Imaging and radiology: X-ray, ultrasound, CT, MRI and PET scans explained

Diagnostic radiology produces and interprets images of the body. Radiologists are doctors who train in imaging and specialise in areas such as chest, breast, musculoskeletal, neuroradiology, paediatrics or interventional radiology. Radiographers, sonographers and nuclear medicine technologists operate the equipment. Radiographers are the healthcare professionals who usually perform X-rays, CT, MRI and PET scans, while ultrasound is carried out by trained healthcare professionals including sonographers.

Interventional radiologists use imaging guidance to carry out procedures through small punctures, such as taking a sample for a biopsy or draining an abscess. The NHS notes that imaging may help doctors see inside the body during a procedure. Radiology is also involved in screening programmes such as breast and abdominal aortic aneurysm screening.

Each technique has strengths. The best choice depends on the part of the body and the question being asked, and your doctor or radiologist chooses it rather than the other way around.

The imaging department will tell you what to do. Common requests include removing jewellery and clothing with metal, not eating for several hours before some CT or PET scans, drinking water for a full bladder before some ultrasound scans, and following instructions on medicines. For PET, the NHS says you may need to stop eating 6 hours beforehand and avoid strenuous exercise for up to 24 hours.

For MRI, you will be asked about pacemakers, metal in the body, surgery, pregnancy and kidney problems. MRI scanners are noisy, and you are given ear plugs or headphones. An MRI scan usually takes between 15 minutes and 1 hour. A CT scan usually takes 10 to 20 minutes, a PET scan 30 to 60 minutes, and an ultrasound 10 to 45 minutes. If you are anxious or claustrophobic, tell your doctor or the department in advance, as there are ways to help.

The NHS says X-rays are usually very safe and serious complications are rare, but that if you have lots of X-rays or CT scans there is a very small chance that radiation could cause cancer, so doctors weigh up the risks before requesting a scan. Ultrasound uses sound waves and no radiation. MRI also does not use ionising radiation but has specific safety checks for metal implants.

Contrast media, given by mouth, injection or enema, help show more detail. Side effects such as a metallic taste, feeling hot or a headache are usually brief. Allergic reactions are rare. PET tracers leave the body within a few hours, and you may be asked to limit close contact with young children or pregnant people for a short time.

On the NHS, a GP or hospital doctor requests the scan, and results go back to the person who requested them. Waiting times differ by scan type, urgency and location. The NHS advises contacting the referring doctor if you have not heard anything after a few weeks.

Privately, scans may be requested by a consultant or arranged on a self-referral basis at some centres, often with a faster appointment. A private centre should be registered with the Care Quality Commission in England and the report should be written by a radiologist. Ask what the price covers, whether the radiologist's report is included, whether previous images can be compared, and how results are sent to your GP.

• Ask why the scan is recommended, what question it is meant to answer and whether a scan without radiation would be as useful.

• Bring your referral, a list of medicines, allergy information and any previous scan reports or images.

• Tell staff about pregnancy, breastfeeding, pacemakers, metal implants, kidney disease, diabetes and previous reactions to contrast.

• Ask who will explain the result and when you should expect it. If you have not heard after a few weeks, contact the doctor who referred you.

• During or after a scan with contrast, tell staff straight away if you develop wheezing, difficulty breathing or swallowing, swelling or a rash. Call 999 if breathing difficulty develops after you have left the department.