Magnetic resonance imaging (MRI) uses a large magnet, radiofrequencies, and a computer to make detailed images of organs and structures within the body. In this case, the images are of the brain and spine. MRI is used to help diagnose a health problem.
The MRI machine is large and tube-shaped. It creates a strong magnetic field around you. Some look like narrow tunnels. Others are more open. This magnetic field, along with a radiofrequency, alters the hydrogen atoms' natural alignment in the body. Computers are then used to form 2-D images of the brain or spine based on the activity of the hydrogen atoms. Cross-sectional views can be done to show more details. MRI does not use radiation, like X-rays or CT scans.
MRI may be used instead of CT when organs or soft tissue are being studied. This is because bones don't obscure the images of organs and soft tissues, as does CT scanning.
Functional MRI of the brain (fMRI) is used to find exactly where a certain function such as speech or memory happens in the brain. The general areas of the brain in which these functions happen are known, but the exact location may vary from person to person. During fMRI imaging of the brain, you will be asked to do a certain task, such as recite the Pledge of Allegiance, while the scan is being done. By pinpointing the exact location of the functional center in the brain, healthcare providers can plan surgery or other treatments for certain brain disorders.
MRI may be used to check the brain or spinal cord for injuries, structural abnormalities, or certain other conditions, such as:
Collections of pus (abscesses)
Problems of the spine or brain you are born with (congenital)
Weakening and ballooning of an artery (aneurysm)
Abnormal and dilated veins (venous malformations)
Bleeding into the brain or spinal cord
Area of bleeding just under the covering of the brain (subdural hematoma)
Degenerative diseases such as multiple sclerosis
Problem in the brain caused by lack of oxygen (hypoxic encephalopathy)
Inflammation or infection of the brain (encephalomyelitis)
Fluid in the brain (hydrocephalus)
Cause of epilepsy (seizures)
Pituitary gland disorders
Herniation or degeneration of disks of the spine
MRI may also be done to help plan surgeries of the spine, such as decompression of a pinched nerve or spinal fusion. Or it can be used to look for problems after surgery, such as scarring or infection. It can also help to identify the specific part of the brain controlling a function, such as speech or memory, to help in treating a condition of the brain.
There may be other reasons for your healthcare provider to advise an MRI of the spine or brain. Talk with your healthcare provider about the reason for your MRI.
There is no risk of exposure to radiation during an MRI procedure.
Because of the strong magnet in an MRI scanner, MRI cannot be used if you have:
Implanted pacemaker or cardiac defibrillator
Some older intracranial aneurysm clips
Certain prosthetic devices
Implanted medicine infusion pumps or medicine ports
Certain intrauterine contraceptive devices
Any other type of iron-based metal implants
Tattoos or body piercings
Internal metal objects or fragments, 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 in the first trimester, MRI should only be used to look at very important problems or suspected problems.
If contrast dye is used, there is a risk for allergic reaction to the dye. Tell your provider if you are allergic or sensitive to medicines, contrast dye, or iodine.
Nephrogenic systemic fibrosis (NSF) 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 dye.
There may be other risks depending on your specific health condition. Be certain your healthcare provider knows about all your health conditions.
Tell your healthcare provider and the technologist doing the test if you:
Have ever had an imaging test (like an MRI or CT scan) with contrast dye
Are allergic to contrast dye, iodine, shellfish, or any medicines
Have a serious health problem, such as diabetes or kidney disease
Are pregnant or may be pregnant, or are breastfeeding
Have any implanted device or metal clips or pins in your body
Your healthcare provider will explain the procedure to you and give you a chance to ask questions. Make a list of questions and discuss these and any concerns with your healthcare provider before the procedure. Consider bringing a family member or trusted friend to the medical appointment. They can help you remember your questions and concerns and take notes.
If your procedure 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, you don't need to fast or limit any activities before an MRI procedure.
Before the MRI, it is very important that you tell the technologist if any of the following 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 metal fragments anywhere in the body
You have permanent eyeliner or tattoos
You are pregnant or think you may be pregnant
You have 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
You may get medicine (sedative) to help you relax before the procedure, so plan to have someone drive you home afterward.
Based on your health condition, your healthcare provider may have other instructions for you on how to get ready.
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 spine and brain follows this process:
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.
If you are asked to remove clothing, you will be given a gown to wear.
If you are to have an MRI with contrast, an IV (intravenous) line will be started in your hand or arm for injection of the contrast dye.
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.
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 procedure. The technologist will be watching you at all times and will be in constant communication.
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.
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.
At intervals, you may be told to hold your breath, or to not breathe for a few seconds. You will then be told when you can breathe. You should not have to hold your breath for longer than a few seconds.
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 last only for a few moments.
You should tell the technologist right away if you feel any breathing difficulties, sweating, numbness, or heart palpitations.
Once the scan is done, the table will slide out of the scanner and you will be helped off the table.
If an IV line was put in, it will be removed.
While the MRI 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 complete the procedure as quickly as possible to reduce any discomfort or pain.
On occasion, some people with metal fillings in their teeth may experience some slight tingling of the teeth during the procedure.
Move slowly when getting up from the scanner table to prevent any dizziness or lightheadedness from lying flat for the length of the procedure.
If any sedatives were used for the procedure, 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 a period for any side effects or reactions to the contrast dye, such as itching, swelling, rash, or trouble breathing.
If you notice any pain, redness, or swelling at the IV site after you go home, tell your healthcare provider. It could be a sign of infection or other type of reaction.
Otherwise, there is no special type of care needed after an MRI scan of the spine and brain. You may go back to your usual diet and activities, unless your healthcare provider tells you differently.
Your healthcare provider may give you more instructions after the procedure, depending on your particular situation.
Before you agree to the test or the 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