1993 年 49 巻 4 号 p. 576-581
Aluminum and copper are widely used as materials in compensating filters in lung hilars tomography. However, using these materials causes a problem : the lung image contrast decreases because of increasing X-ray energy. In this study, gadolinium which has a K-absorption edge of 50 keV was used for preventing the decrease in lung image contrast. In this study, the compensating filter is made of a commercial gadolinium screen. The effective X-ray energy transmitted through a gadolinium filter is about 18 keV which is lower than that transmitted through aluminum at a tube voltage of 100kV. We investigated the differences in the image contrast caused by the difference of the effective energy. As a result, the radiographic contrast between a 5 mm aluminum plate and 10 cm acryl plate when the X-ray beam is transmitted through a gadolinium filter is approximately 0.2 optical density units higher than when it is transmitted through an aluminum filter. Also, it appears that the image contrast of the lung is better on clinical film. Thus, using a gadolinium filter has some advantages : the decrease in the image contrast of the lung can be minimized, it is easy to make the compensating filter, and the filter is not heavy.