A comparison of ability to detect minute calcifications was theoretically made with the geometric conditions varied. The results obtained by this study are summarized as follows : 1) Direct radiographic magnification with a microfocus X-ray tube will be useful detecting dot-like objects such as calcifications, especially with Mo-target tube by the reasons described below. 2) Magnification technique will produce revers effect on differential diagnosis, if it is achieved at the cost of total MTF by using excessively high speed screens. It requires high resolution to distinguish malignant from benign tumors, which is mainly determined by intensifying screens used. On the other hand, fine graininess is required for detecting calcifications, which is limited by mottle size of the film almost regardless of the screens used. This implies that visual performance done by dot-like patterns only might lead to an erroneous conclusion. 3) The MTFs of mammographic screen-film systems using rare-earth screens, which could be approximated by Gaussian distributions, show higher value at low spatial frequencies than those of convential fine screen-film systems approximated by exponential distributions. This makes it effective to use magnification technique because a certain spatial frequency is shifted to lower frequency region. 4) Contact mammography using a tungsten-anode tube with small focal spot, for instance 0.3 mm, could not produce images superior in visibility to those obtained by larger focus, as has been reported previously, because of being accompanied by the use of higher tube voltage. However, a Mo tube minimizes the beam hardning of the X-rays that use of small or microfocal spot will turn to be useful. The Sn-Mo composite filter, studied in the 1st report, will provide higher image contrast than a single Mo filter at higher tube voltage over 40kVp.
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