For subcortical structures, you could consider using a covariate measure that itself includes subcortical gray matter. Not sure if the latest FS version has such a measure automatically constructed or not. In the past, we have used "whole brain volume" as a covariate for analysis of both cortical and subcortical structures, with "whole brain volume" defined as the volume contained within the pial surface (obtained using mris_volume) minus the volume of the lateral ventricles (contained within the aseg).
cheers, -MH
On Tue, 2011-05-17 at 10:19 -0300, Fernanda Palhano wrote:
Thanks, Michael.
I have a follow up question. If I understood, I should use the total cortical gray matter volume to control for a global change in cortical brain volume, so for exemple, if I'm interested in the volume of parahippocampal gyrus, I can normalize this way. And, once I have the measures for both the hemispheres separately, I have to use the total cortical gray matter of each one to normalize? But for other structures like hippocampus or amigdala it makes sense to control using volume of gray matter? Or, I continue using the ICV?
Thanks again,
On Tue, May 17, 2011 at 9:57 AM, Michael Harms mharms@conte.wustl.edu wrote:
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 > > > The information in this e-mail is intended only for the person to whom it is > addressed. If you believe this e-mail was sent to you in error and the e-mail > contains patient information, please contact the Partners Compliance HelpLine at > http://www.partners.org/complianceline . If the e-mail was sent to you in error > but does not contain patient information, please contact the sender and properly > dispose of the e-mail.