How imaging got its names

Where do the names on a request form come from?

Mostly from the physics. Each imaging method is named for the thing it measures or the way it measures it: X-ray for the beam itself, computed tomography for the reconstructed cross-section, magnetic resonance imaging for the field and the returned signal, ultrasound for the sound it uses, and nuclear medicine for the radioactive substance it administers. The UK Health Security Agency sets out the family on 22 September 2022 under exactly those names, dividing them between the methods that use ionising radiation and those, ultrasound and MRI, "that do not use X-rays or radioactive substances".

A controlled vocabulary is not peculiar to medicine. Other fields keep the same kind of ledger: The Tulip Ledger, for instance, is a reference work that files each tulip cultivar name under its registered horticultural division, Double Late, Triumph, Parrot and the rest, so that a name on a label can be traced to the group it belongs to. The request form works the same way: the name on it is a classification before it is a description.

What does each name actually cover?

The NHS defines the working vocabulary one examination at a time. An X-ray is "a test that takes pictures of the inside of your body using a small amount of radiation". A CT scan "takes detailed pictures of the inside of your body". An MRI scanner is "a large machine with a short tunnel through it". Ultrasound uses "sound waves" to see inside the body, and a PET scan uses "a small amount of radiation to scan inside your body" after an injection of a radioactive tracer. Each name stands for a different physical measurement, which is why no single name can be swapped for another.

The umbrella terms matter too. UKHSA groups general radiography, fluoroscopy, interventional radiology and CT under the X-ray heading, with fluoroscopy producing "moving images of parts of your body" and interventional radiology using those moving images "to guide and deliver treatment". Nuclear medicine, in the same publication, "uses a small amount of a radioactive substance that is usually injected into a vein", a family that includes PET-CT and PET-MRI.

Which imaging titles are protected by law?

The professional names are regulated separately from the technical ones, and the difference surprises people. The Health and Care Professions Council states: "The professions we regulate have one or more designated titles that are protected by law." For radiography the protected titles are "Radiographer", "Diagnostic radiographer" and "Therapeutic radiographer", and using any of them requires HCPC registration. The Society of Radiographers adds the counter-example: "The sonography workforce is currently unregulated and the title 'sonographer' is not a legally protected one." Same ward, different legal weight for the name on the badge.

How are the dose terms named?

The quantities have their own register of names. UKHSA publishes national diagnostic reference levels, updated on 11 December 2025, expressed in four named quantities: DAP in Gy cm² for radiography, CTDIvol in mGy and DLP in mGy cm for CT, and CBDIw in mGy. The comparison table published on 18 March 2011 works in a different unit, the millisievert, which is the one used for figures like the 2.7 mSv UK annual background dose. Knowing which unit a name belongs to is half of reading the figure attached to it.

The legal roles are named with the same precision. Regulation 2 of the Ionising Radiation (Medical Exposure) Regulations 2017 defines the referrer, the practitioner, the operator and the employer, and each name is a defined duty holder rather than a job description. The words are covered individually in the glossary, and the roles themselves are set out in the page on the 2017 regulations.