Dear Dr Greve,

Thank you very much for the great explanation. I will definitely correct for 
PVC using PET surfer.

Kindly I have one follow-up question and I highly appreciate your input.

I have PET data for two groups. I studied the difference in PET signal using  
voxel-wise ( FSL/randomise) and surface-based using PET surfer.

My question is about PVC. We correct for PVC in surface based because we 
re-sample PET data to the brain surface which is an output of segmentation 
process, meaning we expect partial volume effects between the grey/white  for a 
possible contamination between them during segmentation.

We don't do PVE in voxel-wise because we don't worry about the contamination 
meaning there are no segmentation lines to separate between brain regions.

Kindly is my understanding for this fact correct ( i.e. why we correct in 
surface based and we don't correct in voxel-wise). By the way, I ran voxel-wise 
using randomise with TFCE and 5000 permutations.

Thank you again for any clarification
John

The PET signal  can change with a lot of anatomical changes in the brain 
including thickness, surface area, and gyrification. There is no known 
regressor that will account for this. Right right way to account for it is with 
partial  volume correction (PVC). It is best to do PVC simultaneously with the 
recon, but software is not available to perform this. You can do it on a 
post-hoc basis in PETsurfer using the PVC options in mri_gtmpvc. See the wiki.

On 08/10/2017 04:11 AM, John Anderson wrote:

>

> Hi Dr Greve,

>

> I have PET data for two groups and I used PET surfer in FSV 6.0 to run

> the analyses. The pipeline is straightforward and the analysis ran

> smoothly without any issues.

>

> Is it correct procedure to adjust PET signal to differences in gray

> matter volume or cortical thinness between two groups?

>

> In other words, is it correct if gray matter volume or cortical

> thickness for subjects be included as EVs in GLM or a nausiance factor

> in QDEC?

>

> Specifically, is the PET signal changeable depending on  differences

> in cortical thickness.

> or differences in gray matter volume?

>

> Thank you  for any clarification

>

>> Thank you !

>> Jon

>>

>

>

>

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> Freesurfer mailing list

> Freesurfer@nmr.mgh.harvard.edu

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--

Douglas N. Greve, Ph.D.

MGH-NMR Center

gr...@nmr.mgh.harvard.edu

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> -------- Original Message --------
> Subject: PET surfer
> Local Time: August 10, 2017 4:11 AM
> UTC Time: August 10, 2017 8:11 AM
> From: john.ande...@protonmail.com
> To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
>
> Hi Dr Greve,
>
> I have PET data for two groups and I used PET surfer in FSV 6.0 to run the 
> analyses. The pipeline is straightforward and the analysis ran smoothly 
> without any issues.
>
> Is it correct procedure to adjust PET signal to differences in gray matter 
> volume or cortical thinness between two groups?
>
> In other words, is it correct if gray matter volume or cortical thickness for 
> subjects be included as EVs in GLM or a nausiance factor in QDEC?
>
> Specifically, is the PET signal changeable depending on  differences in 
> cortical thickness.
> or differences in gray matter volume?
>
> Thank you  for any clarification
>
>> Thank you !
>> Jon
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