>
> Up to now i realized that i had to include the VOI as an explicit mask for the estimation of the model. Using a mask in the Results section, however, did not lead to reasonable results.
> Am I correct with the assumption that only using a mask during the estimation process will effectively resolve the problem of multiple comparisons?
There are two differences in masking at the estimation level and
masking at the result level:
(1) when you mask at the estimation level, you can only ever look at
things in your VOI; and
(2) only voxels in your VOI contribute to the pooled error across
voxels, which could be bad depending on the size of the VOI. The
smaller the VOI, the less stable the variance estimation will be.
I am not sure what you meant by unreasonable results when you masked
at the results level. Did you use small-volume correction? If not, I
would use the SVC button. This should produce better results and
properly control for the actual number of comparisons being made
inside the VOI.
The one issue with VOIs is that you shouldn't run the model for each
VOI and you shouldn't run SVC for each VOI. Rather, you should apply
SVC once with an image of all the VOIs to properly correct for
multiple comparisons
>
> For the issue of defining VOIs: Would it be reasonable to average all volumes and draw the VOIs on the resulting image instead of using the template?
That sounds reasonable.
>
> Best Regards,
> Jakob
>
>
> _______________________________________________________________________________
>
>
> It is a reasonable approach. I'm not sure the best way to define the anatomical ROIs.
>
> Best Regards, Donald McLaren
> =================
> D.G. McLaren, Ph.D.
> Postdoctoral Research Fellow, GRECC, Bedford VA
> Research Fellow, Department of Neurology, Massachusetts General Hospital and
> Harvard Medical School
> Website: http://www.martinos.org/~mclaren
> Office: (773) 406-2464
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