[Mrtrix-discussion] statistical analysis after fiber tracking

[Zhuang Song]

Dear MRtrixers,

There are several questions regrading statistical analysis after fiber
tracking, which may not necessarily relate to each other.

1) Given the tracking output file *.tck, is there any way to read out the
mean direction of selected fibers in every voxel where crossing fibers have
been removed? This voxelwise directional information is anatomically
specific and therefore can be very useful in statistical analysis.

2) For the purpose of statistics (not fiber tracking), what kinds of metric
would you recommend to derive from either the original ODF or fiber ODF? I
haven't seen much this kind of work yet in literature. It would be nice to
have some brainstorming here.

3)  I was wondering how to interpret properly the  physical meaning of the
track number or density that streamtrack generates. The program
streamtrack can generate arbitrary large number of tracks by manipulating
the option "-number". The track density (i.e. "-fraction" outputs of
tracks2prob) seems to remain quite stable even if I increase the total
tracking number 1000 times in streamtrack with option "-number". Different
than the TDI method based on whole brain tracking, I am only interested in
the tracks within a ROI. It seems to me it makes more sense to use the
track density instead of track numbers in statistical analysis. Is it
reasonable to do so even if the tracking is restricted in a ROI?

Thanks,
Zhuang
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