diffusion mri tractography - mcgill university · 2010-01-12 · diffusion mri tractography results...
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Diffusion MRI Tractography:Limitations and advanced solutions
January 2010
Jennifer Campbell
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• Introduction• Considerations for optimal tractography• Applications of advanced diffusion processing
Diffusion MRI Tractography:Limitations and advanced solutions
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Diffusion MRI measures Brownian motion of water molecules
Path of diffusing water molecule
Water displacement distribution
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Tissue structures determine which directions of motion are most probable
White matter fibre bundle: oriented
structure
Water molecules prefer to travel parallel to fibre
direction
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Diffusion tensor imaging (DTI)
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diffusion tensor measurement: model the displacement distribution as 3D Gaussian, which can be described by the diffusion tensor, D.
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Fibre tracking using diffusion MRI data
Diffusion MRI data
Water displacement profile
Fibre directions
Fibre tracts
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Tractography
Streamline integration methods:- “fibre assignment using continuous tracking” (FACT)-Euler-RK4
S. Mori et al, AN 45:265-269, 1999
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Tractography
What does tractography tell us?-is A connected to B?-how are A and B connected?-how confident are we in this
connection?
Applications of tractography:-visualization: localization, education-segmentation (both white matter and
grey matter)-investigating clinically differences
between pathways in different populations-neuroanatomical questions
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Tractography
Lateral connections?
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Considerations for optimal tractography
• angular resolution• choice of processing/modeling• spatial resolution• quantification of uncertainty
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Considerations for optimal tractography
• angular resolution• choice of processing/modeling• spatial resolution• quantification of uncertainty
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Diffusion weighted images
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Diffusion weighted signal intensity: high value in directions perpendicular to fibres
Diffusion weighted signal profile
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Probability of water displacement orientation distribution function (ODF)
Diffusion tensor model
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High Angular Resolution Diffusion Imaging (HARDI)
q-ball imaging
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QBI DTI
High Angular Resolution Diffusion Imaging (HARDI)
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Why use high angular resolution diffusion MRI?• Reduce false positive and false negative tractography results due to
crossings• In voxels where fibres cross, single fibre approaches can yield:
– ambiguous fibre direction– incorrect fibre direction– only one fibre direction
(that of fascicle with largest volume fraction) • Examples of such regions:
– basis pontis, subcortical white matter, superior longitudinal fasciculus, acoustic radiations, projection from subgenual white matter to amygdala, optic chiasm, caudate nucleus, corpus callosum, cortical spinal tract, cingulate bundle.
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DTI vs. HARDI :Tractography in phantom
single fibre multi-fibreCampbell et al. ISBI 2006.
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DTI vs. HARDI: tractography in vivo
single fibre tractography
multi fibre tractography
Catani et al. Cortex 2008. Behrens et al. NeuroImage 2007.
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Considerations for optimal tractography
• angular resolution• choice of processing/modeling• spatial resolution• quantification of uncertainty
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Crossing fibre reconstruction approaches
• multi-tensor approaches (Alexander et al., Parker et al., others)
• multi ball and stick (Behrens et al.)
• Composite hindered and restricted model of diffusion (CHARMED) (Assaf et al.)
• diffusion spectrum imaging (DSI) (Wedeen et al.)
• q-ball imaging (QBI) (Tuch et al.)
• spherical deconvolution (Tournier et al., Anderson, others)
• other variants
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Multi-tensor model
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Behrens’ ball and stick model
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Composite hindered and restricted model of diffusion
(CHARMED)
hindered restricted
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Diffusion Spectrum Imaging (DSI)
3D diffusion pdf 2D diffusion ODF
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q-ball Imaging (QBI)
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Crossing fibre detection:QBI vs. Deconvolution
Diffusion ODF Deconvolved ODF
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Crossing fibre reconstruction approaches
• multi-tensor approaches (Alexander et al., Parker et al., others)
• multi ball and stick (Behrens et al.)
