Digital tomosynthesis (pronounced toh-moh-SIN-thah-sis) creates a 3-dimensional picture of the breast using x-rays. Currently, digital tomosynthesis is available only for research purposes.
Digital tomosynthesis of the breast is different from a standard mammogram in the same way a CT scan of the chest is different from a standard chest x-ray. Or think of the difference between a ball and a circle. One is 3-dimensional, the other is flat.
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.
Mammograms are very good, 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 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 3-dimensional images throughout the breast.