Thank you for uploading your data.
Recall: your concern was that the waytotal for Exclusion+Inclusion
drops more than Inclusion alone, even when the waytotal for Exclusion
does not drop.
There is a very simple explanation for this. In probtrackx, samples
are tracked in both directions from every seed point. When you have
conditions such as Exclusion or Inclusion masks, they need to apply to
both half streamlines. In other words, if a streamline makes it to an
exclusion mask in one direction, but not in the other, then it will
still be counted! Similarly, if a half-streamline does not make it to
an Inclusion mask, but the other half does, it will also be counted in
So what is happening in your case is that, when using "Exclusion",
some streamlines make it to the exclusion mask in one direction, but
not the other, so they are counted. Your waytotal does not drop,
despite the fact that you've reached an Exclusion mask.
When using Inclusion+Exclusion, the half-streamlines that have reached
the exclusion mask need their "other half" to reach the inclusion mask
in order to be counted, so they have less chances to be counted than
just using Inclusion.
Does that make sense?
On 19 Aug 2009, at 16:36, Rachel Hawe wrote:
> I uploaded the files. The reference number is 279188. The seed
> mask is
> CP_R, the waypoint mask is PLIC_R and the exclusion mask is
> Let me know if you need anything else.
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