One of three stages of CBCT reconstruction, which produces raw 3D images from a set of corrected 2D projections. Backprojection is used by most Computed Tomography systems. In contrast, other imaging modalities tend to use different approaches such as Fourier reconstruction. In the CBCT system, the FDK (Feldkamp, Davis, Kress) algorithm creates the filtered backprojection and gradually smooths the projection intensity to zero at the edges of the scan circle. This reduces so-called truncation artifacts that affect images where the patient exceeds the scan circle. Backprojection also uses an internal binning and filtering of the projections. See also CBCT reconstruction.