Salome is crashing because of to many faces and can not create groups

Hello, I am using Salome to create a .med file for Code_Saturne from a geometry which was extracted from a CT scan. Unfortunately the geometry has around 36,000 faces so that Salome works really slow and in the end Salome crashes. So that I am not able to create the groups that I need for Code_Saturne.
Do anybody know if there is something I can do so that Salome still works for many faces. I can not reduce the number of faces because otherwise the details of the geometry get lost.
I am using the version 9.6.0 of Salome in Windows 10.


I guess you have got triangular faces from your CT scan. So you’d better import it in SMESH as a STL file and create the groups from there (with filters for instance).