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