A number of studies have identified breast density as an independent risk factor for breast cancer. The U.S. Food and Drug Administration in January approved a digital mammography system that may give clinicians a powerful tool to perform better diagnoses in women with dense breasts.
The approved system, General Electrics Senographe 2000D, is one of several models of digital mammography machines already in use in Europe and Canada. Clear advantages of digital mammography include reduction of already low radiation exposures, easier storage of mammograms, opportunity to manipulate an image to yield a clearer view of the breast, and facilitation of long distance consultations with mammography specialists.
Proponents of the new technology claim that digital mammograms are better than film. Other researchers caution that existing data show only that digital mammography is as good as conventional mammography but not that it is better.
"[In a recent study,] the General Electric machine found the same number of cancers as film mammography," noted Etta Pisano, M.D., professor of radiology and chief of breast imaging at the University of North Carolina School of Medicine, Chapel Hill. "It is not at all clear that digital mammography is more sensitive."
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The Technology
A conventional mammogram captures a static x-ray image of the breast on film. The term digital mammography refers to two technologies. One involves scanning mammogram films into a computer that digitizes the image. True digital mammography, however, captures breast x-rays with a detector composed of sensitive elements that measure the x-rays coming through and assign a number to each point. The numbers are assigned to tones on a gray scale from black to white. The computer converts the x-ray intensity into numbers and uses them to generate an image. Software can then analyze patterns in the image, and the radiologist can manipulate the picture to increase contrast or highlight certain areas.
At least four companiesGE, Fischer Imaging Corp., Trex Medical Corp., and Fujihave prototype digital mammography machines in clinical trials. Each companys machine would need separate FDA approval, though it is unclear how stringent testing requirements will be for subsequent machines.
Future Research
Researchers and clinicians agree that digital mammography has potential advantages over film mammography, but they dont agree on their nature. Most observers want to see more rigorous scientific testing of digital mammography technology.
Daniel Kopans, M.D., professor of radiology at Harvard Medical School and director of the Breast Imaging Division at Massachusetts General Hospital, Boston, is enthusiastic about digital mammography. He considers digital images "far superior" to film mammograms and thinks digital mammography will find more cancers earlier and reduce false positives.
Martin Yaffe, Ph.D., of Sunnybrook and Womens Health Sciences Center, University of Toronto, Canada, thinks that data collected so far show digital mammography is at least as good as film. In 2000, he expects results to show that it is better, especially for women with dense breasts (see related story, opposite page).
Yaffe also sees a role for digital mammography in risk prediction, indicating which women need frequent screening and helping to unravel the puzzle of what makes breast tissue dense. The digital image can be displayed better and contrast can be manipulated, enabling radiologists to see tumors more easily. A primary use of digital mammography may be to identify what isnt breast cancer, thus reducing the number of unnecessary biopsies, Yaffe said.
"The gut feeling is that digital mammography is better," he said. "Now we need to prove it."
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