Breast Imaging Update

By Barbara C. Bourassa

When it comes to breast-cancer detection, mammograms are considered the gold standard. For most women over the age of 40, an annual mammogram, taken using either film or digital x-rays, is more than adequate for the early detection of breast cancer.

Two existing technologies, however, are now being recognized as useful in special cases: Magnetic resonance imaging (MRI) screening is currently recommended by the American Cancer Society for women at high risk of developing breast cancer, and ultrasound is being used in conjunction with mammography to determine if a biopsy is needed.

What's more, at least one new technology shows promise for use in future breast imaging applications. But will these (or other) technologies ever replace mammograms? How do the different technologies produce images of the breast? What new imaging technologies are currently under evaluation, and which of the developing technologies show the most promise?

The bottom line, say breast imaging experts, is that changes in breast imaging technology move very slowly. "Digital mammography came into being in the early 1990s, and it took 13 years to prove that it's better [than traditional film x-rays] for dense breasts," says Etta Pisano, MD, Kenan professor of radiology and biomedical engineering and director of the Biomedical Imaging Research Center at the University of North Carolina School of Medicine at Chapel Hill. "For the next 10 to 15 years, the mammogram and the MRI are likely to be the best tools we have."

Women with more than a 20 percent lifetime risk of developing breast cancer should get an annual MRI in addition to their mammogram, according to the American Cancer Society (www.cancer.org). This includes women with the breast cancer gene and those with a first-degree relative with the gene, among others. The MRI "is meant to be done in addition to mammography, rather than a replacement," says Dr. Pisano. "The MRI will never replace the mammogram because it does not detect calcification, which is one of the earliest signs of breast cancer." Calcifications are tiny mineral deposits in the breast tissue that show up as small white spots on an x-ray.

An MRI uses magnets and radio waves (as well as contrast material) instead of x-rays to produce very detailed, cross-sectional images of the body. An ultrasound, on the other hand, uses high-frequency sound waves to produce images. Ultrasound is used "to determine if biopsy may be needed in conjunction with mammography," says Dr. Pisano. "It can preclude the need for biopsy when it finds a cyst or definitely benign solid mass. In addition, we are in the middle of studying ultrasound as an adjunct to the mammogram for screening of high-risk women, but it will never replace the biopsy, because today's biopsies are much less invasive (than surgery) and 95 percent effective."

Several new technologies are currently being evaluated for use in breast imaging, including optical imaging (lasers), thermography (digital infrared imaging), and scintimammography (injecting a radioactive tracer that attaches to breast cancer cells), but the data for each is inconclusive. "Optical imaging is not approved by the Food and Drug Administration (FDA), and we are still waiting for data," says Dr. Pisano. "There is no data showing that thermography is useful. Scintimammography is approved for use and being used in some centers, but I am not convinced by the literature [that it is effective]."

Digital tomosynthesis, however, shows some promise, according to Dr. Pisano. This technology uses a procedure similar to a CAT scan to produce high-resolution, cross-sectional, three-dimensional images of the breast. (A traditional mammogram produces a two-dimensional x-ray.) "Two clinical trials of two different tomosynthesis devices are underway that will tell us whether tomosynthesis can replace conventional mammography for breast-cancer diagnosis and screening," says Dr. Pisano.

Whatever the outcome of this or other studies, however, Pisano and other breast imaging experts note that widespread use of 3D breast imaging may be at least 10 years away, if not longer. "Mammograms, including both film and digital versions," says Dr. Pisano, "are still the best screening tool for breast cancer for the foreseeable future."