Hi Giulio,

Although SAMSEG is a deterministic algorithm the default version might give you different results when executed with a different number of threads. These are small differences when looking at seg.mgz (a few voxels with swapped labels), but they are more visible when looking at volumes computed from soft segmentations like the stats files.

Note that you will obtain the same exact results when running SAMSEG with the same number of threads.

If you want to have cross-thread reproducible results with SAMSEG you can download the source files of FS 7.2 and build FS with the flag (GEMS_CROSS_THREAD_REPRODUCIBLE ON when doing cmake). Note that this version of SAMSEG will run slower than the original version.

Source files can be downloaded here: https://github.com/freesurfer/freesurfer/tags?after=v7.3.1

and instructions on how to build FS are here: https://surfer.nmr.mgh.harvard.edu/fswiki/BuildGuide

Hope it helps,
Stefano

Da: giulio siracusano <siracusanogiulio@gmail.com>
Inviato: sabato 27 agosto 2022 04:22
A: freesurfer@nmr.mgh.harvard.edu <freesurfer@nmr.mgh.harvard.edu>
Cc: Cerri, Stefano <SCERRI@mgh.harvard.edu>
Oggetto: Re: [Freesurfer] SAMSEG estimation error
 

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Hi Stefano,

I've investigated the use of SAMSEG for AD/MCI patients. I'm using the 7.2 version of Freesurfer and I've realized that I get different results using the same data but when I run the SAMSEG multiple times.

Differently from using ASEG, SAMSEG provides also the chance to execute the code using multiple threads.

In the first run I've executed SAMSEG on ADNI patient id 002_S_0685 using the MP-RAGE series having ID I18211 (the link below provides the NIFTI version of the series which has been used for the processing).

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The first execution of SAMSEG was with default settings (1 thread) and results are attached, the second was using --threads 6.

These results from the SAME series are similar but they are NOT the same.

How can we explain that?

Regards

Giulio