Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Abstract

The purpose of this work was to investigate and compare the imaging performance of Gd2O2S:Tb and La2O2S:Tb phosphors as well as of Gd2O2S:Tb and La2O2S:Tb mixtures for use in X-ray imaging detectors (intensifying screens). Phosphors were supplied in powder form and were used to prepare test screens. Three types of screens were prepared: Gd2O2S:Tb; (Gd50La50)O2S:Tb; and La2O2S:Tb. Screens were excited by X-rays with tube voltages from 40 to 120 kV and their efficiency (light intensity or light energy flux over exposure) was measured with a photomultiplier and a dosimeter. The light spectrum was also measured with a monochromator. From these measurements, the number of emitted photons per incident X-ray (NEP) and the zero frequency detective quantum efficiency (DQE(0)) of the screens were determined. Additionally, modulation transfer function (MTF) was measured by the square wave response function (SWRF) method. A theoretical model calculating NEP and DQE was also developed to fit experimental data and predict the performance of Gd2O2S:Tb-La2O2S:Tb mixtures by weight from 10-90% to 90-10%. Gd2O2S:Tb screens exhibited highest NEP, DQE, and MTF at tube voltages higher than 55 kV and lower than 45 kV, whereas La2O2S:Tb screens had better NEP, DQE, and MTF within the 45- to 55-kV range. Maximum NEP values were higher than 700 at 100-120 kV while maximum DQE(0) was 0.314 at 80 kV. Gd2O2S:Tb screens are more efficient for high X-ray tube voltage applications (e.g., abdominal imaging, chest radiography, lumbar spine radiography, CT) and for very low voltage applications (e.g., mammography). La2O2S:Tb screens are useful for medium-range X-ray voltages (e.g., pediatric radiography).

Optical photon transport in powdered‐phosphor scintillators. Part 1. Multiple‐scattering and validity of the Boltzmann transport equation

“…23,24 In this study all the phosphor grains are considered to be spheres of identical radius, a = 3.5 μm, corresponding to an average phosphor powder size that is commercially available. 25 Note that this is also the median grain size in some general-purpose commercial screens. 23 The optical emission 75 wavelength in this study is set to, λ = 0.5 μm, which is approximately the peak emission for the Gd 2 O 2 S:Tb phosphor 13 used in Lanex screens.…”

DR with a DSLR: digital radiography with a digital single-lens reflex camera

“…At 10:1 demagnification, a standard F/1.4 camera lens will collect about 0.1% of the light emitted by a Lambertian source. Measured conversion efficiencies (from x-ray energy to optical energy) of Gd 2 O 2 S or La 2 O 2 S screens is in the range 18 – 20% [5], which means that a single 50 keV x-ray photon will yield approximately 4,000 optical photons, each of energy around 2.5 eV (green). If we collect 0.1% of them, then only 4 photons will reach the camera sensor, and if the sensor quantum efficiency is around 25% (see Sec.…”

The Crystal Structures of Er3OFS3 and Er3OF3S2: Two Erbium Oxide Fluoride Sulfides with Condensed Tetrahedral [ZEr4] Units (Z = O and F)

“…Oxide fluoride sulfides of the rare-earth metals demonstrate an interesting research topic, since they are closely related to rare-earth metal oxide sulfides, which are currently used in technical applications, for example as phosphors in X-ray imaging detectors [1][2][3]. Although, the mere oxide sulfides appear yet in many different formulae and structure types (e.g.…”