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Cone beam CT

Last revised by Dr Jeremy Jones on 18 Sep 2021

Cone beam CT (CBCT) is a variant type of computed tomography (CT), and is used particularly in dental and extremity imaging but has recently found new application in dedicated breast imaging 4,5. It differs from conventional CT in that it uses a cone-shaped x-ray beam and two dimensional detectors instead of a fan-shaped x-ray beam and one dimensional detectors. 

Physics

In cone beam CT, a divergent cone-shaped source of radiation is directed through the target. The attenuated x-rays are detected on the opposite side by an x-ray detector, which has multiple dexels in the x and y-axis 2. Volume acquisition can thus be acquired with fewer rotations of the x-ray tube gantry. This differs from fan-beam CT, which uses a 2D fan-shaped x-ray beam in helical progression to acquire image data. Furthermore, fan-beam CT detector only has dexels in the x-axis.

The advent of cone beam CT has brought about several advantages over its fan-beam counterpart, but it also has its inherent disadvantages. 

Advantages
  • decreased examination time
  • decreased patient movement artifact
  • increased x-ray tube efficiency 3
Disadvantages
  • increased scattered radiation
  • potential for cone beam artifact if an inappropriate reconstruction algorithm is used

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Cases and figures

  • Figure 1: comparison of fan beam and cone beam CT
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  • Case 1
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  • Case 2
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  • Case 3: mesially impacted wisdom teeth
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  • Case 4: maxillary cyst
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