Hi Doug. So if I’m understanding you, the 1mm3 voxel overlaps the larger (3 x 3 x 3 mm) functional voxel and so when I pull out the functional data it comes from the entire functional voxel? Is the combination of mri_annotation2label and func2roi-sess a common way to extract data from cortical ROIs? Is there a set of flags that generally works well that I should use to make sure I’m getting data from all the gray matter?

 

Thanks!

 

Dan

 

-----Original Message-----
From: Doug Greve [mailto:greve@nmr.mgh.harvard.edu]
Sent: Monday, March 17, 2008 4:56 PM
To: Dan Dillon
Cc: 'Freesurfer Mailing List'
Subject: Re: [Freesurfer] Question re: extracting functional data from cortical ROIs

 

Yes, it is that 1mm3 voxel on the white (or pial) surface. For sampling into the functional volume, this is usually not an issue as the functional voxels are generally much bigger.

You can change the cortical sampling depth by running mri_label2label with --projfrac (eg, --projfrac 0.5 for midway between the white and pial).

doug

Dan Dillon wrote:

I have a question about extracting functional data from structurally defined cortical labels. Here’s what I’m doing:

 

1)       Run a gammafit analysis;

2)       Define cortical ROIs by using mri_annotation2label to make labels from aparc.annot;

3)       Define sub-cortical ROIs by using mri_cor2label to make labels from aseg.mgz;

4)       Extract functional data from labels using func2roi-sess;

5)       Summarize the data with roisummary-sess.

 

I usually view the cortical ROIs on the inflated (or pial) surface and the subcortical ROIs in the volume, and they usually look great. But when I view the cortical labels in the volume, they seem to consist of a 1-voxel thick strip hugging the white matter; they don’t seem to cover the gray matter at all. Does this mean that I am extracting functional data from a 1-voxel thick strip (!), or am I just mis-understanding something about how a cortical label appears in the volume? Also, I know that “white” is the default surface in mri_annotation2label, but if I switch to “pial”, make a label, and view it in the volume, it still looks like a 1-voxel thick strip, just around the outside edge of the gray matter (instead of around the inside edge if I use “white” as the surface).

 

My simple mind wonders why these cortical labels—which look great on the inflated brain—don’t cover the region between the pial and white surfaces (i.e., the gray matter) in the volume. Am I making a basic error here? If so, what do I need to do to extract functional data from cortically-defined ROIs? I am running version 4.0.2.

 

Thanks!

 

Dan D.

 

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