Dear all,
I've been using ROI analysis for fMRI data analysis for a while, to search for only regions of interest supported by previous data or literature.
But SPM has a SVC button with a similar logic behind. So what are the differences between the two approaches? Thanks a lot.
Andy
Hi Andy,
I think it should technically make no difference.
Do you have the WFU Pick Atlas installed? As far as I remember it is this toolbox that adds the ROI dialog into the SPM GUI, and restricts the search space beforehand, while the built-in SVC does it afterwards.
Both should compute a FWE-corrected p value based on the resels in this restricted search volume. Try out both with the same ROI definitions, and look at the Voxels, FWHM etc. information at the bottom of the table - they should look the same.
Concerning the (mis)use of ROI in general, the following article by Russ Poldrack on the use of ROIs is also quite helpful.
http://scan.oxfordjournals.org/content/2/1/67.abstract
(See also the more recent discussion in the Poldrack/ Mumford/ Nichols book: http://www.fmri-data-analysis.org/)
Hope this helps,
Marcel
Hi all,
I have been trying both WFU Pick atlas and SVC in regression analyses looking at the relationship between cortical thickness of a given area with functional activity of the same areas during a task. After both types of ROIs I have been able to get a table with the FWE corrected p, t, z, and coordinate values so it seems like both seem to be doing the same. I have a different question:
I have been looking at both methods to compare across the two and have been finding that the anatomical ROIs from the aal atlas in WFU Pick atlas seem to give both positive and negative relationships in two frontal areas but when I use SVC with a sphere of 10mm I only get the positive correlations (the negative relationships do not survive the FWE threshold). They are both FWE corrected. Could it be that the anatomical ROIs fom the aal WFU Pick atlas are much bigger and so are covering more cortical space than the SVC at 10mm sphere? Any inputs on this would be of great help.
Thanks,
Aurora
Hi Aurora,
it is possible that the ROI of the WFU pickatlas is bigger than your self-defined small region. Have you looked at the WFU pickatlas ROIs? You can do that very easily with any viewing program, e.g. xjview (http://www.alivelearn.net/xjview8/). It might also be possible to use the WFU pickatlas ROI in the small volume correction, did you try that?
Good luck!
Ines
As far as I know when you use ROI analysis, you have one averaged value per ROI (like ROI is you one big voxel, you assume that all voxels in this ROI do the same work (function) and when you perform SVC, you still have all your voxels with their values in you volume if interest but after you chose this volume for analysis you have fewer voxels than in the whole brain and you activation within this volume of interest is able to survive after correction for multiple comparisons. I think - this is the main difference.
- Badges
- Science topic
- Similar topics
- Correction