Some sources of artefact in computed tomography.

A number of sources of error and artefact that may arise in X-ray computed tomography are considered. The importance of temporal and spatial non-uniformities in X-ray tube output and detector sensitivity, of changes in voltage supply, of an incomplete field of view, and of scattered radiation, are analysed by calculating their effect on the reconstructed image, and by estimating the noise power that they introduce. Computer simulation is used whenever the error is dependent on the object. The particular relevance of these errors in CT scanners employing arrays of detectors, such as an image intensifier, is emphasised.