SUMMARY The goal of this proposal is to disseminate Connectome 2.0, the next-generation 3 Tesla human MRI scanner at the Massachusetts General Hospital designed for imaging human brain circuits across scales, as a unique resource for neuroscience collaborations around the world. This ultra-high gradient strength, high slew-rate 3T MRI scanner was expressly developed through the support of the NIH BRAIN Initiative to enable studies of neural tissue microstructure and brain circuits spanning the microscopic, mesoscopic, and macroscopic scales. The Connectome 2.0 scanner builds upon our expertise in engineering and disseminating the first human Connectome MRI scanner for the Human Connectome Project to hundreds of users worldwide. In order to maximize the resolution of this powerful scanner for studies of tissue structure down to the microscopic level in the living human brain, we have pushed the diffusion resolution limit to unprecedented levels by (1) achieving ultra-high gradient strengths up to 500 mT/m and ultra-fast slew rates up to 600 T/m/s; (2) pushing the limits of the RF receive coils and gradient characterization to enable maximum sensitivity with greatly reduced artifacts using real-time eddy current corrected MRI acquisitions; (3) developing new pulse sequences to achieve the highest diffusion- and spatial-resolution ever achieved in vivo; and (4) calibrating the measurements through systematic validation in high-fidelity phantoms and ex vivo brain tissue at progressively finer scales. As part of this collaborative, center-wide endeavor, we will create novel advances in image acquisition and reconstruction to enable maximal use of the Connectome 2.0 gradients for a wide array of neuroscientific applications. The scanner has been validated in diffusion MRI studies down to sub-millimeter resolution with high-fidelity distortion correction. The stronger gradients offer considerable improvements in diffusion imaging, reaching high b-values with significantly shorter echo times. Funding of the current U24 proposal will facilitate the engineering effort and scientific personnel to support, maintain, and expand the capabilities of this remarkable instrument, enable efficient data transfer, integration, and analysis, as well as the requisite subject recruitment, user access, training, and guidance to advance scientific collaborations nationally and internationally. While the major goal of this project is to provide an innovative resource for unparalleled tissue microstructure and circuit characterization in the living human brain, the research resource also holds great potential for improving our current understanding of a wide range of neurological and psychiatric disorders, including multiple sclerosis, traumatic brain injury, aging, Alzheimer’s disease, and mental disorders. This one-of-a-kind instrument represents the ultimate diffusion MRI machine capable of addressing the BRAIN 2025 mandate to image across scales, from the microscopic sc...