How can I visualize DTI tractography streamlines generated from FSL's probtrackX in 3D? I currently have track files of diffusion tensor imaging (DTI) data generated from FSL's probtrackX tractography tool. What is the best software to visualize the streamlines from FSL in 3D?
I must say I am not an expert, but the following sources look helpful:


Gao et al. (2013) write 



  The voxel value in the resulting dataset represents the number of
  streamline samples passing through this voxel times the expected
  length of these samples. The probabilistic-tractography-derived DDM
  was generated by keeping the values of those voxels located at the WGM
  interface and setting the remaining voxels to zero. Again, the DDMs
  were rendered on the 3D WGM interface in DTI space.



The FDT Userguide discusses tractography and PROBTRACKX in section 2.6.3;
Catani &amp; Thiebaut de Schotten (2008) discuss how diffusion tensor imaging (DTI) tractography can be used to virtually dissect white matter pathways in the living human brain; 
This presentation contains a lot of references;
Specialist fora like this one may be of help.


References
- Catani &amp; Thiebaut de Schotten, Cortex (2008); 44(8):1105-32
- Gao et al., PLoS ONE (2013); 8(10): e75065