Hi Russ -
Yes - it sounds like something is wrong!! What do your MD values look
like? - are they positive? If you look at oyuor data in fslview do the
diffusion weighted scans have lower signal than the non-weighed ones?
Anyway, if you can tar up the directory, and stick it on the web
somewhere, I can take a quick look.
Thanks
Tim
On Fri, 10 Dec 2004, Russ Poldrack wrote:
> Hi - I am having some odd results using dtifit on some of our data.
> When I compute FA maps using an older custom program, I get very
> reasonable results, with FA ranging from zero to one and with high FA
> values where they should be (e.g., corpus callosum). When I run dtifit
> on the same data, I get some odd results. First, the FA values in the
> corpus callosum are very low. Second, the range of FA values is a bit
> strange. Within voxels that are not exactly zero-valued, the minimum
> FA value is about 0.35; this compares to our previous results where the
> minimum FA value was around .01. In addition, the maximum FA value is
> greater than zero (1.15 in this dataset).
>
> Any ideas as to what might be causing this?
>
> cheers
> russ
>
>
>
>
> ---
> Russell A. Poldrack, Ph.D.
> Assistant Professor of Psychology, UCLA
> Franz Hall, Box 951563
> Los Angeles, CA 90095-1563
> email: [log in to unmask]
> phone: 310.794.1224
> fax: 310.206.5895
> web: http://www.poldracklab.org/
>
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Tim Behrens
Centre for Functional MRI of the Brain
The John Radcliffe Hospital
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Oxford University
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