Hi,
In both cases that you have in mind Jacobian determinants could be used although in different concepts, in "optimised VBM" when you spatially normalize (or non-linear registration in FSL terminology) an image to a template when there is contraction there would be underestimation of gray matter concentration and when there is expansion there would be an over estimation of gray matter concentration. In this case you using Jacobian determinants can compensate this difference between an image and a template. This would be called "modulation".
Deformation Based Morphometry (DBM) will give you deformation fields specifically in within subjects' brains. You can use a Jacobian determinant of deformation fields in order to do a tensor based morphometry (TBM). Deformation fields usually give you too much information that may confound your analysis that's why you would want to use Jacobian determinants (and TBM) in longitudinal studies.
Both cases you will use Jacobian determinant for warping an image.
All the very best,
Arman
On Apr 2, 2012, at 4:42 AM, liang wang wrote:
> Hi,
>
> I have such basic question about the measures selected for group-level comparison using FSL-VBM. From the FSL-VBM instructions, I am instructed to use the modulated gray matter images for statistical tests. We also know that Jacobian determinant provides the voxel-wise compression and extension, and that a number of studies also use the deformation-based morphometry by using Jacobian determinant. So I am wondering whether someone can clarify the difference between those two measures in examining the abnormalities of brain structure related to diseases, and give some opinion how to correctly think of both guys. Thanks.
>
> Best,
> Liang
> --
> Liang Wang, PhD
> Neuroscience of Attention and Perception Laboratory
> Princeton Neuroscience Institute
> Princeton University
> Princeton, NJ, 08540
>
>
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