Hi - yes you should divide by the sum of the two numbers.

You can think of it as if your two seed ROIs were just a single ROI that happened to be made of two separate parts, and the spatial histogram (fdt_paths) telling you about the probability that streamlines from the union of both ROIs pass through a voxel of the brain (conditional on the various inclusion/exclusion criteria).

Cheers,
Saad






On 14 Jun 2016, at 10:38, Chiara Maffei <[log in to unmask]> wrote:

Dear FSL Experts,

We performed tractography between pair or ROIs in 2seeds-symmetric masks mode.
We now would like to transform voxels values in probabilities dividing by the way total number. However for each tract we have two waytotal numbers. Which would be the most reasonable approach in this case? Shall we divide by the sum of the two numbers?

Thanks

Best

Chiara 


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Chiara Maffei 
PhD Student, MR Methods Lab
CIMeC Center for Mind/Brain Sciences
Via delle Regole 101, 38123 Mattarello (TN), Italy 
MRI Methods Group: http://r.unitn.it/en/cimec/mri