en españolResonancia magnética: cerebro

What It Is

Magnetic resonance imaging (MRI) of the brain is a safe and painless test that uses a magnetic field and radio waves to produce detailed images of the brain and the brain stem. An MRI differs from a CAT scan (also called a CT scan or a computed axial tomography scan) because it does not use radiation.

An MRI scanner consists of a large doughnut-shaped magnet that often has a tunnel in the center. Patients are placed on a table that slides into the tunnel. Some centers have open MRI machines that have larger openings and are helpful for patients with claustrophobia. MRI machines are located in hospitals and radiology centers.

During the exam, radio waves manipulate the magnetic position of the atoms of the body, which are picked up by a powerful antenna and sent to a computer. The computer performs millions of calculations, resulting in clear, cross-sectional black and white images of the body. These images can be converted into three-dimensional (3-D) pictures of the scanned area. This helps pinpoint problems in the brain and the brain stem when the scan focuses on those areas.

Why It's Done

MRI can detect a variety of conditions of the brain such as cysts, tumors, bleeding, swelling, developmental and structural abnormalities, infections, inflammatory conditions, or problems with the blood vessels. It can determine if a shunt is working and detect damage to the brain caused by an injury or a stroke.

MRI of the brain can be useful in evaluating problems such as persistent headaches, dizziness, weakness, and blurry vision or seizures, and it can help to detect certain chronic diseases of the nervous system, such as multiple sclerosis.

In some cases, MRI can provide clear images of parts of the brain that can't be seen as well with an X-ray, CAT scan, or ultrasound, making it particularly valuable for diagnosing problems with the pituitary gland and brain stem.

Preparation

In many cases, a brain MRI requires no special preparation. However, the technician will have your child remove any objects containing metal (such as eyeglasses and jewelry) because they can produce a bright or blank spot on the diagnostic film. You'll also be asked questions to make sure your child doesn't have any internal metal clips from previous surgery or anything else that might cause a problem near a strong magnetic field. Electronic devices aren't permitted in the MRI room.

To get the highest quality MRI results, your child will need to lie still during the scan. For this reason, sedation may be needed, especially for babies and young kids, who often have trouble staying still for the test. Sedation is also helpful for kids who have trouble relaxing in an enclosed space (claustrophobia).

Sedation medicines usually are given through an intravenous (IV) line (small tube in a vein) to help a child stay asleep during the entire test.

If your child will be sedated, food and liquids will be stopped at a certain point before the MRI to allow the stomach to empty. It's important to notify the MRI technician of any illness, allergy, previous drug reactions, or pregnancy.

You can stay in the MRI room with your child until the test begins, and some centers let parents stay throughout the test. Otherwise, you'll join the technician in an outer room or be asked to stay in a waiting room.

Procedure

An MRI of the brain usually takes 30-45 minutes to perform. Your child will lie on the movable scanning table while the technologist places him or her into position. A special plastic device called a coil may be placed around your child's head. The table will slide into the tunnel and the technician will take images of the head. Each scan takes a few minutes.

To detect specific problems, your child may be given a contrast solution through an IV. The solution is painless as it goes into the vein. The contrast highlights certain areas of the brain, such as blood vessels, so doctors can see more detail in specific areas. The technician will ask if your child is allergic to any medications or food before the contrast solution is given. The contrast solution used in MRI tests is generally safe. However, allergic reactions can occur. Talk to your doctor about the benefits and risks of receiving contrast solution in your child's case.

As the exam proceeds, your child will hear repetitive sounds from the machine, which are normal. Your child may be given headphones to listen to music or earplugs to block the noise, and will have access to a call button in case he or she becomes uneasy during the test. If sedated, your child will be monitored at all times and will be connected to a machine that checks the heartbeat, breathing, and oxygen level.

Once the exam is over, the technician will help your child off the table; if sedation was used, your child may be moved to a recovery area.

What to Expect

An MRI exam is painless. Your child may have to lie still on the MRI table for 30-45 minutes during the procedure, but there are brief breaks between each scan. If your child feels cold lying on the MRI table, a blanket can be provided.

Unless sedation was used or you are told otherwise, your child can immediately return to normal routines and diet. Most sedation wears off within 1-2 hours, and any contrast material given should pass through the body in about 24 hours.

Getting the Results

The MRI images will be viewed by a radiologist who's specially trained in interpreting the scans. The radiologist will send a report to your doctor, who'll discuss the results with you and explain what they mean. In most cases, results can't be given directly to the patient or family at the time of the test. If the MRI was done on an emergency basis, the results can be made available quickly.

Risks

MRIs are safe and relatively easy. No health risks are associated with the magnetic field or radio waves, since the low-energy radio waves use no radiation. The procedure can be repeated without side effects.

If your child requires sedation, you may discuss the risks and benefits of sedation with your provider. Also, because contrast solutions can cause allergic reactions in some kids, be sure to check with your doctor before your child receives any solution. There should be medical staff on hand who are prepared to handle an allergic reaction. 

If your child has decreased kidney function, this is an important medical condition to discuss with the radiologist and technician before receiving IV contrast since it may lead to some rare complications.

Helping Your Child

You can help your child prepare for an MRI by explaining the test in simple terms before the examination. Make sure to explain that pictures of the head will be taken and that the equipment will probably make knocking and buzzing noises.

It also may help to remind your child that you'll be nearby during the entire test.

If an injection of contrast fluid or sedation is needed, you can tell your child that the initial sting of the needle will be brief and that the test itself is painless.

If your child will be awake for the test, be sure to explain the importance of lying still.

If You Have Questions

If you have questions about the MRI procedure, speak with your doctor. You can also talk to the MRI technician before the exam.