I am running probabilistic tractography on a group of 82 subjects. The starting images for each subject were in diffusion space, and there are various seed and target masks I have created in standard space. In order to run tractography, I have found the nonlinear transformation warps for each subject.
When I first ran the Classification method of tractography using one standard space seed and several standard space targets, I indicated the location of the nonlinear warps (diff2standard_warp and standard2diff_warp) within each subject directory.
At the completion of the tractography, I noticed that the waytotal for every subject was identical. Initially I did not find this out-of-place because I assumed that, since the seed started out the same size for everyone, it should end up that way. However, when I think about the warp being applied to the seed mask for each individual, I find it very unusual that the waytotals do not differ at least slightly from subject to subject. How can this be?
Additionally, I ran Waypoint tractography using the same subjects, with the same standard-space seed and only one of the standard space target masks (whole cortex minus seed). These results were even more bizarre. I found that over half of my subjects had waytotals that were less (even as much as two times less) than the max value from the outputted fdt_paths image. It is my understanding that this may be due to the fact that I had applied distance correction in my tractography. Can the distance correction account for these abnormal values, or is something else going on here?
Thanks in advance for your help.
Catherine Gambale, B.S.
Post-Baccalaureate IRTA
Genes, Cognition, and Psychosis Program
Clinical Brain Disorders Branch, NIMH
10 Center Dr., Bldg. 10, Room 3C205
Bethesda, MD 20852
Phone: (301)-496-9672
Email: [log in to unmask]
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