Hello John,
Thanks for discussing this topic, it is really helping me understand the method better.
I have some follow up questions:
> Assuming that the warping is exact (a big assumption), then the warped > grey matter of one image will be identical to the unwarped grey matter of > the other. The expression is essentially i1.*i2 - i1, which is the > modulated image (theoretically identical to a modulated warped other > image) minus the
> unmodulated image.
So, when you subtract the unmodulated GM image from the modulated one, what is the result you are left with? Would you say it is the image of GM volume change over time or something like that? This raises another question: if we are doing stats on these images from a bunch of people, the time interval between the "early" and "late" scans will differ with each individual. Is there a better way to model the interscan interval? It seems to me this method assumes the time between scans is the same for all people in the analysis.
> >
> > Also, I see your point about smoothing log(det), but there are also
> > statistical reasons why people want to take logs; do you think it
> > would be okay to smooth first and then take logs?
> You hit problems in regions containing only zeros.
Would it be feasible to do log(det+eps) or something similar to fix the zeros problem?
Best regards,
Matt Senjem
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