[Mrtrix-discussion] Color and shape of the FODs or ODFs

[Thijs Dhollander]

Hi Ralf,

The shape of the FOD is easy to interpret: you basically start with a
(unit) sphere, and then scale its radius along each orientation by the FOD
amplitude for that orientation.  It's basically the 3D version of polar
coordinates ( http://en.wikipedia.org/wiki/Polar_coordinate_system ), but
used to represent a 2D spherical function in a 3D space.
The RGB values for the colors are simply derived from a normalized vector
that points along each direction.  The colors are nothing more than a
visual aid though; they help you navigate a field of FODs much easier.

The caption in figure 7 refers you to the webversion, because the printed
version probably did not feature colors at the time.  The word
"interpretation" there, only means that whatever is written in the caption
about colors, can only really be visually appreciated in the (colored)
digital version.  The normal PDF at Elsevier basically is that web version.
:-)

Hope this clarifies some things!

Cheers,
Thijs




*Thijs Dhollanderthijs.dhollander at gmail.com
<thijs.dhollander at gmail.com>Tel. +32 475 36 44 27*
Medical Image Computing (MIC), ESAT-PSI, Department of Electrical
Engineering, KU Leuven


On Mon, Apr 28, 2014 at 3:46 PM, Luetzkendorf, Ralf <
Ralf.Luetzkendorf at med.ovgu.de> wrote:

> Hello MRTrix Community,
>
> I have a question about the color and shape of the FODs / ODFs
> I read through the papers and I have to be absolutely sure how to
> interpret them.
>
> At first in the Paper "Direct estimation of the fiber orientation density
> function from diffusion-weighted MRI data using spherical deconvolution,
> 2004" Figure 7 referred you to a web version for color interpretation. Is
> there still a Web Version? I only found the normal PDF at Elsevier.
>
> Do these drop-shaped geometrical bodies, that face each other have exactly
> the same color? And its only a rendering problem, that they very often
> don't have it in figures, like in Figure 7 of the 2004 Article?
>
> Is there a description how to interpret the shape of the ODF /FOD.
> Something like a first and still established paper about it?
>
> Thanks for the help,
>
> Ralf
>
>
>
>
>
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