DTI SubprojectProcessing & Analysis

Norbert SchuffVA Medical Center & University of

C lif i S iCalifornia, San Francisco

ObjectivesObjectives

D t i if DTI • Determine if DTI can:– provide a robust marker of PD progression

serve as an adjunct to clinical assessment and – serve as an adjunct to clinical assessment and PET

Scope Of WorkScope Of Work• DTI computations:

– Rigorous quality control g q y– Accurate alignment to structural MRI– Calculation of:

• standard DTI measures (FA, MD)standard DTI measures (FA, MD)• advanced DTI measures (geodesic FA, generalized

FA)• eigenvectors (tractography)g ( g p y)

• Exploratory Group Analyses – Region-of-interest basedRegion of interest based– Regionally unbiased– Joint analyses of DTI with PET

MRI AcquisitionsMRI Acquisitions

T1ww “Proton density”     T2wStructuralMRI

Bow Diffusion weightedDTI Bow Diffusion weightedDTI

Automated Quality ControlFrame-to-Frame Similarity

Good Quality Motion Instability

ection

s  Brain Signal

Slices

Diffusion Dire

Slices 

Noise

DTI Quality Control: First 8 ScansDTI Quality Control: First 8 Scans

50

Baylor Northwestern JohnH

30

40

SNR

DW

I

3102 3105 3301 3556 3102 3105 3301 3556 3102 3105 3301 3556

Subject ID

20

Baylor Northwestern JohnH

8

10

12

oise

Sim

ilari

ty

3102 3105 3301 3556 3102 3105 3301 3556 3102 3105 3301 3556

4

6

Whi

te N

o

3102 3105 3301 3556 3102 3105 3301 3556 3102 3105 3301 3556

Subject ID

DTI-MRI Co-registrationDTI MRI Co registrationRigid alignment Raw DWI

Nonlinear alignment(in collaboration with Dr. Tom Fletcher, U Utah)

DTI InterpretationDTI Interpretation

High Sensitivity – Low Specificity DTI Intensity Electron MicrographsHigh Sensitivity – Low Specificity  y g p

Axon Model & DTI Components

Summary:1. Mean displacement distance of tissue 

water that is capture on DTI  using a 

(A) Non myelinated olfactory nerve of the garfish

clinical MRI scanner   ~ 10‐20 um 

2. Structural features of axons other than myelin are sufficient to give rise to DTI contrast

(A) Non‐myelinated olfactory nerve of the garfish(B) Myelinated optic nerve of the garfish

C. Beaulieu, NMR in Biomedicine 2002; 15; 435‐55

DTI ComputationsDTI ComputationssMRI Fractional Anisotropy Kullbeck‐Leibler

Anisotropy

SummarySummary• Accomplishments

MRI sites were qualified– MRI sites were qualified– DTI of first 8 subjects QC’ed– MRI quality is generally very good– Standard and advanced DTI measures implemented

What needs to be done• What needs to be done– Format for uploading derived data to LONI– Processing of DTI as data arriveg– Interim group analyses (n=20 per group?)