I have had some success importing a scanned 3D mesh .obj file into Moi using SubD in V4
Method:
I loaded the original high mesh count file into Meshlab (free) and reduced the mesh size -options to select = Filter / remeshing, simplification and reconstruction / simplification: quadric edge collapse decimation
Then typed in the new mesh count of 8000
Converted the mesh to - Filter / Polygonal & Quad Mesh / subdivision surfaces: Catmull-clark = giving 4 sided meshs
then exported the result as a .obj file
then in MOI clicked on SubD / from file and selected the above .obj file and after a few seconds it opened ok
This is fine for me, its not very detailed, but for tracing over it gives the volumes required for me to refine and tweak :-)
Andy