Hi Alain,

Please see below:


On 21 May 2015 at 11:01, Alain Imaging <[log in to unmask]> wrote:
Hi everybody!

I am totally green to MELODIC and I would like to have some hints.

I have performed a longitudinal study with three groups. Each group received a resting state fMRI before and after a treatment. Our hypothesis is that the three different treatment affect the resting state functional connectivity in a different way. So what I thought to do is performing MELODIC (multi-sessions temporal concatenation) on my functional data, in order to perform dual regression as a second step and comparing the three groups.

Here come the questions:

1) Since I have two session for each subject, that are identical as for what the subject does (i.e. nothing) but should differ because of treatment, what should I do ? Should I nonetheless temporally concatenate the two sessions and feed one 4D image for each subject ? Should I feed the two sessions as separate images (i.e. enter subjects x 2 images) ?

You can use both files of all subjects into a single Melodic run, with temporal concatenation. There should be no biases on the IC maps.
 
2) I thought that I should run melodic on the whole sample, without dividing it by group. Am I right ?

Yes. Try to use groups of the same size, using the same logic as with study-specific templates as in, e.g., VBM.

 
3) Related to question 1. If I feed MELODIC with the temporally concatenated session for each subject, how I can get back and observe the effect of time ? And if I feed MELODIC with two sessions for each subjects separately, can I calculate then a delta between the component at time 1 and time 2 and use this delta for testing differences in the group using randomise ?

If you use the dual regression, you'll end up having one spatial map per component, per session, per subject. Then it's possible to subtract session 1 from session 2 for each component, and run a 1-sample t-test in randomise. This will tell something about time changes for each of the components. It's also possible to do a 3-group one-way ANOVA on the subtracted images.

Hope this helps.

All the best,

Anderson


 

I hope that my questions are clear enough.

Thank you in advance

Alain