Hello,
I have two questions about volumetric analysis: First: Are the volume measures in the files aseg.stats or ?h.aparc.stats (Gray Matter Volume) already normalized by ICV? Or should I divide all the structure volumes which I want to compare between subjects by the ICV of each subject? Second: When comparing gray matter volumes the correct is use the ICV or the total cortical gray matter volume to normalize? And if I have to use the total cortical gray matter volume, how can I obtain it? I know that this information is in the aseg.stats file, but I was wondering if I can use asegstats2table to extract it.
Thank you very much,
Fernanda
Hi, Nothing in the stats is normalized. It makes sense to normalize volumes by ICV when comparing across subjects (as that is assumed to stay constant while GM volume of course changes ).
Not sure if aseg...table grabs it, it should, maybe Krish knows.
Best Martin
On May 17, 2011, at 8:19 AM, Fernanda Palhano nandapalhano@gmail.com wrote:
Hello,
I have two questions about volumetric analysis: First: Are the volume measures in the files aseg.stats or ?h.aparc.stats (Gray Matter Volume) already normalized by ICV? Or should I divide all the structure volumes which I want to compare between subjects by the ICV of each subject? Second: When comparing gray matter volumes the correct is use the ICV or the total cortical gray matter volume to normalize? And if I have to use the total cortical gray matter volume, how can I obtain it? I know that this information is in the aseg.stats file, but I was wondering if I can use asegstats2table to extract it.
Thank you very much,
Fernanda
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Hi Fernanda, The choice between ICV vs a measure of total "brain volume" or total cortical gray matter volume depends on whether you want to control for potential overall brain atrophy. Using ICV will control for overall "head size", but not for potential overall brain atrophy (e.g., with age, or related to dementia). Using total cortical gray matter will control for overall brain atrophy and thus would allow you to say that changes in a given structure were "above and beyond" any existing global atrophy.
Personally, I find it more informative to control for potential global atrophy, and thus use total cortical gray matter rather than ICV. After all, if a structure is decreased in size, but the overall brain is decreased as well, you have not established anything regarding the specificity of that change to the structure of interest if you use ICV as the covariate.
cheers, -MH
On Tue, 2011-05-17 at 09:19 -0300, Fernanda Palhano wrote:
Hello,
I have two questions about volumetric analysis: First: Are the volume measures in the files aseg.stats or ? h.aparc.stats (Gray Matter Volume) already normalized by ICV? Or should I divide all the structure volumes which I want to compare between subjects by the ICV of each subject? Second: When comparing gray matter volumes the correct is use the ICV or the total cortical gray matter volume to normalize? And if I have to use the total cortical gray matter volume, how can I obtain it? I know that this information is in the aseg.stats file, but I was wondering if I can use asegstats2table to extract it.
Thank you very much,
Fernanda
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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Fernanda Palhano wrote:
Hello,
I have two questions about volumetric analysis: First: Are the volume measures in the files aseg.stats or ?h.aparc.stats (Gray Matter Volume) already normalized by ICV? Or should I divide all the structure volumes which I want to compare between subjects by the ICV of each subject?
You will need to do the normalization yourself.
Second: When comparing gray matter volumes the correct is use the ICV or the total cortical gray matter volume to normalize? And if I have to use the total cortical gray matter volume, how can I obtain it? I know that this information is in the aseg.stats file, but I was wondering if I can use asegstats2table to extract it.
Whether you should use ICV or GM volume is a matter of debate that depends on exactly what you are trying to do and what structure you are studying. Your hypothesis that you are testing should have a statement about normalization. The ICV and total GM volume automatically show up as a column when you run asegstats2table.
doug
Thank you very much,
Fernanda
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
freesurfer@nmr.mgh.harvard.edu
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Douglas N Greve -
Fernanda Palhano -
Martin Reuter -
Michael Harms