# Data dictionary

## pairs.tsv

This pairing table contains one row per logical volume in the complete dataset, including controlled ADNI volumes that are not redistributed in the public archive.

| Field | Meaning |
|---|---|
| `volume_id` | Unique volume identifier and filename stem |
| `source_dataset` | Stable machine-readable source code |
| `pair_id` | Paired acquisition or visit identifier within a source |
| `modality` | Structural contrast: `T1W`, `T2W` or `T2FLAIR` |
| `field_strength` | Acquisition field strength of this volume |
| `paired_field_strength` | Field strength of the matched volume |
| `relative_path` | Intended path in the complete dataset layout; ADNI paths are reconstruction targets and are not present in the public archive |
| `case_group` | Paired-case grouping key for partitioning; it is not guaranteed to link repeated visits from one participant |

## availability.tsv

`availability.tsv` adds explicit access information keyed by `volume_id`.

| Field | Meaning |
|---|---|
| `access_status` | `public` or `controlled` |
| `public_file_present` | Whether the image is included in the public archive |
| `source_record` | Persistent source record or controlled-access landing page |
| `access_note` | Practical access instruction |

## file_manifest.tsv

Lists the 424 publicly downloadable NIfTI files, their byte sizes and SHA-256 identifiers. The SHA-256 values correspond to the Git LFS object identifiers in the frozen Hugging Face revision.

## dataset_summary.tsv

Contains source-level counts for paired cases, same-contrast image pairs and logical volumes.

## ADNI selection lists

The two CSV files in `adni/` each contain 47 rows corresponding to the 47 paired ADNI cases described in the manuscript. They identify the matched 1.5 T and 3 T images that authorised users can request from LONI. They do not contain MRI image files.