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Full-field breast tomosynthesis.

Breast tomosynthesis is a 3-dimensional (3-D) imaging technology that involves acquiring images of a

stationary compressed breast at multiple angles during a short scan. The individual images are then

reconstructed into a series of thin high-resolution slices that displayed individually or in a dynamic

cin mode. Tomosynthesis can reduce or eliminate the tissue overlap effect. While holding the breaststationary, images are acquired at a nsumber of different x-ray source angles. Objects at different

heights in the breast project differently for each angle. The final step in the tomosynthesis procedure

is reconstructing the data to generate images that enhance objects from a given height by

appropriate shifting of the projections relative to one another. There are 3 specific areas in

tomosynthesis system requirements that warrant a closer review: detector efficiency and dose, field

of view, and equipment geometry. The breast is compressed in a standard way. While holding the

breast stationary, the x-ray tube is rotated over a limited angular range. A series of low dose

exposures are made every few degrees, creating a series of digital images. Typically, the tuben is

rotated about +/-15 degrees, and 11 exposures are made every 3 degrees during a total scan of a few

seconds. The individual images are projections through the breast at different angles and these

arewhat are reconstructed into slices. There are 2 basic tomosynthesis system designs that diiffer in

the motion of the detector during acquisition. One method moves the detector in concert with the x-

ray tube so as to maintain the shadow of the breast on the detector. An altemate method is to keep

the detector stationary relative to the breast platform. The tomosynthesis reconstruction process

consists of computing high-resolution images whose planes are parallel to the breast support plates.

Typically, these images are reconstructed with slice separation of 1 mm; thus, a 5 cm compressed

breast tomosynthesis study will have 50 reconstructed slices. The reconstructed tomosynthesis slices

can be displayed similarly to computed tomography (CT) reconstructed slices. Tomosynthesis could

resolve many of the tissue overlap reading problems that are a major source of the need for recallsand additional imaging in 2-D mammography exams.

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:

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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 theoverlapping 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 isin 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.

Early results with digital tomosynthesis are promising. 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