In the past, I have applied the registration matrices generated by TBSS to
align tractography results before averaging them. You also might consider
this approach to improve tract alignment.
Peace,
Matt.
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Steve Smith
Sent: Sunday, February 10, 2008 10:24 AM
To: [log in to unmask]
Subject: Re: [FSL] t-test for tractography
Hi - I guess you're feeding in the fdt_paths image from each subject
into a group-wise t-test? There are various dangers here.
The obvious one is that you will not have very good alignment between
subjects for such a voxelwise test. This is the primary issue that
TBSS attempts to resolve. However, if you accept this danger (and,
maybe smooth a lot......), you can run the voxelwise t-test on the
tractography output....
Which brings you to a second danger, which is that it will be hard to
correct for multiple comparisons across space, as the spatial
autocorrelation structure will be high and complex. However, you can
probably get over that by using randomise correctly.
I'm sure that Tim/Saad may have further caveats with this....
Cheers, Steve.
On 7 Feb 2008, at 21:06, Paul Geha wrote:
> Dear FSL users,
>
>
> I am running proabilistic tractography (using a mask identified from
> TBSS)
> on a group of patients and age matched controls. Is it
> statisitcally sound
> to do an unpaired t-test between the 2 groups on the tracts maps
> obtained ?
>
> thanks
> Paul
>
>
>
> Paul Geha M.D.
> Northwestern University
> The Feinberg School of Medicine
> Department of Physiology M211
> 303 E. Chicago Ave.
> Chicago, IL 60611
> Tel:312-503 2886
> Fax: 312-503-5101
>
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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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