Tomosynthesis

Tomosynthesis, also digital tomosynthesis, is a method for performing high-resolution limited-angle tomography at radiographic dose levels. It has been studied for a variety of clinical applications, including vascular imaging, dental imaging, orthopedic imaging, mammographic imaging, musculoskeletal imaging, and chest imaging.

The concept of tomosynthesis was derived from the work of Ziedses des Plantes, who developed methods of reconstructing an arbitrary number of planes from a set of projections. Though this idea was displaced by the advent of computed tomography, tomosynthesis later gained interest as a low-dose tomographic alternative to CT.

Tomosythesis reconstruction algorithms are similar to CT reconstructions, in that they are based on performing an inverse Radon transform. Due to partial data sampling with very few projections, approximation algorithms have to be used. Filtered back projection and iterative, expectation-maximization algorithms have both been used to reconstruct the data.

Reconstruction algorithms for tomosynthesis are different from those of conventional CT because the conventional filtered back projection algorithm requires a complete set of data. Iterative algorithms based upon expectation maximization are most commonly used, but are computationally intensive. Some manufacturers have produced practical systems using off-the-shelf GPUs to perform the reconstruction in a few seconds.

Digital tomosynthesis combines digital image capture and processing with simple tube/detector motion as used in conventional computed tomography (CT). However, though there are some similarities to CT, it is a separate technique. In CT, the source/detector makes at least a complete 180-degree rotation about the subject obtaining a complete set of data from which images may be reconstructed. Digital tomosynthesis, on the other hand, only uses a limited rotation angle (e.g., 15-60 degrees) with a lower number of discrete exposures (e.g., 7-51) than CT. This incomplete set of projections is digitally processed to yield images similar to conventional tomography with a limited depth of field. Because the image processing is digital, a series of slices at different depths and with different thicknesses can be reconstructed from the same acquisition. However, since fewer projections are needed than CT to perform the reconstruction, radiation exposure and cost are both reduced.

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