Hi Daniel,
Here’s some stuff I found online. I’m going to go back and look at how I dealt with it, but that was ages ago and I’m not sure I’ll find it soon.
Here are some ideas I found online
https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=FSL;14f3adc9.0808
There was also an exam question, which I think the answer is negative eigenvalues, here:
https://fsl.fmrib.ox.ac.uk/fslcourse/lectures/practicals/fdt1/index.html
This seemed like an interesting answer:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=FSL;859758f.1004
There was a reply for how to deal with negative eigenvalues but I don’t know whether it does anything more than set a limit on the tensor calc:
https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=fsl;4d074d45.1409
HTH,
Sally
On Sep 24, 2018, at 11:49 AM, Durgerian, Sally <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Hi Daniel,
I remember running into that problem. For me, it had to do with a scanner artifact. I’ll have to go back and check to see how I was advised to deal with it and get back to you.
Sally
On Sep 24, 2018, at 11:29 AM, Daniel Callow <[log in to unmask]<mailto:[log in to unmask]>> wrote:
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Hello,
I have just completed tensor estimation using dtifit. A majority of the voxels seem to have reasonable FA values (<.1 for gray matter and .2-.5 in white matter). However, I am finding a few FA values that reach above an FA of 1? Is this common (partial volume effect/artifact)? I plan to use TBSS for my analysis and was curious if I need to correct this issue or if there is an option in dtifit that prevents these random high values from being in the images?
Thank you for any suggestions or feedback you can provide,
Daniel
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Sally Durgerian
Neurolab G2415
Medical College of Wisconsin
8701 W. Watertown Plank Rd.
Milwaukee WI 53226
Sally Durgerian
Neurolab G2415
Medical College of Wisconsin
8701 W. Watertown Plank Rd.
Milwaukee WI 53226
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