Table II.

Quantitative assessment of differences between reconstructions with and without non-negativity for the ACR phantom. The minimum and maximum voxel differences are given, as well as the mean and standard deviation in the root mean square difference over the last 500 iterations. All values are in HU and measured inside the object-specific ROI.

	Min.	Max.	$\overline{\text{RMSD}}$
ACR phantom
Module A, edge-preserving reg.	−1.5	1.8	0.0394 ± 0.0023
Module A, quadratic reg.	−0.2	0.4	0.1828 ± 0.0002
Module D, edge-preserving reg.	−1.6	1.7	0.1295 ± 0.0014
Module D, quadratic reg.	−0.8	0.7	0.2041 ± 0.0001