Q: I have a question about deformation grids obtained from non-linear registration using nlpfit. These grids contain the 3D displacements at each voxel applied to the source to match the template or to the template to match the source?Now if the determinant is calculated from those grids with mincblob and it is found that voxel x has a value greater than 1. Does this mean the region in the neighborhood of x has expanded relative to the source or relative to the target?
http://www.bic.mni.mcgill.ca/pipermail/minc-users/2008-August/002138.html

A: (note that this all presumes you did something like this: where fred.mnc is our input subject)

  bestlinreg fred.mnc template.mnc linear_part.xfm
  nlpfit -init_xfm linear_part.xfm fred.mnc template.mnc nonlinear_part.xfm

If this is so then the nlxfm is from the source to the target. (after the linear transformation if there is one). This incidentally is why we calculate a model to individual transformation when we want to average a number of transformations during building a model.

Perhaps best by example:

0.5 == the area in question is 50% smaller in the template than the source 1 == no change 1.5 == the area in question is 50% larger in the template than the source.