Hi Nasia
It is not the case that the probability of a streamline hitting a target mask necessarily scales linearly (or at all) with the size of the target mask. So there is no simple way to “correct” for the size of your rois. That said, if the rois are anatomically/functionally defined, then their size differences become meaningful and thus it does not necessarily make sense to correct for that.
Cheers,
Saad
> On 14 Jan 2019, at 18:12, Athanasia Metoki <[log in to unmask]> wrote:
>
> Dear Matteo,
>
> Thank you very much for your reply!
> If I were interested in calculating the probability of connection between two masks independent for the rest of the newtwork (ie the rest of the ROIs and their connections) how would I go about it?
> Example
> ROI A with voxel count 100
> ROI B with voxel count 150
> If I run tractography (with 5000 samples) between the two I will get a waytotal file with two numbers corresponding to the total number of generated tracts from each seed mask that have reached the other. Top waytotal number is the tracts from A that reached B and bottom waytotal number the tracts from B that reached A.
> Is it correct to say that the probability of connection from A to B can be calculated like this: Top waytotal number / (100x5000) and the probability of connection from B to A: Bottom waytotal number / (150x5000)
> If this is correct how can I find the total probability? Do I just add the two probabilities or average them?
> Or should I go about this like this: (Top waytotal number + Bottom waytotal number) / (100+150)*5000 for the whole connection between the two?
>
> I hope what I am describing makes sense.
>
> Thank you!
>
> Best,
> Nasia Metoki
>
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