What is magnetic resonance imaging (MRI)?

Magnetic resonance imaging (MRI) uses a large magnet, radio waves, and a computer to make detailed pictures of organs and structures within the body. It is used to diagnose health problems.

The MRI machine is a large, tube-shaped machine that creates a strong magnetic field around the person being examined. Some look like narrow tunnels, while others are more open. This magnetic field, along with a radio wave, briefly redirects the hydrogen atoms' natural alignment in the body. Computers are then used to form 2-D images of a body structure or organ based on the activity of the hydrogen atoms. Cross-sectional views can be done to show more details. MRI does not use ionizing radiation, like X-rays or CT scans. 

Why might I need an MRI scan?

An MRI scan may be used to look at bones, joints, and soft tissues, such as cartilage, muscles, and tendons for things like:

• Injuries, such as fractures or tears to a tendon, ligament, or cartilage

• Structural abnormalities due to aging

• Infection like osteomyelitis

• Tumors

• Inflammatory disease

• Congenital abnormalities (those you’re born with)

• Osteonecrosis (bone cell death caused by a poor blood supply to the area)

• Bone marrow disease

• Degenerative joint problems, like arthritis

• Herniation or degeneration of disks of the spinal cord

• Assessment after surgical procedures

Your healthcare provider may have other reasons to recommend an MRI scan of the bones, joints, or soft tissue.

What are the risks of an MRI scan?

There is no risk of exposure to radiation during an MRI scan.

Because of the strong magnet, an MRI scan can’t be used for people with:

• Implanted pacemakers

• Some older intracranial aneurysm clips

• Cochlear implants

• Certain prosthetic devices

• Implanted medicine infusion pumps

• Neurostimulators

• Bone-growth stimulators

• Certain intrauterine contraceptive devices (IUDs)

• Any other type of iron-based metal implants

• Internal metallic objects in certain areas, such as bullets or shrapnel, surgical clips, pins, plates, screws, metal sutures, or wire mesh

Tell your healthcare provider if you are pregnant or think you may be. In general, there is no known risk of MRI in pregnancy. But particularly in the first trimester, MRI should only be used to address very important problems or suspected abnormalities.

If contrast dye is used, there is a risk for allergic reaction to the dye. Tell your healthcare provider if you are allergic to or sensitive to medicines, contrast dye, or iodine.

MRI contrast may have an effect on other conditions. These include allergies, asthma, anemia, low blood pressure, kidney disease, and sickle cell disease. It can also affect the baby if you are breastfeeding.

Nephrogenic systemic fibrosis is a very rare but serious complication of MRI contrast use in people with kidney disease or kidney failure. If you have a history of kidney disease, kidney failure, kidney transplant, liver disease, or are on dialysis, be sure to tell the MRI technologist or radiologist before getting the contrast.

There may be other risks depending on your specific health condition. Talk about any concerns with your healthcare provider before the procedure.

How do I get ready for an MRI scan?

Your healthcare provider will explain the procedure to you and give you a chance to ask any questions.

If your MRI scan involves the use of contrast dye, you will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if anything is not clear.

Generally, there is no special restriction on diet or activity before an MRI scan.

Before the MRI scan, it is very important that you tell the technologist if any of these apply to you:

• You are claustrophobic and think that you will be unable to lie still inside the scanning machine, in which case you may be given a sedative.

• You have a pacemaker or have had heart valves replaced.

• You have any type of implanted pump, such as an insulin pump.

• You have metal plates, pins, metal implants, surgical staples, or aneurysm clips.

• You have any metallic fragments anywhere in the body.

• You have permanent eyeliner or tattoos.

• You are pregnant or think you may be pregnant.

• You ever had a bullet wound.

• You have ever worked with metal (for example, a metal grinder or welder).

• You have any body piercings.

• You have an intrauterine device (IUD).

• You are wearing a medicine patch.

There is a possibility that you may get a sedative before the procedure. So you should plan to have someone drive you home afterward.

Based on your health condition, your healthcare provider may ask for other specific preparations.

What happens during an MRI scan?

MRI may be done on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare provider’s practices.

Generally, MRI of the bones, joints, or soft tissue follows this process:

1. You will be asked to remove any clothing, jewelry, eyeglasses, hearing aids, hairpins, removable dental work, or other objects that may get in the way of the procedure.

2. If you are asked to remove clothing, you will be given a gown to wear.

3. If you are to have an MRI scan with contrast, an intravenous (IV) line will be started in your hand or arm for injection of the contrast dye.

4. You will lie on a narrow table that slides into the large circular opening of the scanning machine. Pillows and straps may be used to help prevent movement during the scan.

5. The technologist will be in another room where the scanner controls are located. But you will be in constant sight of the technologist through a window. Speakers inside the scanner allow the technologist to talk to you and hear you. You will have a call button so that you can let the technologist know if you have any problems during the scan. The technologist will be watching you at all times and will be in constant communication.

6. A loop of conducting material called a surface coil may be placed over the area to be examined if it is a relatively small area, such as a joint.

7. You will be given earplugs or a headset to wear to help block out the noise from the scanner. Some headsets may provide music for you to listen to. During the scanning process, you will hear clicking and thumping noises as the magnetic field is created and pulses of radio waves are sent from the scanner.

8. It will be important for you to stay very still during the exam. Any movement could cause distortion and affect the quality of the scan.

9. At certain times, you may be told to hold your breath, or to not breathe for a few seconds, depending on the body part being examined. You will then be told when you can breathe. You should not have to hold your breath for longer than a few seconds.

10. If contrast dye is used, you may feel some effects when the dye is injected into the IV line. These effects include a warm flushing sensation or a feeling of coldness, a salty or metallic taste in the mouth, a brief headache, itching, or nausea. These effects usually only last for a few moments.

11. Tell the technologist right away if you have any trouble breathing, sweating, numbness, or heart palpitations.

12. Once the scan is done, the table will slide out of the scanner and you will be helped off the table.

13. If an IV line was put in, it will be removed.

While the MRI scan itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly if you’ve recently been injured or had surgery. The technologist will use all possible comfort measures and do the scan as quickly as possible to reduce any discomfort or pain.

On occasion, some people with metal fillings in their teeth may feel some slight tingling of the teeth during the scan.

What happens after an MRI scan?

Move slowly when getting up from the scanner table so you don't have any dizziness or lightheadedness from lying flat for the length of the procedure.

If any sedatives were used for the scan, you may need to rest until the sedatives have worn off. You will also need someone to drive you home.

If contrast dye is used, you may be watched for some time for any side effects or reactions to the contrast dye, such as itching, swelling, rash, or trouble breathing.

If you had an IV and you notice any pain, redness, or swelling at the IV site after you go home, call your healthcare provider. This could be a sign of infection or other type of reaction.

Otherwise, there is no special type of care needed after a MRI scan of the bones, joints, and soft tissues. You may go back to your usual diet and activities, unless your healthcare provider tells you differently.

Your healthcare provider may give you other instructions after the procedure, depending on your particular situation.

Next steps

Before you agree to the test or procedure, make sure you know:

• The name of the test or procedure

• The reason you are having the test or procedure

• What results to expect and what they mean

• The risks and benefits of the test or procedure

• What the possible side effects or complications are

• When and where you are to have the test or procedure

• Who will do the test or procedure and what that person’s qualifications are

• What would happen if you did not have the test or procedure

• Any alternative tests or procedures to think about

• When and how you will get the results

• Who to call after the test or procedure if you have questions or problems

• How much you will have to pay for the test or procedure