Reconstruction results of an abdomen image after six iterations obtained for a sampling interval of 10°.

First row: ground truth; subsequent rows from top to bottom: images reconstructed using FDK, ART, and the 3-, 6-, and 26-directional gradient operators. Images from left to right show the sagittal, transaxial, and coronal sections of the abdomen. Areas marked by dotted rectangles are enlarged and displayed in Fig 11. Artifacts in the reconstructed images are more obvious than Fig 8. However, as seen in Fig 8, subsequent rows from top to bottom, the lower images in the figure, the smoother they are.