Hi FreeSurfer Experts,
I am trying to use mri_label_volume to correct for head size differences
in volumetric outputs. I know that this command needs a scale factor.
Where do I find this scale factor? Is this scale factor different for
each participant? I read through the eTIV wiki information and found
"To determine the scaling factor, 22 subjects for which the TIV has been
determined manually via their T2-weighted scans (which clearly show the
skull), are used. These subjects are found
in/autofs/space/jc_001/users/nicks/subjects/SASHA(a backup copy is
at/autofs/space/tinia_001/users/nicks/subjects/SASHA). The scaling
factor is determined analytically by first generating the determinant of
the atlas transform for the 22 subjects, plotting this against each
subjects manual TIV, fitting a line to this, and calculating the scale
factor from the slope.
In that SASHA directory, in the the scripts directory, the
scriptrun_rb_xfm.cshwill run themri_label_volumebinary and generate a
matlab data file calleddet_eTIV_matdat.mwhich contains the determinant
and eTIV data. Then, the matlab scriptplot_inv_det.mplots the inverse
determinant against the manual TIV, finds the best fit to this plot,
calculates the scale factor from that fit and then plots the eTIV
against manual TIV, for each subject using that scaling factor. The
fileICVnative_matdat.mcontains the manual TIV data, copied from the
ICVnative column in the filebuckner_tiv.txt, which originates from the
people performing the manual TIV measurements."
Is this what I need to do to get the scale factor?
Thanks in advance!
Colleen
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