Magnetic resonance imaging (MRI) is a diagnostic procedure that uses a
combination of a large magnet, radio frequencies, and a computer to
produce detailed images of organs and structures within the body.
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 hydrogen atoms' natural
alignment in the body. Computers are then used to form two-dimensional
(2D) 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, as do X-rays or computed
tomography (CT scans).
A magnetic field is created and pulses of radio waves are sent from a
scanner. The magnetic field aligns the hydrogen protons in your body
along the same vector. The radio waves then knock the protons out of
this aligned position. As the nuclei realign back into proper position,
they send out radio signals. These signals are received by a computer
that analyzes and converts them into an image of the part of the body
being examined. This image appears on a viewing monitor. Some MRI
machines look like narrow tunnels, while others are more open.
MRI may be used instead of a CT scan in situations where organs or soft
tissue are being studied, because with MRI scanning bones do not obscure
the images of organs and soft tissues, as does CT scanning.
Other related procedures that may be used to assess the heart include
resting or exercise electrocardiogram (ECG), Holter monitor,
signal-averaged ECG, cardiac catheterization, chest X-ray, computed
tomography (CT scan) of the chest, electrophysiological studies,
myocardial perfusion scans, radionuclide angiography, and ultrafast CT
scan. Please see these procedures for additional information.
MRI of the heart may be performed for further evaluation of signs or
symptoms that may suggest:
Atherosclerosis. A gradual clogging of the
arteries over many years by fatty materials and other substances
in the blood stream
Cardiomyopathy. An enlargement of the heart due
to thickening or weakening of the heart muscle
Congenital heart disease. Defects in one or
more heart structures that occur during formation of the fetus,
such as a ventricular septal defect (hole in the wall between
the two lower chambers of the heart)
Congestive heart failure. A condition in which
the heart muscle has become weakened to an extent that blood
cannot be pumped efficiently, causing buildup (congestion) in
the blood vessels, lungs, feet, ankles, and other parts of the
Aneurysm. A dilation of a part of the heart
muscle or the aorta (the large artery that carries oxygenated
blood out of the heart to the rest of the body), which may cause
weakness of the tissue at the site of the aneurysm
Valvular heart disease. Malfunction of one or
more of the heart valves that may cause an obstruction of the
blood flow within the heart
Cardiac tumor. A tumor of the heart that may
occur on the outside surface of the heart, within one or more
chambers of the heart (intracavitary), or within the muscle
tissue of the heart
There may be other reasons for your doctor to recommend an MRI of the
Because radiation is not used, there is no risk of exposure to ionizing
radiation during an MRI procedure.
Due to the use of the strong magnet, MRI cannot be performed on patients
with implanted pacemakers, some older intracranial aneurysm clips,
cochlear implants, certain prosthetic devices, implanted drug infusion
pumps, neurostimulators, bone-growth stimulators, certain intrauterine
contraceptive devices, or any other type of iron-based metal implants.
MRI is also contraindicated in the presence of some internal metallic
objects such as bullets or shrapnel, as well as surgical clips, pins,
plates, screws, metal sutures, or wire mesh.
If you are pregnant or suspect that you may be pregnant, you should
notify your health care provider. MRI is generally considered safe in
pregnancy; however, especially in the first trimester, you and your
doctor should discuss the potential risks and benefits of having the
If contrast dye is used, there is a risk for allergic reaction to the
dye. Patients who are allergic to or sensitive to medications should
notify their doctor. If you have severe kidney disease or are on kidney
dialysis, there is a risk of a condition called "nephrogenic systemic
fibrosis" from the dye. You should discuss this risk with your doctor
prior to the test.
MRI contrast may have an effect on other conditions, such as allergies,
asthma, anemia, hypotension (low blood pressure), kidney disease, and
sickle cell disease.
Nephrogenic Systemic Fibrosis (NSF) is a very rare but serious
complication of MRI contrast use in patients with kidney disease or
kidney failure. If you have a history of kidney disease, kidney failure,
kidney transplant, liver disease or are on dialysis, you must inform the
MRI technologist or radiologist prior to receiving contrast.
There may be other risks depending on your specific medical condition.
Be sure to discuss any concerns with your doctor prior to the procedure.
