Robbert Leonard Harms^{1,2}, Rainer Goebel^{1,2}, and Alard Roebroeck^{1}

Using high resolution HCP WU-Minn data and GPU accelerated software (MDT; https://github.com/cbclab), the aims of this study were to evaluate dMRI microstructure indices over white matter tracts, evaluate the effect sizes between tracts as an upper limit for effect size of diffusion microstructure indices between subjects and finally the influence of possible confounds on those other aims. We report sizeable effects between tracts within subjects for several indices. Also, two clear confounds for diffusion microstructure studies where identified, first, partial volume effects in small and large cross-section tracts, second, model selection on the number of intra-axonal model compartments.

1. Van Essen DC, Smith SM, Barch DM, Behrens TEJ, Yacoub E, Ugurbil K. The WU-Minn Human Connectome Project: An overview. Neuroimage. 2013;80(44):62-79. doi:10.1016/j.neuroimage.2013.05.041.

2. Assaf Y, Basser PJ. Composite hindered and restricted model of diffusion (CHARMED) MR imaging of the human brain. Neuroimage. 2005;27(1):48-58. doi:10.1016/j.neuroimage.2005.03.042.

3. Zhang H, Schneider T, Wheeler-Kingshott CA, Alexander DC. NODDI: Practical in vivo neurite orientation dispersion and density imaging of the human brain. Neuroimage. 2012;61(4):1000-1016. doi:10.1016/j.neuroimage.2012.03.072.

4. Panagiotaki E, Schneider T, Siow B, Hall MG, Lythgoe MF, Alexander DC. Compartment models of the diffusion MR signal in brain white matter: A taxonomy and comparison. Neuroimage. 2012;59(3):2241-2254. doi:10.1016/j.neuroimage.2011.09.081.

5. Harms R, Roebroeck A. The Maastricht Diffusion Toolbox (MDT): Modular, GPU accelerated, dMRI microstructure modeling. submitted to ISMRM 2017. Honolulu; 2017.

6. Basser PJ, Mattiello J, LeBihan D. MR diffusion tensor spectroscopy and imaging. Biophys J. 1994;66(1):259-267. doi:10.1016/S0006-3495(94)80775-1.

7. Behrens TEJ, Woolrich MW, Jenkinson M, et al. Characterization and Propagation of Uncertainty in Diffusion-Weighted MR Imaging. Magn Reson Med. 2003;50(5):1077-1088. doi:10.1002/mrm.10609.

8. Smith SM, Jenkinson M, Johansen-Berg H, et al. Tract-based spatial statistics: Voxelwise analysis of multi-subject diffusion data. Neuroimage. 2006;31(4):1487-1505. doi:10.1016/j.neuroimage.2006.02.024.

9. Mori S, Wakana S, Zijl PCM van, Nagae-Poetscher LM. MRI Atlas of Human White Matter.; 2005. 10. Cohen J. Statistical Power Analysis for the Behavioral Sciences. Routledge; 2 edition (July 1, 1988); 1988.

Sagittal slice through the
genu, body and splenium of the corpus callosum for various parameter
maps. Top row, total Stick fraction for Ball&Stick model with
respectively 1, 2 and 3 Sticks, middle row total restricted fraction
for the CHARMED model with respectively 1, 2 and 3 restricted
compartments, bottom row, respectively Tensor Fraction Anisotropy,
NODDI Restricted Fraction (1 – v_iso * v_ic, when using the
original NODDI notation) the atlas regions of the white matter atlas
regions on the TBSS skeleton.

Histograms over all TBSS atlas skeleton ROI's of the mean tract
values over 490 subjects per parameter map. Parameter maps are laid
out identical to Figure 1. The colored dots above the bars indicate
the position of the six tracts (legend in the bottom right) most
often present among extreme values.

Histograms of the
distribution of the (absolute valued) effect size (Cohen's d)
calculated over 490 subjects between all pairs of white matter tracts
in the skeleton atlas, one histogram per parameter map. All
histograms are clipped between [0, 10]. The colored dots above the
bars indicate the position of six pairs of tracts (legend in the
bottom right).