This question already has an answer here:

Why does fMRI start with a lowercase f? As it stands for functional in functional magnetic resonance imaging.

The fMRI Wikipedia page has a history section, but it does not explain why a lowercase f was used, nor when the term was first used.

Is there any other example?

marked as duplicate by Gary, AmE speaker, Skooba, Xanne, tchrist Nov 4 '17 at 0:54

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 2
    This is interesting and I don't think it'll be easy to find a good answer. I'm editing to add some research to see if we can get this reopened. – Laurel Oct 23 '17 at 20:16
  • 1
    Well, first there was plain MRI. If "FMRI" were used the heritage would not be obvious, but with "fMRI" the fact that it's a modification on "MRI" is more evident. – Hot Licks Oct 23 '17 at 22:09
  • 1
    There is also (f)MRI - sites.google.com/site/mritutorial/functional-mri-tutorials/… – Nigel J Oct 23 '17 at 23:29
  • 2
    Here's what I found so far: Timeline: 1991 - fMRI technique first used; 1992 - the term "functional MRI" is used; 1993 - FMRI and fMRI both used. Also of interest is fNIR... – Laurel Oct 24 '17 at 3:35
  • 3
    I would conjecture the convention may have been inspired by other scientific nomenclature: for example, "mRNA," messenger RNA, discovered in the 1960s according to a quick Google search predates fMRI by decades. – Azor Ahai Oct 24 '17 at 16:56

I think the reason is that fMRI really stands for "functional MRI" rather than for "functional magnetic resonance imaging". That may sound like a distinction without a difference (since MRI stands for "magnetic resonance imaging"), but acronyms and initialisms tend to take on a life of their own. (For example, we wouldn't say *"a magnetic resonance imaging", but "an MRI" is well-attested in reference to an individual scan or an individual machine.) Analogous cases, as noted in comments above and in the question that Gary links to, include mRNA ("messenger RNA") and hPSC ("human PSC").

That said, most similar abbreviations actually don't take this approach. Usually the added letter isn't set off at all (such that a neonatal ICU is a NICU and a hash-based MAC is an HMAC); occasionally it's set off with a hyphen (such that transfer DNA is T-DNA and Broadband ISDN is B-ISDN). I don't think there's any specific factor that leads to one approach or another, other than the personal preference of the people introducing the terms.


CAT scans were followed by positron emission tomography or PET scans, which measured the decay of radioactive chemicals in brain tissue, and also MRI, which detected magnetic force. But all of these early images were static. The “movies” of brain function only became possible with confirmation of the link between blood flow and brain activity. This opened the possibility of using MRI to study more than just brain structure. With this connection, the active functioning of the brain could be predicted. Hence the lower case “f” added to MRI.

  • 1
    But why is it lowercase? – Laurel Oct 26 '17 at 16:18

Not the answer you're looking for? Browse other questions tagged or ask your own question.