Mammographic density assessed on paired raw and processed digital images and on paired screen-film and digital images across three mammography systems

Anya Burton, Graham Byrnes, Jennifer Stone, Rulla M. Tamimi, John Heine, Celine Vachon, Vahit Ozmen, Ana Pereira, Maria Luisa Garmendia, Christopher Scott, John H. Hipwell, Caroline Dickens, Joachim Schüz, Mustafa Erkin Aribal, Kimberly Bertrand, Ava Kwong, Graham G. Giles, John Hopper, Beatriz Pérez Gómez, Marina Pollán, Soo-Hwang Teo, Shivaani Mariapun, Nur Aishah Mohd Taib, Martín Lajous, Ruy Lopez-Riduara, Megan Rice, Isabelle Romieu, Anath Arzee Flugelman, Giske Ursin, Samera Qureshi, Huiyan Ma, Eunjung Lee, Reza Sirous, Mehri Sirous, Jong Won Lee, Jisun Kim, Dorria Salem, Rasha Kamal, Mikael Hartman, Hui Miao, Kee-Seng Chia, Chisato Nagata, Sudhir Vinayak, Rose Ndumia, Carla H. van Gils, Johanna O. P. Wanders, Beata Peplonska, Agnieszka Bukowska, Steve Allen, Sarah Vinnicombe, Sue Moss, Anna M. Chiarelli, Linda Linton, Gertraud Maskarinec, Martin J. Yaffe, Norman F. Boyd, Isabel dos-Santos-Silva, Valerie A. McCormack

Inter-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. We 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. Breast 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 cm(2) 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. MD 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.