Preprocessed versions of the OpenMind dataset (Wald et al., 2025): head & neck 3D MRI pooled from ~800 OpenNeuro datasets. Here the brain T1w, T2w and FLAIR images were preprocessed at using brainprep and packed as WebDataset shards, ready for large-scale (e.g. self-supervised) deep learning. All folders share the same sample identifiers: (datasetid, subject, session, run), with datasetid the shard folder name, so derivatives of the same scan can be joined across folders. Each preprocessing folder holds one folder of WebDataset shards per OpenNeuro dataset and an index.json.gz with the byte offsets of every file of the shards, used by nidl for random access. valsplit.csv (columns datasetid…