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 > <mha...@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. > > > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
