high angular diffusion imaging and its visualization…
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High Angular Diffusion Imaging and its Visualization…
• Limitations of DTI
• Why HARDI is better?!?
• Different HARDI models
• My ideas and current work
Underlying philosophy in DTI
S0
Si
From probability to diffusivity
• DTI: D(g) = D P(r) = Gaussian
~2µm
2 –
3 o
rders
of
mag
nit
ud
e
diff
ere
nce
1-2mm
1r1
2r2
1r1
1r2
Application - DTI
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)
Different approaches
= HARDI
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
Reality check…
• Long (more complicated) acquisition scheme
• Popular for phantom data and simulations
• Tricky mathematical models• Non-intuitive visualization
Reality check…
• Scanning time ~0.5h (and much more!)• Phantoms like it – people don’t like it!• Mathematical models:
PDF = mixture of Gaussians
Reality check…
• Scanning time ~0.5h (and much more!)• Phantoms like it – people don’t like it!• Mathematical models:• m
SH representation of ADC
Reality check…
• Scanning time ~0.5h (and much more!)• Phantoms like it – people don’t like it!• Mathematical models:
HOT representation of ADC
…and of course Visualization issues
[Tuch, PhD Thesis 2002]
[Ozarslan, MRM 2003]
[Liu, MRM 2004 ]
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 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 zonesas seeding regions for whitematter tractography
My current work, ideas, struggles…
[Hardenbergh, IEEE Vis 2005]
[INRIA-McGill]
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
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