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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Douglas N. Greve, Ph.D.

MGH-NMR Center

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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.anderso@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