Cone-beam CT

Last revised by Andrew Murphy on 31 Jul 2022

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

Indications

Dental imaging

Cone-beam CT is used to investigate the exact location of jaw pathologies such as tumors, inflammatory lesions, exact location of impacted teeth before oral or maxillofacial surgery 6

It is also used in endodontics, implant dentistry, orthodontics, peridontics, temporomandibular joint imaging, and forensic dentistry 6.

Breast imaging

The three-dimensional cone-beam CT aims to address the limitation of two-dimensional imaging on mammography with high contrast between pathological and normal breast tissues. It reduces the overlap of breast lesions from surrounding breast parenchyma 4.

Liver imaging

After transcatheter arterial chemoembolisation of hepatocellular carcinoma, cone-beam CT is done to assess the amount of drug retained within the tumor 7.

Lungs imaging

Cone-beam CT guides transbronchial biopsy of peripheral pulmonary lesions and ablation of target lesion during bronchoscopy 8.

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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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