Dear List,
I just wanted to make sure that the solution to my problem is not obvious - or anybody else already found the answer - before going deeper into this topic:
The SPM5 manual explains that the default spatial preprocessing of fMRI-data should involve coregistering the structural file to the mean EPI-image. After this step you are suppose to segment the structural image and subsequently apply the resulting transformation-matrix to all EPI's. The reason for this procedure should obviously be the better normalization that one should get. I processed one of the SPM-example-datasets according to this procedure and compared the normalization quality to that of the same dataset processed the 'old-fashion'-way, i.e. simply taking the EPI-time-series and normalize it directly to the EPI-template. Results (in terms of a correlation-analysis) show nearly no difference in normalization-quality. Now, applying the same test, i.e. comparing the SPM5-procedure to the 'old-fashion'-way to one of our own datasets yields in a big difference, but interestingly the SPM5-procedure is worse!
My questions are:
(a)
What exacty is the reason, that we should use the normalization parameters of the structural file to transform the EPI's into standard-space?
(b)
What are the conditions for this procedure to yield in better results than the normal normalization procedure? Is it the protocols parameters? Is it the initial correspondence between structural and functional files, and if so, which factors do influence this correspondance (protocol again?) and how could one measure the quality of this correspondance?
Thank you very much!
-Lucas
P.S. If needed, I can of course supply more details of my tests so far.
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