The camera is not shifted for each set of projections. In principle a higher angle range is preferable. The 20 were selected due to practical restrictions. Principle of planar tomography. The X-ray tube is shifted alog the surface parallel to the pipe axis and several hundred projections are taken for reconstruction.
Artefacts arise for volumetric indications only due to the missing projection angle problem.
The used reconstruction is based on a modified filtered back projection. This algorithm is a typical analysis method and is applied for cross-sectional analysis of preselected regions of interest. 6 shows a typical indication of a crack in an austenitic pipe weld. We thank Dr. V.A. Baranov and Dr. A. Likhachov for interesting and helpful discussions and for software support. Mai 1986, Berichtsband.