Bruno,
let me answer your question in a most general way: whenever you alter
the processing and/or analysis approach for some, but not all, subjects
in your study, this is a potentially serious problem. If you can go
without the two, I would do that. Alternatives would be to go without
unwarping in all 37 (disproportionate in my mind) or include all, but
label the two with an extra regressor on the second level (only second
best in my mind, but you could argue for this approach if these two were
very hard to recruit, as in a special patient population or so).
Just my 2 cents, but I hope it helps anyway :)
Marko
PS: BTW, I would be surprised if not using the fieldmap does not
influence your first level analysis, because it really should.
Bruno Lambert wrote:
> Dear SPMers,
>
> I have a small question concerning the preprocessing of fMRI data.
>
> I want to use the more advanced Realign & Unwarp function in my preprocessing pipeline, but I discovered that two of the 37 subject do not have fieldmaps, a necessity for the unwarping. Would it be wise to preprocess 35 subject with the Realign & Unwarp function and use them alongside the other two subjects, preprocesed with the common method?
> It does not influence first level analysis, but is it nefast for second level analysis?
>
> Thank you in advance,
> Yours sincerely,
> Bruno
>
--
____________________________________________________
PD Dr. med. Marko Wilke
Facharzt für Kinder- und Jugendmedizin
Leiter, Experimentelle Pädiatrische Neurobildgebung
Universitäts-Kinderklinik
Abt. III (Neuropädiatrie)
Marko Wilke, MD, PhD
Pediatrician
Head, Experimental Pediatric Neuroimaging
University Children's Hospital
Dept. III (Pediatric Neurology)
Hoppe-Seyler-Str. 1
D - 72076 Tübingen, Germany
Tel. +49 7071 29-83416
Fax +49 7071 29-5473
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http://www.medizin.uni-tuebingen.de/kinder/epn/
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