Introduction:Diffusion Tensor Imaging (DTI) is adiffusion-weighted imaging (DWI) techniquethat allows for the measurement of the rateand direction of water diffusion. DTIreconstruction leads to various applicationssuch as fractional anisotropy (FA) maps andfiber tractography to be used as quantifiablebiomarkers in White Matter (WM)degradation. DTI requires a minimum of sixdiffusion-encoding gradient directions toestimate diffusion tensors through eachvoxel. Contention has been over how manydirections are required to provide quality FAmapping and WM fiber tracking. This studylooks to validate claims that 32 and evenonly 6 directions are sufficient parametersfor successful DTI, FA, and fiber tractdetection.

DSI Studios deterministic fiber tracking algorithm track total WM fibers between ROIs as well as whole

brain WM seeding

Means FA values for each ROI taken

Outline regions of interest (ROIs): Corona Radiata, Genu and Body of Corpus Callosum, Cingulum (JHU ICBM-DTI-81 White-Matter Labels atlas)

TOPUP and EDDY preprocessing (FSL, FMRIB). DTI reconstruction (DSI Studio, Yeh et al.)

T2 MRI scan on 3.0 T Siemens scanner taking one b=0s/mm2 and 64 directional b=1000s/mm2

Two healthy subjects, mean age 26

Acknowledgments:This work was greatly supported by the University of Hawaii MRI Research Center and The Queen’s Medical Center’s Summer Research Internship with special thanks to Christoph Rettenmeir Ph.D., Todd Seto M.D., Lori Tsue, and Sherry Chan.

Conclusions:

Validation of the Impact of Increased Gradient Directions on Diffusion Tensor Imaging for White Matter Fiber Separation and Fractional Anisotropy Mapping

Matthew Alexander1,2, Danillo Maziero D.Sc.3, Andrew Stenger Ph.D.31. Brown University; 2. The Queen’s Medical Center; 3. University of Hawaii at Manoa

Literature cited:

Contacts:Please email matthew_alexander@brown.edu.

Fig. 1: Left: acquired A-P direction. Middle: acquired P-A direction. Right: TOPUP and EDDY corrected

Fig. 2: From left to right, 6, 32, and 64 gradient directions.

Results:

Fig. 3: From left to right, 6, 32, and 64 gradient directions

0.35

0.4

0.45

0.5

0.55

0.6

0 10 20 30 40 50 60 70MeanFA

#DirectionGradients

Subject1GenuCorpusCallosum

BodyCorpusCallosum

AnteriorCoronaRadiataR

AnteriorCoronaRadiataL

SuperiorCoronaRadiataR

SuperiorCoronaRadiataL

PosteriorCoronaRadiataR

PosteriorCoronaRadiataL

CingulumR

CingulumL

30000

33500

37000

40500

44000

47500

51000

0 10 20 30 40 50 60 70

#Tracts

#DirectionGradient

NumberofTractsoverWholeBrainWMvs.NumberofDirectionGradients

WholeBrainTractsSubject1

WholeBrainTractsSubject2 0.35

0.4

0.45

0.5

0.55

0.6

0.65

0 10 20 30 40 50 60 70

MeanFA

#DirectionGradients

Subject2

GenuCorpusCallosum

BodyCorpusCallosum

AnteriorCoronoaRadiataR

AnteriorCoronoaRadiataL

SuperiorCoronoaRadiataR

SuperiorCoronoaRadiataL

PosteriorCoronoaRadiataR

PosteriorCoronoaRadiataL

CingulumR

CingulumL

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70

#Tracts

#DirectionGradients

Subject1

L/RAnteriorCoronaRadiata

L/RSuperiorCoronaRadiata

L/RPosteriorCoronaRadiata

Genu/BodyCorpusCallosum

L/RCingulum

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70

#Tracts

#DirectionGradients

Subject2

L/RAnteriorCoronaRadiata

L/RSuperiorCoronaRadiata

L/RPosteriorCoronaRadiata

Genu/BodyCorpusCallosum

L/RCingulum

Qualitatively:-TOPUP and EDDY preprocessing improves T2 MRIs for DWI-Initial results strongly suggest FA mapping and WM fiber tractography rendering was impaired at 6 direction gradients but relatively unaffected at 32 directions.Quantitatively:-WM fiber tracts were significantly decreased at 6 direction gradients but plateaued at 32 directions for both whole brain and inter-ROI tracking.-Mean FA increases at 64 direction gradients although further analysis with increased subjects needs to be completed for statistically significant results.

Materials and Methods:

C. Lebel, T. Benner, C. Beaulieu Six is enough? Comparison of diffusion parameters measured using six or more diffusion-encoding gradient directions with deterministic tractography. Magn. Reson. Med., 68 (2) (2012), pp. 474-483

M. Jenkinson, C.F. Beckmann, T.E. Behrens, M.W. Woolrich, S.M. Smith. FSL. NeuroImage, 62:782-90, 2012

Yeh, Fang-Cheng, et al. "Deterministic diffusion fiber tracking improved by quantitative anisotropy." (2013): e80713. PLoS ONE 8(11): e80713. doi:10.1371/journal.pone.0080713

T2 DWIs~

DTI FA Maps~

Whole Brain WM Tractography~

Fig. 5: Total tracts between ROIs as a function of diffusion gradient directions

Fig. 4: Subjects 1 and 2’s total whole brain WM tracts as a function of diffusion gradient directions

Fig. 6: ROIs Mean FAs as a function of diffusion gradient directions