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Thanks Doug. we double checked the registration with gtm.seg.mgz and it
looks good. Also the uptake in Acc is not much smaller than other regions
and is pretty similar on both hemispheres so we are not sure what could be
causing this. Any suggestions much appreciated.

Many thanks


On Mon, Dec 2, 2019 at 5:15 PM Greve, Douglas N.,Ph.D. <
dgr...@mgh.harvard.edu> wrote:

> It may or may not be something that needs to be fixed. The PVC is just a
> linear model where the regression coefficients are the uptake in each ROI.
> As with any model, it adjusts the regression coefs to minimize the error in
> the fit. If some end up being less than zero when you really expect all to
> be > 0, then this probably indicates an error in the (linear) model. This
> error could come from several sources. For example, the registration could
> be off. The PSF might not be right. Or the uptake might not be constant
> across the ROIs. You should definitely start by checking the registration.
> If the uptake in Nuc Acc is very small relative to other ROIs, then I would
> just leave it the way it is, ie, DON'T just set it to 0 when you go to a
> group analysis.
> On 12/2/2019 4:48 PM, miracle ozzoude wrote:
>         External Email - Use Caution
> Hello Experts,
> I ran the PETsurfer pipeline using AV45 pet and performed pvc using pons
> as reference point. When i looked at the gtm.stats.dat file for one of my
> subjects, the SUVr for right and left nucleus-accumbens areas were in the
> negative (left = -0.361; right = -0.046).
> This is strange because SUVR shouldn't be negative. How do i go about
> fixing this error? Below, is my pvc command.
> mri_gtmpvc --i pet.nii --reg register.lta --psf 6 --seg gtmseg.mgz
> --default--seg-merge --auto-mask PSF .01 --mgx .01 --o subject_gtmpvc
> --rescale 174
> Thanks.
> Best,
> Paul
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