shim

Process of making the magnetic field homogeneous across the scan volume. Passive (iron shims) + active (electric shim coils).

Why it matters to buyers: Poor shim = artifact + failed advanced sequences (spectroscopy, DWI). Shim is set at install and verified during PMs.

Why it matters to engineers: Shim file is magnet-specific — back it up before any service event that could erase it.