Brainmap: Spurious findings due to head motion, and other exciting news for diffusion MRI group studies
Anastasia Yendiki
MGH Martinos Center
I will present results from two lines of work related to our development of tools for the analysis of diffusion MRI (dMRI) data. First, we have recently investigated the effects of head motion on dMRI group studies, using data from children with autism spectrum disorders (ASD) and typically developing (TD) children. We show that, as the differences in head motion between groups increase, so do the differences in dMRI-derived anisotropy and diffusivity measures. The group that moves more tends to have lower fractional anisotropy, higher radial diffusivity, and lower axial diffusivity. We observe similar patterns when we compare groups of TD children only, as we do when we compare groups of ASD vs. TD children. Our results have implications for any dMRI study where one group is less likely to remain still in the scanner than the other.
Second, we have developed a novel framework for reconstructing white-matter pathways from longitudinal dMRI data. The challenge that conventional streamline tractography faces in the presence of degeneration is that, e.g., it may miss part of the pathway in later time points, making side by side comparisons of anisotropy and diffusivity to earlier time points problematic. Our approach is to reconstruct the pathway jointly using a subject's dMRI and T1 data from all time points at once. This method is unbiased, making no assumptions on the direction of longitudinal change. By design, it allows longitudinal analysis of anisotropy and diffusivity measures to be performed as a function of position along the trajectory of a tract. We demonstrate that the proposed approach improves both specificity and sensitivity compared to the conventional approach of performing tractography in each time point independently.
All analyses that I will describe in this talk can be performed with our publicly available tool for automated probabilistic tractography, TRActs Constrained by UnderLying Anatomy (TRACULA).
