DIFFUSION MRI
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Transcript of DIFFUSION MRI
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DIFFUSION MRIPI Dr. Kwan-Jin Jung
TA Priti AlbalDave Frank & Maggie Mahan
12 July 2012
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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
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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
Disclaimer
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Phantom Analysis
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PHANTOM• Model for extra-
cellular restricted diffusion
• Made of interdigitating polyester yarns– 1 leg = 25 bundles– 1 bundle = 8800, 10
mm fibers
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DTI, b800, Direction Comparison6 Directions 50 Directions
All tracts
Center ROI
Bottom left leg ROI
Tracts216Mean FA 0.546
Tracts376Mean FA0.445
Tracts 20Mean FA 0.559
Tracts 58Mean FA 0.556
Tracts72Mean FA0.446
Tracts214Mean FA0.453
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DTI, V50, b-value Comparisonb = 800 s/mm2 b = 2000 s/mm2
All Tracts
Center ROI
Bottom left leg ROI
Tracts376Mean FA0.445
Tracts214Mean FA0.453
Tracts72Mean FA0.446
Tracts458Mean FA0.408
Tracts70Mean FA0.414
Tracts82Mean FA0.430
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DTI, V50, b = 2000 s/mm2 HARDI, V50, b = 2000 s/mm2
DTI/HARDI comparison(ROI placed on center crossing)
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Parallel Orthogonal Parallel OrthogonalTransverse Transverse Coronal Coronal
0100200300400500600700800900
1000
WholeCenterSingle
Num
ber o
f fibe
rs re
solv
edPhantom Orientation
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Phantom Susceptibility
Bo
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Human Analysis
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Motion Correction in Diffusion Imaging
1. Registration of intensity2. Rotation of the diffusion vector
Actually scannedStarting designed vector position
Registrationand vector rotation
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Motion Correction Procedure
1. Acquire diffusion-weighted (DW) images
2. Estimate the diffusion tensor
3. Simulate DW images using tensor
4. Motion detection by comparing the acquired
and simulated DW images
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Global Comparison
No Motion Correction Motion Correction
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Cingulate Comparison
No MC MC
Tracts = 762Mean FA = 0.418
Tracts = 1208Mean FA = 0.493
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fMRI Paradigm• Interested in using dorsolateral prefrontal
cortex as a mask in tracking analysis• DLPFC elicited by memory encoding (cue)
2s
8s
ProbeCue
Rest 18s
Retention
2s
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Group Activation for CueROI: Dorsolateral Prefrontal Cortex
R L
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2 Patterns of ActivationParticipant 2Participant 1
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Crossing Fibers
Participant 2Participant 1
(HARDI, 128 Directions, b2000)
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Crossing Problem
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Ventral-Rostral Fiber Redirection
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Due to Rostral U-Fibers?
U-Fibers?U-Fibers
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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