Cone beam CT

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 . 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 . 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

Disadvantages

• increased scattered radiation
• potential for cone beam artifact if an inappropriate reconstruction algorithm is used