Hello,
 I am trying to use Xiao Han's ThicknessRepeatability methods for a
longitudinal study.  I have successfully completed step one, which is rigid
registration of the pre and post scans, but I am having problems with step
2.  This step uses the mris_thickness_diff function to compute the thickness
difference map.  I use the following command, as suggested by Xiao Han:

mris_thickness_diff -xform $SUBJECTS_DIR/1001/mri/transforms/1001_to_1001a.lta \
  -src_type curv \
  -out $SUBJECTS_DIR/1001/surf/lh.thickness_diff.mgh \
  -nsmooth 0 \

  -abs -S 1001 \
  -L $SUBJECTS_DIR/1001/surf/lh_thickness_diff.log \
  $SUBJECTS_DIR/1001/surf/lh.white \
  $SUBJECTS_DIR/1001/surf/lh.thickness \
  $SUBJECTS_DIR/1001a/surf/lh.white \
  $SUBJECTS_DIR/1001a/surf/lh.thickness

The function successfully reads the surfaces, but if fails when trying to
apply the LTA xform to align surface 1 to surface 2.  The terminal states:

INFO:try to get src info from transform.

ERROR: ComputeDifferenceNew: MHTfindClosestVewrtexNo returned nnindex=-1,
which is invalid

I have experienced this error for multiple subjects and have been unable to
get past it.  I am unsure of what the nnindex is and why it is -1.  Any help
on this issue would be greatly appreciated.  Thanks.

-Scott Beeman
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