We observed the same phenomenon when doing any sort of interpolation
without a prior upsampling of the images: The whole histogram for the FA
was shifted to lower values. This was corrected by doubling the
resolution of the images prior to any interpolation step. Stefano
-----Original Message-----
From: Steve Smith [mailto:[log in to unmask]]
Sent: Friday, March 07, 2008 1:42 PM
To: [log in to unmask]
Subject: Re: [FSL] tbss_1, scaling
Hi - no, this is not related to the scaling in tbss_1_preproc.
It is either likely due to the recently-discussed issues relating to
the big change in voxel dimensions and voxel sampling, or even more
likely due to the upsampling interpolation when you go from native to
standard space in tbss_2/3.
Cheers.
On 6 Mar 2008, at 19:34, James Andrews wrote:
> Hi,
>
> I get different values for FA intensity when I use fslmeants to
> calculate
> mean FA for a given ROI in my all_FA file than when I deproject the
> voxels
> back to native space and use fslstats to calculate the mean FA for
> the ROI.
> The native space FA values are consistently greater by about 25%. I
> am
> wondering if this has to do with the scaling done by
> tbss_1_preproc? Is
> this normal?
>
> Thanks,
> James
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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