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Heart Conditions in Children - Magnetic Resonance Imaging (MRI)

What is MRI?

Picture of a patient in a scanner

MRI (magnetic resonance imaging) is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body. MRI of the heart can be used for the following reasons:

  • To evaluate the heart's structure
  • To assess blood flow to the heart muscle
  • To evaluate infections
  • To detect tumors
  • To assess blood flow to and from the lungs and the body
  • To measure the size of the heart's chambers
  • To measure the size of the heart's major blood vessels 

The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient. This magnetic field, along with a radiofrequency, alters the natural alignment of hydrogen atoms in the body. Computers are then used to form two-dimensional images of the heart's structure based on the activity of the hydrogen atoms. Cross-sectional views can be obtained to reveal further details. MRI does not use ionizing radiation, like X-rays or computed tomography (CT scans).

MRI does not pose any risks unless your child has any kind of implanted metal objects in the body. Be sure to let your child's doctor know if your child has any of the following:

  • Implanted pacemaker
  • Implanted medication device, such as an insulin pump
  • Metal clips or pins, or other metal objects in the body
  • Any bullet wounds, particularly if the bullet remains in the body
  • Any metal joint replacements or heart valve replacements

What is the preparation for a MRI?

Make sure your child is not wearing any metal jewelry, hair clips, or barrettes, as these will have to be removed prior to the test.

If your child's doctor schedules a MRI scan and decides to use contrast dye to enhance the pictures, your child may need to be NPO (fasting, nothing by mouth) for several hours prior to the procedure. You will receive instructions about this from your child's doctor or another health care professional.

You will need to let your child's doctor know if your child has ever had a reaction to any MRI contrast dye, or if he or she is allergic to iodine. The risk of a serious allergic reaction to MRI contrast materials is rare, and radiology departments are equipped to handle them. A reported seafood allergy is not considered to be a contraindication for contrast. If your teenage daughter is pregnant or could be pregnant, you should notify the doctor prior to the procedure.

Children may receive a mild sedative before the procedure to make them feel more comfortable, and to help them to remain still and quiet during the procedure, which may last 30 to 60 minutes.

Parents may be able to stay with their child in the MRI room until he or she becomes sleepy, but are usually asked to wait in another area during the procedure. One or both parents may be allowed to stay with their child during the procedure under certain conditions.

How is a MRI performed?

The MRI scanner is located in a large room. Your child will lie on a narrow table that slides into the hollow tube-shaped scanner.

The MRI technologist will be in an adjacent room where the equipment controls are located. However, they will be able to see your child through a large window and will be monitoring him or her constantly during the procedure. If your child is not sedated, he or she will be given a call bell device to let the staff know if he or she needs anything during the procedure.

The MRI scanning machine makes loud banging or knocking noises when adjustments are being made. Your child will wear a set of headphones to help protect his or her ears from the noise of the scanner and to hear instructions from the MRI staff. Music may be played in the headphones when instructions are not being given.

Once the procedure begins, your child will need to remain very still at all times so that movement will not adversely affect the quality of the images. At intervals, he or she will be instructed to hold his or her breath, if possible, for a few seconds. He or she will then be told when to breathe. Your child should not have to hold his or her breath for longer than a few seconds, so this should not be uncomfortable. Young children who cannot remain still for the procedure will be given medication to help them relax or sleep during the MRI scan.

If the MRI scan is being done "with and without contrast," your child will receive contrast medication through an IV about halfway through the procedure. He or she may feel a warm or flushed sensation just after the dye goes into the vein. This is a normal sensation and it will go away shortly.

Once the procedure is finished, the table will slide out of the scanner. If your child received medication for relaxation or sleep, he or she will be monitored until the medication wears off and he or she is awake again. If an IV was inserted, it will be taken out after the procedure is over and your child is awake.

The test normally takes approximately 30 to 60 minutes, though some may take a couple of hours.

What happens after the procedure?

Without sedation, your child should be able to resume normal activities immediately, unless your child's doctor instructs you otherwise.

With sedation, your child may feel groggy, tired, or sleepy for a period of several hours after the procedure. However, the sedation effects should disappear within a day or so.

Depending on the results of the MRI, additional tests or procedures may be scheduled, to gather further diagnostic information.

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