What Is Cardiac MRI?
Magnetic resonance imaging (MRI) is a safe,
noninvasive test that creates detailed images of your organs and tissues.
Noninvasive means that no surgery is done and no instruments are
inserted into your body.
MRI uses radio waves and magnets to create images of
your organs and tissues. Unlike computed tomography (to-MOG-ra-fee) scans (also
called CT scans) or conventional x rays, MRI imaging doesnt use ionizing
radiation or carry any risk of causing cancer.
Cardiac MRI uses a computer to create images of your
heart as its beating, producing both still and moving pictures of your
heart and major blood vessels. Doctors use cardiac MRI to get images of the
beating heart and to look at the structure and function of the heart. These
images can help them decide how best to treat patients with heart problems.
Cardiac MRI is a common test for diagnosing and
evaluating a number of diseases and conditions, including:
Cardiac MRI images can help explain results from
other tests, such as x ray and CT scans. Cardiac MRI is sometimes used to avoid
the need for other tests that use radiation (such as x rays), invasive
procedures, and dyes containing iodine (these dyes may be harmful to people who
have kidney problems).
Sometimes during cardiac MRI, a special dye is
injected into a vein to help highlight the heart or blood vessels on the
images. Unlike the case with x rays, the special dyes used for MRI dont
contain iodine, so they dont present a risk to people who are allergic to
iodine or have kidney problems.
Other Names for Cardiac MRI
- Heart MRI
- Cardiovascular MRI
- Cardiac nuclear magnetic resonance (NMR)
What To Expect Before Cardiac MRI
Youll be asked to fill out a screening form
before the test takes place. The form may ask whether youve had previous
surgeries, whether you have any metal objects in your body, and whether you
have any medical devices (like a cardiac pacemaker) surgically implanted in
your body.
Most, but not all, implanted medical devices are
allowed near the magnetic resonance imaging (MRI) machine. Ask your doctor or
the technician operating the machine if you have concerns about any implanted
devices or conditions that may interfere with the MRI.
MRI can interfere seriously with some types of
implanted medical devices.
- Implanted cardiac pacemakers and defibrillators
can malfunction.
- Cochlear (inner-ear) implants can be damaged.
Cochlear implants are small electronic devices that are used to help people who
are deaf or who cant hear well to get an idea of the sounds around
them.
- Brain aneurysm (AN-u-rism) clips can move due to
MRIs strong magnetic field. This can cause severe injury.
Your doctor will let you know if you shouldnt
have a cardiac MRI because of a medical device.
Your doctor or technician will tell you whether you
need to change into a hospital gown for the test. Dont bring hearing
aids, credit cards, jewelry and watches, eyeglasses, pens, removable dental
work, and anything thats magnetic near the MRI machine.
Tell your doctor if you have a history of becoming
anxious or fearful when in a fairly tight or confined space. This fear is
called claustrophobia (klaw-stro-FO-be-a). In this case, your doctor might give
you medicine to help you relax. Your doctor may ask you to stop eating 6 hours
before you take this medicine on the day of the test.
Some of the newer cardiac MRI machines are open on
all sides. Ask your doctor to help you find a facility that has an open MRI
machine if youre fearful in tight or confined spaces.
Your doctor will let you know if you need to arrange
for a ride home after the test.
What To Expect During Cardiac MRI
Magnetic resonance imaging (MRI) machines are
usually located at a hospital or at a special medical imaging facility. A
radiologist (ra-de-OL-o-jist) or other physician with special training in
medical imaging oversees MRI testing.
Cardiac MRI usually takes 45 to 90 minutes,
depending on how many images are needed. The test may take less time with some
newer MRI machines.
The MRI machine will be located in a specially
constructed room. This will prevent radio waves from disrupting the machine and
will prevent the strong magnetic fields generated by the MRI machine from
interfering with other equipment.
Traditional MRI machines look like a long, narrow
tunnel. Newer MRI machines called short-bore systems are shorter, wider, and
dont completely surround you. Some of the newer machines are open on all
sides. Your doctor will help decide which machine type is best for you.
Cardiac MRI is painless and harmless. You will lie
on your back on a sliding table that goes inside the tunnel-like machine. The
technician will control the machine from the next room. He or she will be able
to see you through a glass window and will be able to talk to you through an
intercom system. Tell the technician if you have a hearing problem.
A Patient Having Cardiac MRI
The photo shows a patient lying on a
sliding table outside of a cardiac MRI machine. The table will slide into the
machine, and the patient will lie quietly while pictures of the heart are
taken.
The MRI machine makes loud humming, tapping, and
buzzing noises. Earplugs may help lessen the noises made by the MRI machine.
Some facilities let you listen to music during the test.
Remaining very still during the test is important.
Any movement may blur the images. If youre unable to lie still, you may
be given medicine to help you relax. You may be asked to hold your breath for
10 to 15 seconds at a time while the technician takes pictures of your heart.
