Use the `--ompl flag` in `probtrackx2_gpu` call to output mean streamline length (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT/UserGuide#PROBTRACKX_-_probabilistic_tracking_with_crossing_fibres)
Use the
--ompl flaginprobtrackx2_gpucall to output mean streamline length (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT/UserGuide#PROBTRACKX_-_probabilistic_tracking_with_crossing_fibres)