Do the two inputs have different voxel sizes? The gtm.stats.dat file reports the number of voxels so if the volumes have different voxels sizes, you will get different values out. If this is not the source of the problem, please send the gtm.stats files.

On 3/15/2023 4:06 AM, Federica Di Antonio wrote:

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of course: I run the same line of command for both amyloid and tau pet images with a fwhm = 1 in order to see what have happened

mri_gtmpvc --i taupet.nii --reg tau.reg.lta --psf 1 --seg gtmseg.mgz --auto-mask 1 .01 --mgx .01 --no-rescale  --o tau.output

mri_gtmpvc --i amypet.nii --reg amy.reg.lta --psf 1 --seg gtmseg.mgz --auto-mask 1 .01 --mgx .01 --no-rescale  --o amy.output  

when I extract gtm.stats.dat file and I compare the number of voxels for the same regions (and for the same subject of course) I obtain these values (attached files). Can I suppose this effect descends from the flag --automask? maybe the different automatic masks lead to different pixel size.. I don't know, I would be very grateful for any information.

Thanks for all the help you can give me about; sincere greetings from 

Federica Di Antonio

Il giorno lun 6 mar 2023 alle ore 16:31 Douglas N. Greve <dgreve@mgh.harvard.edu> ha scritto:

can you send an example?

On 2/17/2023 9:38 AM, Federica Di Antonio wrote:

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Dear experts,

I hope this email finds you well.

I run the pvc correction with mri_gtmpvc for subjects data obtained with two different PET tracers. 

In gtm.stats.dat, for every subject and every region, the number of voxels evaluated for amyloid tracer is approximately twice the volume evaluated for the second tracer.

I'd expect that the volume of a region for the same subject doesn't change with the tracer. 

Do you think this error can result from previous errors in the analysis? Or is it in some way plausible?

Thank you for your patience,

Federica

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