Hi Stefano,
yes it does (labelled dti_MO.nii.gz).
Cheers,
Gwenaelle
--- En date de : Jeu 24.6.10, Marenco, Stefano (NIH/NIMH) [E] <[log in to unmask]> a écrit :
> De: Marenco, Stefano (NIH/NIMH) [E] <[log in to unmask]>
> Objet: Re: [FSL] Anisotropy mode
> À: [log in to unmask]
> Date: Jeudi 24 juin 2010, 19h58
> Does DTIfit output mode? If not, how
> should it be calculated? Stefano Marenco
>
> -----Original Message-----
> From: Gwenaëlle DOUAUD [mailto:[log in to unmask]]
>
> Sent: Thursday, June 24, 2010 2:50 PM
> To: [log in to unmask]
> Subject: Re: [FSL] Anisotropy mode
>
> Hi Mahinda,
>
> to add a few words to Stam's answer: very generally, you
> can see an increase of mode when there is a transition from
> "disc" shape to more "cigar" shape anisotropy.
>
> This can mean a selective degeneration in two crossing
> fibres in a neurodegenerative disorder for instance (as in
> my poster that you're mentioning), this can also mean a more
> linear anisotropy, which you would maybe see in healthy
> subjects with, say, motor learning for instance, just like
> an increase of FA would then also be seen.
>
> Hope this helps,
> Gwenaelle
>
>
> --- En date de : Mer 23.6.10, Stamatios Sotiropoulos
> <[log in to unmask]>
> a écrit :
>
> > De: Stamatios Sotiropoulos <[log in to unmask]>
> > Objet: Re: [FSL] Anisotropy mode
> > À: [log in to unmask]
> > Date: Mercredi 23 juin 2010, 22h03
> > Hi Mahinda,
> >
> > The mode characterises directly the tensor shape. A
> > negative mode indicates an oblate profile (i.e. l1
> roughly
> > equal to l2, both much larger than l3) and a positive
> mode a
> > prolate profile (l1 much larger than both l2 and l3),
> where
> > l's are the tensor eigenvalues. Therefore, you can
> interpret
> > directly changes in the mode to changes in the
> relative
> > relationship between the tensor eigenvalues.
> >
> > It has been empirically observed that voxels with two
> > crossing fibres tend to have an oblate tensor shape
> (and
> > this approximation improves as the crossing becomes
> more
> > perpendicular, the fibres more similar and the volume
> > fractions more identical). That's why a negative mode
> value
> > may indirectly suggest a fibre crossing.
> >
> > Cheers,
> > Stam
> >
> >
> >
> > On 23 Jun 2010, at 17:33, Mahinda Y wrote:
> >
> > > Dear All,
> > >
> > > I have seen some recent and papers using the mode
> of
> > anisotropy to distinguish between where changes in FA
> are
> > due to changes in voxels containing 2 fibre bundles to
> 1
> > fibre bundle (causing an increase in the mode to more
> > positive values) - is this interpretation only
> valid
> > in areas where one knows there are crossing fibres -
> how
> > does one interpret such changes in the mode in areas
> where
> > crossing fibres are less likely ?
> > >
> > > Thanks.
> > >
> > > Mahinda
> > >
>
>
> --------------------------------------------------------------------
>
> Gwenaëlle Douaud, PhD
>
> FMRIB Centre, University of Oxford
> John Radcliffe Hospital, Headington OX3 9DU
> Oxford UK
>
> Tel: +44 (0) 1865 222 523 Fax: +44 (0) 1865 222 717
>
> www.fmrib.ox.ac.uk/~douaud
>
> --------------------------------------------------------------------
|