Maxime Descoteaux¹, Jasmeen Sidhu¹, Eleftherios Garyfallidis¹, Jean-Christophe Houde¹, Peter Neher², Bram Stieltjes³, and Klaus H. Maier-Hein^2
1Computer Science, Université de Sherbrooke, Sherbrooke, QC, Canada, ²German Cancer Research Center, Heindeberg, Germany, ³Basel University, Basel University Hospital, Switzerland

This work provides novel insights in false positive bundles produced by tractography using a highly realistic diffusion MRI phantom with known underlying white matter ground truth anatomy. This MRI phantom was used in the ISMRM 2015 Tractography Challenge. We show that regardless of the tractography pipeline used, many invalid bundles with dense and meaningful structures are found in the tractograms.

Chantal Tax^1,2, Tom Dela Haije³, Andrea Fuster³, Carl-Fredrik Westin², Max A. Viergever¹, Luc Florack³, and Alexander Leemans^1
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands, ²Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, ³Mathematics and Computer Science, Eindhoven University of Technology, Eindhoven, Netherlands

The prevalence of sheet structure in the brain has been a debated issue since its proposal. This structure can be analyzed by means of the Lie bracket, which can be derived from diffusion MRI (dMRI) data. Due to the occurrence of noise, however, it is difficult to quantify to what degree the local structure effectively resembles a sheet. In this work, we propose a new and robust local measure based on the Lie bracket that can be interpreted as the sheet probability index (SPI).

Aurobrata Ghosh¹, Daniel C Alexander¹, and Hui Zhang^1
1Centre for Medical Image Computing, University College London, London, United Kingdom

We conduct model comparison experiments on the widely available HCP dataset to assess the importance of fibre-dispersion when modelling the brain’s tissue-microstructure from diffusion MRI (dMRI). Although many fibre dispersion configurations have been identified in the brain, most dMRI methods only model parallel or crossing fibres. To highlight the importance of dispersion, we design k-fold cross-validation experiments, on two HCP subjects, and compare ten compartment-based models using three metrics. We find that up to 50% of the brain-voxels, including white matter regions, support dispersion models over crossing models. Hence we conclude that it is important to model dispersion in dMRI.

Ørjan Bergmann^1,2, Carl-Fredrik Westin¹, and Ofer Pasternak^1
1Dept of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, ²Norwegian Competency Center for MS, Haukeland University Hospital, Bergen, Norway

In this work we explore the solution space of the two-compartment free-water problem under different noise levels. Based on the shape of the solution space we show that solving this model in an intuitive and straightforward manner may result in solutions which are sensitive to noise, and that are biased towards neglecting the free-water component. Although multi-shell techniques improve the situation we show that more advanced methods are required to further stabilize the solution.

Ileana O Jelescu¹, Magdalena Zurek¹, Kerryanne V Winters¹, Jelle Veraart¹, Anjali Rajaratnam¹, Nathanael S Kim¹, James S Babb¹, Timothy M Shepherd¹, Dmitry S Novikov¹, Sungheon G Kim¹, and Els Fieremans^1
1Center for Biomedical Imaging, Radiology, New York University School of Medicine, New York, NY, United States

White Matter Tract Integrity (WMTI) metrics derived from diffusion data provide a compartment-specific characterization of white matter. Here, we evaluated the specificity of the axonal water fraction (AWF) and extra-axonal radial diffusivity (D_e,-) by assessing their correlations to metrics derived from electron microscopy (EM), in the splenium of control, cuprizone-treated and recovering mice. As the model predicted, the WMTI-derived AWF correlated very strongly with the EM-derived AWF, but not with the g-ratio, while D_e,- correlated with the g-ratio, but not with the EM-derived AWF. WMTI parameters are therefore promising biomarkers for specific biophysical aspects of white matter pathology in vivo.

Jeroen Mollink^1,2, Michiel Kleinnijenhuis¹, Stamatios N Sotiropoulos¹, Michiel Cottaar¹, Anne-Marie van Cappellen van Walsum², Menuka Pallebage Gamarallage³, Olaf Ansorge³, Saad Jbabdi¹, and Karla L Miller^1
1FMRIB centre, University of Oxford, Oxford, United Kingdom, ²Donders Institute for Brain, Cognition and Behaviour, Department of Anatomy, Radboud University Medical Centre, Nijmegen, Netherlands,³Department of Neuropathology, University of Oxford, Oxford, United Kingdom

In this study we explored fibre orientation dispersion in the corpus callosum using diffusion-weighted MRI, Polarized Light Imaging and Histology. Microscopic fibre orientations were derived from Polarized Light Imaging and histological myelin and glial cell staining, with the aim of understanding the microstructural features that correlate with the diffusion signal.