Speed of Medical X Ray Screen/Film/Processing System in Danish Hospitals

The speed of screen/films in cassettes used for the lumbar spine examination in 25 Danish X ray departments has been examined under field conditions. The film is exposed in seven steps at a focus - film distance of approximately 1.8 m at 90 kV with an aluminium absorber of 29 mm in the beam, in addition to the filtration of tube and diaphragm. Prior to the exposure of the film the air kerma in the plane of the film is measured and at the same time a reading is taken from a monitor chamber placed close to the light beam diaphragm. When exposing the film the air kerma in the plane of the film is calculated from this monitor reading. The speed is calculated as 1 mGy multiplied by the reciprocal of the air kerma in the plane of the film needed to produce a net density of 1.0. Of the systems 28% had a measured speed equal to or higher than the nominal speed and 72% of the systems had a lower: 12% of the systems met the guidelines of the Commission of the European Communities concerning speed whereas 88% did not.