USE OF MULTIPLE CT SCANS TO ACCOMMODATE LARGE OBJECTS AND STRETCH DYNAMIC-RANGE OF DETECTABILITY

Rotate-only X-ray CT scanners are preferred for inspection purposes be cause of their speed and dose utilization, but suffer from the restric tion that the scanned object must fit within the radiation beam. In ad dition, the ratio of signals unattenuated by air paths to those penetr ating thick, dense objects often exceeds the dynamic range of conventi onal X-ray detectors. Both of these disadvantages can be removed for o bjects larger than the X-ray beam by taking multiple scans, each of wh ich exposes only part of the object. These partial data sets can then be merged to produce a complete data set. For most objects, it is also possible to separately expose regions in which the ratios between the extremes of attenuation are much lower than the ratio between air and the maximum path length. In this case, it is possible to use a higher flux to image denser regions, and thus improve signal-to-noise ratios and produce images superior to those of larger scanners with the same dynamic range.