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Hi Jon,

The bias field is an estimate of scanner-related inhomogenity of the intensities in the image. This has already been taken into account by FAST when producing the segmentations, so you do not need it when calculating the WM volume.

Hope that helps,
Eelke


> On 14 Oct 2015, at 11:22, Jon Anderson <[log in to unmask]> wrote:
> 
> Hi FSL experts,
> Following T1 segmentation in FSL using the tool FAST I got files for the segmented white matter, gray matter and ventricles.
> In addition I generated map for the bias field.
> In order to calculate white matter volume I used the following command line:
> fslstats structural_bet_pve_2 -M -V | awk '{ print $1 * $3 }' 
> 
> What is the exact usage of the bias field map. Do I need to correct the white matter volume using the  bias field map?
> 
> Thanks
> Jon