Dear SPM and VBM experts,
I'm addressing to you in order to try to solve an open debate we're encountering during the review of a VBM study.
My colleagues and I explained in the manuscript that, since we modulated the images by their Jacobian determinants, we were looking at differences in Grey Matter Volume or Amount of GM. However, one of the reviewers stated that, even though one takes into account the Jacobian determinants, one's still dealing with corrected probabilities after warping that are called concentrations or GM density. So, he/she strongly recommends us to use GM Density "because the term Volume can only be used when one does manual segmentation of T1 images but not with VBM".
That wasn't our understanding, we thought that GM Density is the term when one doesn't do the modulation by the Jacobian determinants (leaving this option by default in SPM) and Volume is the term when one applies such modulation. All the information from older messages regarding this topic and from previous reports and manuals (by Ashburner and other users of VBM) seems to confirm our original concept, but we still have doubts and we should be pretty sure if we're trying to keep our terminology despite what the reviewer is asking us to do (change the term GM volume by GM density)...
Thank you so much in advance for your time and help!
Best wishes,
LucĂa Vaquero
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Ph.D Student
Cognition and Brain Plasticity Unit
http://www.brainvitge.org/
University of Barcelona
Barcelona (Spain)
Tel: +34 93 402 10 38
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