Finding tracts from one region to another region

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Hi Mrtrix3 developers,

I want to clarify few things which I couldn’t understand from the track results I got.

  1. I tried extracting tracks from left thalamus to say left frontal (freesurfer defined ROIs and in diffusion space) using connectome2tck after whole brain tractography(100M) and SIFT(10M).
    The number of tracks that I get differs significantly among healthy controls, is it the behaviour of the algorithms, could you please share me any insights on such results.

  2. I tried different ways of extracting the tracks between 2 regions like
    a) tckgen with seed as left thalamus and include region as left frontal, 1M tracks
    b) whole brain tractography 100M ->SIFT 10M->connectome2tck between the 2 regions
    c) tckgen with seed as thalamus 10M ->connectome2tck between the 2 regions
    For the same subject, I get different count of tracks for the different ways. Is it due to the number of desired tracks being different in each of the cases, is there a reliable method that I should follow for all the subjects (so that I can compare the track counts between the subjects)?

Thank you,
Rajikha