The bias field was corrected to fix intensity non-uniformities using the N4BiasFieldCorrection command in the ANTs program.  ANTs Version 2.2.0 was used, downloaded from git://github.com/stnava/ANTs.git.  An option (-d) was included to indicate that the images being processed were 3 dimensional.  This option forced the program to treat the image as 3 dimensional, rather than leaving it to infer dimensionality.  A second option (-s), a shrink factor set to 4, was also applied to resample the images.  Because processing large images can often be time consuming for the program, the shrink option was used to speed computation.  The b-spline fitting parameters (-b) were set to [200], and convergence (-c) was set to [50x50x50x50,0.000001], both standard options.