An mri file extension is related to the Pittsburgh MRI File Format (also known as PGH_MRI).
MRI file extension - Pittsburgh MRI File Format
What is mri file? How to open mri files?
File type specification:
The mri file extension is used for Pittsburgh MRI File Format. PGH_MRI is a data directory which contains examples of files stored in a format for magnetic resonance imaging (MRI) data.
This mri file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.