[Optical density of phantom images of different mammography equipment using various exposure conditions]

The requirements for the target value of the mean optical density (o.d.) including proper tolerances of mammograms are determined in the "European Protocol for the Quality of the Physical and Technical Aspects of Mammography Screening (EPMS)". These requirements are not only applicable to screening mammography. 22 mammography devices were tested with exposures of test phantoms using different kV and thickness of PMMA and with sensitometric step wedges to check the processing conditions. Only five of 22 devices fulfill all requirements of EPMS to the opt. density. These results are caused by three reasons: first, wrong locking of optical density under standard exposure conditions; second, wrong compensation of the optical density by the automatic exposure control due to varing tube voltage (kV) and PMMA thickness and third, an inadequate back coupling to the processing conditions. All tested devices are not conspicuous in respect to the results of constancy tests according DIN 6868-2 [2] and DIN 6868-7 [3]. It is obvious, that the claimed devices are not properly adjusted in the acceptance test according DIN 6868-52 (1990-12) [4]. Respectively the tolerances, used do not fulfill the requirements to proper density in mammograms.