Figure 3.

(a) Reconstruction time for each technique vs number of iterations for the 90kVp images with 602 projections, required by an AMD Opteron^™ Processor 6272, 32 physical cores and 128 GB of RAM. CG image after (b) three and (c) 40 iterations (45 h). Iterative FDK image after (d) one and (e) three iterations. SART image after (f) one and (g) three iterations. (h) SIRT image after 100 iterations for a grid of (512 pixels)³ with pixel size of (0.2 mm),³ which took 80 h—if the 1024 grid used for the other methods was repeated here the reconstruction times would be even longer. (i) FDK reconstruction. The numbers in the top right corner indicate the number of iterations used in each image. Figures b-i were extracted from a central region of the 7 cm phantom. (b) and (h) present a background different colour because they have not yet converged. (j) Reconstruction times using a smaller grid of 250 pixels × 250 pixels × 200 pixels and voxel size of (0.2 mm)³ to illustrate a scenario closer to a pre-clinical practice workflow, where only a region of interest in the object is selected. Vertical scale is in minutes here, while in panel a it is in hours. CG, conjugate gradient; FDK, Feldkamp, Davis, and Kress; SART, simultaneous algebraic reconstruction technique.