MRI Scan: Uses, Procedure & Results

An MRI scan is one of the most detailed pictures modern medicine can take of the soft tissues inside your body, and it does it without any x-ray radiation. If your doctor has ordered one, it helps to know why, what the appointment involves, and how the results make their way back to you. This guide walks through the essentials in plain language.

What an MRI scan is

MRI stands for magnetic resonance imaging. According to RadiologyInfo.org, the scanner uses a powerful magnetic field, radiofrequency pulses, and a computer to build detailed pictures of organs and structures inside the body. Crucially, it does not use x-rays or other ionizing radiation.

The physics is easier to picture than it sounds. Your body is full of hydrogen atoms, mostly in water and fat. The magnet briefly nudges those atoms into line, the radio waves knock them out of line, and as they settle back they release small amounts of energy. Different tissues release that energy differently, and the computer turns those differences into an image. This is also why MRI is sometimes called a magnetic resonance image. For a wider view of how imaging tests fit together, see our overview of what radiology involves.

Why a doctor might order one

MRI shines when a clinician needs to see soft tissue in fine detail. RadiologyInfo and MedlinePlus list common reasons that include:

• Examining the brain, spinal cord, and nerves for stroke, tumours, or multiple sclerosis.
• Assessing joints, muscles, ligaments, and tendons after injury, such as a suspected knee or shoulder tear.
• Looking at abdominal and pelvic organs, including the liver, kidneys, and reproductive organs.
• Studying blood vessels, and in some cases the heart, with specialised sequences.

An MRI is often ordered after a first-line test, or when a doctor needs more information than an x-ray or ultrasound can provide. It answers a specific question, so the type of MRI is tailored to the body part in question.

How to prepare

Preparation is usually simple, but the safety screening is not optional. When you book, the clinic will ask a set of questions about metal and medical devices. Answer them fully and honestly.

• Remove jewellery, watches, hairpins, and anything metallic. You may be given a gown to wear.
• Tell the team about pacemakers, cochlear implants, aneurysm clips, artificial joints, or metal fragments from an old injury.
• Mention pregnancy, breastfeeding, kidney problems, allergies, and claustrophobia in advance.
• Ask whether you need to fast. The NHS notes that eating and drinking rules vary by exam and facility.

What happens during the scan

You lie on a padded table that slides into the scanner, which is shaped like a short tunnel. The NHS describes the scan itself as taking anywhere from about 15 minutes to an hour, depending on the area and the number of sequences.

The machine is loud. It makes clicking, tapping, and thumping sounds as the images are captured, so you will usually be offered earplugs or headphones. A radiographer runs the scan from an adjoining room and can see and hear you the whole time, often through a two-way intercom. The single most important thing you can do is stay still, because movement blurs the pictures.

Contrast dye, and who needs it

Some MRI exams use an injection of contrast material, usually a gadolinium-based agent, to make certain tissues and blood vessels stand out. Not everyone needs it. When it is used, RadiologyInfo notes some people feel a brief coolness, warmth, or a metallic taste. Serious allergic reactions are rare.

Because the kidneys clear the contrast, the team may check kidney function first, especially if you have known kidney problems. This is one of many reasons to complete the pre-scan questionnaire carefully. If you are comparing where to have a scan done, our guides to choosing an open MRI facility and finding an MRI centre walk through what to ask.

Safety, metal, and claustrophobia

MRI has an excellent safety record and uses no radiation, which is a genuine advantage over CT and x-ray. The main risks come from the magnet interacting with metal. Certain older pacemakers, some cochlear implants, and specific aneurysm clips can make an MRI unsafe, which is exactly why the screening questions exist.

If enclosed spaces make you anxious, say so early. Options can include a more open scanner design, a mild sedative arranged by your doctor, or simply extra reassurance and a clear view of the intercom. Many people who expect to struggle get through the scan comfortably once they know what to expect.

Types of MRI you might have

MRI is not a single test but a family of techniques, and the type is matched to the clinical question. Your appointment letter may name one of these.

• Standard anatomical MRI: the most common form, producing detailed still images of a body part such as the knee, spine, or brain.
• MR angiography (MRA): focuses on blood vessels, sometimes with contrast, to look at flow and narrowing.
• Functional MRI (fMRI): maps activity in the brain by detecting small changes in blood flow, used mainly in specialist settings.
• Contrast-enhanced MRI: uses a gadolinium injection to highlight tissues, such as some tumours or areas of inflammation.

You do not need to memorise these. The point is that the radiographer will run the specific sequences your doctor requested, which is why two people booked for an MRI can have quite different appointments. If your scan is described as a magnetic resonance image of a particular organ, our related guide to the magnetic resonance image covers the same ground from another angle.

What your results mean

After the scan, a radiologist reviews the images and sends a written report to the doctor who ordered the test. The NHS notes results often take one to two weeks to come back, because careful interpretation takes time. The images alone are not a diagnosis. They are one piece of information that your clinician combines with your symptoms, history, and other tests.

MRI compared with other scans

No single scan is best for everything. The right test depends on the question being asked, and often on speed, cost, and radiation.

• MRI: best for soft tissue detail, no radiation, but slower and noisier, and unsuitable for some implants.
• CT: very fast and excellent for bone, bleeding, and trauma, but it uses ionizing radiation. See our CT scan guide and the real cost of a CT scan.
• Ultrasound: no radiation, low cost, and great for real-time views, but limited by bone and air.

Your doctor chooses the test that answers their question with the least burden to you. If you are told you need an MRI rather than a CT, it usually reflects a need for that soft-tissue detail.

Frequently asked questions

Is an MRI scan safe?

For most people, yes. MRI uses a magnetic field and radio waves rather than ionizing radiation, so it can be repeated when needed. The main safety concern is metal in or on the body, which is why the clinic screens you carefully before the scan. Tell the team about any implants or devices.

Does an MRI hurt?

The scan itself is painless. You may find it uncomfortable to lie still for a long time, and the machine is loud, but you should not feel the imaging. If contrast dye is used, you might feel a brief pinch from the injection and a short-lived cool or metallic sensation.

How long does an MRI take?

Most scans take between about 15 minutes and an hour, depending on the body part and how many sequences are needed. The clinic can give you an estimate for your specific exam when you book.

Can I have an MRI if I have metal implants?

It depends on the implant. Many modern implants are MRI-safe, but some older pacemakers, cochlear implants, and aneurysm clips are not. Never assume. Tell the clinic exactly what you have and when it was fitted so they can confirm it is safe before your appointment.

When will I get my MRI results?

A radiologist reviews the images and sends a report to your referring doctor, which often takes one to two weeks. Your doctor will then explain what the findings mean for you. The scan is one part of the picture, not a diagnosis on its own.