Uncertainties Generated By Computed Tomography (CT) Beam-Hardening Corrections

Ira J. Kalet

doi:10.1117/12.957150

6 July 1979 Uncertainties Generated By Computed Tomography (CT) Beam-Hardening Corrections

Ira J. Kalet

Proceedings Volume 0173, Application of Optical Instrumentation in Medicine VII; (1979) https://doi.org/10.1117/12.957150
Event: Application of Optical Instrumentation in Medicine VII, 1979, Toronto, Canada

Abstract

Since the X-ray tubes used in CT scanners produce a polychromatic spectrum, the beam quality changes as the X-ray beam penetrates the scanned object, giving rise to differential beam hardening. Because of this effect, one cannot interpret CT numbers directly in terms of material densities or X-ray attenuation coefficients. Various schemes to correct for the beam hardening effect have been published and are used in commercial scanners. Although computer simulations have demonstrated the potential effectiveness of these schemes, uncertainties in the correction data limit the precision of the results, totally aside from limitations of photon counting statistics. In this work, the most basic beam hardening correction scheme, the water-equivalent correction, is analyzed. A formula is derived which relates uncertainties in the correction data to uncertainties in the reconstructed coefficients. Numerical estimates are given, showing that the uncertainties in the CT numbers can be on the order of 2½% to 10% even with the best correction data available. More sophisticated correction schemes are discussed from the point of reference developed for the water-equivalent correction. The analysis allows one to set requirements on the precision and stability of machine parameters and correction data.

Citation Download Citation

Ira J. Kalet "Uncertainties Generated By Computed Tomography (CT) Beam-Hardening Corrections", Proc. SPIE 0173, Application of Optical Instrumentation in Medicine VII, (6 July 1979); https://doi.org/10.1117/12.957150

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