Hi Woo-Suk Just adding to Bruce's reply: area isn't a "technically more noisy and usually thus less sensitive" as the reviewer suggests. Area isn't noisier on its own right, and it's measured from the very same surfaces from which thickness is measured. However, there is a much larger variability of area across subjects than of thickness, even within the normal range, such that the variance of volume, that can be explained by or associated with other indices, is largely explained by the variance in area. The first paper that (as far as I know) showed this is Voets et al. (Neuroimage, 2008), and we keep observing this repeatedly in different datasets, published or not.
About the Schmaal et al. paper (Molecular Psychiatry, 2016): it is an excellent paper in which the authors didn't spend time (or space) discussing volume, going instead straight to the more interesting bits: area and thickness. All the best, Anderson On 29 August 2016 at 13:56, Bruce Fischl <fis...@nmr.mgh.harvard.edu> wrote: > Hi Woo-Suk > > why not just do the surface analysis that they are requesting? I'm not > sure what you are asking, but certainly volume = surface area * thickness > in general, and so a volumetric effect can be driven by one or both of > surface area and thickness > > cheers > Bruce > > > > On Sat, 27 Aug 2016, Woo-Suk Tae wrote: > > Dear FreeSurfer experts and developers >> >> I am confronted with some technical question of a reviewer. >> I am not sure about "volume = thickness-by-surface area" and the review's >> opinion (attached below) about volume, surface area, and thickness was >> correct. >> Any comments from FreeSurfer's experts would help me. >> >> Sincerely yours >> >> Woo-Suk Tae >> Seoul, Korea >> >> I added the reviewer's comments. >> --------------------- >> 1. Volume/thickness: The authors cite many papers that show volume and >> thickness differences in MDD. The unresolved part here, however, is the >> RELATION between cortical thickness and cortical volume: There is no >> doubt, >> that both measures are found affected in MDD. This is, because cortical >> thickess multiplied by the surface area of a gyrus results in its volume, >> so >> volumse = thickness-by-surface area. Surface area values themselves are >> technically more noisy and usually thus less sensitive (due to the problem >> of false attributions to an area). >> >> So, volume is influenced by thickness and surface and is the less specific >> measure. If a volume effect is detected in a study, it is unclear, if it >> is >> driven by thickness, or surface area, or both. In this respect, the study >> of >> Schmaal et al. is telling, as it analyzed BOTH measures, finding only >> thickness effects of MDD, and (practically) no surface area changes except >> for adolescent MDD. In the adolescent MDD samples gross surface area >> differences were detected. >> >> This means, that the question of "superiority" is rather a question of >> "specificity": (Cortical) volume findings in adult MDD are mostly driven >> by >> thickness differences and are in on way independent from thickness >> differences. In this respect, the authors should follow the basic >> geometric >> principles of morphometry and point out the relatedness of the two. They >> can >> simply check this in their FreeSurfer variables (e. g. for total grey >> matter >> volume). Not reporting surface area is leaving an interpretational gap as >> surface area differences could in addition drive volume differences. The >> authors may want to decide not to present surface area results, but then >> they should discuss this as limitation to disentangle the origin of >> volumetric (cortical) effects. This seems important as methylation effects >> and FKBP5 interact with early life time stress, so effects on surface area >> as seen in adolescent MDD highlight that surface area effects could play >> in. >> >> >> >> >> >> >> >> ------------------------------------------------------------ >> --------------- >> ------------- >> Woo-Suk, Tae Ph.D. Research Professor >> Brain Convergence Research Center, Medical Research Center >> Anam Hospital, Korea University Medical Center, Seoul, Korea >> mobile: 82-10-9120-4629 >> office: 82-2-920-6831 >> email: woosuk....@gmail.com, woos...@gmail.com >> ------------------------------------------------------------ >> --------------- >> ------------- >> >> >> > _______________________________________________ > 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 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.
