Optimal magnification ratio of direct macroradiography in high magnification. Modulation transfer function study on system combined with intensifying screen-film and object.

Calculation of the composite modulation transfer function ( MTF) of macroradiography in high magnification conducted with an X-ray tube having a very fine focal spot of 50 p. was performed with the purpose of obtaining the optimal magnification ratio. The optimal magnification ratio of a macroradiogram taken without the object of scatterer was 4-fold when a Fuji KX medical X-ray film combined with fine definition intensifying screen of Kyokko FS was used, 5-fold with medium speed screen of Kyokko MS and 6-fold with high speed screen of Kyokko HS. The optimal magnification ratio was 8-fold regardless of the kind of intensifying screen-film system when the experiment was made with a water phantom of 5-15 em in thickness as scatterer. It was indicated from MTFs of macroangiograms of various magnifications obtained in animal experiments that the image quality of the macroangiogram of 6or 8-fold magnification was superior to those of 2-, 4-, 10and 15-fold ones. It was concluded from the examination of macroangiograms of animals (the part of the rabbit examined was 3-5 em thick) and macrolymphograms of patients (the examined part was 13 em thick) that the macroradiogram of 6or 8-fold magnification produces better findings of the fine structure of vessels than macroradiogram of other magnifications. The results accorded well with those obtained by phantom experiments with water of 5-15 em in thickness as scatterer.