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MR Diffusion Tensor Imaging, Tractography

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BJ Casey, Matt Davidson, Katie Thomas. Outline. Background. Diffusion ... D.J. Werring, C.A. Clark, G.J.M. Parker, D.H. Miller, A.J. Thompson, G.J. Barker ... – PowerPoint PPT presentation

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Title: MR Diffusion Tensor Imaging, Tractography


1
MR Diffusion Tensor Imaging, Tractography
  • Richard Watts, D.Phil.
  • Citigroup Biomedical Imaging Center
  • Weill Medical College of Cornell University
  • Box 234, 1300 York Avenue, New York, NY 10021
  • Email riw2004_at_med.cornell.edu, Telephone 212
    746-5781

2
Acknowledgements
  • Weill Medical College of Cornell University
  • Department of Radiology
  • Aziz Ulug, Linda Heier.
  • Citigroup Biomedical Imaging Center
  • Doug Ballon, Jon Dyke, Katherine Kolbert.
  • Sackler Institute
  • BJ Casey, Matt Davidson, Katie Thomas.

3
(No Transcript)
4
Outline
  • Background
  • Diffusion
  • Restricted Diffusion and Anisotropy
  • Methods
  • Data Acquisition
  • Display of Diffusion Tensor Data
  • Fiber Tracking
  • Problems and Limitations
  • Examples

5
Diffusion
6
Diffusion Equation
r Displacement (mm) D Diffusion
constant (mm2/s) t Time (mm)
7
Distance Scales
Question What distance do protons travel during
an EPI readout time?
Assume Diffusion constant 10-3 mm2/s Time
100 ms 0.1s
The root mean square (RMS) distance is 0.02mm
20µm
Such an experiment is sensitive to changes in
diffusion caused by structures on this scale or
smaller
8
Diffusion Imaging of Leukemia
9
Diffusion Imaging of Leukemia
10
Spin Echo
11
Spin Echo
12
Spin Echo
13
Data Acquisition Spin Echo
Echo
14
Restricted Diffusion
15
Diffusion Ellipsoid in White Matter
16
Anisotropy
Isotropic Having the same properties in all
directions
Anisotropic Not isotropic having different
properties in different directions
Websters Dictionary
17
Data Acquisition Spin Echo
Echo
Linear combination of gradients - measure
component of diffusion in any direction
18
Diffusion Tensor Imaging
  • Tensor is a mathematical model of the directional
    anisotropy of diffusion
  • Represented by a 3x3 symmetric matrix ? 6 degrees
    of freedom
  • Fit experimental data to the tensor model
  • From the tensor, we can calculate
  • Direction of greatest diffusion
  • Degree of anisotropy
  • Diffusion constant in any direction

19
Calculated Quantities
Various definitions
T2-Weighted Image
Average Diffusion
Degree of Anisotropy
Diffusion along X
Diffusion along Y
Diffusion along Z
20
1. (Approximately) Isotropic Diffusion
How a blob of ink would spread out
21
2. Anisotropic Diffusion
How a blob of ink would spread out
22
Vector Plot
In-plane
Through-plane
23
Direction of Greatest Diffusion



X-component
Y-component
Z-component
Anisotropy
Color (Hue) Direction of highest
diffusion Brightness Degree of anisotropy

24
Diffusion Tensor Colour Map
Left-Right
Anterior-Posterior
Superior-Inferior
25
DTI Color Map
26
Diffusion Tensor 3D Colour Map
Left-Right
Anterior-Posterior
Superior-Inferior
27
How Many Measurements?
28
Which Directions?
Isotropic resolution diffusion tensor imaging
with whole brain acquisition in a clinically
acceptable time D.K. Jones, S.C.R. Williams, D.
Gasston, M.A. Horsfield, A. Simmons, R.
Howard Human Brain Mapping 15, 216-230 (2002)
29
Fiber Tracking Discrete Case
Direction of Greatest diffusion
30
Fiber Tracking Discrete Case
Direction of Greatest diffusion
31
Fiber Tracking Continuous Case
Direction of Greatest diffusion
Mori et al, 1999
32
Fiber Tracking Where to Start
  • Everywhere Seed points distributed evenly
    throughout volume

33
DTI Tractography
34
Fiber Tracking Where to Start
  • Within a plane All fibers within or crossing a
    selected plane are tracked

35
Fiber Tracking Corpus Callosum
36
Fiber Tracking Corpus Callosum
37
Fiber Tracking Where to Start
  • Within a small volume

