[Mristudio-users] number of fibers

[susumu mori]

Hi Andreas,

please see below;


> (1) in FACT, tract statistics give out a number of fibers. What does this
> number mean? Is it possible that more than one fiber goes through one
> voxel?
>

The number of the fiber itself doesn't carry anatomical meaning. In
DtiStudio, we use the exhaustive approach, meaning fiber tracking is
initiated from the center of all pixels above the threshold. If the number
of the seed points is increased, the number of the fibers increases too. So,
it is parameter-dependent. You may be able to compare the numbers between
subjects but it may simply reflect the size of the tracts, which can be also
obtained from the number of pixels. The number of pixels is also reported in
DtiStudio and has a physical dimension, which may be easier to use.


>
> (2) what is the physical measure of diffusivity values (e.g. radial
> diffusivity: 10 exp-4 what? cm/s or m/s?)
>
>
It depends on the unit you use for the b-value.


>
> Thanks a lot
> Andreas
>
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