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Dear Mark,

Thank you for your insights. The Y shape example is absolutely clarifying
and now I see why reversing the seed and target may give different results
depending on the anatomy even if the diffusion information at each point is
the same.

All the best,
Noelia

2017-08-05 12:09 GMT+02:00 Mark Jenkinson <[log in to unmask]>:

> Dear Noelia,
>
> Although the diffusion information at each point is the same in either
> direction, tracing a tract through the brain differs.  For instance, if you
> consider a tract that splits into two parts (like a Y shape) then starting
> at the common end (the base of the Y) and tracing in one direction will
> give you both parts of the split, whereas starting at the end of one of the
> splits (e.g. the top left part of the Y) and tracing in the opposite
> direction will ignore the other split, since the angle at the junction is
> too great for the tractography algorithm (which is a deliberately imposed
> constraint).
>
> So in general it is useful to see what you get when reversing the seed and
> target, since this can show you different aspects of the anatomy.
>
> All the best,
>         Mark
>
>
> > On 3 Aug 2017, at 16:05, Noelia Martinez Molina <
> [log in to unmask]> wrote:
> >
> > Dear experts,
> >
> > I've performed a probabilistic tractography study using BEDPOSTX and
> PROBTRACKX tools in FSL. My question is: can the roles of seed and target
> be exchanged since probabilistic tractography does not contain
> directionality information?
> >
> > Thank you in advanced for your assistance.
> >
> > Kind regards,
> > Noelia
>



-- 

Noelia Martínez-Molina
Cognition and Brain Plasticity Group
Department of Basic Psychology
Universitat de Barcelona
Campus Mundet, Edifici de Ponent
Passeig de la Vall d'Hebron 171
08035 Barcelona, Spain

Office: (34) 93 403 47 68
http://brainvitge.org/member/martinez_n/
twitter:@NoeliaMrtnez

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