Featured · By scan type · In the room and after · By person and body area
How medical scans work, and how to get ready for one
Medical imaging is a family of methods, each using a different kind of energy to picture the inside of the body. This independent guide explains X-ray, CT, MRI, ultrasound and nuclear medicine in plain language, what the safety questions mean, and how results are reported. It cannot tell you what you need. Your own doctor and imaging team can.
01
Start here
Three main guides that map the whole subject. Each links out to the shorter guides.
- Main guideTypes of medical imagingFive main methods, the kind of energy each one uses, and what doctors use each picture for.
- Main guideRadiation, contrast and safetyWhat dose means, what contrast agents are, and the safety questions staff ask before a scan.
- Main guidePreparing for a scan and your resultsBefore, during and after: what the day involves and how a report reaches your doctor.
02
By scan type
One guide for each way of making a picture, with the questions people usually bring to it.
- GuideX-ray, CT and MRI comparedHow the three differ in what they show, how long they take and what they involve.
- GuideUltrasound basicsPictures made from sound waves: how a scan works and what it is used to look at.
- GuideNuclear medicine in plain termsScans that follow a small amount of tracer through the body, and what to expect.
- GuideMammography and screeningBreast X-ray, screening versus diagnostic, and why guidance differs by country.
03
In the room and after
Questions to ask, who does what on the day, and what a written report contains.
- GuideQuestions to ask before a scanPractical questions for your doctor or imaging team, grouped by topic.
- GuideReading a radiology reportHow a report is laid out, who writes it and where it goes.
- GuideWhat a radiologic technologist doesThe person who positions you and runs the scanner, and how that differs from the radiologist.
04
By person and body area
Children, pregnancy, bones and joints, and the back: where public guidance has specific things to say.
- GuideImaging, children and pregnancyWhat public bodies say about scans for children and during pregnancy.
- GuideBones, joints and handsWhich scans are used for fractures, joints and soft tissue, and why X-ray often comes first.
- GuideBack and nerve painWhen imaging helps with back pain and when guidance says it may not.
05
The energy table
Each scan type makes its picture from a different kind of energy. That one fact explains most of what differs between them.
| Scan type | Picture made from | Ionizing radiation |
|---|---|---|
| X-ray and CT | A beam of X-rays passes through the body and is recorded on a detector | Yes |
| MRI | A strong magnetic field and radio waves | No |
| Ultrasound | High-frequency sound waves and their echoes | No |
| Nuclear medicine | A small amount of radioactive tracer, detected by a special camera | Yes |
How this guide is made
Every factual page lists the public sources it draws on, such as hospital-run patient pages, national health agencies and research institutes. Read the editorial standards for how pages are checked and corrected, or about this guide for what it is not: a clinic, a professional body or a place to get personal advice.