Hi Benno,
I would guess that Chloe's statement overrides the manual :) I had some
discussions with her on that topic some time ago and it seems that the
fieldmap toolbox will regrid the fieldmap data in any case. This does
not mean that it is not a good idea to acquire fMRI and fieldmap with
the same slice prescription (at least I do) as this will, theoretically,
minimize interpolation between the sequences, but it is not, strictly
speaking, necessary.
Hope this helps,
Marko
Benno Gesierich wrote:
> Dear SPM fellows,
>
> I found some information on the selection of field map parameters (on the mailing list and the FieldMap manual), which appears to be in conflict with each other. Could anybody help me to resolve this conflict?
>
> In the Manual_FieldMap_v2.0.pdf, I found a sentence stating: "For the geometric distortion correction to work, it is extremely important that the number of slices, voxel size and slice orientation of the EPI and field map are the same."
>
> However, in a mailing list contribution from Dr. Chloe Hutton 2009-06-08 (Email subject: Re: On the optimum settings for B0 field maps; item# 036809), I found following statement: "Ideally, as described above, the field map should be acquired with the
> same shim values as is acquired for the EPI data. The actual number of slices acquired and voxel size is not important as the FieldMap toolbox can take care of this using the positioning information encoded in the image headers."
>
> Maybe, I misunderstand this, but to me these statements seems to be in conflict, right?
>
> I am asking this, because I got problems with field map corrections, and I am trying to figure out whether the selection of my parameters could be the reason. Please see also my Email from yesterday, describing this problem (Email subject: FieldMap: unexpected jump and stretch of unwarped scan).
>
> Thanks a lot,
> Benno
>
--
____________________________________________________
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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