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