38
Fiber Tracking - CST
39
Human Neuroanatomy Carpenter Sutin 1981
Upper Extremity
Trunk
Lower Extremity
40
Human Neuroanatomy Carpenter Sutin 1983
Upper Extremity
Trunk
Lower Extremity
41
Fiber Tracking - CST
42
Fiber Tracking - CST
43
Combining DTI and fMRI
44
fMRI Feet Movement
45
fMRI Finger Tapping
46
fMRI Tongue Movement
47
Results fMRI Feet, Fingers, Tongue
48
Images of Mind, Posner and Raichie, 1999
49
Fiber Tracking - CST
Subject 1
Subject 2
Subject 3
Subject 4
50
Crossing Fibers
51
DTI Tracking below SLF
Tongue
Feet
Fingers
Upper
Trunk
Lower
52
DTI Tractography Clinical Example
53
DTI Tractography Clinical Example
54
Limitations of DTI/Fiber Tracking
  • Partial volume
  • A single voxel may contain fibers running in
    multiple directions average anisotropy measured
  • Tensor may not be a good representation
  • Need to distinguish kissing and crossing

55
More Pretty Pictures
  • Isotropic resolution diffusion tensor imaging
    with whole brain acquisition in a clinically
    acceptable time
  • D.K. Jones, S.C.R. Williams, D. Gasston, M.A.
    Horsfield, A. Simmons, R. Howard
  • Human Brain Mapping 15, 216-230 (2002)

56
Conclusions, the Future
  • DTI provides the only non-invasive method to
    study organization white matter fibers. Previous
    studies have been limited to animal models and
    stroke patients
  • Current limitations on DTI and Fiber Tracking
  • Partial volume effects
  • SNR
  • Acquisition time/physiological noise
  • Advances
  • High field, faster gradients, more efficient
    coils, motion detection/correction, new pulse
    sequences (eg. 3D, spiral)
  • Higher SNR can be traded for smaller voxels,
    reducing partial volume effects
  • Beyond the tensor model HARD imaging, q-space
    imaging
  • New tracking algorithms

57
DTI Tracking below SLF
58
DTI Tracking below SLF
59
References
  • High-resolution isotropic 3D diffusion tensor
    imaging of the human brain.
  • X. Golay, H. Jiang, P.C.M. van Zijl, S. Mori
  • Magn. Res. Med. 47, 837-843 (2002)
  • White matter mapping using diffusion tensor MRI
  • C.R. Tench, P.S. Morgan, M. Wilson, L.D.
    Blumhardt
  • Magn. Res. Med. 47, 967-972 (2002)
  • Three-dimensional tracking of axonal projections
    in the brain by magnetic resonance imaging
  • S. Mori, B.J. Creain, V.P. Chacko, P.C.M. van
    Zijl
  • Ann. Neurol. 45, 265-269 (1999)
  • Diffusion tensor imaging Concepts and
    applications
  • D. Le Bihan et al
  • J. Magn. Res. Imaging 13, 534-546 (2001)
  • In vivo three dimensional reconstruction of rat
    brain axonal projections by diffusion tensor
    imaging
  • R. Xue, P.C.M. van Zijl, B.J. Cain, M.
    Solaiyappan, S.Mori
  • Magn. Res. Med. 42 1123-1127 (1999)
  • A direct demonstration of both structure and
    function in the visual system combining
    diffusion tensor imaging with functional magnetic
    resonance imaging
  • D.J. Werring, C.A. Clark, G.J.M. Parker, D.H.
    Miller, A.J. Thompson, G.J. Barker
  • NeuroImage 9, 352-361 (1999)
  • Orientation-independent diffusion imaging without
    tensor diagonalization anisotropy definitions
    based on the physical attributes of the diffusion
    ellipsoid

60
References
  • Imaging cortical association tracts in the human
    brain using diffusion-tensor based axonal
    tracking
  • S. Mori et al
  • Magn. Res. Med. 47, 215-223 (2002)
  • Isotropic resolution diffusion tensor imaging
    with whole brain acquisition in a clinically
    acceptable time
  • D.K. Jones, S.C.R. Williams, D. Gasston, M.A.
    Horsfield, A. Simmons, R. Howard
  • Human Brain Mapping 15, 216-230 (2002)
  • Diffusion tensor imaging and axonal tracking in
    the human brainstem
  • B. Stietjes et al
  • NeuroImage 14 723-735 (2001)
  • Tracking neuronal fiber pathways in the living
    human brain
  • T.E. Conturo et al
  • Proc. Natl. Acad. Sci. 96 10422-10427 (1999)
  • The future for diffusion tensor imaging in
    neuropsychiatry
  • K.H. Taber et al
  • J. Neuropsychiatry Clin. Neurosci. 14 1-5 (2002)
  • Tensorlines Advection-diffusion based
    propogation through diffusion tensor fields
  • D. Weinstein, G. Kindlmann, E. Lundberg

61
The Diffusion Tensor
where
Identical if
62
How Many Measurements?
7 degrees of freedom S0, Dxx, Dyy, Dzz, Dxy,
Dxz, Dyz
Need at least 7 directions but more is
better! 30 slices x 32 directions 960 images
63
Corresponding Tensor
mm2/s
64
Eigenvalues and Eigenvectors of the Diffusion
Tensor
65
Corresponding Tensor
mm2/s
66
Eigenvalues and Eigenvectors of the Diffusion
Tensor
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