Showing papers by "George Fountos published in 2020"

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

Abstract: 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.

On the Optical Response of Tellurium Activated Zinc Selenide ZnSe:Te Single Crystal

Abstract: In this study, the light output of a zinc selenide activated with tellurium (ZnSe: Te) single crystal was measured for X-ray radiography applications. A cubic crystal (10 × 10 × 10 mm) was irradiated using X-rays with tube voltages from 50 to 130 kV. The resulting energy absorption efficiency, detective quantum efficiency, and absolute luminescence efficiency were compared to published data for equally sized GSO: Ce (gadolinium orthosilicate) and BGO (bismuth germanium oxide) crystals. The emitted light was examined to estimate the spectral compatibility with widely used optical sensors. Energy absorption efficiency and detective quantum efficiency of ZnSe: Te and BGO were found to be similar, within the X-ray energies in question. Light output of all three crystals showed a tendency to increase with increasing X-ray tube voltage, but ZnSe: Te stood at least 2 EU higher than the others. ZnSe: Te can be coupled effectively with certain complementary metal–oxide–semiconductors (CMOS), photocathodes, and charge-coupled-devices (CCD), as the effective luminescence efficiency results assert. These properties render the material suitable for various imaging applications, dual-energy arrays included.

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

Abstract: 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.

Temperature Dependence of the Luminescence output of CdWO4 Crystal. Comparison with CaF2:Eu

Abstract: Scintillators are radiation converters applied in medical imaging detectors, in applications at harsh environments, including in geophysical detectors for deep geology boreholes, non-destructive testing (NDT) in gas and oil facilities, space, marine exploration, etc. In this study the luminescence efficiency dependence of single-crystal scintillators was examined with increasing temperature. Cadmium tungstate (CdWO4) was examined against calcium fluoride doped with europium (CaF2:Eu). The dimensions of the single crystals’ samples were 10x10x10 mm3 and were irradiated using X-ray radiographic exposures (90 kVp, 63mAs) to measure the light output with temperature (22 to 128 °C). The luminescence efficiency was found in both cases maximum at the lowest examined temperature (23.06 efficiency units-E.U for CdWO4 and 22.01 E.U. for CaF2:Eu, at 22 °C-environmental). With increasing temperature, the luminescence efficiency constantly decreased for both crystals due to thermal quenching (5.32 efficiency units for CdWO4 and 4.43 for CaF2:Eu, at 128 °C). In the mid-range (50-80 °C) CdWO4 shows increased differences compared to CaF2:Eu. CdWO4 has a higher density (7.9 g/cm 3) and luminescence signal than CaF2:Eu (3.18 g/cm 3), thus it is suitable, besides medical imaging, also for operation in harsh environments.

Poly(Methyl Methacrylate) Structure Modification through Zn-Cu-In-S / ZnS Quantum Dot Nanocrystals Dispersion

Abstract: The aim of the current study was to present a simple method for the fabrication of quantum dot (QD)/polymer films for possible use as a luminescent material in medical applications. To this aim the poly(methyl methacrylate) (PMMA) polymer matrix was modified in order to host Zinc Copper Indium Sulfide encapsulated by an outer core of Zinc Sulfide (ZnCuInS/ZnS) QD nanocrystals, through dispersion. Four composite PMMA films of ZnCuInS/ZnS nanocrystals with maximum emission at 530 nm and concentrations of 1.0, 4.0, 6.0 and 10.0 %w/v, were prepared. X-ray irradiation and scanning electron microscopy (SEM) micrographs were used to evaluate the volume homogeneity of the final samples, as a measure of QD dispersion. The coefficient of variation (CV) estimated from homogeneity measurements, increased with increasing concentration, for the 1.0, 4.0 and 6.0 %w/v samples. The minimum CV value was obtained for the 10.0 %w/v sample which is attributed to the incorporation of sonication in the final product, during the fabrication process. Homogenous dispersion was observed from the SEM micrographs.