When it comes to characterizing microcalcifications, full-field digital mammography (FFDM) has a slight edge over conventional screen-film systems, according to researchers from Germany.
Comparison of screen-film and digital contact mammograms of patients with microcalcification clusters, performed at the Georg-August University Goettingen, put FFDM on top in terms of image quality in 50% of the cases. Subsequent histopathological analysis also revealed FFDM to be more sensitive and reliable than screen-film mammography in detecting and describing the clusters.
Dr. Uwe Fischer and colleagues identified 37 microcalcification clusters on digital mammography in 35 patients between November 1999 and February 2000. This group then underwent a conventional screen-film examination. FFDM images for an additional 20 patients with stable microcalcification clusters over a two-year period were also obtained and compared with their previous screen-film exams. Full details of the study, forthcoming in European Radiology, are available in the journal online.
Four experienced readers reviewed each case independently, ranking image quality, number of visible calcifications, and characterization. Diagnoses were evaluated following vacuum or open biopsy of suspicious findings, and overall performance indictors calculated. FFDM proved superior in both sensitivity and specificity:
- sensitivity, 95.2% vs. 91.9%
- specificity, 41.4% vs. 39.3%
The Goettingen team attributed FFDM's modest superiority to its increased contrast-detail detection, which allows better visualization of small high-contrast structures.
"Phantom studies have already shown that FFDM has a higher detection rate of small particles than screen-film using the same parameters and the same exposure dosage," they said.
Dr. John Lewin, codirector of breast imaging at the University of Colorado Health Sciences Center, suggests that FFDM also benefits from decreased noise and windowing functions, which optimize the available contrast. This helps counteract the lower spatial resolution of digital systems.
"This effect is even more pronounced on true geometric magnification views which, in my opinion, are clearly superior on digital," he said.
While noting that the slight differences in sensitivity and specificity in the Goettingen study are unlikely to be statistically significant, Lewin said that digital mammography may eventually replace conventional systems in some clinical settings.
"I see FFDM as an able substitute for film mammography that will fit well into an all-digital department. It opens the door to many new advanced applications including computer-aided detection, contrast-enhanced mammography, tomosynthesis, and others that we have not even thought of yet," he said.
-- By Paula Gould
For more information from the Diagnostic Imaging archives:
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