Hello experts,

I've recently run into a case the gtmstats uptake (reference region: cerebellum) for the pericarlcarine ROI's are as low as 0.40,

however computing the voxel wise mean using input.rescaled.nii.gz and mgx.ctxgm.nii.gx and aux/seg.nii.gz, the values are closer to 1, 

as expected:

| vol                   | psf | roi                  | gtmstats_uptake | mean_uptake |

| --------------------- | --- | -------------------- | --------------- | ----------- |

| input.rescaled.nii.gz |   0 | ctx-rh-pericalcarine |           0.807 |      1.226… |

| input.rescaled.nii.gz |   0 | ctx-lh-pericalcarine |           0.758 |      1.083… |

| input.rescaled.nii.gz |   6 | ctx-rh-pericalcarine |           0.409 |      1.197… |

| input.rescaled.nii.gz |   6 | ctx-lh-pericalcarine |           0.470 |      1.058… |

| mgx.ctxgm.nii.gz      |   0 | ctx-rh-pericalcarine |           0.807 |      1.007… |

| mgx.ctxgm.nii.gz      |   0 | ctx-lh-pericalcarine |           0.758 |      0.888… |

| mgx.ctxgm.nii.gz      |   6 | ctx-rh-pericalcarine |           0.409 |      0.915… |

| mgx.ctxgm.nii.gz      |   6 | ctx-lh-pericalcarine |           0.470 |      0.809… |

This is using Freesurfer 6.0, and the PET to anatomical registration looks fine.

Any ideas why we get such bad values from the GTM method?

Thanks for any help,

Ryan

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