I just discover these 2 progs
Ready : https://code.google.com/p/reaction-diffusion/ Open Source

ParaView http://www.paraview.org/ Open Source

And from this video



So Ready vti--> ParaView STL --> Blender ---> OBJ or any 3D format : that's very cool!
And Moi can surelly works somewhere in the Pipeline ;)

Ok, thank you for all the suggestions. I'll check out ViaCAD, and hope for the dxf import/export feature in the full V3.

If you only need 2d, the Viacad 2d version is also a converter at 40$.