Dianne,

 Surfice should read VTK files saved with the extension .fib

  http://www.princeton.edu/~efeibush/visco...

Therefore, I suspect you are referring to the Matlab format files with the extension .fib used by DSI studio:

 https://dsi-studio.labsolver.org/doc/cli_data.html#:~:text=fib%20files%20are%20readily%20loadable,fa0%2C%20fa1%2C%20fa2).

These are per-voxel values, not streamlines, so they are not supported by Surfice.

DSI Studio does have a streamline format with the .tt extension (TinyTrack) which also use a Matlab based format. In theory, other tools like Surfice could adopt these, but in general it seems like using DSI Studio to export to common interchange formats (.TRK, .TRX) avoids any issues. In particular, the .tt format does not provide a spatial transformation matrix so I am not sure how it transforms the vertex coordinates to world space (perhaps it must be paired with a voxel-based image, or perhaps the fact that you divide each integer by 32 means that the stored values are in world space). 

Make sure you use a recent version of DSI Studio when converting its internal formats to interchange formats:

  https://github.com/tee-ar-ex/trx-python/...

 I am a huge fan of DSI Studio, and think it is a terrific tool. I am just reluctant to support a format that I do not fully understand.