Just in case you want to use the MRtrix3 functionality here, the commands you’re after are tcksample and tckresample. These admittedly need to be better documented.
The process consists of first re-sampling the streamlines at equivalent locations along the tract of interest, by ‘cutting’ them up according to a set of uniformly-spaced planes. For example:
tckresample CST.tck -line 20 1,2,3 4,5,10 CST_samples.tck
will re-sample each of your
CST.tck streamlines at 20 equivalent locations uniformly spaced between real-space positions
1,2,3 at one end and position
4,5,10 at the other. For more exotic tracks, you can also resample them along an arc of a circle, using the
-arc option along with a mid-point for the arc (the arc will then pass through all 3 of your start, mid and end points, and the cut planes will be perpendicular to its tangent).
Once you’ve resampled your streamlines, you can use them to sample whichever scalar map you’re interested in, for example:
tcksample TCK_samples.tck fa.mif fa_values.txt
This will produce a text file with all sampled FA values for a given streamline in a row, each streamlines in its own row. You can then produce whatever plots you want or perform whatever analysis is required in Excel, Matlab, R, SPSS, etc.
Clearly there is no actual statistics produced by this process - all you get are the sampled values. This may be sufficient for your needs, but there’s a good chance that other packages provide more advanced, more powerful statistical analyses than this process would allow.