Symmetry-based analysis of diffusion MRI for the detection of brain impairments

We present a novel computational approach to detect white-matter brain impairments following stroke or Traumatic Brain Injuries (TBI). A key assumption in our study is that the two hemispheres are not affected identically. The pathology of white matter (WM) tracts can be thus identified according to the asymmetry level of brain diffusivity measures, such as Fractional Anisotropy (FA) and Mean Diffusivity (MD), extracted from Diffusion Tensor Imaging (DTI). The proposed methodological contribution is based on the construction of a sequence of isosurfaces of these scalar measures and their symmetrical counterparts, obtained by reflecting the original isosurfaces. The modified Hausdorff distance is then used to measure the dissimilarity between each corresponding pair of aligned surfaces. The proposed method is assessed using datasets of normal controls (NCs), stroke patients and longitudinal brain scans of football players that might have been exposed to mild head traumas. Increased asymmetry with respect to NCs is shown for the stroke patients and some of the players indicating possible WM injuries.