Women’s features and inter-/intra-rater agreement on mammographic density assessment in full-field digital mammograms (DDM-SPAIN)
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Measurement of mammographic density (MD), one of the leading risk factors for breast cancer, still relies on subjective assessment. However, the consistency of MD measurement in full-digital mammograms has yet to be evaluated. We studied inter- and intra-rater agreement with respect to estimation of breast density in full-digital mammograms, and tested whether any of the women’s characteristics might have some influence on them. After an initial training period, three experienced radiologists estimated MD using Boyd scale in a left breast cranio-caudal mammogram of 1,431 women, recruited at three Spanish screening centres. A subgroup of 50 randomly selected images was read twice to estimate short-term intra-rater agreement. In addition, a reading of 1,428 of the images, performed 2 years before by one rater, was used to estimate long-term intra-rater agreement. Pair-wise weighted kappas with 95% bootstrap confidence intervals were calculated. Dichotomous variables were defined to identify mammograms in which any rater disagreed with other raters or with his/her own assessment, respectively. The association between disagreement and women’s characteristics was tested using multivariate mixed logistic models, including centre as a random-effects term, and taking into account repeated measures when required. All quadratic-weighted kappa values for inter- and intra-rater agreement were excellent (higher than 0.80). None of the studied women’s features, i.e. body mass index, brassiere size, menopause, nulliparity, lactation or current hormonal therapy, was associated with higher risk of inter- or intra-rater disagreement. However, raters differed significantly more in images that were classified in the higher-density MD categories, and disagreement in intra-rater assessment was also lower in low-density mammograms. The reliability of MD assessment in full-field digital mammograms is comparable to that for original or digitised images. The reassuring lack of association between subjects’ MD-related characteristics and agreement suggests that bias from this source is unlikely.
KeywordsMammographic density Digital mammograms Agreement Kappa Rater Risk factors
Body mass index
This study was supported by research grants from Fundación Gent per Gent (EDEMAC Project); grants FIS PI09/1230 & PI060386 from Spain’s Health Research Fund (Fondo de Investigación Sanitaria); the EPY 1306/06 Collaboration Agreement between Astra-Zeneca and the Carlos III Institute of Health (Instituto de Salud Carlos III); and a grant from the Spanish Federation of Breast Cancer Patients (FECMA). We thank the participants of the study DDM-Spain for their contribution to breast cancer research. We wish also to acknowledge the collaboration from other DDM-Spain members: Pilar Moreo, Pilar Moreno and Soledad Abad (Aragón); Francisca Collado and Magdalena Moyá (Baleares); Isabel González, Carmen Pedraz and Francisco Casanova (Castilla-León); Mercé Peris (Cataluña); Carmen Santamariña, José Antonio Vázquez Carrete, Montserrat Corujo and Ana Belén Fernández (Galicia); Nieves Ascunce, María Ederra, Milagros García and Ana Barcos (Navarra); Manuela Alcaraz, Jesus Vioque (C. Valenciana); Virginia Lope, Nuria Aragonés, Anna Cabanes (Madrid).
Conflict of interest
The authors declare that they have no competing interests.
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