Abstract
BackgroundInter-women and intra-women comparisons of mammographic density (MD) are needed in research, clinical and screening applications; however, MD measurements are influenced by mammography modality (screen film/digital) and digital image format (raw/processed). We aimed to examine differences in MD assessed on these image types.MethodsWe obtained 1294 pairs of images saved in both raw and processed formats from Hologic and General Electric (GE) direct digital systems and a Fuji computed radiography (CR) system, and 128 screen-film and processed CR-digital pairs from consecutive screening rounds. Four readers performed Cumulus-based MD measurements (n = 3441), with each image pair read by the same reader. Multi-level models of square-root percent MD were fitted, with a random intercept for woman, to estimate processed–raw MD differences.ResultsBreast area did not differ in processed images compared with that in raw images, but the percent MD was higher, due to a larger dense area (median 28.5 and 25.4 cm2 respectively, mean √dense area difference 0.44 cm (95% CI: 0.36, 0.52)). This difference in √dense area was significant for direct digital systems (Hologic 0.50 cm (95% CI: 0.39, 0.61), GE 0.56 cm (95% CI: 0.42, 0.69)) but not for Fuji CR (0.06 cm (95% CI: −0.10, 0.23)). Additionally, within each system, reader-specific differences varied in magnitude and direction (p < 0.001). Conversion equations revealed differences converged to zero with increasing dense area. MD differences between screen-film and processed digital on the subsequent screening round were consistent with expected time-related MD declines.ConclusionsMD was slightly higher when measured on processed than on raw direct digital mammograms. Comparisons of MD on these image formats should ideally control for this non-constant and reader-specific difference.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0787-0) contains supplementary material, which is available to authorized users.
Highlights
Inter-women and intra-women comparisons of mammographic density (MD) are needed in research, clinical and screening applications; MD measurements are influenced by mammography modality and digital image format
MD is increasingly being incorporated into breast cancer (BC) research and clinical practice, for example in BC risk prediction models [2], as a marker for the effectiveness of therapeutic drugs mediated through MD [3], and in risk-based stratification for tailored BC screening regimens [4]
Obtaining directly comparable MD measurements is challenged by the fact that no single MD measurement tool is used universally; there are more than 10 quantitative methods currently in use [5,6,7,8]
Summary
Inter-women and intra-women comparisons of mammographic density (MD) are needed in research, clinical and screening applications; MD measurements are influenced by mammography modality (screen film/ digital) and digital image format (raw/processed). MD is increasingly being incorporated into BC research and clinical practice, for example in BC risk prediction models [2], as a marker for the effectiveness of therapeutic drugs mediated through MD [3], and in risk-based stratification for tailored BC screening regimens [4]. To enable these applications, estimates of differences in MD between women and within women over time are needed. Images originate from a variety of imaging modalities and mammography systems; that is, from older screen-film mammography (SFM) or more recently from digital mammography
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