1. Hybrid Visualization for White Matter Tracts using Triangle Strips and Point Sprites D. Merhof 1,2, M. Sonntag 1, F. Enders 1,2, C. Nimsky 2, P. Hastreiter 1,2, G. Greiner 1 1 Computer Graphics Group 2 Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg

2. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg2 Outline Motivation Diffusion tensor imaging Fiber tracking 3D visualization approaches Results Conclusion Acknowledgements

3. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg3 Motivation White matter tracts Neural structures within the human brain Transmission of motor, sensor and other impulses Tract systems: Pyramidal tract Corpus callosum Optic tract

4. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg4 Motivation Reconstruction and visualization of white matter tracts of interest for different research areas: Development of the brain Study of brain diseases Neurosurgery

6. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg6 Diffusion tensor imaging (DTI) MR imaging sequence (echo planar imaging) Measures diffusion of water molecules White matter consists of long, cylindrical cells Diffusion within white matter is anisotropic Diffusion tensor: Gaussian diffusion per voxel Anisotropic diffusion Anisotropic diffusion Isotropic diffusion Isotropic diffusion

7. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg7 Basic Idea: Reduce tensor field to vector field of major eigenvector Vector field of main diffusion Perform streamline propagation Recostruction - Fiber Tracking

8. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg8 Visualization Lines + Fast rendering - Gaps, if lines wider than one pixel - Width fix, independent of distance Tubes + Significantly improved Visualization - Slow rendering, due to geometric complexity Lines Tubes

9. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg9 Visualization - Idea Rectangular cross section of tube for v t Use triangle strips Spherical cross section of tube for v || t Use point sprites Hybrid combination of both techniques

10. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg10 Triangle strips - construction

11. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg11 Triangle strips - texturing 1D texture with luminance and alpha channel Textures for ambient und specular illumination Decreasing value when approaching the border (sine function) diffuse specular 1D texture channel 1 channel 2

12. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg12 Flipping artifacts Occur when viewing and segment direction are nearly parallel Use point sprites in this case textured quads, rotated towards camera resemble cross section of tube

13. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg13 Point Sprites - Texturing 2D-RGB-Texture: draw and illuminate point sprites R channel: alpha channel G / B channel: diffuse / specular illumination

14. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg14 Point Sprites - Rotation Rotate point sprite according to segment direction: Project fiber tangent t to image plane t p Normalize t p t p 0 Alpha provides rotation of segment

15. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg15 Point Sprites When v close to t: Staggered point sprites Results in natural appearance of a tube v v Point Sprites

16. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg16 Visualization – Hybrid approach Triangle Strips Represent rectangular cross section Displayed for v t < 0.98 Point Sprites Represent circular cross section Displayed for v t > 0.93

17. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg17 Terminating textured quads Problem – Beginning and end of each fiber No tube-like appearance Solution Terminating textured quads

18. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg18 Results Hybrid visualization approach based on triangle strips and point sprites provides High visual quality (similar to tubes) Visual drawbacks of lines are circumvented High performance (due to reduced complexity) Lines HybridTubes

19. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg19 Results Tracking of whole brain (4 500 fibers, 300 000 segments) Tubes: 16 / seg. ca. 4.8 million Triangle strips: 2 / seg. ca. 0.6 million Graphics card: Nvidia Geforce 6800 Ultra, 256 MB Viewport: 600x800 Pixel

20. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg20 Results Clinical relevance: Combination with Volume Rendering Realtime visualization improves inspection of data Improved analysis of the data Tumor

22. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg22 Conclusion Improved visualization for streamlines based on DT-MRI data Technical aspects Hybrid approach instead of tubes/lines Rendering performance Lines Visual quality Tubes Medical aspects Improved analysis in real-time

23. IEEE Vis 2006Computer Graphics Group + Neurocenter, Dept. of Neurosurgery University of Erlangen-Nuremberg23 Fundings Graduiertenkolleg Dreidimensionale Bildanalyse und –synthese Deutsche Forschungsgemeinschaft (DFG), SFB 603, Project C9

24. Thank you! Questions? Thank you! Questions?