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 S0S0 SiSi
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
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: gradient directions –Use high b-values: <2000s/mm 2 (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 2 nd 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 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