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Inside the ScannerPlain English notes on medical imaging in the UK.

Medical imaging, explained without advice

Inside the Scanner

An imaging examination is a picture taken to answer a question a clinician has already asked. This site explains what each kind of picture is, how it is made, and who decides that it should be made at all.

  1. 2.7 mSv a year, UK average Natural background dose
  2. 0.014 mSv for a chest X-ray From the same UKHSA table
  3. 4 Duty holders in law Referrer, practitioner, operator, employer
  4. 1897 The Roentgen Society The first X-ray association

The two dose figures are read in the UK Health Security Agency comparison table Ionising radiation: dose comparisons, published 18 March 2011. The four duty holders are defined in regulation 2 of the Ionising Radiation (Medical Exposure) Regulations 2017 on legislation.gov.uk. The 1897 date is published by the Royal College of Radiologists. All four were read on 6 September 2026. The same figures are published in modalities at a glance.

01 to 04

The four sections

From the methods themselves to the rules that govern their use.

  1. A wide empty imaging room lit from above, a scanner bore facing a padded table and a control window in the far wall

    Scans Explained: X-ray, CT, MRI, Ultrasound

    Five methods, five different physical measurements, and the reason no single scan answers every question.

    Section 01

  2. A hospital corridor with a row of empty seats along one wall and a set of double doors marked with a plain directional sign

    Having a Scan: How the Appointment Runs

    A request, a set of checks, an examination and a report: the four steps that every imaging appointment shares.

    Section 02

  3. A heavy shielded door standing ajar in a bare clinical corridor, a warning trefoil sign and a wall mounted dose meter beside it

    Radiation and Safety in Medical Imaging

    Every exposure has to be justified before it is optimised, and both words have a legal meaning in the UK.

    Section 03

  4. A dim reporting room with two blank display screens on an adjustable arm and an empty chair pushed back from the desk

    Who Does What in an Imaging Department

    Different jobs, different registers, and a discipline barely older than photography of the living body.

    Section 04

Reference

The two standing references

Cited by every section, each row carrying the source it was read from.

  1. A row of blank light boxes on a wall in a darkened room, their frames catching a faint reflection from a window out of shot

    Modalities at a glance

    The comparison table: what each method measures, and where that was read.

    Reference

  2. A long hospital corridor at dusk, the ceiling lights receding towards a far corner and every door along it closed

    Glossary of imaging

    The vocabulary of a request form, a report and a leaflet.

    Reference

Latest

Every page on this site

The full list, with the date of the work that produced each one.

  1. Having an MRI scan

    Magnetic resonance

    Magnetic resonance imaging makes pictures from radio signals given off by the body inside a strong magnetic field. It uses no ionising radiation, and that single fact shapes everything else about it.

  2. CT scans

    Computed tomography

    A CT scanner is an X-ray tube that travels around the body while a ring of detectors records what gets through. The picture is calculated, not photographed.

  3. Ultrasound

    Sonography

    Ultrasound sends pulses of high frequency sound into the body and listens for the echoes. Nothing is emitted that the body has not already been exposed to in kind.

  4. Plain X-rays

    Radiography

    A radiograph is a shadow. What reaches the detector is what the beam was not stopped by, which is why bone is white and air is black.

  5. The referral

    The request

    No imaging examination starts with the person having it. It starts with a written request from a clinician, and in the UK that request has a legal weight.

  6. Contrast agents

    Contrast media

    A contrast agent does not make a picture. It changes how a tissue or a vessel appears in a picture that would have been taken anyway.

  7. Radiation doses

    Dose

    Dose figures are only meaningful next to the source they were published in and the year that source was written. Every number on this page carries both.

  8. IR(ME)R 2017

    Regulation

    Referrer, practitioner, operator, employer. Four defined roles decide whether a medical exposure happens at all, and each one carries a duty that is written down.

  9. Who does what

    The professions

    The person who positions you is very unlikely to be the person who writes the report. In the UK the two jobs sit on different registers and follow different training routes.

  10. The British institutions

    Institutional history

    The history of the machines is told everywhere and sourced almost nowhere. The history of the British bodies that govern their use is published by those bodies themselves, with dates.

Start here

Six pages to begin with

One scan, one appointment, one set of figures and one set of rules.

  1. The open bore of a magnetic resonance scanner seen head on in an empty room, the padded table withdrawn and the lighting flat

    Having an MRI scan

    Magnetic resonance imaging makes pictures from radio signals given off by the body inside a strong magnetic field. It uses no ionising radiation, and that single fact shapes everything else about it.

    6 September 2026

  2. A computed tomography gantry photographed from the side, the circular opening lit from within and the couch rails leading into it

    CT scans

    A CT scanner is an X-ray tube that travels around the body while a ring of detectors records what gets through. The picture is calculated, not photographed.

    6 September 2026

  3. A reception desk in an imaging department with an empty chair behind it and a blank appointment screen mounted on the wall

    The referral

    No imaging examination starts with the person having it. It starts with a written request from a clinician, and in the UK that request has a legal weight.

    6 September 2026

  4. A single wall mounted radiation monitor with a blank grey display beside a painted steel door frame in an empty corridor

    Radiation doses

    Dose figures are only meaningful next to the source they were published in and the year that source was written. Every number on this page carries both.

    6 September 2026

  5. A heavy steel door closed in a bare corridor, a small red indicator lamp glowing above its frame and nobody in sight

    IR(ME)R 2017

    Referrer, practitioner, operator, employer. Four defined roles decide whether a medical exposure happens at all, and each one carries a duty that is written down.

    6 September 2026

  6. A scanner control room seen through the observation window, two empty operator chairs and a bank of dark monitors on the desk

    Who does what

    The person who positions you is very unlikely to be the person who writes the report. In the UK the two jobs sit on different registers and follow different training routes.

    6 September 2026

Inside the Scanner explains what happens during an imaging examination: how it is requested, how it is carried out and how it is reported. Every figure is taken from a named primary source and dated, and the checking method is set out in sources and method.