Accuracy of image reconstructions. (a) For RMSD = 2.0 HU, the fewest iterations required for SQS were M = 66, N = 140 and (b) for Nes were M = 18, N = 15. (Note the different x-axis scalings.) (c) Reference volume μ* and region used for RMSD evaluation annotated in the white dashed circle, display window [−400 400] HU. The SQS and Nes reconstructed images are shown on the left half of (d) and (e), respectively, for RMSD = 2.0 HU, while the right half shows the difference image with μ*, display window [−20 20] HU.