Breast density: agreement of measures from film and digital image

Mammographic density, in particular density from digital images, is increasingly used in breast cancer research. We investigated the concordance between density assigned by the same radiologist to a mammogram film and a digital image of the same mammogram. Two density measures were investigated, Wolfe parenchymal patterns and a six category classification (SCC) system of density. Included in the study were 78 women, 528 mammograms. Crude and weighted Kappa statistics were used to estimate agreement between the density assigned from the film and the image. Kappa for Wolfe measures was 71%, p<0.001 and for SCC measures was 54%, p<0.001. Weighted Kappa values were 79%, p<0.001 and 77%, p<0.001, respectively. There was some evidence to suggest that the digitized image may be assigned a higher Wolfe but not numerical category than the original film, and the magnitude of these differences was small. Neither age nor mammogram view (craniocaudal or mediolateral oblique) were related to the likelihood of agreement of the two density measurements. This evidence justifies the use of digital images in the visual assessment of breast density in research studies.