| 摘要 |
In a CT scanner attenuation data are determined for a plurality of sets of radiation paths through a body and a representation of the distribution of attenuation in the body is obtained from them. It is known to recompute attenuation data for such paths from a first estimate of the representation to take account of heavily attenuating regions which cause errors due to, for example, changes of radiation hardness therein and to then recompute a corrected representation. Conventionally the original data are for sets of parallel beams and the recomputation (or second pass) is performed for parallel paths using the same algorithm, i.e. the same procedure of modifying electrical signals by electronic circuits specially constructed and configured to carry out the desired procedure. The original data can be for fan distributed sets of paths and processed in that form. Then the second pass, using the same algorithm, is for fan distributed paths. This invention proposes to achieve the first processing to the first estimate using a procedure and electronic circuits for fan distributed paths and to achieve the second pass using the algorithm a procedure and circuits for parallel paths.
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