Dear Christine,
I am pleased that you have sorted out your diffusion tensor estimation.
However, I would advise you not to try tractography with 6 diffusion
direction data. We usually advise that data is acquired with at least 25
diffusion encoding directions if it is going to be used for tractography.
See the FSL faq:
http://www.fmrib.ox.ac.uk/fslfaq
for more details about e.g. suggested voxel resolutions.
Thanks
Tim
On Thu, 2 Dec 2004, Christine Ojango wrote:
> Hi,
>
> The lines of the eigenvectors were not right- in the meaning that what
> should have been left-right (and red) was anterior-posterior (and
> green). So, at first I started to change the vectors to negative with
> many different combinations.
>
> But yesterday I was told to change the values themselves (so the value
> of x to y and y to x) and after processing, I have now lines with right
> directions (so, corpus callosum fibers are from left to right, not from
> anterior to posterior).
>
> So, now with the right directions, I can do the tractography.
>
> Thanks,
> Christine
>
>
>
>
> >>> [log in to unmask] 12/01/04 1:16 PM >>>
> Can you give me a little more detail. What is wrong with your
> eigenvectors?
>
> Or, is there anyway you can take a screen grab of the problem, and put it
> on the web somewhere?
>
> Thanks
> Tim
> -------------------------------------------------------------------------------
> Tim Behrens
> Centre for Functional MRI of the Brain
> The John Radcliffe Hospital
> Headley Way Oxford OX3 9DU
> Oxford University
> Work 01865 222782
> Mobile 07980 884537
> -------------------------------------------------------------------------------
>
> On Wed, 1 Dec 2004, Christine Ojango wrote:
>
> > Hi,
> >
> > the higher -level analysis worked now. Thank you.
> >
> > But I have another question about fdt.
> >
> > I have processed data from Philips scanner. And running the eddy current, dtifit and bedpost have been without errors. Bedpost datacheck is not giving me errors.
> >
> > The bvals are:
> > 0 1000 1000 1000 1000 1000 1000
> >
> > And the bvecs:
> > 0 0 1 0 0.70710678 0 0.70710678
> > 0 1 0 0 0.70710678 0.70710678 0
> > 0 0 0 1 0 0.70710678 0.70710678
> >
> >
> > But the lines (and colours) watching with fsl view are not right. I have been told that it can be the difference of how the vectors are acquired and I ran all the possible changes in vector directions.
> > Putting negative in front of x or x/y or x/z etc. And also turning the slices order from descending to ascending.
> >
> > But in all cases the lines of main eigenvector are not right.
> >
> > Is there somehing else what could I do?
> >
> > Thank you for the help.
> >
> > Christine
> >
> >
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>
>
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--
-------------------------------------------------------------------------------
Tim Behrens
Centre for Functional MRI of the Brain
The John Radcliffe Hospital
Headley Way Oxford OX3 9DU
Oxford University
Work 01865 222782
Mobile 07980 884537
-------------------------------------------------------------------------------
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