[Mrtrix-discussion] Tracks2prob colour TDI for deformed tracks

[Daan Christiaens]

Dear all,

I am trying to calculate the colour TDI map of a full-brain track set that was generated in subject space and warped (non-rigidly) to atlas space using the 'normalise_tracks' command. In doing so, however, the distance between successive samples on each track can change. This got me thinking about the calculation of the colour TDI: as each track contributes to the colour in each voxel it crosses by the average of the tangent vectors in all samples, an unequal distance between successive samples could have an effect on the colour, especially if the distance between samples also affects the size of the tangent vectors.

The 'tracks2prob' command allows to specify a resampling factor, which might solve this issue if it would ensure equidistant samples. Thijs and I have been looking at the code to see if this is indeed the case, but we can't quite figure it out. So basically, I have 2 questions:

  1.  Does Hermite interpolation in the tracks2prob command generate samples at equal distance, or will it only add (let's say 5) samples between every pair of original samples?
  2.  Does the distance between successive samples influence the size of the tangent vectors that contribute to the RGB colour? In other words, are the tangent vectors in all samples normalised before averaging, or will samples that are further apart have a larger contribution to the colour TDI?

Many thanks and kind regards,

Daan


ir. Daan Christiaens
Ph.D. Researcher

<mailto:daan.christiaens at uzleuven.be>daan.christiaens at esat.kuleuven.be<mailto:daan.christiaens at esat.kuleuven.be>
tel +32 16 34 90 42
fax +32 16 34 90 01

Medical Image Computing – ESAT/PSI – Department of Electrical Engineering

Medical Imaging Research Center<http://www.medicalimagingcenter.be/> | Katholieke Universiteit Leuven<http://www.kuleuven.be/> | campus Gasthuisberg<http://www.uzleuven.be/> | Herestraat 49 bus 7003 | B - 3000 Leuven

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