The Food and Drug Administration (FDA) last week approved the first three-dimensional (3-D) mammography machine. Already in use in several other countries, American hospitals can start adding these machines to their women's imaging centers and will likely improve breast cancer screening and treatment outcomes.
Radiologists found that the images created from the 3-D machine were better at detecting cancers, especially those found in women with dense breast tissue. The images also better allow them to see the difference between cancerous and noncancerous findings. Results of clinical trials showed a 15% increase in the amount of cancers caught, and a 30% decrease in callback rates. Approximately 10% of women proceed to further testing.
The 3-D imaging, also known as tomosynthensis, provides physicians with a picture that is remarkably different from current 2-dimensional mammography. Two-dimensional images deliver a flat representation of the breast tissue and the physician has to convert these images in his or her mind into a breast. Because of the overlapping tissue present in breasts, especially those with dense tissue, lesions may not always be visible.
Dr. Mary Hayes, MD, the medical director of Women's Imaging at Memorial Health Care System in Hollywood, Florida, says that the difference between 2D and 3D mammography is like the difference between looking at a closed book and looking at all the pages. "If there is a red dot on one of the pages and the book is closed, you can't see it. However, if you have a picture of each page of the book, you'll see that red dot."
Dr. Hayes adds that she and her colleagues looked at hundreds of readings in 2D and 3D during the trial, having to go back to reading only 2D away from the trial was "like going from driving a Maserati to driving a clunker." She also pointed out that radiologists were surprised to learn that the 3-D improved readings in fatty breast tissue as well as dense.
The breast is put in the same position in the 3-D mammography machine as it is in the 2-D mammography machine. However, the 3-D machines do not require as much pressure on the breast so patients report less discomfort during that portion of the exam.
The X-ray tube moves around the breast and takes 11 pictures during a 7-second exam. Because radiologists still prefer a 2-D and a 3-D image, the amount of radiation to which the patient is exposed is slightly increased. However, the amount is equivalent to what someone would be exposed to over the course of two months of "background radiation," meaning just everyday life. The FDA panel of 11 experts voted 11-0 that the benefits of the improved picture outweigh the risks of increase radiation exposure.
Called the Selenia Dimensions 3-D mammography system, it is made by Hologic. Hospitals and clinics that currently use Hologic's 2-D machines only need a software upgrade to convert the traditional machine over to a 3-D. The display itself is larger than traditional displays, but most digital mammography sites are accustomed to dealing with displays that size. Archiving, however, may take some adjustments. A 2-D mammogram occupies about 20MB of space, while a 2-D and a 3-D comprises about 170MB.
"With 3-D mammography, we hope to be able to detect earlier cancers that we could not otherwise see because they are hidden by normal breast tissue density," says Katherine Hall, MD, FACR, the medical director of the Women's Diagnostic and Breast Center at Texas Health Presbyterian in Dallas.