Your doctor will explain the procedure to you and offer you the
opportunity to ask any questions that you might have about the
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
something is not clear.
Notify the technologist if you have ever had a reaction to any
contrast dye, or if you are allergic to iodine or seafood.
Generally, there is no special restriction on diet or activity
prior to an MRI procedure.
Notify the technologist if you are pregnant or suspect you may
Before the examination, it is extremely important that you
inform the technologist if any of the following apply to you:
You are claustrophobic and think that you will
be unable to lie still while inside the scanning
machine, in which case you may be given a
You have a pacemaker or have had heart valves
You have any type of implanted pump, such as an
You have metal plates, pins, metal implants,
surgical staples, or aneurysm clips
You have any metallic fragments anywhere in the
You have permanent eye liner or tattoos
You are pregnant or suspect you may be pregnant
You ever had a bullet wound
You have ever worked with metal (for example, a
metal grinder or welder)
You have any body piercing
You have an intrauterine device (IUD)
Sedative medication may be given if you have claustrophobia
and/or anxiety that would make it difficult for you to remain
still during the procedure.
Based on your medical condition, your doctor may request other
MRI may be performed on an outpatient basis or as part of your stay in a
hospital. Procedures may vary depending on your condition and your
an MRI follows this process:
You will be asked to remove any clothing, jewelry, eyeglasses,
hearing aids, hairpins, removable dental work, or other objects
that may interfere with the procedure.
If you are asked to remove clothing, you will be given a gown to
If you are to have a procedure done with contrast, an
intravenous (IV) line will be started in the hand or arm for
injection of the contrast dye.
You will lie on a scan table that slides into a large circular
opening of the scanning machine. Pillows and straps may be used
to prevent movement during the procedure.
The technologist will be in another room where the scanner
controls are located. However, you will be in constant sight of
the technologist through a window. Speakers inside the scanner
will enable the technologist to communicate with 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
A surface coil may be placed over the area to be examined.
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, a clicking noise will sound as the
magnetic field is created and pulses of radio waves are sent
from the scanner.
It will be important for you to remain very still during the
examination, as any movement could cause distortion and affect
the quality of the scan.
At intervals, you may be instructed 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 for your procedure, you may feel some
effects when the dye is injected into the IV line. These effects
include coolness or discomfort at the IV site, and should only
last for a few moments.
You should notify the technologist if you feel any breathing
difficulties, sweating, numbness, or heart palpitations.
Once the scan has been completed, the table will slide out of
the scanner and you will be assisted off the table.
If an IV line was inserted for contrast administration, the line
will be removed.
While the MRI procedure itself causes no pain, having to lie still for
the length of the procedure might cause some discomfort or pain,
particularly in the case of a recent injury or invasive procedure such
as surgery. The technologist will use all possible comfort measures and
complete the procedure as quickly as possible to minimize any discomfort
On occasion, some patients with metal fillings in their teeth may
experience some slight tingling of the teeth during the procedure.
You should move slowly when getting up from the scanner table to avoid
any dizziness or lightheadedness from lying flat for the length of the
If any sedatives were taken for the procedure, you may be required to
rest until the sedatives have worn off. You will also need to avoid
If contrast dye is used during your procedure, you may be monitored for
a period of time for any side effects or reactions to the contrast dye,
such as itching, swelling, rash, or difficulty breathing.
If you notice any pain, redness, and/or swelling at the IV site after
you return home following your procedure, you should notify your doctor
as this could indicate an infection or other type of reaction.
Otherwise, there is no special type of care required after a MRI scan of
the heart. You may resume your usual diet and activities, unless your
doctor advises you differently.
Your doctor may give you additional or alternate instructions after the
procedure, depending on your particular situation.
The content provided here is for informational purposes only, and was
not designed to diagnose or treat a health problem or disease, or
replace the professional medical advice you receive from your physician.
Please consult your physician with any questions or concerns you may
have regarding your condition.
This page contains links to other Web sites with information about this
procedure and related health conditions. We hope you find these sites
helpful, but please remember we do not control or endorse the
information presented on these Web sites, nor do these sites endorse the
information contained here.
For more information, call 1.866.CALL.MLH.