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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 plain closed double doors at the end, soft daylight

    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.

  11. Magnetic fields, not X-rays

    Magnetic resonance

    An MRI scanner makes its pictures from magnetic fields and the signals the body returns inside them. No ionising radiation is involved, and that fact organises everything else about the examination.

  12. Attenuation

    Computed tomography

    Attenuation is the word for what tissue does to the beam: how much of it is stopped on the way through. A CT report turns that stopping into a number.

  13. When the patient is an animal

    Beyond the patient

    The physics of a scan does not change with the species on the table. The paperwork does, because the regulations this site covers are written for human patients.

  14. The route of a request

    The journey

    A scan is the middle of a journey, not the start of one. The request, the justification, the exposure and the report each have their own rule and their own owner.

  15. The American bill

    Another system

    The same examination, a different paper trail. In the United States a scan can arrive afterwards as two separate bills, and a body of federal rules exists to govern what may be charged.

  16. The paper trail

    The record

    A scan produces an archive as well as an image. Most of that trail is compulsory under the 2017 regulations, and each document in it answers to a written duty.

  17. Where the pictures go

    The archive

    The pictures stay; the report travels. The images go into the department’s archive under record-keeping duties, while the interpretation makes the journey back to whoever asked the question.

  18. What the scan room is made of

    The room

    An X-ray room is built, not just furnished. The door, the sign and the screen are each the physical form of a written duty.

  19. Does a dose add up?

    Dose

    Every exposure has a figure, and the figures can be summed. What the sum means is the harder question, and the regulations answer it exposure by exposure.

  20. Reading an image

    The craft

    Reading is the trained act that turns a picture into a report. In the UK the people who acquire the image and the people who read it sit on different registers.

  21. How imaging got its names

    The vocabulary

    Every method is named for the thing it measures. The professional titles, the dose quantities and the legal roles each have a register of names of their own.

  22. The software in the room

    The systems

    A modern scanner is a computer wrapped in a machine. The image is calculated, the record is stored, and the regulations assume the software works.

  23. How pages are checked

    The method

    Every page of substance is re-read against the sources it names before it is published. This page describes the check, and the same discipline applied elsewhere.

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.

Elsewhere

Five more reading rooms

Independent publications that follow the same rule as this one: every claim next to the source it was read from.

  1. A tethered balloon platform hanging above a flat landscape, its camera slung beneath the envelope

    Low Altitude Review

    A reading site on aerial photography made between roughly thirty and five hundred feet, with the lift arithmetic and the US rules for moored balloons printed beside it.

    Reading room

  2. A stack of paper invoices on an office desk beside a calculator and a closed laptop

    the unpaid invoice guide

    An editorial guide to business-to-business unpaid invoices: evidence files, reminder sequences, and the escalation rules across the UK, the US and the EU.

    Reading room

  3. A steel pipeline crossing an open field under a flat sky, marker posts running alongside it

    pipeline incident records

    A documentary site on US pipeline safety data: incident records by system, the causes named in official filings, and the 49 CFR framework each figure answers to.

    Reading room

  4. A small film camera on a tripod in an empty room lit by a single portable lamp

    independent film production

    A blog about making short and medium-length independent films: shoot planning, small crews, portable light, and the route into festivals.

    Reading room

  5. A stone war memorial cross on a village green with names carved into its plinth, overcast daylight

    Tadcaster war memorials

    A local history site on the war memorials of Tadcaster and the First World War records behind the names, from dedication ceremonies to pension files.

    Reading room