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MR Diffusion Tensor Imaging, Tractography

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@med.cornell.edu , Telephone 212 746-5781. Acknowledgements.

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MR Diffusion Tensor Imaging, Tractography

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  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@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. Outline • Background • Diffusion • Restricted Diffusion and Anisotropy • Methods • Data Acquisition • Display of Diffusion Tensor Data • Fiber Tracking • Problems and Limitations • Examples

  4. Diffusion

  5. Diffusion Equation r = Displacement (mm) D = Diffusion constant (mm2/s) t = Time (mm)

  6. 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

  7. Diffusion Imaging of Leukemia

  8. Diffusion Imaging of Leukemia

  9. Spin Echo

  10. Spin Echo

  11. Spin Echo

  12. 180º 90º RF time  TE Diffusion Gradients g Gx  where Data Acquisition – Spin Echo Echo

  13. Restricted Diffusion

  14. Diffusion Ellipsoid in White Matter

  15. Anisotropy Isotropic: Having the same properties in all directions Anisotropic: Not isotropic; having different properties in different directions Webster’s Dictionary

  16. 180º 90º RF time TE Gx Gy Gz Data Acquisition – Spin Echo Echo Linear combination of gradients - measure component of diffusion in any direction

  17. 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

  18. * Various definitions Calculated Quantities… T2-Weighted Image “Average” Diffusion* Degree of Anisotropy* Diffusion along X Diffusion along Y Diffusion along Z

  19. 1. (Approximately) Isotropic Diffusion How a blob of ink would spread out

  20. 2. Anisotropic Diffusion How a blob of ink would spread out

  21. Vector Plot In-plane Through-plane

  22. Direction of Greatest Diffusion + + + X-component Y-component Z-component Anisotropy Color (Hue) = Direction of highest diffusion Brightness = Degree of anisotropy =

  23. Diffusion Tensor – Colour Map Left-Right Anterior-Posterior Superior-Inferior

  24. DTI – Color Map

  25. Diffusion Tensor – 3D Colour Map Left-Right Anterior-Posterior Superior-Inferior

  26. How Many Measurements?

  27. 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)

  28. Fiber Tracking – Discrete Case Direction of Greatest diffusion

  29. Fiber Tracking – Discrete Case Direction of Greatest diffusion

  30. Fiber Tracking – Continuous Case Direction of Greatest diffusion Mori et al, 1999

  31. Fiber Tracking – Where to Start • Everywhere: Seed points distributed evenly throughout volume

  32. DTI Tractography

  33. Fiber Tracking – Where to Start • Within a plane: All fibers within or crossing a selected plane are tracked

  34. Fiber Tracking – Corpus Callosum

  35. Fiber Tracking – Corpus Callosum

  36. Fiber Tracking – Where to Start • Within a small volume

  37. Fiber Tracking - CST

  38. “Human Neuroanatomy” Carpenter & Sutin 1981 Upper Extremity Trunk Lower Extremity

  39. “Human Neuroanatomy” Carpenter & Sutin 1983 Upper Extremity Trunk Lower Extremity

  40. Fiber Tracking - CST

  41. Fiber Tracking - CST

  42. Combining DTI and fMRI

  43. fMRI – Feet Movement

  44. fMRI – Finger Tapping

  45. fMRI – Tongue Movement

  46. Results – fMRI – Feet, Fingers, Tongue

  47. “Images of Mind”, Posner and Raichie, 1999

  48. Fiber Tracking - CST Subject 1 Subject 2 Subject 3 Subject 4

  49. Cingulum Feet movement Tongue movement Corpus Callosum Longitudinal Fasciculus Corticospinal Tract Crossing Fibers

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