3D Slicer + VMTK extension on MRI Time-of-flight for cerebrovascular segmentation

Operating system: Mac OS v.10.14.6
Slicer version: v.4.11
Expected behavior: I tried to segment the cerebrovasculature from MRI ToF images using the local threshold feature on “Segmentation”, as seen in this youtube tutorial here. The tutorial uses CT images, but I wanted to repeat the same process on MRI ToF
Actual behavior: The process got stuck on the “3D show” step as it wouldn’t recreate the volume rendering after the local threshold step.

Many of the other automated segmentations in 3D slicer use Houndsfield units, appropriate for CT, but I am trying to segment cerebrovasculature from MRI time-of-flight images.

Eventually, the goal is to take the segmented cerebrovasculature and run them through the VMTK extension in 3D slicer to take advantage of the vascular measures available as part of VMTK.

Any guidance on this would be much appreciated
Thank you

Can you post a few screenshots of your data set and how it appears in Slicer?