Fig 1.

Calculation of ROIs used to control for differences in the spatial location of MR imaging metrics. A, Representative FLAIR image of a patient with periventricular and deep white matter hyperintensities. B, WMH are highlighted in yellow and overlaid on the FLAIR image. C, WMH (yellow) with the underlying FLAIR image removed. D, The WMH are left-right flipped about the y-axis (pink). This transformation is in Montreal Neurological Institute coordinates but retains the native structure (no warping of the brain). E, WMH (C) is subtracted from contralateral NAWM (pink). This is the final NAWM mask used in the statistical comparison between WMH and contralateral NAWM. F, Contralateral NAWM is left-right flipped and combined with the initial WMH ROI (C) by using a logical “and” operation; the resulting WMH mask includes only those voxels that have homologous NAWM in the contralateral hemisphere. This is the final WMH mask used in statistical comparisons between WMHs and contralateral NAWM. G, Final masks (E and F) overlaid on a FLAIR image.