Part of ants registration suite
ANTSIntegrateVectorField \,VecImageIN.nii.gz ROIMaskIN.nii.gz FibersOUT.vtk LengthImageOUT.nii.gz\/
The vector field should have vectors as voxels , the ROI is an integer image, fibers out will be vtk text files ....
ROI-Mask controls where the integration is performed and the start point region ...
e.g. the brain will have value 1 , the ROI has value 2 , then all starting seed points for the integration will start in the region labeled 2 and be constrained to the region labeled 1.