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The physical performance metrics of computed-radiology (CR) systems used in screening mammography are lower than those of digital-radiology (DR). Also, the lack of quality assurance procedures in some countries might have a technology-dependent impact on image quality and dose. The Mexican Secretary of Health owns over 300 mammography units for breast cancer screening, about half of them of CR technology. We´ve investigated the performance of 20 CR and 4 DR units in 13 Mexican States, applying over 30 quality-control tests associated with general equipment performance, X-ray source, automatic exposure control, mean glandular dose (MGD), image receptor and image quality, and display conditions. Tests were applied following international protocols and their compliance criteria. None of the systems passed all the significative tests. For CRs, the worst performance was observed in compensation for breast thickness, signal-to-noise ratio (SNR) homogeneity, CDMAM thresholdthickness, sensitivity matching of CR plates, and the presence of artefacts. The worse performance of DRs was in compression force, SNR homogeneity, and artefacts. MGD values agreed with recommendations for 2-7 cm PMMA thickness in 50% of CRs and 75% of DRs. The dominance of quantum noise over other components was evaluated by 4 criteria endorsed by different organizations, and results depended on the applied criterium. Analysis of the maintenance procedures suggested that one explanation for these poor results might be the complex CR technology, where the x-ray generation is controlled by a unit fabricated by one manufacturer and the image generation occurs in a non-integrated unit from a different manufacturer.
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