### Abstract

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 language | English (US) |
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Pages (from-to) | 64-74 |

Number of pages | 11 |

Journal | Journal of computer assisted tomography |

Volume | 1 |

Issue number | 1 |

DOIs | |

State | Published - Jan 1977 |

### Keywords

- Computed tomography
- Statistical noise

### ASJC Scopus subject areas

- Radiology Nuclear Medicine and imaging

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## Cite this

*Journal of computer assisted tomography*,

*1*(1), 64-74. https://doi.org/10.1097/00004728-197701000-00009