Digital tomosynthesis, commonly known as 3D mammography, creates a three-dimensional picture of the breast using digital x-ray technology. The procedure is approved by the U.S. Food and Drug Administration (FDA) but is not yet considered the standard of care for breast cancer screening. Because it is relatively new, it is available at only a limited number of hospitals.
Digital tomosynthesis of the breast is different from standard mammography in the same way a CT scan of the chest is different from a standard chest x-ray. It’s like the difference between a ball and a circle: the former is three-dimensional; the latter is flat.
Regular (2D) mammography usually takes two x-rays of each breast from different angles: top to bottom and side to side. The breast is pulled away from the body, compressed and held between two glass plates to ensure that the whole breast is viewed. Regular mammography records the pictures on film, and digital mammography records the pictures on the computer. The images are then read by a radiologist. Breast cancer, which is denser than most healthy nearby breast tissue, appears as irregular white areas — sometimes called shadows.
Regular mammograms are very useful for screening and diagnosis, but they have some significant limitations:
- The compression of the breast that’s required during a mammogram can be uncomfortable. Some women hate it, and it could deter them from getting the test.
- The compression also causes overlapping of the breast tissue. A breast cancer can be hidden in the overlapping tissue and not show up on the mammogram.
- Mammograms take only one picture, across the entire breast, in two directions: top to bottom and side to side. It’s like standing on the edge of a forest, looking for a bird somewhere inside. To find the bird, it would be better to take 10 steps at a time through the forest and look all around you with each move.
Digital tomosynthesis (3D mammography) is a new kind of test that’s trying to overcome these three big issues. It takes multiple x-ray pictures of each breast from many angles. The breast is positioned the same way it is in a conventional mammogram, but only a little pressure is applied — just enough to keep the breast in a stable position during the procedure. The x-ray tube moves in an arc around the breast while 11 images are taken during a 7-second examination. Then the information is sent to a computer, where it is assembled to produce clear, highly focused three-dimensional images throughout the entirety of the breast.
Early results with 3D mammography are promising. A group of radiologists who participated in two studies of the benefit of 3D mammograms reported that when used along with regular, 2D mammography, there is a 7% increase in accuracy. Researchers believe that this new breast imaging technique will make breast cancers easier to see in dense breast tissue and will make breast screening more comfortable.
Adapted from online article posted by breastcancer.org, a nonprofit organization dedicated to providing information and community to those touched by the disease.
WHAT IS THE RISK OF 3D MAMMOGRAMS
Because the tests are new, insurance companies may not cover them and may require patients to pay out of pocket.
More importantly, the procedures give women twice as much radiation as a standard mammogram, notes surgeon Susan Love, author of Dr. Susan Love’s Breast Book. That’s because women who get 3-D imaging still undergo traditional 2-D mammography as well.
Radiation is a known cause of breast cancer. Researchers in recent years have become concerned about radiation exposure from medical imaging, particularly CT scans. A 2009 analysis estimated that CT scans cause about 29,000 cancers and 14,500 deaths a year. The total radiation dose from 3-D mammography is still relatively low, in spite of this increase — from 0.5 millisieverts to 1.0 millisieverts.
The American College of Radiology now advises patients to ask questions before undergoing scans, such as, “How will this exam improve my care?” and “Are there alternatives that don’t involve radiation?”
– USA Today