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DIFFUSION MRI

DIFFUSION MRI. PI Dr. Kwan-Jin Jung TA Priti Albal Dave Frank & Maggie Mahan 12 July 2012. Outline. Phantom Analysis Orientation Direction b-value Tensor vs HARDI models Human Analysis Motion correction in DWI fMRI paradigm & ROI mask creation Tracking Activation patterns

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DIFFUSION MRI

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  1. DIFFUSION MRI PI Dr. Kwan-Jin Jung TA PritiAlbal Dave Frank & Maggie Mahan 12 July 2012

  2. Outline • Phantom Analysis • Orientation • Direction • b-value • Tensor vs HARDI models • Human Analysis • Motion correction in DWI • fMRI paradigm & ROI mask creation • Tracking • Activation patterns • Crossing • Limitations

  3. Disclaimer During this presentation we will use the words “tracts” and “fibers” These refer to the trace of the principal diffusion directions We do not presume to know the physiological constructs these may or may not reflect

  4. Phantom Analysis

  5. PHANTOM • Model for extra-cellular restricted diffusion • Made of interdigitating polyester yarns • 1 leg = 25 bundles • 1 bundle = 8800, 10 mm fibers

  6. DTI, b800, Direction Comparison Tracts 216 Mean FA 0.546 Tracts 376 Mean FA 0.445 All tracts Center ROI Bottom left leg ROI 6 Directions 50 Directions Tracts 58 Mean FA 0.556 Tracts 214 Mean FA 0.453 Tracts 72 Mean FA 0.446 Tracts 20 Mean FA 0.559

  7. DTI, V50, b-value Comparison Tracts 376 Mean FA 0.445 Tracts 458 Mean FA 0.408 All Tracts Center ROI Bottom left leg ROI b = 800 s/mm2 b = 2000 s/mm2 Tracts 70 Mean FA 0.414 Tracts 214 Mean FA 0.453 Tracts 72 Mean FA 0.446 Tracts 82 Mean FA 0.430

  8. DTI/HARDI comparison (ROI placed on center crossing) DTI, V50, b = 2000 s/mm2 HARDI, V50, b = 2000 s/mm2

  9. Phantom Orientation

  10. Phantom Susceptibility Bo

  11. Human Analysis

  12. Motion Correction in Diffusion Imaging • Registration of intensity • Rotation of the diffusion vector Actually scanned Registration and vector rotation Starting designed vector position

  13. Motion Correction Procedure • Acquire diffusion-weighted (DW) images • Estimate the diffusion tensor • Simulate DW images using tensor • Motion detection by comparing the acquired and simulated DW images

  14. Global Comparison No Motion Correction Motion Correction

  15. Cingulate Comparison No MC MC Tracts = 1208 Mean FA = 0.493 Tracts = 762 Mean FA = 0.418

  16. fMRI Paradigm • Interested in using dorsolateral prefrontal cortex as a mask in tracking analysis • DLPFC elicited by memory encoding (cue) Rest 18s Retention 8s Cue 2s Probe 2s

  17. Group Activation for Cue ROI: Dorsolateral Prefrontal Cortex R L

  18. 2 Patterns of Activation Participant 2 Participant 1

  19. Crossing Fibers (HARDI, 128 Directions, b2000) Participant 2 Participant 1

  20. Crossing Problem

  21. Ventral-Rostral Fiber Redirection

  22. Due to Rostral U-Fibers? U-Fibers? U-Fibers

  23. Take Home Messages • Diffusion imaging dependent on: • ROI, b-value, # of directions, & orientation • Diffusion imaging particularly susceptible to subject motion • Subject comparisons in diffusion imaging not trivial • Tracking is a useful exploratory technique

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