In vivo mapping of macroscopic neuronal projections in the mouse hippocampus using high-resolution diffusion MRI.

Recent developments in diffusion magnetic resonance imaging (MRI) make it a promising tool for non-invasive mapping of the spatial organization of axonal and dendritic networks in gray matter regions of the brain. Given the complex cellular environments, in which these networks reside, evidence on the capability of diffusion MRI-based tractography to study these networks is still lacking. In this study, we used a localized diffusion MRI approach to acquire high spatial and angular resolution images of the live mouse hippocampus. The diffusion MRI and tractography results were compared with histology and the Allen mouse brain connectivity atlas using a multi-step image registration pipeline. The results demonstrated that in vivo diffusion MRI data at 0.1mm isotropic resolution revealed the organization of axonal and dendritic networks in the hippocampus and the tractography results shared remarkable similarity with the viral tracer data in term of their spatial projection patterns. Quantitative analysis showed significant correlations between tractography- and tracer-based projection density measurements in the mouse hippocampus. These findings suggest that high-resolution diffusion MRI and tractography can reveal macroscopic neuronal projections in the mouse hippocampus and are important for future development of advanced tractography methods.