1. VIRTUAL ARTHROSCOPIC KNEE SURGERY TRANING SYSTEM Yang Xiaosong The Chinese University of Hong Kong Tsinghua University

2. VIRTUAL ARTHROSCOPIC KNEE SURGERY TRANING SYSTEM A joint project between the Chinese University of Hong Kong Tsinghua University, sponsored by The National Natural Science Foundation of China RGC of Hong Kong

3. Minimally Invasive Microsurgical Technique Less trauma Reduced pain Quicker convalescence

4. Restrictions of Arthroscopy Restricted vision Poor hand-eye coordination Limited mobility of surgical instruments

5. Surgical Skill Training Animals Cadavers Virtual reality based simulation systems

6. Arthroscopy Surgery

7. Virtual Arthroscopic Knee Surgery Training System Modeling using data from Visible Human Project Simulation of the deformation of soft tissue with topological change by FEA User interaction – Force feedback

8. Hardware System Architecture Central Computer ( PIV 1.5G, Nivdia Geforce 3, Windows 2000) Input Device Display Screen

9. Software System Architecture 3D Segmentation CT, MRI Volume Data Segmented Volume Data Geometry Modeling Preprocess Stage  Real-time simulation of non-linear deformation with cutting  Force feedback calculation of soft tissues  Real-time simulation of non-linear deformation with cutting  Force feedback calculation of soft tissues Force Feedback Device Physical Attributes Set Force Collision Detection Manipulation of Operation Facilitie s Contacted Realistic Rendering  View from outside  Arthroscopy Realistic Rendering  View from outside  Arthroscopy Surface mesh Simplify & Smooth Local Remesh in Operation Area On the FLY Stage Surface and Tetrahedral mesh 3D Tetrahedral mesh Surface mesh

10. Mesh Generation of Human Organs Segmentation Surface boundary meshes creation Tetrahedral mesh generation Mesh smoothing

11. Collision Detection Prevent the arthroscope and operation facility from entering a solid object Get the initial intersection point for cutting simulation Collision detection for deformable objects, different from that of rigid objects AABB tree

12. Simulation of Soft Tissue Deformation With Flexible Cutting Physically reality Real-time interaction Hybrid Finite Element Method

13. Hybrid FEM Non-linear deformation and topology changing model in operating region (Region 1). – The local small region, fast to compute Linear deformation and topology constant model in non-operating region (Region 2) – The remaining large region, accelerated by pre-processing

14. 2-Dimension Sample

15. Cutting of a single element Normal Cases Degeneration cases

16. 3-Dimension Example A simplified model of thigh Tetrahedral meshes simplification

17. Input Device Four DOFs for arthroscope and instruments – Pitch – Yaw – Insertion – Rotation Force feedback – Three DC motors attached for the first three DOF – The fourth DOF need no force feedback

18. Input Device Picture

19. System Interface

20. Sample

21. Work to do More effective interactive 3-D segmentation system Realistic Rendering Simulation of complicated operation facilities

22. Tetrahedral Mesh Generation of Human Organs on Segmented Volume

23. Tetrahedralization Algorithm on Segmented Volume Voxel-Split tetrahedralization 3D conforming Delaunay tetrahedralization algorithm Feature point based tetrahedralization

24. Voxel-Split tetrahedralization

28. Simplification of Segmentation Volume

29. Voxel-Split tetrahedralization Global Simplification of Segmentation Volume – Boundary voxel decomposition – The order of voxel merge

30. 3D conforming Delaunay tetrahedralization algorithm

31. Tissue boundary extraction

32. 3D conforming Delaunay tetrahedralization algorithm

33. Feature point based tetrahedralization Accurate. Small scale. Well-shaped.

34. Feature point based tetrahedralization Placement of the mesh vertices Delaunay Triangulation Restore the tissue boundary and set element’s tissue type

35. Feature point based tetrahedralization Point Displacement – feature point, steiner point and structured mesh point

36. Feature point based tetrahedralization Feature Point

37. Feature point based tetrahedralization Feature Point 1.Gradient computation of the mid point of each voxel edge 2.Compare of the gradient in the local neighbors 3.Error bounded simplification of feature point

38. Feature point based tetrahedralization Steiner point displacement

39. Feature point based tetrahedralization

40. Cross Tissue Boundary Detection Criterion for crossing boundary Boundary Points (BP) Voxel Points (VP) Edge: VP-VP BP-VP BP-BP

41. Feature point based tetrahedralization Remesh to restore the tissue boundary No=3, flip32 to delete the crossing edge. No=4, Flip4Diagonal to swap the diagonal crossing edge. No>4

42. Feature point based tetrahedralization Remesh to restore the tissue boundary

43. Feature point based tetrahedralization Volume 297 x 341 x 180= 18,229,860 Tetehedral Mesh 94,953 nodes, 490,409 elements

44. Thanks