Hi,
I’m using tckgen
to generate a certain number of streamlines between two ROIs. However, I’m having trouble understanding the termination criterion for the algorithm. I understand that tckgen
terminates when one of the following three criteria are reached:
-
When the number of fibers generated reaches the desired maximum value (as given by the
-maxnum
parameter). -
When the number of fibers selected reaches the desired value (as given by the
-number
parameter). -
When the number of seeds used are finite.
I notice in my case that tckgen
most often does not generate the number of streamlines specified (as specified by -maxnum
) and stops as soon as it has selected 1000 fibers. In fact, it seems to terminate when it either reaches the specified maximum number of fibers generated or when it has selected 1000 fibers, whichever happens first. I have attached two snippets of code that I used to identify the problem; one where I set -maxnum
to 50000 and another where I set -maxnum
to 500000. In the former case, tckgen stopped as soon as 50000 streamlines were generated whereas in the latter, it stopped as soon as 1000 fibers were selected, even though the maximum number of streamlines required to be generated was not reached.
tckgen -force -include -46.17,15.89,38.81,15 -include -30.53,-63.44,36.25,15 -seed_sphere -46.17,15.89,38.81,15 -seed_sphere -30.53,-63.44,36.25,15 -act ACT_5tt.nii -backtrack -crop_at_gmwmi CSD.mif track_1.tck -maxnum 50000
tckgen: [WARNING] existing output files will be overwritten
tckgen: [100%] 50000 generated, 310 selected
tckgen -force -include -46.17,15.89,38.81,15 -include -30.53,-63.44,36.25,15 -seed_sphere -46.17,15.89,38.81,15 -seed_sphere -30.53,-63.44,36.25,15 -act ACT_5tt.nii -backtrack -crop_at_gmwmi CSD.mif track_1.tck -maxnum 500000
tckgen: [WARNING] existing output files will be overwritten
tckgen: [100%] 162618 generated, 1000 selected
I’m not sure why this is happening. Any help would be appreciated.
Thanks,
Varsha