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

Implemantation of an informative system in radiography

In this dedactorical thesis the transformation way is presented of a classic radiographic department to a full digital, step by step, taking into account educational, economical, etc. data. The advent of digital imaging in radiology combined with the explosive growth of technology has dramatically improved imaging techniques. Throughout the world, film/screen radiography systems are being rapidly replaced with digital systems. With current technology offerings CR systems are the most readily available and cost effective technology. However direct digital radiography systems have distinct advantages. Further more the introduction of flat panel detectors, promises not only increased image quality but also significant reduction in the radiation dose, due to improved detective quantum efficiency. Digital solutions are likely best accomplished with complementary mix of technologies, such as placing DR systems in high work load areas such as dedicated chest rooms and using CR for general radiography applications and portable imaging. In the current time, forces acting upon the radiology practice are mandating the conversion from the analog film/screen based systems to a purely digital department. This seems to be not far behind. Three systems, RIS, HIS the PACS and the speech recognition system forms the spinal cord of a pure digital radiography department. The benefits of PACS systems are obvious and clear. In this thesis a small private hospital has been studied for digital upgrade. An estimation of the educational level of radiographers has been made through a questioner among the Athens’s hospitals about the digitalization of health services. A careful study drives the PACS candidates about the way who must ask and depend from a PACS supplier. Finally a test phantom has been designed and tested in a computed radiography systemΣε αυτή την διδακτορική διατριβή παρουσιάζεται η μεταγωγή ενός κλασσικού ακτινολογικού εργαστηρίου σε ψηφιακό, βήμα προς βήμα, λαμβάνοντας υπ’ όψιν εκπαιδευτικά, οικονομικά, κοινωνικά κλπ. δεδομένα. Η είσοδος της ψηφιακής εικόνας στην ακτινολογία σε συνδυασμό με την αλματώδη εξέλιξη της τεχνολογίας, έχει βελτιώσει της απεικονιστικές τεχνικές. Σ’ όλο τον κόσμο τα συστήματα κλασσικής ακτινολογίας αντικαθίστανται τάχιστα με ψηφιακά συστήματα. Με τα δεδομένα της παρούσης τεχνολογίας τα συστήματα CR είναι περισσότερο προσιτά. Πάντως και τα συστήματα DR έχουν ξεχωριστά πλεονεκτήματα. Η εισαγωγή της τεχνολογίας των επίπεδων ημιαγώγιμων ανιχνευτών υπόσχεται αφ’ ενός πολύ καλή ποιότητα εικόνας αλλά και χαμηλή δόση ακτινοβολίας λόγω της υψηλής κβαντικής απόδοσης των ανιχνευτών. Οι ψηφιακές λύσεις είναι πιθανόν καλύτερες εάν συνυπάρχουν συστήματα CR και DR. Τα συστήματα DR μπορούν να εγκαθίστανται εκεί όπου υπάρχει μεγάλος φόρτος εργασίας π.χ. στους θαλάμους όπου γίνονται αποκλειστικά ακτινογραφίες θώρακος. Τα συστήματα CR μπορούν να εγκαθίστανται σε θαλάμους γενικής χρήσης ή όπου υπάρχουν φορητά μηχανήματα. Στις μέρες μας δεν φαίνεται να αργεί η μεταγωγή της αναλογικής ακτινολογικής πράξης σε αμιγώς ψηφιακή, λόγω των τάσεων που ασκούνται. Τα συστήματα RIS, HIS, PACS και το σύστημα υπαγόρευσης αποτελούν τη ραχοκοκαλιά ενός αμιγώς ψηφιακού ακτινολογικού τμήματος. Τα οφέλη ενός συστήματος PACS είναι προφανή. Σ’ αυτή τη διατριβή έχει μελετηθεί η ψηφιακή αναβάθμιση μικρού ιδιωτικού Νοσοκομείου. Έγινε εκτίμηση του επιπέδου γνώσεων των Τεχνολόγων ακτινολογίας που εργάζονται στα Νοσοκομεία της περιοχής Αθηνών μέσω ερωτηματολογίου. Μελετήθηκαν διεξοδικά οι απαιτήσεις και τα ερωτήματα που θα πρέπει να τεθούν από έναν υποψήφιο αγοραστή σε προμηθευτή συστήματος PACS. Στο τέλος παρουσιάζεται ο σχεδιασμός και η χρήση ενός ομοιώματος για τη μελέτη συστημάτων υπολογιστικής, ψηφιακής ακτινογραφίας CR

On the Response of a Micro Non-Destructive Testing X-ray Detector

Certain imaging performance metrics are examined for a state-of-the-art 20 μm pixel pitch CMOS sensor (RadEye HR), coupled to a Gd2O2S:Tb scintillator screen. The signal transfer property (STP), the modulation transfer function (MTF), the normalized noise power spectrum (NNPS) and the detective quantum efficiency (DQE) were estimated according to the IEC 62220-1-1:2015 standard. The detector exhibits excellent linearity (coefficient of determination of the STP linear regression fit, R2 was 0.9978), while its DQE peaks at 33% and reaches 10% at a spatial frequency of 3 cycles/mm, for the measured with a Piranha RTI dosimeter (coefficient of variation CV = 0.03%) exposure value of 28.1 μGy DAK (detector Air Kerma). The resolution capabilities of the X-ray detector under investigation were compared to other commercial CMOS sensors, and were found in every case higher, except from the previous RadEye HR model (CMOS—Gd2O2S:Tb screen pair with 22.5 μm pixel pitch) version which had slightly better MTF. The present digital imager is designed for industrial inspection applications, nonetheless its applicability to medical imaging, as well as dual-energy is considered and certain approaches are discussed in this respect

Evaluation of Cerium-Doped Lanthanum Bromide (LaBr3:Ce) Single-Crystal Scintillator’s Luminescence Properties under X-ray Radiographic Conditions

In the present study, the response of the crystalline scintillator LaBr3:Ce when excited with X-rays at tube voltages from 50 kVp to 150 kVp was investigated, for possible use in hybrid medical-imaging systems. A single crystal (10 × 10 × 10 mm3) was irradiated by X-rays within the aforementioned tube-voltage range, and the absolute efficiency (AE), as well as the detective quantum efficiency for zero spatial-frequency (DQE(0)), were measured. The energy-absorption efficiency (EAE), the quantum-detection efficiency (QDE) and the spectral compatibility with various optical photodetectors were also calculated. The results were compared with the published data for the LaCl3:Ce, Bi4Ge3O12 (BGO), Lu2SiO5:Ce (LSO), and CdWO4 single crystals of equal dimensions. The AE values of the examined crystal were found to be higher than those of the compared crystals across the whole X-ray tube-voltage range. Regarding the EAE, LaBr3:Ce demonstrated a comparatively better performance than the LaCl3:Ce crystal. The emitted-light spectrum of LaBr3:Ce was found to be compatible with various types of photocathodes and silicon photomultipliers. Moreover, the LaBr3:Ce crystal exhibited excellent performance concerning its DQE(0). Considering these properties, the LaBr3:Ce crystal could be considered as a radiation-detector option for hybrid medical-imaging modalities, such as PET/CT and SPECT/CT

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

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