORETICAL MODEL. THE EFFECT OF FAT AND COLLAGEN WAS STUDIED USING FAT AND COLLAGEN PHANTOMS. THE MEASURED CA/P RATIO IS INCREASED WITH FAT AND DECREASED WITH COLLAGEN. THE CA/P RATIO WASALSO MEASURED AT RABBIT BONES. THE RABBITS WERE UNDER SPECIAL DIETS AND IMO.IN EACH CASE A STATISTICALLY SIGNIFICANT DECREASE WAS OBSERVED. TEN HEALTHY INDIVIDUALS WAS MEASURED FOR CA/P IN VIVO AT THE MIDDLE FINGER AND A CV OF 3% WAS CALCULATED WHILE USING HIGHER INTENSITY SOURCES THE CV CAN BE REDUCED TO 1%.Η ΠΑΡΟΥΣΑ ΔΙΑΤΡΙΒΗ ΕΧΕΙ ΣΑΝ ΣΤΟΧΟ ΤΗΝ ΑΝΑΠΤΥΞΗ ΜΕΘΟΔΟΥ ΜΕΤΡΗΣΗΣ ΤΟΥ ΛΟΓΟΥ CA/P ΣΤΑ ΟΣΤΑ ΧΡΗΣΙΜΟΠΟΙΩΝΤΑΣ Γ-ΑΚΤΙΝΟΒΟΛΙΑ. ΔΙΝΟΝΤΑΙ ΣΥΝΤΟΜΑ ΠΛΗΡΟΦΟΡΙΕΣ ΣΧΕΤΙΚΑ ΜΕ ΤΗΝ ΣΥΣΤΑΣΗ ΤΩΝ ΟΣΤΩΝ ΑΛΛΑ ΚΑΙ ΓΙΑ ΤΙΣ ΥΠΑΡΧΟΥΣΕΣ ΜΕΘΟΔΟΥΣ ΜΕΛΕΤΗΣ ΤΟΥ ΟΣΤΙΤΗ ΙΣΤΟΥ. ΜΕΛΕΤΗ ΕΔΕΙΞΕ ΟΤΙ ΓΙΑ ΤΟΝ IN VIVO ΠΡΟΣΔΙΟΡΙΣΜΟ ΤΟΥ ΛΟΓΟΥ CA/P ΣΤΑ ΟΣΤΑ ΑΠΑΙΤΟΥΝΤΑΙ ΔΥΟ ΜΟΝΟΕΝΕΡΓΕΙΑΚΕΣ ΔΕΣΜΕΣ ΑΚΤΙΝΟΒΟΛΙΑΣ-Γ ΚΑΙ ΕΜΒΑΠΤΙΣΗ ΤΟΥ ΕΞΕΤΑΖΟΜΕΝΟΥ ΜΕΛΟΥΣ ΣΕ ΛΟΥΤΡΟ ΝΕΡΟΥ. ΟΙ ΔΕΣΜΕΣ ΑΚΤΙΝΟΒΟΛΙΑΣ ΑΠΟΚΤΗΘΗΚΑΝ ΑΠΟΔΥΟ ΡΑΔΙΟΙΣΟΤΟΠΙΚΕΣ ΠΗΓΕΣ GD-153 ΚΑΙ Ι-125. ΚΑΤΑΣΚΕΥΑΣΤΗΚΕ ΣΥΣΤΗΜΑ ΓΙΑ ΤΟΝ ΠΡΟΣΔΙΟΡΙΣΜΟ ΤΟΥ ΛΟΓΟΥ CA/P ΣΤΑ ΟΣΤΑ ΤΩΝ ΔΑΚΤΥΛΩΝ, ΣΤΟ ΣΥΣΤΗΜΑ ΕΓΙΝΑΝ ΟΙ ΑΠΑΡΑΙΤΗΤΟΙ ΠΟΙΟΤΙΚΟΙ ΕΛΕΓΧΟΙ. ΜΕΤΡΗΘΗΚΑΝ ΙΣΟΔΥΝΑΜΑ ΒΙΟΛΟΓΙΚΩΝ ΥΔΡΟΞΥΑΠΑΤΙΚΩΝ ΚΑΙ Η ΑΚΡΙΒΕΙΑ ΣΤΗ ΜΕΤΡΗΣΗ ΗΤΑΝ 4-8%. ΤΑ ΑΝΩΤΕΡΩ ΙΣΟΔΥΝΑΜΑ ΒΙΟΛΟΓΙΚΩΝ ΥΔΡΟΞΥΑΠΑΤΙΚΩΝ ΜΕΤΡΗΘΗΚΑΝ ΠΑΡΟΥΣΙΑ ΛΙΠΟΥΣ ΚΑΙ ΚΟΛΛΑΓΟΝΟΥ ΚΑΙ ΠΑΡΑΤΗΡΗΘΗΚΕ ΟΤΙ Η ΥΠΑΡΞΗ ΛΙΠΟΥΣ ΑΥΞΑΝΕΙ, ΦΑΙΝΟΜΕΝΙΚΑ ΤΟΝ ΜΕΤΡΟΥΜΕΝΟ ΛΟΓΟ CA/P ΕΝΩ Η ΥΠΑΡΞΗ ΚΟΛΛΑΓΟΝΟΥ ΤΟΝ ΜΕΙΩΝΕΙ ΟΠΩΣ ΓΙΝΕΤΑΙ ΚΑΙ ΣΕ ΑΛΛΕΣ ΜΕΘΟΔΟΥΣ. ΕΠΙΣΗΣ ΜΕΤΡΗΘΗΚΑΝ ΠΕΙΡΑΜΑΤΟΖΩΑ(ΚΟΥΝΕΛΙΑ) ΣΤΑ ΟΠΟΙΑ ΠΡΟΚΛΗΘΗΚΕ ΤΕΧΝΗΤΑ ΟΣΤΕΟΠΟΡΩΣΗ ΜΕ ΔΙΑΙΤΕΣ ΚΑΙ ΙΜΟ. ΣΕ ΟΛΕΣ ΤΙΣ ΠΕΡΙΠΤΩΣΕΙΣ ΠΑΡΑΤΗΡΗΘΗΚΕ ΜΙΑ ΣΤΑΤΙΣΤΙΚΑ ΣΗΜΑΝΤΙΚΗ ΔΙΑΦΟΡΑ. ΜΕΤΡΗΣΕΙΣ ΣΕΔΕΚΑ (10) ΥΓΙΕΙΣ ΑΝΘΡΩΠΟΥΣ ΕΔΕΙΞΑΝ ΟΤΙ Η ΕΠΑΝΑΛΗΠΤΙΚΟΤΗΤΑ ΤΗΣ ΜΕΘΟΔΟΥ ΕΙΝΑΙ ΠΕΡΙΠΟΥ 3% ΜΕ ΜΙΑ ΔΟΣΗ ΔΕΡΜΑΤΟΣ 48-66ΜGΦ. ΘΕΩΡΗΤΙΚΟΣ ΥΠΟΛΟΓΙΣΜΟΣ ΕΔΕΙΞΕ ΟΤΙ ΗΕΠΑΝΑΛΗΠΤΙΚΟΤΗΤΑ ΤΗΣ ΜΕΘΟΔΟΥ ΜΕ ΠΗΓΕΣ ΥΨΗΛΗΣ ΕΝΕΡΓΗΤΙΚΟΤΗΤΑΣ ΦΤΑΝΕΙ ΣΤΟ 1%

