Dear FreeSurfer experts,

 

I simply do not understand the LME setup for longitudinal analyses.

 

Here is what I have: 3 groups each with variable longitudinal data (in terms of umber of time points and interval between timepoints). I am interested in detecting if the rates of longitudinal atrophy in each of the 3 groups and whether it is significantly different between the 3 groups.

 

1. My Qdec file contains: fsid, fsid_base, time, age, group, gender
2. I read in the relevant files with (output of surf2surf, lh.cortex, lh.sphere)
3. I read the Qdec file removed the first column, obtained the subject IDs, keep numerical data and get a sorted ‘M’ matrix
4. X=[intercept time grp1 time*grp1 grp2 time*grp2 grp3 time*grp3 age@timepoint1 gender]
5. After that, should I use voxel wise mass-univariate model or spatiotemporal mass-univariate model lme_mass_fit_vw or lme_mass_fit_EMinit?
6. After that I don’t understand the subsequent steps. Can you help me understand?

 

Any help is appreciated.

 

Thanks!

Swati