DIFFUSION MRI PI Dr KwanJin Jung TA Priti

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 – f. MRI paradigm & ROI mask creation – Tracking • Activation patterns • Crossing • Limitations 2

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 3

Phantom Analysis

PHANTOM • Model for extracellular restricted diffusion • Made of interdigitating polyester yarns – 1 leg = 25 bundles – 1 bundle = 8800, 10 mm fibers 5

DTI, b 800, Direction Comparison 6 Directions All tracts Center ROI Bottom left leg ROI Tracts 216 Mean FA 0. 546 Tracts 58 Mean FA 0. 556 Tracts 20 Mean FA 0. 559 50 Directions Tracts 376 Mean FA 0. 445 Tracts 214 Mean FA 0. 453 Tracts 72 Mean FA 0. 446 6

DTI, V 50, b-value Comparison b = 800 s/mm 2 All Tracts Center ROI Bottom left leg ROI Tracts 376 Mean FA 0. 445 b = 2000 s/mm 2 Tracts 458 Mean FA 0. 408 Tracts 214 Mean FA 0. 453 Tracts 70 Mean FA 0. 414 Tracts 72 Mean FA 0. 446 Tracts 82 Mean FA 0. 430 7

DTI/HARDI comparison (ROI placed on center crossing) DTI, V 50, b = 2000 s/mm 2 HARDI, V 50, b = 2000 s/mm 2 8

Number of fibers resolved Phantom Orientation 1000 900 800 700 600 500 400 300 200 100 0 Whole Center Single Parallel Orthogonal Transverse Coronal 9

Phantom Susceptibility Bo 10

Human Analysis

Motion Correction in Diffusion Imaging 1. Registration of intensity 2. Rotation of the diffusion vector Starting designed vector position Actually scanned Registration and vector rotation 12

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 13

Global Comparison No Motion Correction 14

Cingulate Comparison No MC Tracts = 762 Mean FA = 0. 418 MC Tracts = 1208 Mean FA = 0. 493 15

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

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

2 Patterns of Activation Participant 1 Participant 2 18

Crossing Fibers (HARDI, 128 Directions, b 2000) Participant 1 Participant 2 19

Crossing Problem 20

Ventral-Rostral Fiber Redirection 21

Due to Rostral U-Fibers? 22

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 23