[Paraview] help with streamlines (units?)

[Richard Beare]

Hi,
I'm hoping to examine some MRI derived blood flow velocity data using
paraview. I've transformed the original data into a time series of vtk
images, which have the velocity vector at each point. However I
suspect I need to set up the units for velocity appropriately. Should
I ensure that the distance component is in the same units as the voxel
spacing in the images, or doesn't it matter? I haven't experimented
with streamlines before so I'm not sure what I should be tweaking.
Also, I notice that some examples assume separate vector and magnitude
information. Is this essential? Should I be normalizing my vectors
instead?

Thanks