We estimated SNR, which could be diminished by subject movement, in a sample of highly coherent white matter in the centrum semiovale of the inner 55% of the supratentorium masked on the SRI24 atlas and applied to each individual's MRI at each session. This white matter region, which was approximately 110 cc volume across subjects, began inferiorly at midpons, extended superiorly to the superior reaches of the centrum semiovale, just inferior to the cortical gyri and sulci, and medially to the sylvian fissures and excluded the corpus callosum. To further ensure homogeneity of tissue, the region was also masked by each individual scan's white matter segmentation. SNR was calculated as the mean divided by the standard deviation of the signal intensity of all voxels in this white matter sample.
