High resolution and high field diffusion MRI in the visual system of primates

Objective: Establishing a primate multiscale genetic brain network linking key microstructural brain components to social behavior remains an elusive goal. Background: Diffusion MRI, which quantifies the magnitude and anisotropy of water diffusion in brain tissues, offers unparalleled opportunity to link the macroconnectome (resolution of ~0.5mm) to histological-based microconnectome at synaptic resolution. Design/Methods: We tested the hypothesis that the simplest (and most clinically-used) reconstruction technique (known as diffusion tensor imaging, DTI) will yield similar brain connectivity patterns in the visual system (from optic chiasm to visual cortex) compared to more sophisticated and accurate reconstruction methods including diffusion spectrum imaging (DSI), q-ball imaging (QBI), and generalized q-sampling imaging. We obtained high resolution diffusion MRI data on ex vivo brain from Macaca fascicularis: MRI 7T, resolution 0.5 mm isotropic, 515 diffusion volumes up to b-value (aka diffusion sensitivity) of 40,000 s/mm 2 with scan time ~100 hrs. Results: Tractography results show that despite the limited ability of DTI to resolve crossing fibers at the optic chiasm, DTI-based tracts mapped to the known projections of layers in lateral geniculate nucleus and to the primary visual cortex. The other reconstructions were superior in localized regions for resolving crossing regions. Conclusions: In conclusion, despite its simplifying assumptions, DTI-based fiber tractography can be used to generate accurate brain connectivity maps that conform to established neuroanatomical features in the visual system. Study Supported by: NIH/NIMH R01MH100635 NIH/NICHD R01HD067731