Hi
On 5 Mar 2007, at 11:09, Jeroen Siero wrote:
> Dear Dr. Behrens,
>
> I am working with your wonderful diffusion software package and I
> have one
> question concerning the sample data for the Fdt tutorial,
> especially about
> the direction scheme. Looking at the given bvecs file I noticed
> that the
> gradient vectors are not unit vectors; they all sum up to
> approximately
> 1.019. Could you explain me why?
No reason - In early versions of FDT this would matter, and would
give you an underestimate of the diffusivity (leaving all other
parameters unchanged). In the current version, I believe they are
normalised internally in FDT code, so it should make no difference at
all.
> I am currently investigating directionschemes on a Philips system
> and I was
> wondering whether the tensor fitting is affected when using non-unit
> gradient vectors.
See above.
> Also, looking at the number of digits for each component in your
> bvecs file
> I was wondering whether some post-processing was done on the bvecs
> file? I
> am asking this because on the Philips system used here only 4
> digits can be
> entered for each gradientvector component.
No - none.
> Thank you for your time and I am looking forward to hearing from you.
>
Cheers
T
> Best regards,
>
> Jeroen Siero
> Undergraduate student
> Biomedical Engineering
> Rijksuniversiteit Groningen, The Netherlands
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