Legarreta, J. H.; Rushmore, R. J.; Yeterian, E. H.; Makris, N.; Rathi, Y.; O'Donnell, L. J.

Cerebellar pathways form extensive structural circuits linking the cerebellum with the brainstem, thalamus, and cerebrum, underlying motor, cognitive, and affective functions. Diffusion MRI tractography provides the only non-invasive method for mapping these pathways in vivo, but reconstruction of cerebellar connectivity remains challenging due to crossing fibers, peduncular bottlenecks, decussations, multi-synaptic circuits, and numerous small nuclei that define pathway origins and terminations. Here we introduce Anatomically Constrained and CURAted Tractography (ACCURAT), an open framework for reconstructing cerebellar pathways from diffusion MRI using anatomical priors and rule-based streamline queries. ACCURAT combines anatomical segmentation, densely seeded tractography, and vertex-level evaluation of anatomical constraints along streamline trajectories, enabling the isolation of pathway segments within specific nuclei while preventing their propagation across synaptic boundaries. To define these constraints, we provide a concise, pathway-by-pathway synthesis of cerebellar connectional anatomy based on experimental tract-tracing literature and organized for tractography applications. We identify pathway-specific origins, trajectories, terminations, decussation patterns, and tractography challenges, and use this information to inform tractography-ready cerebellar pathway definitions. Using ultra-high-resolution submillimeter diffusion MRI (0.76 mm gSlider acquisition) from healthy participants, we reconstruct multiple extrinsic and intrinsic cerebellar pathways, including specific components of the inferior, middle, and superior cerebellar peduncles; challenging decussating pathways such as the olivocerebellar and dentato-olivary projections; and intrinsic cerebellar pathways, including Purkinje corticonuclear projections and intracortical parallel fibers. ACCURAT generalizes across tractography algorithms, producing comparable reconstructions with both probabilistic parallel transport tractography and deterministic unscented Kalman filter tractography. Together, the ACCURAT framework and accompanying neuroanatomical reference provide an anatomically grounded, tractography-oriented resource for reconstructing cerebellar pathways in vivo and for supporting future development and evaluation of cerebellar tractography methods.