When fMRI are resliced to match a structural image, the resulting
resliced images will have the same resolution etc as the structural.
An image at 1mm isotropic resolution is about 27 times as big as one
at 3mm.
Coregistration in SPM gives the option to "Coregister Only". Instead
of reslicing images to match the reference, this option merely changes
some matrices in the image headers in order to reflect the relative
pose of the images. I'd suggest that you use this option instead.
Best regards,
-John
On 15 October 2012 13:01, Anoop Jacob Thomas <[log in to unmask]> wrote:
> Hi everybody,
>
> I wanted to co-register a functional image and an anatomical image,
> the functional image is a 4D NIfTI image and the anatomical image is a
> 3D NIfTI image. I selected the anatomical image as the "reference
> image" and wanted to specify all the volumes in the functional image
> in the "source image", but it allowed me to select only one volume, so
> I selected the rest of the volumes using the "Other Images" option and
> the module ran without producing an error. Now the problem is, it
> generated an output file which is 389MB while the input file was just
> 24.4MB. Why has SPM produced such a large image while the input file
> was just 24.4MB? Earlier I ran slice time correction, "realign and
> unwarp" modules, and there the output images produced were of the same
> size as the input images.
>
> In the second try I did not select any images in the "Other Images"
> option, and the other options being,
> Reference Image - anatomical.nii,1
> Source Image - functional.nii,1
>
> It generated a 3D NIfTI image(required is 4D) with just 1 volume with
> the size of the file 4MB, while the space required for storing just
> one volume would be around 500KB and not in MB.
>
> Am I missing something here? Or am I doing it the wrong way?
>
> I have a set of functional images (a set of 4D NIfTI images) which I
> want to co-register with the anatomical image.
>
> Thanks in advance,
>
> Anoop Jacob Thomas
>
> Research Scholar,
> Computer Science & Engg. Dept.
> Indian Institute of Technology Ropar.
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