This is a tittle of some paper I found online.

A quantitative theory of the Hounsfield unit and its application to dual energy scanning

There are two energies in this CT system. But why the author used "Dual Energy" instead of "Dual Energies"?

Another example: Multi-energy CT imaging, multi panel canvas set, etc.

"Dual energy" is also commonly written as "dual-energy".

This is not the first time I notice this kind of naming method. The title above is just an example I found recently.

  • "dual energy" is name of scientific technique, "Dual Energy" is name of company Jul 11, 2019 at 7:39
  • @A-312 It's not the name of a certain company. "Dual energy" here refers to scientific techniques that use two energies to scan an object. Hence my confusion, another example: multi-energy X-ray imaging.
    – Eva
    Jul 11, 2019 at 7:52

1 Answer 1


When used as adjectives, nouns are in general singular. Here the noun is uncountable scanning, and dual energy is used as an adjective.

For example:

  • a five metre yacht
  • a two horse race
  • a £10 note ("ten pound")
  • some multi-site companies
  • some five door cars

Some style guides prefer hyphens in the adjectival phrase, some suggest only when it is ambiguous.

  • a ten-year-old child
  • some five-door cars
  • five thousand-person towns (five towns, each with 1,000 persons)
  • a five-thousand-person town (one town, with 5,000 persons)

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