Flat-panel digital mammography system: contrast-detail comparison between screen-film radiographs and hard-copy images

Abstract

Purpose: To compare the contrast-detail (CD) characteristics of screen-film (SF) and postprocessed digital images by using a phantom-based method.

Materials and methods: Images of a CD phantom with polymerized methyl methacrylate were acquired with SF and full-field digital mammography systems at matched exposure conditions. A four-alternative forced-choice experiment was conducted with seven observers participating in the study. Each observer was required to identify randomly located disks in phantom images from which detection curves were computed. The CD diagrams for the SF and digital systems were estimated from the detection curves and compared at 50% and 62.5% threshold levels. Furthermore, a theoretic model was used to estimate the CD performance of the SF and digital systems.

Results: Analysis of covariance for mixed models was used with the natural logarithm of disk thickness as the dependent variable, the natural logarithm of disk diameter as the covariate, and the observer as a random factor. The results of statistical analysis indicated significant differences between the CD characteristics of SF and digital mammographic images at both 50% (P <.001) and 62.5% (P <.001) detection thresholds.

Conclusion: The authors conclude that digital CD curves, on average, exhibit threshold contrast characteristics that are lower (better) than those of SF mammography.