Radiologic techniques and changes in exposure doses to patients

A survey questionnaire was sent to 200 randomly selected hospitals in Japan, and 118 hospitals (59.5%) responded. The results were compared with those of the similar surveys performed in 1973 (1973's survey) and 1979 (1979's survey). According to plain radiography, obstetric radiography, infantile radiography, and mammography, the following items were surveyed: tube voltage, tube current, and exposure time; intensifying screen and kinds of film; grid ratio; added filter; and focus-film distance. Average tube voltage was almost the same as that in the 1979's survey, except for the high voltage radiography for the chest. The usage of both green fluororescence intensifying screen and orthofilm increased in number, as compared with that in the previous two surveys. The grid ratio of 8:1 was found to be more frequently used in the present survey than the previous two surveys. Focus-film distance for the breast varied widely (30-100 cm), which was similar to that in the 1979's survey. In the present survey, a distance of 100 cm in infantile radiography for the chest was seen in 27.5%, as compared with 41.2% in the 1979's survey. A distance of 150-200 cm was also found to be used. The present survey revealed exposure doses to be decreased by 56% as compared with the 1973's survey and by 39% as compared with the 1979's survey. (N.K.)