On 9/27/2023 10:17 AM, Matteo Parodi wrote:
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Sure I try, thank you for the replay.
I'm using the above-mentioned analisis to obtain the Uptake for the
region in Desikan atlas, but the results are strange.
I think the error is in the last command but I'm not sure.
The first time I had used mri command without --psf FWHM to not use
Partial volume correction.
mri_gtmpvc --i ${SUBJECTS_DIR}/PET.nii.gz --reg
${SUBJECTS_DIR}/PET.reg.lta --seg gtmseg100.mgz --no-rescale
--auto-mask 1 .01 --mgx .01 --o $GTM_DIR/gtmpvc_PET.output
But the result in gtm.stats.dat have some region ( those region with
less voxel) with negative Uptake. Physically inconsistent but I had
thought the problem was in the tissue fraction effect.
This can and will happen since the GTM is just a general linear model
trying to fit the data. It has no idea about what is physically
realizable, and there are no constraints to enforce. This is just
something that happens with the GLM at times.
The second command uses the --no-tfe option like indicated in the wiki
page, buth instead of negative count it returns high counts iven in
regions indicated with 0 voxel. Again Physically inconsistent.
I'm not sure what you mean
I tried different combination of the option to --auto-mask ang --mgx
but it's not work differently or not at all.
I don't have an idea of what and how the problem is, and not even
where I can study to find the correct application metod.
Thank you for any suggestions you can give me.
Il giorno mar 26 set 2023 alle ore 16:03 Douglas N. Greve
<dgr...@mgh.harvard.edu> ha scritto:
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I'm not sure what problem you are describing. Can you elaborate?
On 9/25/2023 9:16 AM, Matteo Parodi wrote:
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Hello,
I'm trying to perform a pet ROI analysis on an image recon from a
T1.
I have to perform the analysis without normalization and partial
volume correction.
I'm having problems with regions with few or no voxels which
makes me think I'm doing the analysis completely wrong .
With this command I obtain negative values for these regions:
mri_gtmpvc --i ${SUBJECTS_DIR}/PET.nii.gz --reg
${SUBJECTS_DIR}/PET.reg.lta --seg gtmseg100.mgz --no-rescale
--auto-mask 1 .01 --mgx .01 --o $GTM_DIR/gtmpvc_PET.output
While with this I get many counts even for regions without voxels:
mri_gtmpvc --i ${SUBJECTS_DIR}/PET.nii.gz --reg
${SUBJECTS_DIR}/PET.reg.lta --seg gtmseg100.mgz --no-rescale
--auto-mask 1.01 --no-tfe --o $GTM_DIR/gtmpvc_PET.output
Could you help me understand my mistake.
Thank you very much.
Parodi Matteo.
I will insert the commands I used before the ROI analysis:
recon-all -s Subj -i $IMAGED -all -threads 10
gtmseg --keep-cc --s Subj --xcerseg --o gtmseg100.mgz
mri_coreg --s Subj --mov ${SUBJECTS_DIR}/PET.nii.gz --reg
${SUBJECTS_DIR}/PET.reg.lta --threads 10
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