Tomography (also referred to as x-ray computed tomography or computed tomography (CT)) is a well known medical digital imaging method created by computer processing. Digital image processing is used to generate a three-dimensional image of the inside of an object from a series/collection of two-dimensional x-ray images taken around a single axis of rotation. In CT, a source/detector makes a complete 360-degree rotation about the subject obtaining a complete volume of data from which images may be reconstructed. The volume of data produced by the CT system is manipulated to generate body structures. The images can be generated in the axial or transverse plane (e.g., perpendicular to the long axis of the body) or reformatted in various planes or a volumetric three-dimensional representation.
Tomosynthesis combines digital image capture and processing with source/detector motion used in tomography. While there are some similarities to CT, some view it as a separate technique. As noted above, in CT, the source/detector makes a complete 360-degree rotation about the subject obtaining a complete set of data from which images may be reconstructed. In digital tomosynthesis, a small rotation angle (e.g., 30 degrees) with a small number of discrete slices/exposures (e.g., 10) are used. This incomplete set of data is digitally processed to yield images similar to tomography with a limited depth of field. Since the image is digitally processed, a series of slices at different depths and with different thicknesses can be reconstructed from the same acquisition, thereby saving time and radiation exposure. Because the tomosynthesis data acquired is incomplete, tomosynthesis does not offer the narrow slice widths that CT offers.