Source: J Can Dent Assoc 2006; 72(1):75–80

Advantages of Cone Beam CT (CBCT)

CBCT is well suited for imaging the craniofacial area. It provides clear images of highly contrasted structures and is extremely useful for evaluating bone. The use of CBCT technology in clinical practice provides a number of potential advantages for maxillofacial imaging compared with conventional CT:

  • X-ray beam limitation: Reducing the size of the irradiated area by collimation of the primary x-ray beam to the area of interest minimizes the radiation dose. Most Cone Beam CT units can be adjusted to scan small regions for specific diagnostic tasks. Others are capable of scanning the entire craniofacial complex when necessary.
  • Image accuracy: The volumetric data set comprises a 3D block of smaller cuboid structures, known as voxels, each representing a specific degree of x-ray absorption. The size of these voxels determines the resolution of the image. In conventional CT, the voxels are anisotropic rectangular cubes where the longest dimension of the voxel is the axial slice thickness and is determined by slice pitch, a function of gantry motion. Although CT voxel surfaces can be as small as 0.625 mm square, their depth is usually in the order of 1–2 mm. All CBCT units provide voxel resolutions that are isotropic equal in all 3 dimensions. This produces sub-millimetre resolution (often exceeding the highest grade multi-slice CT) ranging from 0.4 mm to as low as 0.125 mm (Accuitomo).
  • Rapid scan time: Because Cone Beam CT acquires all basis images in a single rotation, scan time is rapid (10–70 seconds) and comparable with that of medical spiral MDCT systems. Although faster scanning time usually means fewer basis images from which to reconstruct the volumetric data set, motion artifacts due to subject movement are reduced.
  • Dose reduction: Published reports indicate that the effective dose of radiation (average range 36.9–50.3 microsievert [µSv])10–14 is significantly reduced by up to 98% compared with “conventional” fan-beam CT systems (average range for mandible 1,320–3,324 µSv; average range for maxilla 1,031–1,420 µSv).10,11,15–17 This reduces the effective patient dose to approximately that of a film-based periapical survey of the dentition (13–100 µSv)18–20 or 4–15 times that of a single panoramic radiograph.
  • Display modes unique to maxillofacial imaging: Access and interaction with medical CT data are not possible as workstations are required. Although such data can be “converted” and imported into proprietary programs for use on personal computers (e.g., Sim/Plant, Materialise, Leuven, Belgium), this process is expensive and requires an intermediary stage that can extend the diagnostic phase. Reconstruction of CBCT data is performed natively by a personal computer. In addition, software can be made available to the user, not just the radiologist, either via direct purchase or innovative “per use” licence from various vendors (e.g., Imaging Sciences International). This provides the clinician with the opportunity to use chair-side image display, real-time analysis and MPR modes that are task specific. Because the CBCT volumetric data set is isotropic, the entire volume can be reoriented so that the patient’s anatomic features are realigned. In addition, cursor-driven measurement algorithms allow the clinician to do real-time dimensional assessment.
  • Reduced image artifact: With manufacturers’ artifact suppression algorithms and increasing number of projections, our clinical experience has shown that Cone Beam CT images can result in a low level of metal artifact, particularly in secondary reconstructions designed for viewing the teeth and jaws.

Source: J Can Dent Assoc 2006; 72(1):75–80

Authors: William C. Scarfe, BDS, FRACDS, MS; Allan G. Farman, BDS, PhD, DSc; Predag Sukovic, BS, MS, PhD

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