The diagnostic worth of the Chest Roentgenogram seems to be attributed to the affairs that the blood vessel shadows are clear and the ends of them also can firmly be followed up. Now, when the tube voltage is variously changed, what differences should appear on the blood vessel shadows? Analyzing and investigating, I have made clinical observations regarding the phenomena from both sides of the primrry rays and the scattered rays. The lower the tube voltage is, the more clearly the change of the X-ray contrast reaches to the middle part of the blood vessel; moreover, the finer the blood vessel is, the more remarkable the teddency become. And the scattered rays have the tendency to harm the image, if the tube voltage is higher than 80kVp-90kVp. On the contrary, when the tube voltage is higher than 80kVp-90kVp, the X-ray contrast will happen only nearer the blood vessel;and the higher the tube voltage rises, the larger the volume of the scattered rays become : ; and the higher the tube voltage rises, the larger the volume of the scattered rays becomes; accordingly it has the tendency to make the contrast worse. But as for “unsharpness”, it does not harm the image too much. When the two tendencies of the primary rays and the scattered rays are uniten and, besides, the tube voltage is low, it is thought that the blood vessel shadows are unclearly seen and hard to be followed up. In addition, this has well been concordant with clinic observations. Therefore, in case of combination of the present day film and the intensifying screen, the tube voltage of 80kVp-90kVp is more excellent than the photography heretofore in use. So-called high voltage technique is recommendable. if man uses a movable grid which can completely remove the stripes.
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