TABLE 3.

Pairwise T1w image similarity measures for intra- and inter-scanner comparisons.

Scanner comparison - T1w image	Affine similarity (mean ± SD)	WM/GM contrast (mean ± SD)	Max scale factor (mean ± SD)
Intra-scanner variability
Achieva	0.32 ± 0.02	0.04 ± 0.03	1.00 ± 0.00
Ingenia	0.37 ± 0.03	0.04 ± 0.04	1.00 ± 0.00
GE	0.37 ± 0.03	0.03 ± 0.02	1.00 ± 0.00
Inter-scanner variability
Achieva – Ingenia	0.28 ± 0.01	0.15 ± 0.07	1.01 ± 0.00
Ingenia – GE	0.21 ± 0.02	0.15 ± 0.07	1.01 ± 0.00
Achieva – GE	0.20 ± 0.02	0.30 ± 0.06	1.01 ± 0.00

The scanner models of the considered image pairs, irrelevant of order, i.e., irrelevant of which image is considered as reference. Affine similarity: mean ± SD of the affine similarity index where >0.2 corresponds to a reliable affine similarity index. WM/GM contrast difference: The absolute difference in WM/GM contrast-to-noise ratio (mean ± SD), with a threshold of acceptability between 0.1 and 0.2. Max scale factor: The mean ± SD of the maximum scaling factor over the three spatial directions, where a value of 1.00 indicates that no scaling is needed, and 1.01 indicates 1% scaling is required. Note that the standard deviation is approximately 0, showing that the scaling needed in pairwise comparisons is subject-independent.