Three-dimensional (3-D) mammography, also known as digital breast tomosynthesis (DBT), is a type of digital mammography in which x-ray machines are used to take pictures of thin "slices" of the breast from different angles and computer software is used to reconstruct an image. This process is similar to how a computed tomography (CT) scanner produces images of structures inside of the body. 3-D mammography uses very low dose x-rays, but, because it is generally performed at the same time as standard two-dimensional (2-D) digital mammography, the radiation dose is higher than that of standard mammography. Newer tomosynthesis strategies allow DBT to be done alone, potentially reducing the radiation dose to a level closer to that of standard mammography.
Although many women are offered DBT, it has not yet been determined conclusively whether it is superior to 2-D mammography at identifying early cancers and avoiding false-positive results.
A large-scale randomized breast screening trial is comparing 3-D mammography with 2-D mammography. The Tomosynthesis Mammography Imaging Screening Trial (TMIST) is comparing the number of advanced cancers detected in women screened for 4 years with DBT with that detected in women screened with standard digital mammography.