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Normally, to display hologram in hololens, you need to create your hologram throught Unity, but your mesh need to be a .OBJ or .FBX file. On GitHub, there is a .VTK to .OBJ converter (https://github.com/daviddoria/vtkOBJWriter). After, you can take your .OBJ and import it inside your Unity project. I've not tried, but I hope that you don't want to do a real-time project, because it will be impossible!
I've the same problem. I want to display VTK mesh in Hololens, and I've no solution. Did you manage to do that since last year ?