Cardiac Nuclear Imaging

Overview

Cardiac nuclear medicine tests are indicated for individuals with unexplained chest pain or chest pain brought on by exercise 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 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 evaluated with cardiac gating, which is a technique that synchronizes the images of the heart with different parts of the cardiac cycle (contracting or relaxing) as determined by an electrocardiogram, which records the electrical currents that activate the heart muscle and cause it to pump.

Test Procedure

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 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.

For the stress part of the examination, you will exercise by either walking on a treadmill or pedaling a stationary bicycle for several moments. 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 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 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 evaluate for coronary artery disease.

If you are unable to use a treadmill or bicycle, 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, 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.

Test Results

It can take time for the test results and how long will depend on the reasons for the scan. Usually, a specialist in radiology examines the scan and a report sent to your physician, who reviews the results to you.