Heart MRI

MRI scans

MRI stands for magnetic resonance imaging. It allows imaging of the interior of the body without using x-rays or other types of ionizing radiation. An MRI scan is capable of showing fine detail of different tissues.

Definition

Heart magnetic resonance imaging (MRI) is a method that uses powerful magnets and radio waves to create pictures of the heart. It does not use radiation (x-rays).

The test may be done as part of a chest MRI.

How the test is performed

You will be asked to lie on a narrow table, which slides into a large tunnel-like tube. The health care provider may inject a dye through one of your veins. This helps certain diseases and organs show up better on the images.

Unlike and computed tomographic (CT) scans, MRI does not use radiation. Instead, it uses powerful magnets and radio waves. The magnetic field produced by an MRI forces certain atoms in your body to line up in a certain way. It's similar to how the needle on a compass moves when you hold it near a magnet.

The radio waves are sent toward these atoms and bounce back, and a computer records the signal. Different types of tissues send back different signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue.

A technologist will operate the machine from a room next door and watch you during the entire study.

Several sets of images are usually needed. Each one takes about 2-15 minutes. A complete scan may take up to 1 hour. Newer scanners may complete the process in less time.

How to prepare for the test

There is usually no preparation needed. An MRI can be done immediately after other imaging studies. If contrast (dye) or sedation is used, you may be asked not to eat for 4 to 6 hours prior to the scan.

The strong magnetic fields created during an MRI can interfere with certain implants, particularly cardiac pacemakers. People with cardiac pacemakers can not have an MRI and should not enter the MRI area.

If you have any of the following metallic objects in your body, you should not get an MRI:

• Brain aneurysm clips
• Certain artificial heart valves
• Inner ear (cochlear) implants
• Older vascular stents
• Recently placed artificial joints

You will be asked to sign a consent form that says you do not have any of these items in your body. You may be asked to wear a hospital gown.

Certain metallic objects are not allowed into the room.

• Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
• Pins, hairpins, metal zippers, and similar metallic items can distort the images.
• Removable dental work should be taken out just prior to the scan.

When the MRI magnet is turned on, pens, pocketknives, and eyeglasses may fly across the room. This can be dangerous, so such items are not allowed into the scanner area.

How the test will feel

A heart MRI exam causes no pain. Some people may become anxious when inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.

The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. Ear plugs are usually given to help reduce the noise.

An intercom in the scanner allows you to speak to the person operating the exam at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.

There is no recovery time, unless sedation was necessary. (You will need someone to drive you home if sedation was given.) After an MRI scan, you can resume your normal diet, activity, and medications, unless otherwise instructed by your doctor.

Why the test is performed

MRI provides detailed pictures of the heart and blood vessels from many views.

It may be used to diagnose:

• Heart muscle damage after a heart attack
• Birth defects of the heart
• Heart tumors and growths

MRI is sometimes used to avoid the dangers of angiography, repeated exposure to radiation, or the use of iodine-based dye (contrast).

It may provide additional information when an echocardiogram is unclear.

What abnormal results mean

The sensitivity of MRI depends, in part, on the experience of the radiologist.

A heart MRI may reveal the following disorders:

• Heart valve disorders
• Pericardial effusion
• Tumor invasion of blood vessels or pericardium (around the heart)
• Atrial myxoma
• Congenital heart abnormalities (such as pulmonary atresia)
• Fibrosis or scarring of heart muscle
• How much heart muscle is dead (after a heart attack)

What the risks are

There is no ionizing radiation involved in MRI, and there have been no documented significant side effects of the magnetic fields and radio waves used on the human body to date.

The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.

People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.

MRI is usually not recommended for traumatic injuries, because traction and life-support equipment cannot safely enter the scanner area, and scans can take a long time.

Special considerations

MRI is more accurate than CT scan or other tests for certain conditions, but less accurate for others. Disadvantages include the high cost, long duration of the scan, and sensitivity to movement. People with claustrophobia or who are confused or anxious may have difficulty lying still for the relatively long scan times. MRI is not portable and is incompatible with some metallic implants, life support devices, traction, apparatus, and similar equipment.

MRI is superior in most cases in which differentiation of soft tissues is necessary. It can view organs without obstruction by bone and foreign bodies. It is capable of showing the tissues from multiple viewpoints and is a non invasive way to evaluate blood flow.