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Hi Vidya:

You can just open one the u_*.nii as a nifti image using SPM or 
MRICron/MRICro, or other software, however, each flow field is actually 
saved as a 5D image. Actually, there are 3 flow fields scalar image 
images (it is a vector field) saved in one u_*.nii file. But because the 
way John create the flow field (he said he didn't expect people would 
like to visualize the flowfield anyway), you can only see one of the 
flow field, I think it shows the flow in X direction only. However, you 
can still access the other 2 images manually.

If you load any flow field in SPM say,
 p=spm_select(inf,'image');
 N=nifti(p)
N=
NIFTI object: 1-by-1
            dat: [5-D file_array]
            mat: [4x4 double]
     mat_intent: 'Aligned'
           mat0: [4x4 double]
    mat0_intent: 'Aligned'
        descrip: 'Flow Field'

N.dat

        fname: [1x85 char]
          dim: [121 145 121 1 3]
        dtype: 'FLOAT32-LE'
       offset: 352
    scl_slope: 1
    scl_inter: 0

By changing the N.datl.dim field, you would be able to access the 3 
images via MRICro or SPM now
N.dat.dim=[[121 145 121  3],

To access the other 2 images, when the SPM select file window pop up, 
change the number in the Edit Field right next to "Filt" button. By 
modifying the number into 2 or 3, you can access the other images.
Just remember to set the filter to ^u.*nii first, as SPM will try to 
read all the header, and it takes a while. By setting the filter option, 
it will reduce the headers which are required to be read.

Best,
Carlton


Vidya Rajagopalan wrote:

>Hello Everyone,
>
>I would like to visualize the flowfields that have been generated using
>DARTEL. Is there such a function in SPM or any other visualization packages?
>
>Thank you.
>
>Vidya Rajagopalan
>
>
>
>  
>