NIfTI metadata extension

The current NIfTI header definition does not contain enough metadata to completely describe a dataset. We propose a NIfTI header extension that is a JSON object using NeuroLex IDs as the field names, with values stored as strings (as per the JSON standard). We need a machine-readable JSON schema that defines the specific NeuroLex terms that may be included, the data types (e.g., int, float, array, ...), and the common human-readable names. This schema should be maintained and hosted by the NIF/INCF.

Note that only the NeuroLex ID will be stored. But the JSON object will also contain a reference to the schema that provides the definitive definition of the field names and the human-readable string. Any software parsing this header extension will either look up the names from the provided URI of the definitive schema, or use a cached version of the schema. (This is similar to the DICOM dictionary concept.)

We propose to structure the JSON object like this:

We should provide a reference implementation in nibabel that includes a selected set of metadata from the dicom header that is deemed (by us) to be useful and that is guaranteed to not include PHI. Any implementation writing a file that includes the proposed object could chose to include addition data, including fields containing PHI. Maybe we should define a field that flags files containing PHI? Or add information to the field definitions in the schema that indicates whether a particular field may contain PHI?