We show how to model an implant for cranioplasty with Rhino3DMedical.
Live session video
Watch here the full workflow:
In the following we will briefly note all the necessary steps to create the cranioplasty implant.
1. Open image
Open a 3D image with command RMOpenImage (button Open Image).
2. Image analysis
Run command RMImageAnalysis (button Image Analysis). With the controls navigate through the image and set a threshold to show the bone in green color. Click Surface Preview to see a 3D preview of the segmented area and click Close to close the window.
Run command RMSegmentation (button Segmentation). Press button Surface from Threshold with Close Surface and Extract Largest Region checked on to extract only the skull. This will work as long as the skull represents the largest region segmented by the threshold.
Go to Image Analysis and uncheck Superimpose 3D surfaces to see the full mesh in all views.
4. Symmetry plane
Hide the layer Images and run command Plane to draw the symmetry plane in sagittal view. Position and orient it to match the symmetry plane of the skull (run Gumball On to show the handlers to do so).
5. Mirror skull
Run command Mirror over the skull and the symmetry plane (when selecting plane, click 3Point and turn Osnap with End option at the bottom of Rhino to select three points of the plane) to obtain its symmetric representation. Move it a bit so that the model properly overlaps the fracture.
6. Draw implant border
Use command PolylineOnMesh over the mirrored model to draw the contour of the fracture. Run command CurveThroughPolyline to convert the polyline to curve.
Draw implant border.
7. Smoothing implant border curve
Use command Rebuild over the curve to obtain a smoother one. You can modify Rebuild parameters or curve control points to refine it.
Smoothing implant border curve.
8. Implant mesh
Use command RMExtractMeshFacesWithBrush (section MeshRepair button ExtractMeshFaces) to paint and extract the area of the fracture over the mirrored model.
9. Implant patch
Use command Patch taking as input the curve of point 7 and the mesh of point 8. The surface of the implant will appear.
10. Implant solid
Use command OffsetSrf to convert the implant surface to solid. Be careful here with properly defining the thickness of the implant; you can extrude to one or other side, or to both sides.
11. Fillet implant edges
Optionally, use command FilletEdge over the edges of the implant with a very small radius to obtain smoother edges.
Fillet implant edges.
12. Export to STL
Go to top menu File -> Export Selected… and select the implant, then choose directory and format (typically STL) and the STL object will be placed there. This is ready for 3D printing or for export into other CAD software.
Export to STL.
Thanks to Dr. Suresh Ludhwani, radiologist and 3D printing specialist at IDDS and Oroscan, for providing the CT scan used here.