 |
 |
Yes it is because of distance correction, which adds 1 for each voxel travelled. Peace, Matt. -----Original Message----- From: Catherine T Gambale [mailto:[log in to unmask]] Sent: Monday, September 26, 2011 12:47 PM To: [log in to unmask]; Matt Glasser Cc: Catherine T Gambale Subject: Re: Does nonlinear warping alter waytotal? Thank you Matt, that answers my first question regarding individual waytotals after nonlinear warping of the seed. However, I am still confused as to how almost half of my subjects could have fdt_paths with a higher max value than their waytotal. Do you have an idea of how this could happen? Perhaps it has something to do with the fact that I used distance correction when running the waypoint tractography? Thanks again, in advance. Katie ----------------------------------------------------------------- Date: Thu, 22 Sep 2011 16:28:34 -0500 From: Matt Glasser <[log in to unmask]> Subject: Re: Does nonlinear warping alter waytotal? The position of each see voxel is mapped into the individual subject's diffusion space using the nonlinear warp, so the same number of voxels are used for tracking across all subjects in this case. If you use only a single ROI for tractography, your waytotal will just equal the number of streamlines sent out, which will also be the same across subjects. Peace, Matt. -----Original Message----- From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Catherine T Gambale Sent: Thursday, September 22, 2011 4:09 PM To: [log in to unmask] Subject: [FSL] Does nonlinear warping alter waytotal? 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]