A study published in the August issue of Radiology has determined that image display contrast variations account for the differences between digital and film-screen mammography in detecting cancer in the Digital Mammographic Imaging Screening Trial (DMIST).
In DMIST—co-sponsored by the National Cancer Institute (NCI) and American College of Radiology Imaging Network (ACRIN), participants underwent both digital and film-screen mammography between September 2001 and November 2003. The diagnostic accuracy of digital mammography was found to be “significantly greater” than that of film-screen mammography for women with dense breasts, women younger than 50 and pre- and perimenopausal women.
In the study, Etta D. Pisano, MD, of University of North Carolina School of Medicine, and colleagues had seven radiologists review film-screen and digital mammograms in DMIST cancer cases to assess the factors that contributed to lesion visibility on both images. The radiologists reviewed 307 cancer cases—13 cases with two cancers, for a total of 320 cancers available for review.
According to the authors, the readers varied “considerably” in their opinions on the relative visibility of cancer.
For women with both fatty and dense breasts, the most frequent reason given for the difference in visibility between film-screen and digital mammography was contrast differences between the two modalities. For women with dense breasts, contrast differences accounted for 70 of the 378 reasons given by the readers for better visibility. Positioning, compression, and technique differences accounted for only 37 of the reasons given for improved visibility.
The authors concluded that the “significantly better diagnostic accuracy” of digital mammography over film-screen mammography was most likely due to differences in image contrast, which were “attributable primarily to differences in the display and acquisition characteristics of the mammography devices rather than to reader variability.”