1. 1 Interactive Thickness Visualization of Articular Cartilage Author :Matej Mlejnek, Anna Vilanova,Meister Eduard GröllerMatej MlejnekAnna VilanovaMeister Eduard Gröller Source :Proceedings of Visualization 2004, pages 521-527. October 2004 Speaker : Ren-LI Shen Advisor : Ku-Yaw Chang

2. 2 Outline   Introduction   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

3. 3 Introduction   Articular cartilage   Surfaces of knee joints are covered by tissue   Is a curved structure   difficult to read the thickness changes

4. 4 Introduction   Main functions of the cartilage   Distribution of weight   Frictionless motion   Shock absorption

5. 5 Introduction   Height field   Unfolding and depicting   Eliminates the complexity of the 3D shape   concentrate solely on the inspection   Offers several visualization modes   Color mapping   Scaling   Glyphs   Iso-lines

6. 6 Introduction

7. 7   Distortion   Minimize the distortion, in a user-defined area   Flattening   Requires parameterization of the surface

8. 8 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

9. 9 Pipeline for thickness visualization   Consists of the following steps

10. 10 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

11. 11 Cartilage segmentation   Two main classes of segmentation methods   Manual segmentation   Time-consuming   Requires an experienced user   Semi-automatic segmentation   use thresholding, region growing, snakes, or edge detection filters   In this paper they use an active contour model (snake)   controlled by internal and external forces

12. 12 Cartilage segmentation

13. 13 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

14. 14 Thickness measurement   Several possibilities to calculate   Vertical distance   Is not appropriate for curved surfaces   Proximity method   This paper uses   Normal distance

15. 15 Thickness measurement   Euclidean distance   Optimizations of distance transforms   Chamfer distance transforms   propagates the local distance by adding the neighborhood values   Vector distance transforms   propagates the distance vector to the nearest sample point of the object surface

16. 16 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

17. 17 Flattening of articular cartilage   Flattening cartilage into the corresponding 2D plane should fulfill the following criteria   Need a parameterization   Minimizes area distortion   Local and global intersections have to be prevented   Common problem in the area on surface parameterization

18. 18 Flattening of articular cartilage   Do not allow multiple patches   In order to keep spatial relations.   Parameterization has to be fast

19. 19 Flattening of articular cartilage   Efficiently prevent local as well as global intersections   Align all points onto a line   Reduces the distortion minimization issue

20. 20 Flattening of articular cartilage   In order to meet all of the constraints   Grow a planar patch   First, the focal triangle includes the focal point is rigidly transformed into the 2D plane   The distance is defined by the height of the focal triangle (height = 2·area / |p2−p1|)   Next step, patch is iteratively flattened by adding active points ai to the patch

21. 21 Flattening of articular cartilage

22. 22 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

23. 23 Operations on the height field   Slight changes in the thickness on the reconstructed surface may, however, not be noticeable   In order to enhance the thickness information   Propose a non-uniform scaling only in the height direction

24. 24 Operations on the height field

25. 25 Operations on the height field

26. 26 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

27. 27 Thresholded non-linear scaling

28. 28 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

29. 29 Non-linear scaling on interval   Thresholded scaling

30. 30 Non-linear scaling on interval

31. 31 Non-linear scaling on interval   Show the extraction of thickness information enhanced by color coding

32. 32 Non-linear scaling on interval   By iso-lines

33. 33 Non-linear scaling on interval   By glyphs

34. 34 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

35. 35 Scale transfer function   Need a tool enables detection of subtle thickness changes on each range of the thickness values   Using non-linear scaling approach, interesting features may be occluded by other scaled areas   Can be overcome by thresholded non-linear scaling

36. 36 Scale transfer function   Define a continuous linear scaling transfer function   Maps the original thickness values   Assigned to each vertex   To the scaled values   Thickness preservation is performed on intervals, where x = y

37. 37 Scale transfer function

38. 38 Outline   Introduction and medical background   Pipeline for thickness visualization   Cartilage segmentation   Thickness measurement   Flattening of articular cartilage   Operations on the height field   Thresholded non-linear scaling   Non-linear scaling on interval   Scale transfer function   Summary and conclusions

39. 39 Summary and conclusions   The approach has been illustrated on the visualization of articular cartilage   Detection of slight thickness changes is vital for diagnosis   Has been shown that unfolding of anatomic organs is promising   Future work   Continue with a broader clinical study on a variety of datasets