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

Computed tomography can be divided into 2 categories based on acquisition x-ray beam geometry; namely: fan beam and cone beam.

Traditional CT

In conventional fan-beam scanners, an x-ray source and solid-state detector are mounted on a rotating gantry (Fig. 1a). Data are acquired using a narrow fan-shaped x-ray beam transmitted through the patient. The patient is imaged slice-byslice, usually in the axial plane, and interpretation of the images is achieved by stacking the slices to obtain multiple 2D representations. The linear array of detector elements used in conventional helical fan-beam CT scanners is actually a multi-detector array. This configuration allows multidetector CT (MDCT) scanners to acquire up to 64 slices simultaneously, considerably reducing the scanning time compared with single-slice systems and allowing generation of 3D images at substantially lower doses of radiation than single detector fan-beam CT arrays.

Advanced Cone Beam CT Technology

CBCT scanners, on the other hand, are based on volumetric tomography, using a 2D extended digital array providing an area detector. This is combined with a 3D x-ray beam (Fig. 1b). The cone-beam technique involves a single 360° scan in which the x-ray source and a reciprocating area detector synchronously move around the patient’s head, which is stabilized with a head holder. At certain degree intervals, single projection images, known as “basis” images, are acquired. These are similar to lateral cephalometric radiographic images, each slightly offset from one another. This series of basis projection images is referred to as the projection data. Software programs incorporating sophisticated algorithms including back-filtered projection are applied to these image data to generate a 3D volumetric data set, which can be used to provide primary reconstruction images in 3 orthogonal planes (axial, sagittal and coronal).

Cone Beam

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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