• Composite hindered and restricted model of diffusion (CHARMED) (Assaf et al.)
• diffusion spectrum imaging (DSI) (Wedeen et al.)
• q-ball imaging (QBI) (Tuch et al.)
• spherical deconvolution (Tournier et al., Anderson, others)
• other variants
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Inferring higher angular resolution from limited datasets
DTI QBI regularized DTI
Curve Inference using neighbourhood information
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Savadjiev et al. NeuroImage 2008.
Beyond crossing: other complex subvoxel geometries
Curve Inference to distinguish fanning from bending fibres
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Beyond crossing: other complex subvoxel geometries
subvoxel fanning of fibres
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Beyond crossing: other complex subvoxel geometries
tracking without fanning
tracking with fanning
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Considerations for optimal tractography
• angular resolution• choice of processing/modeling• spatial resolution• quantification of uncertainty
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Jumping from tract system to tract system
Effects of limited spatial resolution
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Jumping from tract system to tract system
Effects of limited spatial resolution
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Interpreting results:using priors in tractography
Mori 2001
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Missing information: small volume fractions
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Missing information: small volume fractions
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Missing information: small volume fractions
user-assisted tractography using priors
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Considerations for optimal tractography
• angular resolution• choice of processing/modeling• spatial resolution• quantification of uncertainty
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residual bootstrap statistical technique to estimate uncertainty in fibre directions
Fibre directions and uncertainty
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Fibre directions and uncertainty
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Tractography incorporating uncertainty
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Uncertainty and fanning fibres
no fanning fanning
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Tractography
Lateral connections?
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Tractographydifferent algorithmic approaches to the problem:
“ are A and B connected, and what is our confidence in this connection?”
vs.“A and B are connected. What is our confidence in this connection?”
Jbabdi et al. NeuroImage 2007
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SummaryDiffusion MRI tractography results include many false positives and false negatives: priors are essential.– Tractography is good for segmentation of parts of
pathways, but segmenting the entire pathway can be challenging.
– Characterizing unknown new anatomy is much more difficult than studying known anatomy.
– Tractography does not distinguish between afferent and efferent pathways, or between mono- and multisynapticconnection.
– Diffusion MRI has relatively course resolution: jumping from pathway to pathway is common.
– Tractography gives us a nice way to visualize fibredirectionality in 3D.
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Applications: studies using crossing fibre approaches
• basic neuroanatomy• nonhuman primates• structure and function• understanding disease• understanding therapies
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Applications: basic neuroanatomy
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Applications: tractography in regions of crossing fibres
fibre crossings in regions of partial volume averaging of pathways, e.g., SLF - CC - CST
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Applications: tractography in regions of crossing fibres
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Applications: basic neuroanatomy
Frey et al. J.NSci 2008.
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Applications – nonhuman primates
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Applications – nonhuman primates
Schmamann et al. Brain 2007.
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Applications: structure and function
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Applications: structure and function
Powell et al. NeuroImage 2006.
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Applications: structure and function
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Applications: structure and function
Boorman et al. Curr. Biol. 2007.
paired pulse transcranialmagnetic stimulation
correlate modulation of motor evoked potentials (MEPs) with fractional anisotropy (FA)
seed tractography in correlated regions
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Applications: clinical research
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Applications: clinical research
Yogarajah et al. NeuroImage 2008.
Findings:
increased left intratract FA in L TLE
22% reduction in left tract volume in L TLE
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Applications: understanding therapies
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Gutman et al. Biol. Psych. 2009
Applications: understanding therapies
tractography seeded at sites used for deep brain stimulation
overlap in tractography maps corresponds to areas involved in depression
furthers our understanding of why this therapy is effective
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Acknowledgements
G. Bruce PikeKaleem SiddiqiIlana LeppertPeter SavadjievParya Mamayyez SiahkalSteve FreyVladimir Rymar
Ives LevesqueJean ChenMike FerreiraChristine TardifClarisse MarkIleana Jelescu