gmane.comp.graphics.spm.marsbar

Questions about gray volume through clusters

Dear Marsbar users and Mathew,

I recently learned how to extract mean voxel value (summary time courses) using extract ROI full options on a spm cluster and by exporting it to the matlab workspace.

I have few basic questions. The VBM design I used was in SPM5 using full factorial having 2 groups and 3 covariates. I also used ancova for global normalization. Extract ROI has 2 options 1) obtain raw data 2) From SPM design.

I obtained the raw data first which I assume has not been adjusted for the covariates. When I tried comparing the volumes for the 2 groups using ancova and adjusting for the covariates using SPSS there were no significant differences? Any comment s or suggestions? Maybe I am doing something wrong in SPSS.

If I use the SPM design to get the GM values will it control/adjust for the various design parameters applied including the covariates? Or will it just adjust for global normalization but not for covariates? If I use this option do I have to look for the 'y' or do I still export the summary time course in my matlab workspace to look at the volumes?

Lastly, are the volumes reported in mL?

Kindly advise,
Manish Dalwani
Sr. PRA
University of Colorado

-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/

_______________________________________________
Marsbar-users mailing list
Marsbar-users <at> lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/marsbar-users

headers

Matthew Brett | 27 Aug 03:33

Re: Questions about gray volume through clusters

Hi,

>  I obtained the raw data first which I assume has not been adjusted for the
> covariates. When I tried comparing the volumes for the 2 groups using ancova
> and adjusting for the covariates using SPSS there were no significant
> differences? Any comments or suggestions? Maybe I am doing something wrong
> in SPSS.

It's true that marsbar makes no attempt to adjust for the factors in
the SPM model, it only replicated the SPM image scaling for session
effects.  You will need to make sure you have replicated the full SPM
design, including any constant columns, to get something similar in
SPSS.

> If I use the SPM design to get the GM values will it control/adjust for the
> various design parameters applied including the covariates? Or will it just
> adjust for global normalization but not for covariates? If I use this option
> do I have to look for the 'y' or do I still export the summary time course
> in my matlab workspace to look at the volumes?

I would export the summary time course for safety.

> Lastly, are the volumes reported in mL?

The scaling is from the SPM design and the images.  I'm afraid I don't
know what units in VBM scans are, I guess unmodulated would be
probability, and modulated a more complex function of probability...

Best,

Matthew

-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/