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,

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


"Where words fail, music speaks."

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Christian Andersen*