An MRI is a test that uses a magnetic field and pulses of radio wave energy to make pictures of the spine. In many cases, an MRI gives different information than an X-ray, an ultrasound, or a CT scan. An MRI also may show problems that cannot be seen with other imaging tests.
For an MRI, your body is placed inside a machine that contains a strong magnet. Pictures from an MRI can be saved and stored on a computer for further study. In some cases, a contrast material may be used during the MRI to show certain parts of the body more clearly.
The MRI can find changes in the spine and in other tissues. It also can find problems such as infection or a tumour. MRI can look at the spine in the neck (cervical), upper back (thoracic), or lower back (lumbosacral). The entire spine can be seen in one series of pictures to find a tumour. More detailed pictures of one area, such as the lumbar spine, may be taken.
MRI may be used to check low back problems.
You may be able to have an MRI with an open machine that doesn't enclose your entire body. But open MRI machines aren't available everywhere. The pictures from an open MRI may not be as good as those from a standard MRI machine.
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Why It Is Done
An MRI of the spine is done to:
- Find problems of the spinal discs, such as a ruptured disc. The test may also show if a disc is pressing on a nerve, causing symptoms such as sciatica.
- Find areas of the spine where the canal is abnormally narrowed (spinal stenosis) and may need surgery.
- Find tumours affecting the bones or nerves of the spine. The tumours that most commonly spread to the spine include those from prostate, breast, or lung cancer.
- Find compression fractures of the spine.
- Check areas of joint inflammation (arthritis) or bone loss found during an X-ray test or a bone scan.
- Find areas of the spine that do not have good blood supply.
- Find an infection.
- Find nerve damage caused by injury or disease, such as multiple sclerosis.
- Check problems of the spine that have been present since birth (congenital).
An MRI may be done using contrast material to see abnormal tissue more clearly. The contrast material also may help tell the difference between old surgical scars and a new disease or injury.
How To Prepare
Before your MRI test, tell your doctor and the MRI technologist if you:
- Are allergic to any medicines. The contrast material used for MRI does not contain iodine. If you know that you are allergic to the contrast material used for the MRI, tell your doctor before having another test.
- Have a health condition, such as diabetes, sickle cell anemia, or kidney problems. You may need to change your medicine schedule. And some conditions may prevent you from having an MRI using contrast material.
- Are or might be pregnant.
- Have any metal implanted in your body. This helps your doctor know if the test is safe for you. Tell your doctor if you have:
- Heart and blood vessel devices such as a coronary artery stent, a pacemaker, an ICD (implantable cardioverter-defibrillator), or a metal heart valve.
- Metal pins, clips, or metal parts in your body, including artificial limbs and dental work or braces.
- Any other implanted medical device, such as a medicine infusion pump or a cochlear implant.
- Cosmetic metal implants, such as in your ears, or tattooed eyeliner.
- Had recent surgery on a blood vessel. In some cases, you may not be able to have the MRI test.
- Have an intrauterine device (IUD) in place. An IUD may prevent you from having the MRI test done.
- Become very nervous in confined spaces. You need to lie very still inside the MRI magnet, so you may need medicine to help you relax. Or you may be able to have the test done with open MRI equipment. It is not as confining as standard MRI machines.
- Wear any medicine patches. The MRI may cause a burn at the patch site.
You may be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .
How It Is Done
An MRI is usually done by an MRI technologist. The pictures are usually read by a radiologist. But some other types of doctors can also read an MRI scan.
You will need to remove all metal objects (such as hearing aids, dentures, jewellery, watches, and hairpins) from your body, because these objects may be attracted to the powerful magnet used for the test.
You will need to take off all or most of your clothes, depending on which area is examined. (You may be allowed to keep on your underwear if it is not in the way.) You will be given a gown to use during the test. If you are allowed to keep some of your clothes on, you should empty your pockets of any coins and cards (such as credit cards or ATM cards) with scanner strips on them. The MRI magnet may erase the information on the cards.
During the test, you usually lie on your back on a table that is part of the MRI scanner. Your head, chest, and arms may be held with straps to help you remain still. The table will slide into the space that contains the magnet. A device called a coil may be placed over or wrapped around the area to be scanned. A belt strap may be used to sense your breathing or heartbeat. This triggers the machine to take the scan at the right time.
If you feel very nervous inside the machine, you may be given a sedative to help you relax. You may be able to have an MRI with an open machine that doesn't enclose your entire body. But open MRI machines aren't available everywhere. The pictures from an open MRI may not be as good as those from a standard MRI machine.
Inside the scanner you will hear a fan and feel air moving. You may also hear tapping or snapping noises as the MRI scans are taken. You may be given earplugs or headphones with music to reduce the noise. It is very important to hold completely still while the scan is being done. You may be asked to hold your breath for short periods of time.
During the test, you may be alone in the scanner room. But the technologist will watch you through a window. You will be able to talk with the technologist through a two-way intercom.
