Metadata provides the essential tools for discovery, such as a bibliographic citation, and reuse. It is important to add metadata tags to your data. Including keywords and phrases that describe your data and research ensure that other researchers can search and locate your data in a given repository.
The Digital Curation Centre (DCC) -- General list of metadata standards
Biological Magnetic Resonance DataBank - MRI data
National Center for Biotechnology Information (NCBI) - Numerous databases with a genomic/proteomic focus
Neuroscience Information Framework - A virtual community of data, materials, and web-based neuroscience resources with the goal of enabling discovery and access to public research data and tools worldwide through an open source, networked environment
The PhysioBank archives of PhysioNet -- Digital recordings of physiologic signals and related data for use by the biomedical research community
OpenNeuro is a free and open platform for sharing MRI, MEG, EEG, iEEG, and ECoG data. It could be suitable for sharing MRI data from your project.
National Institute of Mental Health Data Archive (NDA): The NDA is a cloud-based data repository that stores and shares data from all research funded by the National Institute of Mental Health (NIMH). This repository could be suitable for demographic, clinical, neurocognitive, and MRI data.