New 3-D mammography system may improve breast imaging

Developed at MGH, digital tomosynthesis may better identify malignant lesions

A new approach to mammography, developed by researchers at Massachusetts General Hospital (MGH), holds the potential for greatly improving the detection of breast lesions and the ability to predict whether they are benign or malignant. In a presentation earlier this month at the scientific assembly of the Radiological Society of North America (RSNA), Elizabeth Rafferty, MD, of the MGH Breast Imaging Service described initial results of a study comparing the new technique, called digital tomosynthesis, to standard mammography. Among the new technique’s advantages, she explains, is a significant reduction in false positive test results.

“The overlap of breast structures presents a major challenge for radiologists, both because these tissues can hide cancers and because they produce shadows which mimic a lesion on conventional mammography,” Rafferty says. “These false positive studies account for almost 25 percent of the instances when women are recalled for additional imaging from their screening mammograms. By eliminating this structure overlap, tomosynthesis prevents virtually all of these unnecessary callbacks, along with the anxiety they create.”

Tomosynthesis differs from standard mammography in the way a CT scan differs from a standard X-ray procedure. In tomosynthesis, the X-ray tube moves in a 50-degree arc around the breast while 11 low-dose images are taken during a 7-second examination. A computer then assembles the information to provide high-resolution cross-section and three-dimensional images that can be reviewed by the radiologist at a computer workstation.

“Tomosynthesis takes digital mammography to the next level,” adds Daniel Kopans, MD, MGH director of breast imaging and a coauthor of Rafferty’s presentation. “It is a modification of a standard digital mammography unit. The breast is held the same way, but women will be happy to learn that the test requires only one compression of each breast rather than the two currently required by standard mammography.” Kopans is one of the inventors of the digital tomosynthesis system, which has been patented by the MGH.

Rafferty’s report covers data from the first 100 women to volunteer for tomosynthesis in addition to standard mammography at MGH. Her data indicates that tomosynthesis makes lesions easier for the radiologist to see and also makes visible some lesions not detectable by conventional procedures. The radiologists who reviewed both standard mammograms and tomosynthsis images for the study reported being significantly more confident in determining the malignancy of lesions with tomosynthesis, Rafferty said.

Richard Moore, head of MGH Breast Imaging Research, says, “We can now see the tree in the forest. Digital tomosynthesis opens up multiple new avenues of investigation into better ways to detect and diagnose breast cancer early.” Moore and physicist Tao Wu, PhD, helped develop the tomosynthesis device and algorithms for analyzing data and producing images.

Kopans and his team worked closely with representatives of General Electric to produce a prototype digital tomosynthesis system under a grant from the U.S. Department of Defense, and he is optimistic that ongoing clinical trials at the MGH will soon lead to FDA approval. “Tomosynthesis is going to revolutionize the way we look for breast cancers,” Kopans says. “We have only begun to realize the potential of this technology.”

The Massachusetts General Hospital, established in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH conducts the largest hospital-based research program in the United States, with an annual research budget of almost $300 million and major research centers in AIDS, the neurosciences, cardiovascular research, cancer, cutaneous biology, transplantation biology and photomedicine. In 1994, the MGH joined with Brigham and Women’s Hospital to form Partners HealthCare System, an integrated health care delivery system comprising the two academic medical centers, specialty and community hospitals, a network of physician groups and nonacute and home health services.