&lt;title&gt;An Analysis Of The Fundamental Limitations Of Screen-Film Systems For X-Ray Detection I. General Theory&lt;/title&gt;

Med. Biol. Eng. Comput.

Panayiotakis

et al. 2002

An integrated model describing the signal and noise transfer characteristics of the objective image quality and information content in phosphor-produced images is presented. In the context of this model, important imaging parameters, namely optical gain, modulation transfer function, noise transfer function, detective quantum efficiency and information capacity were experimentally evaluated using seven laboratory-prepared CdPO3Cl:Mn test phosphor screens of varying coating thickness. This phosphor has been previously shown to exhibit high spectral compatibility properties with the films and optical sensors used in digital imaging systems. Experiments were performed using 50-120 kVp X-rays produced by a medical X-ray unit. Results showed that, for thick screens, optical gain attained peak values close to 200 optical photons per incident X-ray at 50 kVp. The noise transfer function was higher than the modulation transfer function. For the thin screen of 21 mg cm-2, the modulation transfer function was 0.25 at 100 line pairs mm-1, and the corresponding noise transfer function was 0.4. The detection quantum efficiency peak value was 0.22 at 50 kVp. These values are within acceptable performance limits, and, given the phosphor material's high spectral compatibility and medium temporal response, CdPO3Cl:Mn could be considered for use in X-ray detectors of static radiography imaging.

Section: (U W) = 6xop(w)mentioning

confidence: 99%

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Integrated model for estimating phosphor signal and noise transfer characteristics on medical images: application to CdPO3Cl:Mn phosphor screens

Med. Biol. Eng. Comput.

Panayiotakis

et al. 2002

“…where [36]: It is noted that X-ray phosphors are detectors producing an output optical signal (light photons), which is determined by the energy of the incident X-ray beam (energy fluency); hence, the input SNR should be determined by the incident X-ray energy fluency. However, as has been demonstrated [17], the signal-to-noise ratio of an ideal detector, which captures all the information conveyed by the beam (DQE = 1), is equal to the mean number of incident photons (photon fluency).…”

Section: Theoretical Mtfmentioning

confidence: 99%

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

2001

Eur Radiol

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).

A method for determining the information capacity of x-ray imaging scintillator detectors by means of luminescence and modulation transfer function measurements

Med. Biol. Eng. Comput.

Κανελλόπουλος

et al. 1999

A method to determine the information capacity of x-ray phosphor screens used in the detectors of medical imaging systems is described. Information capacity was determined via x-ray luminescence efficiency (XLE), modulation transfer function (MTF) and emission spectrum measurements. The method was applied to laboratory prepared screens from commonly employed phosphor materials. The screen coating weight varied from 50 mg cm-2 to 140 mg cm-2. Results indicated that information capacity decreased with screen coating thickness but also depended on intrinsic phosphor properties (density, effective atomic number, intrinsic conversion efficiency, light wavelength). The Gd2O2S:Tb phosphor, exhibiting high density and effective atomic number, was found to be superior to La2O2S:Tb and Y2O2S:Tb.