Dual-energy digital mammography for calcification imaging: Improvement by post-image processing

Overlapping fibroglandular tissue structures may obscure small calcifications, essential to the early detection of breast cancer. Dual-energy digital mammography (DEDM), where separate low- and high-energy images are acquired and synthesized to cancel the tissue structures, may improve the ability to detect and visualize calcifications amidst fibroglandular structures. We have developed and implemented a DEDM technique under full-field imaging conditions using a commercially available flat-panel based digital mammography system. We have developed techniques to suppress residual structures due to scatter contamination and non-uniformity in the x-ray field and detector response in our DEDM implementation. The total mean-glandular dose from the low- and high-energy images was constrained to be similar to screening examination levels. The low- and high-energy images were combined using a calibrated nonlinear (cubic) mapping function to generate the calcification images. To evaluate the dual-energy calcification images, we have designed a special phantom with calcium carbonate crystals to simulate calcifications of different sizes superimposed with a 5 cm thick breast-tissue-equivalent material with a continuously varying glandular-tissue ratio from 0.0 to 1.0. The suppression of tissue-structure background by dual-energy imaging comes with the cost of increased noise hi the dual-energy images. We report on the effects of different image processing techniques on the dual-energy image signal and noise levels. The effects of image processing on the calcification contrast-to-noise ratios are also presented.