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Tomosynthesis

6 February, 2011 | Tomosynthesis, X-ray

Tomosynthesis

Tomosynthesis is a method for producing images of slices through the body using a general radiographic X-ray system with a direct digital radiography detector. This is accomplished by obtaining a large number of image acquisitions across a range of projection angles of the X-ray tube. Currently, tomosynthesis is an optional add-on for suitable DR systems. The additional software controls the movement of the X-ray tube and the reconstruction of the images.

One of the disadvantages of planar imaging is that organs and structures overlying the region of interest are superimposed on the image, which can make interpretation more difficult. Tomosynthesis overcomes this by reducing the visibility of superimposed anatomical clutter in the image.

As the availability of digital flat panels increase, tomosynthesis is becoming a more practical option. A number of clinical applications of tomosynthesis have been described. These applications have been through early evaluation, though still in the optimization stage, and have yet to progress to full clinical trials. Tomosynthesis images are produced by equipment used to acquire planar images. Tomosynthesis acquires a series of planar images at different projection angles to produce image slices of the body. Tomography is a forerunner to tomosynthesis and so is explained here to help to understand tomosynthesis.

As with planar X-ray imaging, tomography uses the differences in attenuation between the tissues to form an image. However, while planar imaging acquires an image with the X-ray source and detector stationary, tomography uses a moving detector and source. They move with the center of rotation in the focal plane. Information above and below the focal plane is blurred out in the resulting image. Therefore, the image contains predominantly information in the focal plane. While tomography produces an image of a single slice through an object, tomosynthesis can produce many slices at different depths, from a single set of image acquisitions.

The acquisitions of discrete exposures, at different angles, as opposed to one long exposure in tomography, allows for the reconstruction parameters to be altered, in order to reconstruct slices with different focal planes . The maximum number of slices which can be reconstructed is limited by the number of discrete images acquired. Tomosynthesis produces images much like tomography, but the images are set at different cut heights as opposed to a single image.

Modern digital RF equipment with flat panel detector can be operated in tomosynthesis mode. In order for a flat panel detector system to undertake Tomosynthesis, it requires the following :

  • Control of the smooth movement of the X-ray tube, at the required speed
  • Rapid pulsing generator
  • Modern fast flat-panel detector

There are significant advantages from an economic point of view for tomosynthesis as there is a reduction in the numbers of patients having CT, MRI or nuclear medicine scans.

Tomosythesis has advantages over the planar X-ray in the following applications:

  • Chest imaging
  • Mammography
  • Orthopedics
  • Brachytherapy
  • Dental imaging
  • Nephrology