Patient Basics: Magnetic Resonance Imaging (MRI)

An MRI (magnetic resonance imaging) scan uses a strong magnet and radio waves to make detailed pictures of the inside of the body. It uses no X-rays or other radiation. You lie still inside a tube-shaped machine for about 15 to 60 minutes while it makes loud knocking sounds. Because of the strong magnet, you must tell the staff about any metal or medical device in your body before the scan.

Key points

• MRI gives clear, detailed views of the brain, spinal cord, nerves, ligaments, cartilage and many organs.
• Pacemakers, some implants and metal fragments can be dangerous in an MRI. The staff will screen you first.
• Some scans use a contrast dye given through a vein to make certain tissues show up better.
• If small spaces bother you, ask about medicine to help you relax, or a wider or open scanner.
• A radiologist reads the images and sends a report to your doctor, usually within a few days.

Why an MRI is done

Doctors order an MRI when they need a closer look than X-rays, ultrasound or CT can give. Common reasons include:

• Brain and spine: stroke, multiple sclerosis, tumors, headaches with warning signs, slipped discs and pinched nerves. A neck MRI is often used for neck pain that spreads into the arm.
• Joints and muscles: a knee MRI can show torn ligaments, cartilage or meniscus, and a shoulder MRI can show rotator cuff tears. MRI also finds hidden fractures.
• Heart and blood vessels: heart muscle disease, heart damage, and narrowed or bulging arteries (an MRI of the blood vessels is called MRA)
• Belly and pelvis: the liver, pancreas, bile ducts, kidneys, uterus, ovaries and prostate
• Breasts: screening for people at high risk of breast cancer, and checking known cancers
• Cancer: finding out how far a cancer has spread and checking how treatment is working

Before the MRI

Safety screening

You’ll fill out a safety form. Tell the staff if you have:

• A pacemaker or implanted defibrillator, even if it’s labeled as MRI-safe
• A cochlear implant, nerve or brain stimulator, or a medicine pump
• Clips on a brain aneurysm, or other metal from surgery
• Metal fragments in your eyes or body, for example from welding, grinding or a war injury
• A medicine patch, since some have a metal backing that can heat up
• Kidney disease, if you might get contrast dye
• A chance you could be pregnant

Many implants, such as joint replacements, dental fillings and most modern stents, are safe. Bring your implant card so staff can check the exact model. You may need an X-ray first if there’s a chance of metal in your eyes.

Getting ready

• Follow any instructions about eating and drinking. Some belly scans need an empty stomach.
• Take your usual medicines unless told otherwise.
• Leave jewelry, watches and hairpins at home. Phones, credit cards, keys and hearing aids stay outside the scan room.
• You’ll likely change into a gown. Some makeup and clothing with metallic threads can heat up.
• If you feel anxious in tight spaces, ask your doctor ahead of time about a mild sedative. You’ll need someone to drive you home if you take one.

During the MRI

You lie on a padded table, usually on your back. A frame called a coil may be placed over the area being scanned, such as your head or knee. The table slides into the opening of the machine. Most scanners are open at both ends, and for some scans your head stays outside.

The machine makes loud tapping, knocking and buzzing sounds while it takes pictures. You’ll get earplugs or headphones, and sometimes music. Staying very still keeps the pictures sharp. The technologist can see you, talks to you through a speaker between sets of pictures, and gives you a call button to squeeze if you need help. You may feel a little warm.

If you need contrast dye, it goes in through a small IV line in your arm partway through the scan. You may feel a cool sensation. Most scans take 15 to 60 minutes.

Afterward

You can go back to your usual activities right away unless you had a sedative. If you had contrast dye, drinking extra fluids for the rest of the day is a good idea. People who are breastfeeding can usually continue as normal after contrast.

Possible risks

• Metal and devices. The magnet can pull on metal objects, move fragments in the body, heat wires and affect devices. Careful screening prevents nearly all of these problems.
• Contrast reactions. Allergic reactions to the gadolinium dye used in MRI are uncommon and usually mild, such as hives or nausea. Serious reactions are rare.
• Kidney disease. In people with severe kidney disease, some older types of contrast dye were linked to a rare skin and organ problem. Newer dyes have made this extremely rare, but your kidney function may be checked first.
• Anxiety in tight spaces, which a sedative, a wider scanner or a support person can help with
• Noise, which is why ear protection is always used

Your results

A radiologist, a doctor who specializes in reading scans, studies the images and sends a report to the doctor who ordered the test. That usually takes a day to a few days. Your results may show up in your online patient portal before your doctor has talked with you. Reports use technical words, so ask your doctor to go over what the findings mean for you.

MRI often picks up small findings that turn out to be harmless, such as minor disc bulges or tiny cysts. Your doctor will tell you whether any finding needs follow-up.

When to call your doctor

• Itching, a rash or swelling after contrast dye
• Pain, redness or swelling where the IV was placed
• You haven’t heard about your results within a week

Call 911 for trouble breathing, throat tightness or swelling of the face after contrast.

Common questions about MRI

How long does an MRI take?

Most MRI scans take 15 to 60 minutes, depending on the body part and whether contrast dye is used. Detailed scans of the heart, or of several body areas, can take longer. Plan for extra time to check in, change your clothes and fill out the safety form before the scan.

What is the difference between an MRI and a CT scan?

A CT scan uses X-rays and takes only a few minutes, so it’s often used in emergencies and for the lungs and bones. An MRI uses a magnet and radio waves, takes longer, and shows the brain, nerves, ligaments, cartilage and other soft tissues in more detail without radiation.

Can I have an MRI while pregnant?

An MRI without contrast dye is generally considered safe during pregnancy, and it’s often used when an ultrasound doesn’t give enough information. Contrast dye is usually avoided unless it is truly needed. Tell the staff before the scan if you are pregnant or might be.

Can I move during an MRI?

Try to stay as still as you can while the machine is making noise, because movement blurs the pictures and some may need to be repeated. You can usually shift slightly or scratch an itch between sets of pictures. Ask the technologist when it’s a good time to move.

Questions to ask your doctor

• Why do I need an MRI instead of another test?
• Will I need contrast dye?
• Is my implant or device safe in an MRI?
• Can I have medicine to help me relax during the scan?
• When and how will I get my results?

Learn more

• MRI scans (MedlinePlus, U.S. National Library of Medicine)

This guide is general information and doesn’t replace advice from your own doctor. Last updated October 2026.