Researchers are studying ways that will allow someone having a cardiac MRI to
breathe freely during the exam, while achieving the same image quality.
A contrast dye, such as gadolinium
(gad-oh-LIN-ee-um), may be used to highlight your blood vessels or heart in the
images. Contrast dye is usually injected into a vein in your arm with a needle.
You may feel a cool sensation during the injection, and you may feel discomfort
where the needle was inserted. Gadolinium doesnt contain iodine so it
wont create problems for people who are allergic to iodine.
If your cardiac MRI includes a stress test to detect
blockages in your coronary arteries, you will receive other medicines to
increase the blood flow in your heart or to increase how fast your heart
beats.
What To Expect After Cardiac MRI
Once the cardiac magnetic resonance imaging (MRI) is
done, if you havent received medicine to help you relax, you will be able
to return to normal activities immediately.
If you did receive medicine to help you relax during
the test, your doctor will tell you when you can return to normal activities.
You will need someone to drive you home.
What Does Cardiac MRI Show?
The doctor supervising your scan will provide your
doctor with the results of your cardiac MRI. Your doctor will discuss the
findings with you.
Cardiac MRI can reveal various heart conditions and
disorders, such as:
Cardiac MRI is a fast, accurate tool that can help
diagnose a heart attack by detecting areas of the heart that dont move
normally, have poor blood supply, or are scarred. Cardiac MRI can show whether
any of the coronary arteries are blocked, causing reduced blood flow to your
heart muscle.
Currently, coronary angiography is the procedure
most commonly used to look at blockages in the coronary arteries. Coronary
angiography is an invasive procedure that uses x rays and iodine-based contrast
dye. Researchers have found that cardiac MRI can replace coronary angiography
in some cases, avoiding the need to use x-ray radiation and iodine-based
dyes.
Cardiac MRI
Figure A shows the hearts
position in the body and the location and angle of the MRI images shown in
figure C. Figure B is a MRI angiogram, which is sometimes used instead of a
standard angiogram. Figure C shows MRI pictures of a normal left ventricle
(left image), a left ventricle damaged from a heart attack (middle image), and
a left ventricle that isnt getting enough blood from the coronary
arteries (right image).
Researchers are discovering new ways to use cardiac
MRI. In the future, cardiac MRI may be able to replace x rays as the main way
to guide invasive procedures such as
cardiac
catheterization (KATH-e-ter-i-ZA-shun). Also, improvements in cardiac MRI
are likely to lead to better methods for detecting heart disease in the
future.
What Are the Risks of Cardiac MRI?
Cardiac magnetic resonance imaging (MRI) produces no
side effects from the magnetic fields and radio waves. This method of obtaining
images of organs and tissues doesnt carry a risk of causing cancer or
birth defects.
Serious reactions to the special contrast dyes used
for MRI are very rare. However, side effects are possible and include the
following:
- Headache
- Nausea
- Dizziness
- Changes in taste
- Allergic reactions
Rarely, the contrast dyes can be harmful in patients
with severe kidney disease.
If your cardiac MRI includes a stress test, more
medicines will be used during the test. These medicines may have additional
side effects that arent expected during a regular MRI scan, such as:
- Arrhythmias
(irregular heartbeats)
- Chest pain
- Shortness of breath
- Palpitations (a sensation of the heart beating
hard or fast)
Key Points
- Cardiac magnetic resonance imaging (MRI) is a
safe, noninvasive test that uses radio waves and magnets to create detailed
images of the heart without using x rays.
- Cardiac MRI can help diagnose and evaluate a
number of diseases and conditions. The test helps doctors decide how to treat
patients who have heart problems.
- Sometimes during cardiac MRI, a special dye is
injected into a vein to help highlight the heart or blood vessels on the
images.
- People who have certain types of implanted
medical devices in their bodies shouldnt have cardiac MRI. Your doctor
will let you know if you shouldnt have a cardiac MRI because of a medical
device.
- Cardiac MRI usually takes 45 to 90 minutes,
depending on how many images are needed. The test may take less time with some
newer MRI machines.
- During the test, you will be asked to lie still
on a sliding table that goes inside a tunnel-like machine. You may be given
medicine to help you relax.
- A doctor who has experience with MRI will provide
your doctor with the results of your test. Your doctor will discuss the
findings with you.
- Cardiac MRI produces no side effects from the
magnetic fields and radio waves. Serious reactions from the contrast dyes used
for MRI are rare.
- In some cases, cardiac MRI can replace coronary
angiography to look at the flow of blood through the coronary arteries,
avoiding the need to use x-ray radiation and iodine-based dyes.
- Researchers are finding new ways to use cardiac
MRI. In the future, cardiac MRI may be used to guide invasive procedures such
as cardiac
catheterization.
Links to Other Information About Cardiac MRI
NHLBI Resources
Non-NHLBI Resources
Clinical Trials
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