Hi,
you cannot remove a gradient from individual voxels. But you can remove a
gradient for all voxels, i.e. in your example you will be left wih 31
gradients for all voxels. In this case, you need to make sure that you
remove the respective entry from the bvals and bvecs file.
What analysis are you trying to do? If you are fitting a tensor using
dtifit, you might be able to do something like what you requested, by using
the weighted fitting option (--wls). That way, measurements with high
variance will be down-weighted in the estimation process, but the success of
that depends on the artifact you are trying to eliminate.
Cheers,
Stam
----- Original Message -----
From: "bettyann BA" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, January 29, 2011 4:13 AM
Subject: Re: [FSL] Mask out artifacts in DTI processing?
is there a way to omit voxels from a particular gradient, rather than
omitting a voxel from *all* gradients?
i see that removing an area of artifact from the b0 nodiff mask would remove
that area from all processing. but what if, of the 32 gradients, there is
only 1 gradient that contains the artifact? in other words, for this voxel,
use 31 gradients and drop the gradient containing the artifact.
thanks,
- bettyann
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