Thank you for your kind response.

I think we need to talk about the design matrix X first (sorry, I did not look at your xlsx file; I think it's probably better to send simple csv files if at all).
I attached longitudinal data in csv format. 

Besides the covariates that you mention, the matrix needs to contain an intercept, a variable for ?time?, a variable for ?group? (assuming you have a control group also), and a group-by-time interaction term in order to asses differential change over time (again, if you have a control group).
I do not have a control group. Right now I have only schizophrenia patients who underwent 2 scans: the first is the baseline and the second one is after 3 months of yoga therapy. Wish to know how can I proceed with my available data.

Just to make sure: ?age? should be ?age at baseline? (i.e. constant across time per subject), otherwise, it will be confounded with time.

Yes, I used the same across the study.

Could you review (and possibly adapt) your design matrix X with respect to which columns it contains, and write it in the reply?

I tried but couldn't get there. 

Looking forward to your response.

Thanks,

Vittal