Dual Energy X-ray Methods for the Characterization, Quantification and Imaging of Calcification Minerals and Masses in Breast

Dual energy (DE) technique has been used by numerous studies in order to detect breast cancer in early stages. Although mammography is the gold standard, the dual energy technique offers the advantage of the suppression of the contrast between adipose and glandular tissues and reveals pathogenesis that is not present in conventional mammography. Both dual energy subtraction and dual energy contrast enhanced techniques were used in order to study the potential of dual energy technique to assist in detection or/and visualization of calcification minerals, masses and lesions obscured by overlapping tissue. This article reviews recent developments in this field, regarding: i) simulation studies carried out for the optimizations of the dual energy technique used in order to characterize and quantify calcification minerals or/and visualize suspected findings, and ii) the subsequent experimental verifications, and finally, the adaptation of the dual energy technique in clinical practice

Mineral Characterization in Human Body: A Dual Energy Approach

Kidney and uteric stones are a common cause of pain and disturbance in numerous people worldwide, as they tend to reappear. There are several studies investigating the association of urolithiasis and nephrolithiasis with atherosclerosis, as patients suffering from the former diseases were found to have been diagnosed with atherosclerotic plaques. Hydroxyapatite and calcium oxalate are the most common mineral crystals found in both kidney/uteric stones and atherosclerotic plaques’ calcifications. Even though for stones smaller than 5 mm surgery is not recommended, the knowledge of the stone composition is an important tool for the physician in order to provide better treatment for the patient. The mineral crystal characterization of atherosclerotic plaques’ calcifications smaller than 3 mm (spotty calcifications) will assist the physician to limit the possibility of myocardial infraction and stroke, as the presence of hydroxyapatite indicates possible plaque rapture. To this aim, a dual energy (DE) X-ray method was developed in this work. The calcium/phosphorus mass ratio (mCa/mP) was determined through analytical simulations and the results were verified experimentally. Both monoenergetic and polyenergetic simulation studies were implemented for hydroxyapatite, calcium carbonate and calcium oxalate with thicknesses ranging from 0.50 to 3.00 mm, at 100 μm increments, to obtain the optimized irradiation conditions. The experimental verification of the proposed method was performed using an X-ray tube combined with a high resolution complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) detector. The Mann–Whitney U test indicated that statistically significant differences were found between the different types of minerals examined for thicknesses of 0.70 mm or higher

