Hello all,

I'm interested in correcting the geometric distortion introduced by the non-linearity of the gradients of our Sonata MR system. I noticed that mri_convert has an option to do this: --unwarp_gradient_nonlinearity

When I try to use this option, I get an error message: INFO: unwarping ... Error: couldn't open /usr/local/bin/freesurfer/data/gradientNonlinearitySonata.mff

So this file seems to be missing in the freesurfer distribution. Can I request that file somewhere, or is any software available to calculate it from the spherical harmonics as provided by Siemens?

cheers -- Joost