[Mristudio-users] question about eigenvalues/vectors

[susumu mori]

On Fri, Dec 3, 2010 at 11:02 AM, Katherine L. Ragland <klragland at umc.edu>wrote:

> Hello-
>
> I am a fourth year medical student at the University of Mississippi Medical
> Center working with Dr. Judy James.  We have been using your DTIStudio
> software for fiber tracking in the fetal brain.  I would like to preface my
> questions by saying my current knowledge of DTI, eigenvalues, eigenvectors,
> etc. is quite limited.  If I say something incorrectly, please let me know!
>
> My questions for you deal with eigenvalues and eigenvectors.
>
> 1)  What is the clinical applicability of these measurements?  For example,
> does a shorter primary eigenvector signify a loss of anisotropy and possibly
> decreased myelination?  What can one infer from increasing or decreasing
> trends in eigenvalues?
>
>  I have some description about it in our Neuron paper (Mori and Zhang, 51,
527, 2006, Descriptions related to Fig. 10) and entire chapter 7 of my book
"Introduction to Diffusion Tensor Imaging" is dedicated to this topic.

2)  Do the eigenvalue 0 and eigenvector 0 correspond to the primary
> value/vector parallel to axon fibers?
>

Correct.


>
> 2)  How do you calculate the primary eigenvector from the statistics
> derived from DTIstudio?  (the 3 eigenvectors are given as x, y, and z
> coordinates)
>

Not sure about your question. DtiStudio provides Eigenvector0, 1, 2, right?
Are you asking how they are calculated internally? In DTI, the first thing
we calculate is a 3x3 tensor, from which we can obtain 3 eigenvectors and 3
eigenvalues.


>
> I appreciate any insight you can give.
>
> Thank you very much for this software and your time in reading this.
>
> Sincerely,
>
> Katie Ragland
>
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