Information Capacity of Positron Emission Tomography Scanners

Background: The aim of the present study was to assess the upper information content bound of positron emission tomography (PET) images, by means of the information capacity (IC). Methods: The Geant4 Application for the Tomographic Emission (GATE) Monte Carlo (MC) package was used, and reconstructed images were obtained by using the software for tomographic image reconstruction (STIR). The case study for the assessment of the information content was the General Electric (GE) Discovery-ST PET scanner. A thin-film plane source aluminum (Al) foil, coated with a thin layer of silica and with a 18F-fludeoxyglucose (FDG) bath distribution of 1 MBq was used. The influence of the (a) maximum likelihood estimation-ordered subsets-maximum a posteriori probability-one step late (MLE-OS-MAP-OSL) algorithm, using various subsets (1 to 21) and iterations (1 to 20) and (b) different scintillating crystals on PET scanner’s performance, was examined. The study was focused on the noise equivalent quanta (NEQ) and on the single index IC. Images of configurations by using different crystals were obtained after the commonly used 2-dimensional filtered back projection (FBP2D), 3-dimensional filtered back projection re-projection (FPB3DRP) and the (MLE)-OS-MAP-OSL algorithms. Results: Results shown that the images obtained with one subset and various iterations provided maximum NEQ values, however with a steep drop-off after 0.045 cycles/mm. The single index IC data were maximized for the range of 8⁻20 iterations and three subsets. The PET scanner configuration incorporating lutetium orthoaluminate perovskite (LuAP) crystals provided the highest NEQ values in 2D FBP for spatial frequencies higher than 0.028 cycles/mm. Bismuth germanium oxide (BGO) shows clear dominance against all other examined crystals across the spatial frequency range, in both 3D FBP and OS-MAP-OSL. The particular PET scanner provided optimum IC values using FBP3DRP and BGO crystals (2.4829 bits/mm2). Conclusions: The upper bound of the image information content of PET scanners can be fully characterized and further improved by investigating the imaging chain components through MC methods

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

Luminescence Efficiency of Cadmium Tungstate (CdWO4) Single Crystal for Medical Imaging Applications

Background: In this study, the light output of a cadmium tungstate (CdWO4) single crystal was measured under various X-ray radiographic energies. Methods: A CdWO4 single crystal (10 × 10 × 10 mm3) was exposed to X-rays in the 50–130 kVp range. Measurements were evaluated against published data for single crystals of equal dimensions (CaF2:Eu and Lu3Al5O12:Ce). Since the crystal was examined for application in medical imaging detectors, the emitted optical spectrum was classified with respect to the spectral compatibility of numerous commercial optical sensors. Results: The luminescence efficiency (LE) was found to constantly increase with X-ray energy and was higher than that of CaF2:Eu for energies above 90 kVp. However, the efficiency of the previously published Lu3Al5O12:Ce was found to be constantly higher than that of CdWO4. The light emitted from CdWO4 can be optimally detected by certain charge-coupled devices (CCDs), amorphous silicon photodiodes, and photocathodes. Conclusions: The high density (7.9 g/cm3) of CdWO4 and the luminescence signal of this material make it suitable for medical imaging (such as dual energy), high-energy physics or for applications of scintillators in harsh environments

Absolute Luminescence Efficiency of Europium-Doped Calcium Fluoride (CaF₂: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

Response of Lead Fluoride (PbF₂) Crystal under X-ray and Gamma Ray Radiation

Background: In this research, the response of a 10 × 10 × 10 mm3 commercially available PbF2 crystal was experimentally assessed under X-ray and gamma ray radiation to verify the possible application of this material in X-ray medical imaging. Methods: The measurements were performed under X-ray from 50 to 130 kVp and gamma ray excitation (Tc-99m 140 keV and I-131 365 keV). The PbF2 response was experimentally assessed by the determination of the absolute luminescence efficiency (AE), X-ray luminescence efficiency (XLE), and the stopping power of this scintillating crystal in terms of the energy absorption efficiency (EAE). The results were compared with bismuth germanate (BGO) crystal, which is commonly used in medical imaging modalities. Results: The AE of PbF2 gradually decreased from 50 kVp up to 130 kVp. The maximum value was 0.61 efficiency units (EU) at 140 keV, and the minimum value was 0.03 EU at 71 keV (130 kVp). Similarly, low values appeared for the XLE, where the maximum value was 16.9 × 10−5 at 140 keV. Conclusions: These findings show that the PbF2 scintillator has unacceptably low luminescence efficiency. Although PbF2 can effectively absorb radiation, the scintillation light, at room temperatures, is negligible, and, thus, it could not be used in medical imaging applications in the examined energy range