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

  • D. Cavouras
  • I. Kandarakis
  • G. S. Panayiotakis
  • C. D. Nomicos
Article
  • 69 Downloads

Abstract

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 mgcm−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.

Keywords

X-ray imaging Phosphor screens Modulation transfer function Detective quantum efficiency Information capacity 

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References

  1. Barnes, G. T. (1979): ‘The use of bar pattern test objects in assessing the resolution of film/screen systems’ inHaus, A. G. (Ed.): The physics of medical imaging: recording systems, measurements and techniques’ (American Association of Physicists in Medicine, New York, 1979), pp. 138–151Google Scholar
  2. Beutel, J., Mickewich, D. J., Issler, S. L., andShaw, R. (1983): ‘The image quality characteristics of a novel ultra-high resolution film/screen system’,Phys. Med. Biol.,38, pp. 1195–1206Google Scholar
  3. Bunch, P. C., Huff, K. E., andvan Metter, R. (1987): ‘Analysis of the detective quantum-efficiency of a radiographic film-screen combination’,J. Opt. Soc. Am. A,4, pp. 902–909Google Scholar
  4. Cavouras, D., Kandarakis, I., Prassopoulos, P., Kanellopoulos, E., Nomicos, C. D., andPanayiotakis, G. S. (1998): ‘Experimental evaluation of noise equivalent passband, information capacity, and informational efficiency of yttrium based europium activated phosphors’,Phys. Medica,14, pp. 119–126Google Scholar
  5. Dainty, J. C., andShaw, R. (1974): ‘Image science’ (Academic Press, London, 1974)Google Scholar
  6. Evans, A. L. (1981): ‘The evaluation of medical images’ (Adam Hilger, Bristol, 1981)Google Scholar
  7. Greening, J. R. (1985): ‘Fundamentals of radiation dosimetry’ (Medical Physics Handbooks, Institute of Physics, London, 1985)Google Scholar
  8. Icru (1986): ‘Modulation transfer function of screen-film systems’. ICRU report 41Google Scholar
  9. Kalivas, N., Kandarakis, I., Cavouras, D., Costaridou, L., Nomicos, C. D., andPanayiotakis, G. (1999): ‘Modeling quantum noise of phosphors used in medical X-ray image detectors’,Nucl. Instrum. Methods Phys. Res. A,430, pp. 559–569CrossRefGoogle Scholar
  10. Kanamori, H., andMatsumoto, M. (1984): ‘The information spectrum as a measure of radiographic image quality and system performance’,Phys. Med. Biol.,29, pp. 303–313CrossRefGoogle Scholar
  11. Kandarakis, I., Cavouras, D., Panayiotakis, G. S., andNomicos, C. D. (1997): ‘Evaluating x-ray detectors for radiographic applications: A comparison of ZnSCdS:Ag with Gd2O2S:Tb and Y2O2S:Tb screens’,Phys. Med. Biol.,42, pp. 1351–1373CrossRefGoogle Scholar
  12. Kandarakis, I., Cavouras, D., Kanellopoulos, E., Nomicos, C. D., andPanayiotakis, G. S. (1999): ‘A method for determining the information capacity of X-ray imaging scintillator detectors my means of luminescence and mtf measurements’,Med. Biol. Eng. Comput.,37, pp. 25–30Google Scholar
  13. Kandarakis, I., andCavouras, D. (2001a): ‘Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb−La2O2S:Tb mixtures for x-ray imaging’,Eur. Radiol.,11, pp. 1083–1091Google Scholar
  14. Kandarakis, I., andCavouras, D. (2001b): ‘Role of the activator in the performance of scintillators used in x-ray imaging’,Appl. Rad. Isot.,50, pp. 821–831Google Scholar
  15. Kandarakis, I., Cavouras, D., Panayiotakis, G. S., andNomicos, C. D. (2001a): ‘Experimental investigation of the optical signal, gain, signal to noise ratio and information content characteristics of X-ray phosphor screens’,Appl. Phys. B,72, pp. 877–883Google Scholar
  16. Kandarakis, I., Cavouras, D., Nomicos, C. D., andPanayiotakis, G. S. (2001b): ‘Measurement of X-ray luminescence and spectral compatibility of CdPO3Ci:Mn phosphor’,Radiat. Meas.,33, pp. 217–224CrossRefGoogle Scholar
  17. Ludwig, G. W. (1971): ‘X-ray efficiency of powder phosphors’,J. Electrochem. Soc.,118, pp. 1152–1159Google Scholar
  18. Lumilux (1989): ‘Lumilux data book’ (Riedel-deHaen, Seelze, Germany, 1989)Google Scholar
  19. Sandborg, M., andCarlsson, G. A. (1992): ‘Influence of x-ray spectrum, contrasting detail and detector on the signal to noise ratio and detective quantum efficiency in projection radiography’,Phys. Med. Biol.,33, pp. 1245–1263Google Scholar
  20. Shannon, C. E. (1948): ‘A mathematical theory of communication’,Bell. Syst. Tech. J.,27, pp. 379–423MathSciNetGoogle Scholar
  21. Shaw, R., andvan Metter, R. (1984): ‘An analysis of the fundamental limitations of screen-film systems for x-ray detection’,Proc. SPIE,454, pp. 128–132Google Scholar
  22. Storm, E. (1972): ‘Calculated bremsstrahlung spectra from thick tungsten targets’,Phys. Rev. A,5, pp. 2328–2338CrossRefGoogle Scholar
  23. Swank, R. K. (1973): ‘Calculation of modulation transfert function of x-ray fluorescent screens’,Appl. Opt.,12, pp. 1865–1870Google Scholar
  24. Tucker, D. M., Barnes, G. T., andChakraborty, D. B. (1991): ‘Semi-empirical model for generating tungsten turget X-ray spectra’,Med. Phys.,18, pp. 211–218Google Scholar
  25. van Metter, R. (1992): ‘Describing signal transfer-characteristics of asymmetrical radiographic screen-film systems’,Med. Phys.,19, pp. 53–58Google Scholar
  26. Williams, M. B., Mangiafico, P. A., andSimoni, P. U. (1999a): ‘Noise power spectra of images from digital mammography detectors’,Med. Phys.,26, pp. 1279–1293Google Scholar
  27. Williams, M. B., Simoni, P. U., Smilowitz, L., Stanton, M., Phillips, W., andStewart, A. (1999b): ‘Analysis of the detective quantum efficiency of a developmental detector for digital mammography’,Med. Phys.,26, pp. 2273–2285Google Scholar

Copyright information

© IFMBE 2002

Authors and Affiliations

  • D. Cavouras
    • 1
  • I. Kandarakis
    • 1
  • G. S. Panayiotakis
    • 2
  • C. D. Nomicos
    • 3
  1. 1.Department of Medical Instrumentation TechnologyTechnological Educational Institution of AthensAthensGreece
  2. 2.Department of Medical Physics, Medical SchoolUniversity of PatrasPatrasGreece
  3. 3.Department of ElectronicsTechnological Educational Institution of AthensAthensGreece

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