well, the toatl numebr of samples sent out is the number of samples sent out from each voxel times the number of voxels. so you can use this as a denominator. the waytotal is, strictly speaking, only to convert the fdt paths output into <some> probability measure given you are sure that the tract is there is each and every subject.
cheers-
andreas
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Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von Massieh Moayedi [[log in to unmask]]
Gesendet: Dienstag, 22. Juni 2010 18:17
An: [log in to unmask]
Betreff: [FSL] Gray matter parcellation using tractography
Hi Everyone,
We've got tractography results from a gray matter seed for each of our subjects. However, we are interested in doing a few things. I've read the literature, and am still not entirely clear on the methods.
1) we'd like to quantify the data between groups (e.g., come up with some sort of measure that will allow us to say whether 2 regions are more/less connected between regions). I assume the way to do this is to run tractography using a seed, and a waypoint mask, both of which are in the same space. This puts out a waytotal text file.
However, if I want to get a probability distribution for each voxel within the mask, how do I do this? For instance, Rushworth et al, (2005) state that "for each voxel, the number of samples reaching a parietal target was recorded as a proportion of the total number of samples going to all parietal target areas." and further "For each target area, we then took a mean value for all voxels in the seed area with any connectivity to that target".
I'm not familiar on how to get the values 1) for each voxel, and 2) the total number of samples.
In the Diffusion MRI book (Johansen_Berg and Behrens), the methods described suggest to convert the the 3D Fdt image (tractogram) into a 1D vector- I suppose this is another way to describe what's done above, but I'm not sure how to actually do it.
thanks for your help-
Massih
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