External Email - Use Caution

Sorry about that! I'm resending with previous emails.

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On 2/22/2022 9:15 AM, Laura Willers de Souza wrote:

Thanks so much for the explanation!

There is something different in the analysis of volume and surface area in relation to the analysis of cortical thickness? Like some more command, or some other detail that must be changed (besides, of course, the flag that specifies the measure to be analyzed) - I'm already using permutation in the correction of multiple comparisons.

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On 2/21/2022 15:20 PM, Douglas N. Greve wrote:

Yes, it is. It is confusing when you talk about area and volume since these are not point measures like thickness (ie, what is the volume or area of a vertex?). The area of a vertex is computed as the mean of the adjacent triangles of the vertex. The volume is the mean of the neighboring truncated tetrahedra. When you run mris_preproc, it will apply a jacobian correction (like VBM). Otherwise, it operates the same as if you had a thickness value at the vertex, ie, same GLM, etc. Make sure to use permutation for correction of multiple comparisons.

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On 2/21/2022 12:13 PM, Laura Willers de Souza wrote:

Hello FreeSurfer Developers,

I would like to know if it is correct to perform volume and surface area analysis using freesurfer's GLM!?

In several mailing list questions I have already seen instructions for performing these types of analysis. But I understand that freesurfer does vertex-wise analysis in the 2D surface space. So, it is not clear to me how it is possible to evaluate a 3D measurement, as volume, with a 2D method!?

I've also read that surface area analysis via vertex-wise analysis doesn't make much sense. The best would be to do ROI-based analysis. Can you explain that to me?

Thanks in advance!

________________________________ De: Douglas N. Greve dgreve@mgh.harvard.edu Enviado: terça-feira, 22 de fevereiro de 2022 20:01 Para: Laura Willers de Souza laura.w.desouza@hotmail.com Cc: freesurfer@nmr.mgh.harvard.edu freesurfer@nmr.mgh.harvard.edu Assunto: Re: [Freesurfer] GLM analysis - volume and surface area

Sorry, your previous emails were cut off so I'm not sure what command you are referring to.

On 2/22/2022 9:15 AM, Laura Willers de Souza wrote:

External Email - Use Caution

Thanks so much for the explanation!

There is something different in the analysis of volume and surface area in relation to the analysis of cortical thickness? Like some more command, or some other detail that must be changed (besides, of course, the flag that specifies the measure to be analyzed) - I'm already using permutation in the correction of multiple comparisons.

Best,

Laura Willers de Souza

Master Student in Biochemistry

Zimmer Lab - Federal University of Rio Grande do Sul

- Porto Alegre/RS - Brazil