Optimization of GEM-based detector readout electrode structure for SXR imaging of tokamak plasma

The paper presents an optimization of a readout structure of the GEM-based detector designed for X-ray imaging for DTT tokamak in the energy range of 2–15 keV. The readout electrode of approximately 100 cm2 surface is composed of hexagonal pixels connected in a way that allows reducing the actual number of signal pixels (electronics channels). At the same time, based on time coincidence analysis, it makes possible to unambiguously identify the position of the recorded X-ray photon. For the input spectrum, the Detective Quantum Efficiency (DQE) of the detector was calculated using the Geant4 program and the spatial distributions of electron avalanches at the readout electrode were simulated using the Garfield++ program. These were conducted for a given energy range of radiation and a statistical distribution consistent with the shape of the spectrum considering the DQE of the detector. As a result, the size of a single hexagonal pixel was proposed to capture the position of the recorded radiation quanta in an optimal and effective way.

Application of DQE for quantitative assessment of detectors to estimate AEC efficiency in digital mammography

Optimisation of the detector’s exposure parameters settings for image quality and patient dose is an important task in digital mammography. Assessment of a digital detector’s performance can be done objectively and without operator bias by determining the Detective Quantum Efficiency (DQE). The authors of this article aim to prove that the performance of the AEC system can be objectively portrayed through DQE. The results were examined for influence of KAD changes on DQE values and to determine if it was possible to obtain similar DQE values for different exposures. While analysing the effect of the operation of the AEC system described with DQE, the doses received by women during mammography examinations were considered, as well. The AEC system’s exposure control mechanism cannot guarantee the same DQE value for different object thicknesses. When the object thickness increases, the AEC system should increase the KAD value to obtain the same DQE value. The result of increasing KAD would be the increase of mean glandular dose for some women. However, assuming that DQE is a good indicator of image quality, introducing the proposed changes to the AEC system’s operation would result in the same image quality for all breast thicknesses. This approach to DQE use for AEC system evaluation is independent of the image processing procedure and can be the basis for changes to system calibration done by the manufacturer’s technical support team.

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

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.