多軌道断層撮影装置(Polytome U)における照射野とGrodel効果について

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In recent years, a number of multi-orbit tomographic units have been put to practical applications in this country. But these units generally have great magnification. Therefore, if the units could be used to bring out Grodel effect as expected, considerable reduction in the irradiation dose would be possible. Scattered X-rays tend to lower the response at a low frequency, but the grid has an effect to offset this phenomenon. In case both a subject and a field size are sufficiently small, the grid is not usually used from experience, but Grodel effect is utilized in obtaining tomograms. There are no standards, however, for the field size, thickness of the subject and the MFD (model film distance) that necessitate the use of grid. All the processes are followed from experience only. In order to determine in which case the grid is necessary, we have conducted experiments on the content of scattered X-rays on the film surface. The magnification of the multi-orbit tomographic unit (Polytome U) is approximately 1.3,and the MFD changes from 12〜35 cm depending on the layer height. It was confirmed from the experiments that if the content of the scattered X-rays was less than 70 per cent, or more severely 60 per cent, then tomograms suitable for intended diagnosis could be taken. There should be no difficulty in the diagnosis of the following cases, even if the grid is not employed. (Case 1) Tomography of the Lateral or Lumbar Vertebra of an Adult, Body thickness…approx. 28cm, Field size…13×17 cm, MFD…18〜20 cm (Layer height, 15〜17 cm), Content of Scattered X-rays…approx. 70 per cent. (Case 2) Tomography of the Base of the Skull of an Adult, Body thickness…approx. 20 cm, Field size…12×15 cm, MFD…20 cm (Layer height, 15 cm), Content of Scattered X-rays…approx. 50 per cent.
公益社団法人日本放射線技術学会の論文
1977-03-01

多軌道断層撮影装置(Polytome U)における照射野とGrodel効果について

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