Dear mailinglist,

I am trying to draw a sphere of 10mm around a peak voxel by using the fslmaths '-kernel sphere 10' option. However, whenever I build a sphere of more than 5mm, I get a really distorted image, for a screenshot, see here: http://postimg.org/image/fawbgvy7p/

All spheres of 5mm or smaller look as expected..

I followed an earlier post in the mailinglist to first define the peak voxel, and then build the sphere around it:

# define the point mask
fslmaths MNI152_T1_1mm_brain_mask -roi 90 1 176 1 72 1 0 1 mpfc_mid_peakvoxel -odt float

# build the sphere around the point mask
fslmaths mpfc_mid_peakvoxel.nii.gz -kernel sphere 10 -fmean mpfc_mid_10sphere

What is going wrong?

Thank you in advance!
Best,
Zsuzsi