If contrast material is needed, the technologist will put it in an intravenous (IV) line in your arm. The material may be given over 1 to 2 minutes. Then more MRI scans are done.
An MRI usually takes 30 to 60 minutes but can take as long as 2 hours.
How It Feels
You will not have pain from the magnetic field or radio waves used for the MRI. The table you lie on may feel hard, and the room may be cool. You may be tired or sore from lying in one position for a long time.
If a contrast material is used, you may feel some coolness when it is put into your IV.
In rare cases, you may feel:
- A tingling feeling in the mouth if you have metal dental fillings.
- Warmth in the area being examined. This is normal. Tell the technologist if you have nausea, vomiting, headache, dizziness, pain, burning, or breathing problems.
There are no known harmful effects from the strong magnetic field used for MRI. But the magnet is very powerful. The magnet may affect pacemakers, artificial limbs, and other medical devices that contain iron. The magnet will stop a watch that is close to the magnet. Any loose metal object has the risk of causing damage or injury if it gets pulled toward the strong magnet.
Metal parts in the eyes can damage the retina. If you may have metal fragments in the eye, an X-ray of the eyes may be done before the MRI. If metal is found, the MRI will not be done.
Iron pigments in tattoos or tattooed eyeliner can cause skin or eye irritation.
An MRI can cause a burn with some medicine patches. Be sure to tell your health professional if you are wearing a patch.
There is a slight risk of an allergic reaction if contrast material is used during the MRI. But most reactions are mild and can be treated using medicine. There also is a slight risk of an infection at the IV site.
A dye (contrast material) that contains gadolinium may be used in this test. Be sure to tell your doctor if:
- You are pregnant or think you may be pregnant.
- You have kidney problems.
- You've had more than one test that used gadolinium.
Health Canada has safety warnings about gadolinium. But for most people, the benefit of its use in this test outweighs the risk.
If you breastfeed and are concerned about whether the dye used in this test is safe, talk to your doctor. Most experts believe that very little dye passes into breast milk and even less is passed on to the baby. But if you prefer, you can store some of your breast milk ahead of time and use it for a day or two after the test.
The radiologist may discuss some of the results of the MRI with you right after the test. Complete results are usually ready for your doctor in 1 to 2 days.
The bones of the spine, discs, and nerves are normal.
No tumours, inflammation, or areas of nerve damage in the spine are present.
No disease or bone loss in the spine is present.
No ruptured discs are present. There are no structures pressing on a nerve.
No structural problems that have been present from birth (congenital problems) are found.
Tumours, inflammation, or areas of nerve damage in the spine are present. A disease of the spinal cord, such as multiple sclerosis, is found.
Narrowing of the spinal canal ( spinal stenosis) is present.
Broken bones or bone loss in the spine caused by injury or disease, such as arthritis, is found.
One or more discs of the spine are bulging or ruptured or pressing on a nerve.
A condition that has been present from birth (congenital condition) is found in the spine or the vertebrae.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Medical devices that use electronics, such as a pacemaker or medicine infusion pump. The MRI magnet may cause problems with these devices, and that may keep you from having an MRI.
- Medical devices that have metal in them. The metal might make some of the detailed MRI pictures blurry. This may prevent your doctor from seeing the organ that is being looked at. For example, any metal in your spine may prevent your doctor from seeing it clearly.
- Inability to remain still during the test.
- Obesity. A person who is very overweight may not fit into standard MRI machines.
Many modern medical devices that do not use electronics—such as heart valves, stents, or clips—can be safely placed in most MRI machines. But some newer MRI machines have stronger magnets. The safety of MRI scans with these stronger MRI magnets in people with medical devices is not known.
What To Think About
- Sometimes your MRI test results may be different from the results of CT, ultrasound, or X-ray tests, because the MRI scan shows tissue differently.
- Magnetic resonance imaging (MRI) of the spine can often be used instead of other tests that use X-rays, such as a computed tomography (CT) scan or myelography.
- MRI is a safe test for looking at structures and organs inside the body. It costs more than other methods and may not be available in your area.
- Open MRI machines are now made so that the magnet does not completely surround you. But these machines may not be available in all medical centres. Open MRI is useful for people who are claustrophobic or obese.
Current as of: September 23, 2020
Author: Healthwise Staff
William H. Blahd Jr. MD, FACEP - Emergency Medicine
Brian D. O'Brien MD - Internal Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Kathleen Romito MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Howard Schaff MD - Diagnostic Radiology
Current as of: September 23, 2020
Author: Healthwise Staff
Medical Review:William H. Blahd Jr. MD, FACEP - Emergency Medicine & Brian D. O'Brien MD - Internal Medicine & E. Gregory Thompson MD - Internal Medicine & Adam Husney MD - Family Medicine & Kathleen Romito MD - Family Medicine & Martin J. Gabica MD - Family Medicine & Howard Schaff MD - Diagnostic Radiology