A letter in the New Scientist of 17 April 1999, signed by Terry McStea, Whitburn, Tyne and Wear:
Your article on MRI (This Week, 3 April, p 7) reminded me of a story, probably untrue, related by a doctor friend.
MRI used to be known in hospitals as nuclear magnetic resonance, or NMR.
Unfortunately, patients who arrived at the hospital asking for "an NMR" often received a treatment that they were not expecting.
Hence the change to MRI.