There is nothing special to do in terms of longitudnial for PET. For the MRI, you may want to use the longitudinal stream (depending upon how far apart your time points are and whether you are expecting atrophy or other changes), and then use the closest time point for the GTM and sampling on the surface.

On 07/11/2018 05:25 AM, Elijah Mak wrote:

Hi Freesurfer Team and Doug,

Is there any way to derive the gtmstats from Petsurfer within a longitudinal design?

Could I get your take on the steps below?

1. Extract GTM stats from each PET time-point (registered to the

closest structural MRI in time). 2. Manually compute the percent change per region across time-points.

Alternatively, would it be more ideal to resample the PET data to the surfaces at each time point before extracting the MGX-based ROI PET data with mri_segstats? With this approach, it would be possible to use the longitudinal commands, right?

Thanks! Elijah

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