Comparison of 3 Diffusion Models to Track the Hand Motor Fibers within the Corticospinal Tract Using Functional, Anatomical and Diffusion MRI

In this paper, we propose to compare three diffusion models to track the portion of the corticospinal tract dedicated to the hand motor function (called hand motor fibers hereafter), using diffusion, functional and anatomical MRI. The clinical diffusion data have few gradient directions and low b-values. In this context, we show that a newly introduced model, called diffusion directions imaging (DDI) outperforms both the DTI and the ODF models. This new model allows to capture several diffusion directions within a voxel, with only a low number of parameters. Two important results are that i) the DDI model is the only one allowing consistent tracking from the mesencephalon to the most lateral part of the cortical motor hand area, and that ii) the DDI model is the only model able to show that the number of hand motor fibers in the left hemisphere is larger than in the contralateral hemisphere for righthanded subjects; the DDI model, as the other two models, fails to find such a difference for left-handed subjects. To the best of our knowledge, this is the first time such results are reported, at least on clinical data.