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.