[Comments on the topic of determining mean optical density in roentgen images]

The determination of the mean optical density in an X-ray film by means of an integral measurement with a photometer at long distances from the radiograph yields values which are too low for the high contrasts in a few portions of the image. By arithmetic comparison with the true mean optical density as computed by a scan measurement, one can obtain a correction quantity delta D, which, in the extreme case, can increase up to a value of 0.7 and has to be added to the result of the integral measurement. Because the mean optical density has an influence on the image quality and therefore on the diagnostic value of a radiograph, this correction has to be taken into account in practice and especially at measurements in the "Arztliche Stellen". These institutions are authorized by the BAK to check the radiographs made by practitioners and radiologists for a sufficient image quality.