Hello Everyone,

could someone please give us an advice about which method you consider is the best for our study ?

we have two groups with MRI at Time 1. Each group received medication. After this we performed another MRI at Time 2 after 2 weeks.

The best method for this study is a longitudinal one or a cross-sectional GLM ?

We consider that the distance between the time points is too small, and the longitudinal method is not the best choice. Hence, this study should be treated as a cross-sectional one. In this case we think about performing a simple GLM with the contrasts:
0.5 0.5 0.5 0.5
or 1 -1 -1 1

for the groups:
1) grp 1 time 1
2) grp 1 time 2
3) grp 2 time 1
4) grp 2 time 2

we are searching to see whether medication had any impact on the cortical morphology in each group and between the groups.

Thank you !
Best regards,
Alex.