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Author Topic:   Small Volume Correction
tali
Junior Member
posted 02 September 2004 23:30     Click Here to See the Profile for tali   Click Here to Email tali     Edit/Delete Message   Reply w/Quote
Does anyone know how to do a small volume correction with brain voyager? (this is for when you have an apriori hypothesis about where the activation is and you want to adjust your p).
Thanks, Tali

lara
Junior Member
posted 16 September 2004 16:02     Click Here to See the Profile for lara     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by tali:
Does anyone know how to do a small volume correction with brain voyager? (this is for when you have an apriori hypothesis about where the activation is and you want to adjust your p).
Thanks, Tali

Hi Tali,

as far as I know..you will have to do it manually. It's a bit tricky in the beginning but it works.
You define the Roi first (e.g. a sphere around amygdala ...voi file). So you know how many voxels are included in the region you are examining. Let's say 1000

Ok..for whole head correction the programm would just divide p(uncorrected) by the number of ALL voxels in your brain (huge..). Thus it is most conservative, while uncorrected is of course least conservative. SVC instead is somewhere in between...

What you do then is not to divide the UNCORRECTED p by the number of all BUT by the number of 1000 voxels (just an example) instead! You calculate the new p (uncorrected), which can be adjusted manually then.

Hope it helped!
Take care,

LARA

lara
Junior Member
posted 23 September 2004 15:36     Click Here to See the Profile for lara     Edit/Delete Message   Reply w/Quote
Concerning SVC in QX I would like to add something important.
Herre you have to do FDR-Correction which does this implicit. If you are planning to do the SVC for the Amygdala example you would then just calculate a ROI GLM and enable FDR. The FDR correction does only take the significant voxels into account as the SVC in SPM (random field theory based) does.

Hope it helped,
LAra

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