I need a bit more information here. Are these the Jacobians from the DARTEL
toolbox, or from some other part of SPM? If it is DARTEL, then the boundary
conditions are such that if you sum up the values in the Jacobian maps, then
all of them should give approximately the same value. Therefore, if one
population of subjects has larger brains (bigger Jacobians in the brain),
then the Jacobians outside the brain are forced to be smaller. This could
maybe explain your differences.
Best regards,
-John
> I ran an analysis on jacobian images in spm5 and overlayed them onto the
> custom template used for registration but they results overlay poorly
> because some of the ares of volume change show up outside the brain. Could
> a problem with the hdr files (either in the template or in the jacobians
> images themselves) be accounting for this or is there another factor or
> cause I need to consider? Any input on this is much appreciated!
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