Fig. 3.

Distribution of voxel-wise FWHM for ADNI images smoothed with 6 mm (left) and 12 mm (right) Gaussian smoothing kernels. Voxel-wise FWHM gives an indication of local smoothness and corresponds to the ‘full-width at half-maximum’ of a Gaussian kernel required to produce a random (white noise) image of equivalent smoothness. A perfectly stationary image would have constant FWHM at all voxels. In contrast, a highly non-stationary image would have a large spread in FWHM, as is seen here.