External Email - Use Caution Dear Lauren, This is a very interesting question! Site harmonization matters aside (there’s a vast literature on it), whether you correct by ICV or whole hippocampal volume essentially answers to different questions: - ICV: you’re asking whether there’s an effect of X on subfield Y. - whole hippo volume: you’re asking whether X has an effect on the fraction of hippocampal volume attributed to Y. Both questions are interesting; it depends on what you’re trying to answer. Of course, if you’re correcting by whole hippocampal volume, then don’t correct by ICV… I hope this helps! /Eugenio
-- Juan Eugenio Iglesias Centre for Medical Image Computing (CMIC) Department of Medical Physics and Biomedical Engineering University College London http://www.jeiglesias.com From: <freesurfer-boun...@nmr.mgh.harvard.edu> on behalf of Lauren Salminen <les...@gmail.com> Reply-To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu> Date: Friday, 26 October 2018 at 22:40 To: "freesurfer@nmr.mgh.harvard.edu" <freesurfer@nmr.mgh.harvard.edu> Subject: [Freesurfer] subfield normalization vs. covarying for whole hippocampal volume External Email - Use Caution Hello, I’m working on a multi-site hippocampal subfields project (FSv. 6) and am wondering if it is “better” to normalize subfield volumes by dividing each subfield by whole hippocampal volume, or covary for hippocampal volume as an independent predictor variable in the regression models. Ultimately the goal is to determine the degree that each subfield may be uniquely associated with my target predictor variable, and we would like to know if this effect can be observed independent of potential differences in the whole hippocampus. Traditionally we have covaried for whole hippocampal volume, but I’ve found more interesting effects by normalizing each subfield to their hippocampal volume. Any guidance is appreciated. Thank you! ____________________ Lauren E. Salminen, Ph.D. Imaging Genetics Center Stevens Neuroimaging and Informatics Institute Keck School of Medicine University of Southern California http://igc.ini.usc.edu/
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