Noise due to photon counting statistics in computed X-ray tomography

David A. Chesler, Stephen J. Riederer, Norbert J. Pelc

Research output: Contribution to journalArticlepeer-review

152 Scopus citations


A general expression is derived for the noise due to photon counting statistics in computed X-ray tomography. The variance is inversely proportional to the cube of the resolution distance. For scanners using a water box, the noise in the reconstructed image depends inversely on the number of detected primary photons, summed over all angles, that have passed through a resolution element. Predictions of this formula agree well with the results of computer simulations. It is shown how this formula can be used to determine such parameters as required X-ray flux, detector counting rate, and dose, with special emphasis on tradeoffs between these parameters and resolution. It is also shown that to determine the X-ray attenuation coefficient of a resolution element to a given precision, the number of photons required by computed X-ray tomography is close to a theoretical limit.

Original languageEnglish (US)
Pages (from-to)64-74
Number of pages11
JournalJournal of computer assisted tomography
Issue number1
StatePublished - Jan 1977


  • Computed tomography
  • Statistical noise

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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