An evaluation of the Y₂O₃:Eu³⁺ scintillator for application in medical x‐ray detectors and image receptors

Abstract

The suitability off a Y2O3:Eu3+ scintillator for use in radiation detectors and medical image receptors was studied. Y2O3:Eu3+ was used in the form of laboratory prepared screens of different coating thicknesses. The x-ray luminescence efficiency of the screens was measured for tube voltages between 50-200 kVp and in both transmission and reflection modes of observation. The intrinsic x ray to light conversation efficiency (nc) and other parameters of the Y2O3:Eu3+ phosphor material related to optical scattering, absorption, and reflection were determined. These were used in the calculation of the image transfer characteristics, MTF and zero frequency DQE, for various screen coating thicknesses and x-ray tube voltages. The light emission spectrum of Y2O3:Eu3+ was measured (narrow band peak at 613 nm) and its spectral compatibility to the spectral sensitivity of several commonly employed optical photon detectors was determined. The x-ray luminescence efficiency varied with x-ray tube voltage, attaining maximum value at about 80 kVp for all screen thicknesses. It also varied with coating thickness reaching 25 microW m(-2)/mR s(-1) and 18 microW m(-2)/mR s(-1) at 175 mg/cm2 for reflection and transmission modes, respectively. The intrinsic x ray to light conversion efficiency and the image transfer characteristics were found to be comparable to several commercially used phosphors: nc = 0.095, MTF0.05 ranged between 10 and 25 line pairs per mm and peal values of DQE(0) varied between 0.33 and 0.14 in the coating thickness and kVp ranges useful for x-ray imaging. Spectral compatibility to some red sensitive optical photon detectors was excellent (0.9 or better). Results indicated that Y2O3:Eu3+ is a medium to high overall performance material that could be used in medical x-ray detectors and image receptors.

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

“…where m is the mass attenuation coefficient of the phosphor for X-rays calculated using published data [27] and T is the screen-coating weight; h Q is the intrinsic X-ray to light conversion efficiency, giving the fraction of absorbed X-ray energy converted to light within the phosphor material; G L (a,s) is the light transmission efficiency, expressing the fraction of light produced that reaches the screen output [3,5,9,10,25,28,29], with a and s being the coefficients of light absorption and light scattering, and " E is the mean energy of X-rays determined by the relation:…”

“…For voltages outside this range phosphor ranking was reversed, with Gd 2 O 2 S:Tb showing higher NEP values. Figure 2 shows MTF curves measured by the SWRF method [19,23,24,25]. The MTF decreases with increasing spatial frequency.…”

“…The modulation transfer function of each screen was determined following the square wave response function (SWRF) method, which has been explicitly described in previous studies [10,19,21,22,23,24,25]. The screens were used in combination with the Agfa Curix Ortho GS radiographic film.…”

“…The NEP, MTF, and DQE can be theoretically calculated employing the theoretical models of Hamaker [27], Ludwig [3,19,22,25], and Swank [19,25,29]. These models describe the aforementioned parameters in terms of intrinsic physical properties of the phosphor materials, namely: the total mass energy absorption coefficient m (in cm 2 /g); the intrinsic X-ray to light conversion efficiency h C ; and the coefficients related to the attenuation (absorption and scattering) of the light produced inside the phosphor screen (see Appendix).…”

“…Sixtyfour successive density variations were selected and averaged to eliminate noise. The MTF was then calculated by the formula of Coltman [19,21,23,24,25], which gives the MTF as a function of SWRF. This calculation, however, includes the MTF of the scanner and of the film.…”