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High Angular Diffusion Imaging and its Visualization…

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- Limitations of DTI
- Why HARDI is better?!?
- Different HARDI models
- My ideas and current work

Si

S0

1r1

1r1

2r2

1r2

- DTI: D(g) = D P(r) = Gaussian

~2µm

2 – 3 orders of magnitude difference

1-2mm

DTITool, BMIA group TU/e

?

- 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/mm2 (w.r.t gradient strength and effective time)

= 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

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

PDF = mixture of Gaussians

- Scanning time ~0.5h (and much more!)
- Phantoms like it – people don’t like it!
- Mathematical models:

SH representation of ADC

- Scanning time ~0.5h (and much more!)
- Phantoms like it – people don’t like it!
- Mathematical models:
- m

HOT representation of ADC

- Scanning time ~0.5h (and much more!)
- Phantoms like it – people don’t like it!
- Mathematical models:

[Ozarslan, MRM 2003]

[Tuch, PhD Thesis 2002]

[Liu, MRM 2004 ]

- 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 2nd order tensor is sufficient!
- Segmentation on HARDI data.

- 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

- Use of fMRI activation zones

[INRIA-McGill]

[Hardenbergh, IEEE Vis 2005]

- 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