[Supine thoracic images with a mobile roentgen unit: comparison between the soft-ray and hard-ray technics].

To compare the influence of kilovoltage on the quality of supine chest roentgenograms obtained with a mobile x-ray unit, we examined the films of 50 patients on whom supine chest radiographs had been taken incidentally within a period of 24 hours both with high and with low-kVp technique. For evaluation of the image quality, a total of 11 criteria were compared and quantitated by 5 observers using a simple score method. The same advantages that have been attributed to the high-kVp technique on upright films were found on the corresponding supine examinations. These films showed a more balanced penetration and greater sharpness than those taken with low-kVp. The wider latitude of the high-kVp technique simplifies the exposure, and fewer repeat takes will therefore be necessary. The diagnostic gain outweights the few disadvantages, which are mostly coupled to the increase in scattered radiation. This, as well as the availability of more powerful and efficient mobile generators, should promote routine application of high-kVp technique for supine chest examinations.