Hi Saad, thanks for the answer. Some questions just to make sure that
I understood correctly.
I've often come across the symmetric mode (---mask2) in the
discussions and I was assuming that this is something like:
Track from RegionA to RegionB AND from RegionB to RegionA - only those
tracts survive that fullfill both conditions. From your answer I
understand that they don't necessarily have to take the same way.
However - wouldn't that be a strong confirmation of the certainty of
the tract travelling this route? I guess depending on seed and target
chances are sometimes low that one sample from AtoB has a counterpart
BtoA and one would need a huge sample number to find those. One would
have to store for every sample of seed region A the "voxelway" and
then compare this with the table of voxelways from regionB. I guess
the problem is how to visualize the results of this - hower just an
idea.
My question really is for the symmetric mode. Does this show (as in
network-mode) connections from A that pass through B AND connections
from B that pass through A. Or is it connections from A that end in B
AND from B that end in A.
Another question re the network mode:
You said:
> It will show you an overlay of the following three distributions:
> . connections from A that pass through either B or C
> . connections from B that pass through either A or C
> . connections from C that pass through either A or B
Is there an option of tracking:
. connections from A that end in either B or C
. connections from B that end in either A or C
. connections from C that end in either A or B
I guess I could use the target mode for every combination and overlay
the results - correct? Is there already an option or script to
automate this?
Thanks a lot, Michael
On 24-May-09, at 2:45 AM, Saad Jbabdi wrote:
> Hi Michael,
>
> On 23 May 2009, at 21:56, Michael Scheel wrote:
>
>> Hi fsl-gurus,
>>
>> I have 2 questions re the probtrackx network mode:
>>
>> Say I have a Region A, B and C defined as masks and enter them as
>> Multiple seed masks.
>> What connections will be shown to me:
>> 1) Any connections between A and B, A and C, B and C or 2) just
>> connections that connect all of them, i.e. A-B-C, A-C-B and B-A-C.
>
> neither exactly 1) nor exactly 2).
> It will show you an overlay of the following three distributions:
> . connections from A that pass through either B or C
> . connections from B that pass through either A or C
> . connections from C that pass through either A or B
>
>
>>
>>
>> Assuming it is (1), and looking only at connections between A and B.
>> As I understand from previous discussions, tracking samples are send
>> from A to B and B to A and only those that reach their target in
>> both conditions 'survive'.
>> What I'm wondering about is what are the constraints regarding that:
>> Does the sample has to go the exact same voxelway to be found valid
>> or is it rather an overlay where voxels survive that were passed
>> from either direction, i.e. at least one sample passed from AtoB AND
>> BtoA.
>
> It is the latter. A tract survives if it reaches its target,
> regardless of the route it has taken.
>
> Cheers,
> Saad.
>
>
>>
>>
>> Thanks, Michael
>>
>
> --
> Saad Jbabdi
> Oxford University FMRIB Centre
>
> JR Hospital, Headington, OX3 9DU, UK
> +44 (0) 1865 222545 (fax 717)
> www.fmrib.ox.ac.uk/~saad
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