| Cardiac Nuclear Medicine
What is Cardiac Nuclear Medicine? Back to Top
Nuclear
medicine is a healthcare specialty involving the use of radioactive
compounds to perform diagnostic imaging examinations that can lead to
the effective treatment of many diseases. Although nuclear medicine is
often considered an independent discipline, it is closely related to
radiology in that radiation is used to develop images of human anatomy.
Cardiac nuclear medicine refers to these diagnostic tests that are used to examine the anatomy and function of the heart.
What are some common uses of the procedure? Back to Top
Cardiac
nuclear medicine tests are indicated for individuals with unexplained
chest pain or chest pain brought on by exercise (called angina) to
permit the early detection of heart disease.
The most common cardiac nuclear medicine procedure, called
myocardial perfusion scanning, enables the visualization of blood-flow
patterns to the heart walls. The test is important for evaluating the
presence and extent of suspected or known coronary artery disease
(blockages) as well as the results of previous injury to the heart from
a heart attack, called a myocardial infarction. It also can be done to
evaluate the results of bypass surgery or other percutaneous
revascularization procedures designed to restore the blood supply to
the heart.
Heart-wall movement and overall heart function can be evaluated with
cardiac gating, a technique that synchronizes the images of the heart
with different parts of the cardiac cycle (contracting or relaxing) as
determined by an electrocardiogram (ECG), which records the electrical
currents that activate the heart muscle and cause it to pump.
How should I prepare for the procedure? Back to Top
You
should avoid caffeine (coffee, tea, etc.) and smoking for 48 hours
before the examination. You should not eat or drink anything after
midnight before the procedure, but continue taking medications with
small amounts of water unless your physician says otherwise. Wear
comfortable, walking shoes and loose-fitting clothes for your
procedure. Tell the technologist and supervising physician if you have
asthma or a chronic lung disease or have problems with your knees, hips
or keeping your balance, which may limit your ability to perform the
exercise needed for this procedure.
What does the equipment look like? Back to Top
The imaging
equipment, called a gamma camera or scintillation camera, consists of
specialized detectors enclosed within a metal housing. The detector
portion of the camera can be changed to a variety of positions to
obtain images of the body from different directions. A nearby computer
console, possibly in another room, is used to develop the images of the
heart.
How does the procedure work? Back to Top
Coronary arteries
are best evaluated by determining the changes in blood flow to the
heart due to exercising. Consequently, you will undergo a stress
test—most commonly through physical exercise—to make your heart work
harder than normal. Then you will be given a radioactive compound,
called a radiopharmaceutical agent or tracer. This compound will
collect in parts of your heart with good blood flow and will give off
gamma rays. The gamma camera detects the rays. Subsequently, a computer
following a set of complicated mathematical formulas will construct
images of the heart based on the detected gamma rays.
How is the procedure performed? Back to Top
For the stress
part of the examination, you will exercise by either walking on a
treadmill or pedaling a stationary bicycle for a few minutes. While you
exercise, the electrical activity of your heart will be monitored by
electrocardiography (ECG), and your blood pressure will be measured
frequently. Before you stop exercising, you will be given the
radiopharmaceutical through an IV leading into a vein in your arm. The
compound is given when the blood flow to the heart is at its peak
because of your exercising. This provides the best opportunity to
identify regions of the heart that are not receiving adequate blood
flow.
One minute later, you will stop exercising. Approximately one
half-hour later, as you lay on an examining table, the compound will
have collected in your heart. The gamma camera will then be used to
obtain images. The gamma camera likely will move slowly and
automatically in an arc over the front of your chest after it is
positioned initially by the technologist.
The images obtained after exercise must usually be compared with
images of your heart obtained after injection of the same
radiopharmaceutical while you are resting. This may be performed before
or after the exercise part of the examination, depending on the
protocol used. Comparison of the exercise and resting images is done to
determine whether coronary blood flow has changed once you have rested
and to check for coronary artery disease.
If you are unable to use a treadmill or bicycle, you will not
exercise, but you will be given a drug that will cause your heart to
work as hard as if you had exercised. You will then be given the
radiopharmaceutical.
Immediately after the procedure, a diagnostic radiologist with
specialized training in nuclear medicine will check the quality of the
images to ensure that an optimal diagnostic study has been performed.
What will I experience during the procedure? Back to Top
You may experience some minor discomfort from the intravenous injection of the radiopharmaceutical.
You will be asked to exercise until you are either too tired to
continue or short of breath, or if you experience chest pain, leg pain,
or other discomfort that causes you to want to stop.
If you are given a medication to increase blood flow because you are
unable to exercise, the medication may induce a brief period of feeling
anxious, dizzy, nauseous, shaky or short of breath. In rare instances,
if the side effects of the medication are severe or make you too
uncomfortable, other drugs can be given to stop the effects.
Most patients can resume regular activities immediately after the
procedure. The radioactivity in your body will decrease due to the
natural process of radioactive decay. In addition, radioactivity will
decrease because the radiopharmaceutical passes out of the body in the
urine or stool.
Who interprets the results and how do I get them? Back to Top
Generally,
patients undergo a nuclear medicine examination because a referring
physician has recommended it. A physician who has specialized training
in nuclear medicine will interpret the images. It usually takes one to
three days to interpret, report, and deliver the information to your
referring physician. Your referring physician will then inform you of
the results.
What are the benefits vs. risks? Back to Top
Benefits
- The functional information regarding blood flow to the
heart and the pumping function of the heart is well demonstrated. This
information may be used to determine what treatment or additional
testing, if any, is needed.
- Computers are involved
in the generation of the images, so measurements or quantification of
function, as well as the determination of abnormalities, are possible.
- Because
the procedure is generally performed according to standardized
protocols, the type of examination done at one hospital is likely to be
similar to that performed at other hospitals, making the information
easy to understand or to transfer to all doctors who may be involved in
your care.
Risks
- If you have coronary artery disease, it is possible that
you could experience chest pain, or angina, when stress due to exercise
or a drug is applied to your heart. However, your test will be carried
out under the supervision of a specialist trained to monitor you and
your heart by using information being provided by the
electrocardiogram, by your heart rhythm, and by your blood pressure. If
necessary, medication can be given for your chest pain. You will be
monitored long enough to ensure that you are at your baseline; that is,
the condition you were in when you came for the test.
- The
use of a radioactive substance will result in exposure to a small
amount of radiation to the heart and to the body. However, the amount
of radioactivity administered is the smallest amount necessary to
provide adequate images. Cardiac nuclear medicine procedures have been
done for more than three decades, and no long-term adverse effects have
been reported from such low-dose studies.
- Allergic reactions to radiopharmaceuticals can occur but are extremely rare.
- As
with all radiologic procedures, it is important that you inform your
physician and the technologist if you are pregnant. In general,
exposure to radiation during pregnancy should be kept to a minimum.
Depending on the nature of your medical problem, the cardiac nuclear
medicine procedure may be postponed until after your pregnancy.
What are the limitations of Cardiac Nuclear Medicine? Back to Top
Compared
with most radiology studies, cardiac nuclear medicine procedures are
time-consuming. They involve either exercise or the administration of a
drug to increase blood flow to the heart, obtaining gamma-camera images
(usually two sets of images separated by a few hours), and then
computer manipulation of the information. Depending on the exact
procedure performed, the myocardial perfusion scan takes between two
and five hours. Occasionally, a patient may be asked to return to the
nuclear medicine department the next day. An outpatient may be allowed
to leave the hospital between the two sets of images. An inpatient will
usually return to his or her hospital room between the imaging
sessions. Back to Top
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