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Hybrid Visualization for White Matter Tracts using
Triangle Strips and Point Sprites
D. Merhof1,2, M. Sonntag1, F. Enders1,2,C. Nimsky2, P. Hastreiter1,2, G. Greiner1
1Computer Graphics Group2Neurocenter, Dept. of Neurosurgery
University of Erlangen-Nuremberg
IEEE Vis 20062 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Outline
Motivation
Diffusion tensor imaging
Fiber tracking
3D visualization approaches
Results
Conclusion
Acknowledgements
IEEE Vis 20063 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Motivation
White matter tractsNeural structures within thehuman brain
Transmission of motor, sensor and other impulses
Tract systems:Pyramidal tract
Corpus callosum
Optic tract
IEEE Vis 20064 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Motivation
Reconstruction and visualization of white matter tracts of interest for different research areas:
Development of the brain
Study of brain diseases
Neurosurgery
IEEE Vis 20066 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
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
AnisotropicdiffusionAnisotropicdiffusion
IsotropicdiffusionIsotropicdiffusion
IEEE Vis 20067 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Basic Idea:Reduce tensor field to vector field of major eigenvector
Vector field of main diffusion
Perform streamline propagation
Recostruction - Fiber Tracking
IEEE Vis 20068 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
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
IEEE Vis 20069 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
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
IEEE Vis 200610 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Triangle strips - construction
IEEE Vis 200611 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Triangle strips - texturing
1D texture with luminance and alpha channelTextures for ambient und specular illuminationDecreasing value when approaching the border(sine function)
diffusediffuse specularspecular
1D texture1D texture
channel 1channel 1 channel 2channel 2
IEEE Vis 200612 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Flipping artifacts
Occur when viewing and segment direction are nearly parallelUse point sprites in this case
textured quads, rotated towards cameraresemble cross section of tube
IEEE Vis 200613 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Point Sprites - Texturing
2D-RGB-Texture: draw and illuminate point spritesR channel: alpha channelG / B channel: diffuse / specular illumination
IEEE Vis 200614 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Point Sprites - Rotation
Rotate point sprite according to segment direction:
Project fiber tangent t to image plane tp
Normalize tp tp0
Alpha provides rotation of segment
IEEE Vis 200615 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Point Sprites
When v close to t:Staggered point sprites
Results in natural appearance of a tube
vvPoint Sprites
IEEE Vis 200616 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Visualization – Hybrid approach
Triangle StripsRepresent rectangular cross section
Displayed for v t < 0.98
Point SpritesRepresent circular cross section
Displayed for v t > 0.93
IEEE Vis 200617 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Terminating textured quads
Problem – Beginning and end of each fiber No tube-like appearance
SolutionTerminating textured quads
IEEE Vis 200618 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
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
IEEE Vis 200619 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
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 MBViewport : 600x800 Pixel
IEEE Vis 200620 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Results
Clinical relevance:Combination with Volume Rendering
Realtime visualization improvesinspection of data
Improved analysis of the data
Tumor
IEEE Vis 200622 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Conclusion
Improved visualization forstreamlines based on DT-MRI data
Technical aspectsHybrid approach instead of tubes/lines
Rendering performance ≈ Lines
Visual quality ≈ Tubes
Medical aspectsImproved analysis in real-time
IEEE Vis 200623 Computer Graphics Group + Neurocenter, Dept. of Neurosurgery • University of Erlangen-Nuremberg
Fundings
Graduiertenkolleg „Dreidimensionale Bildanalyse und –synthese“
Deutsche Forschungsgemeinschaft (DFG), SFB 603, Project C9
Thank you!Questions?Thank you!Questions?