1. High Angular Diffusion Imaging and its Visualization… Limitations of DTI Why HARDI is better?!? Different HARDI models My ideas and current work

2. Underlying philosophy in DTI S0S0 SiSi

3. From probability to diffusivity DTI: D(g) = D P(r) = Gaussian ~2µm 2 – 3 orders of magnitude difference 1-2mm 1 r 1 2 r 2 1 r 1 1 r 2

4. Application - DTI DTITool, BMIA group TU/e

5. What if… –Measure > 6(20) gradient directions –Give more time to the molecules to do their job What if… –Measure: 200-300 gradient directions –Use high b-values: <2000s/mm 2 (w.r.t gradient strength and effective time) Different approaches = HARDI

6. HARDI Many different approaches –DSI, q-ball –High-order tensor models w.r.t. ADC –SH representation –PAS-MRI –Multi-compartment models etc.. All in common: avoid Gaussian model fitting

7. Reality check… Long (more complicated) acquisition scheme Popular for phantom data and simulations Tricky mathematical models Non-intuitive visualization

8. Reality check… Scanning time ~0.5h (and much more!) Phantoms like it – people don’t like it! Mathematical models: PDF = mixture of Gaussians

9. Reality check… Scanning time ~0.5h (and much more!) Phantoms like it – people don’t like it! Mathematical models: m SH representation of ADC

10. Reality check… Scanning time ~0.5h (and much more!) Phantoms like it – people don’t like it! Mathematical models: HOT representation of ADC

11. …and of course Visualization issues [Tuch, PhD Thesis 2002] [Ozarslan, MRM 2003] [Liu, MRM 2004 ]

12. My current work, ideas, struggles… Comparing most promising methods (w.r.t. feasibility on vivo data) and improve it –DOT and q-ball Answer the mysterious 42 question: “How high should be the “high” b-value?” DTI is not dead! Combining with HARDI. Define measure where 2 nd order tensor is sufficient! Segmentation on HARDI data.

13. More intuitive HARDI visualization => doctors don’t like glyphs Fiber tracking on HARDI Combining different modalities –Use of fMRI activation zones as seeding regions for white matter tractography My current work, ideas, struggles… [Hardenbergh, IEEE Vis 2005] [INRIA-McGill]

14. Multi-fieldity in HARDI Multiple measurements over same domain High-dimensional data High-order mathematical models (HOT and SH) Combining HARDI+fMRI =>Jorik Sufficient order w.r.t. encapsulated information => Stef