Hi,
I am trying to use the bias field output by fast as a weight
volume in flirt ( -inweight <volume> ). Could you explain
how flirt uses the -inweight volume values as weights ? I see the FAQ says
"To do this a weighting image must be made which has the value of 1.0
everywhere except in the region of interest where a higher weight (e.g.
10.0) should be used."
Does the weight volume have to be a volume with just 2 intensity values, 1
and N (eg 10), or is that just an example ?
In looking at the fast bias volume I think it is 1 at "uncorrected" voxels
and then has bias values both above and below 1. I would think that to
transform the bias volume into a weight volume, I might want to
downweight voxels proportionate to their distance from 1, eg for
bias volume B
weight volume = 10 / (1 + abs(B-1))
but I am not sure. That would make 10 the "no correection" value.
Also, does it matter what weight I assign in the
weight volume to voxels that are non-brain and set to zero in the
flirt input volume ?
thanks
kate
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