Acquisition of projection images

The x-ray beam used in CBCT for body imaging is a full cone with a solid angle defined by the size of the detector and the source-to-imager distance (SID). In specialized applications, for example, dedicated breast CBCT, a half-cone is used, where the central ray stays parallel to the chest wall for maximum coverage of breast tissue. Most clinical CBCT systems use circular gantry rotation with minimum angular coverage of 180 + cone angle. Typically, 200 to 300 images are acquired for each scan to avoid streak artifact. The gantry rotation speeds depend both on the mechanical stability of the gantry and the image acquisition speed of the detector.