Cardiac Nuclear Medicine

Published On 07/11/2011

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.

Cardiac nuclear medicine refers to these diagnostic examinations that result in images of the heart.

What are some common uses of the procedure?

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 heart chamber size, heart wall thickness, and blood-flow patterns to the heart walls. The test also is important for the evaluation of possible or known coronary artery disease, 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 revascularization procedures designed to restore the blood supply to the heart.

Heart-wall movement and overall heart function can be determined with an advanced technique called gating. In short, gating requires that while heart images are being obtained, the information is synchronized with the results of electrocardiography, that is, the recording of electrical currents that traverse the heart and cause it to pump.

How should I prepare for the procedure?

You should avoid caffeine 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, rubber-soled 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?

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. A nearby computer console is used to develop the images of the heart.

How does the procedure work?

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 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, called algorithms, will construct images of the heart based on the detected gamma rays.

How is the procedure performed?

First, you will exercise by walking on a treadmill for several moments. While you exercise, the electrical activity of your heart will be monitored by 12-lead electrocardiography, and your blood pressure will be measured frequently. Before you stop exercising, you will be given the radiopharmaceutical through a line leading into a vein in your arm. The compound is given when the blood flow to the heart is at its peak caused by 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 15 minutes 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 will move slowly and automatically in an arc over the front of your chest after it is positioned initially by the technologist.

Usually, three to four hours later, you will receive another intravenous injection of the radiopharmaceutical. Additional images will be obtained for comparison studies, to determine whether coronary blood flow has changed once you have rested, and to evaluate for coronary artery disease.

If you are unable to walk on a treadmill, you will not exercise but 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, our radiologist will check the quality of the images to ensure that an optimal diagnostic study has been performed.

What will I experience during the procedure?

You may experience some 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 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?

Generally, patients undergo a nuclear medicine examination because a referring physician has recommended it. Our radiologist will interpret the images. Your referring physician then will be faxed the report and then inform you of the results.

What are the benefits of Cardiac Nuclear Medicine?

Benefits

  • The functional information regarding blood flow to the heart and the pumping function of the heart is well demonstrated.
  • 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 provided at other hospitals, making the information easy to understand or to transfer to all doctors who may be involved in your care.

Risk
If you have coronary artery disease, it is possible that you could experience chest pain, or angina, when stress by exercise or by being given a drug is applied to your heart. However, your test will be carried out under the supervision of our radiologist and 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 possible to provide adequate images. 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?

Compared to 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 over a two hour period), and then computer manipulation of the information.