The GTM is just a general linear model, so there are no constraints on
sign. The GTM makes some assumptions about the nature and magnitude of
the PVEs (linear, gaussian, with the FWHM that you supply). Violations
of these assumptions can cause negative values. There are a lot of other
things that can cause it too, such as errors in various corrections
(scatter, atten, randoms, etc). Are they all showing up neg or just this
one subject?
On 1/26/18 10:50 AM, Chakmeedaj Sethanandha wrote:
Dear Freesurfer experts,
We found that a stat file in gtmpvc output folder shows that one area
has negative avg uptake value. What could explain this result?
Quoted the row from the file:
11 26 Left-Accumbens-area subcort_gm 3 2.351
-0.490 2.3033
The command used is as in the log file.
Best regards,
Jak
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