Radionuclide imaging is a procedure used to diagnose heart disease. Small amounts of radioactive materials known as tracers are injected into the patient’s body. The tracers give off gamma rays, a form of energy that is then detected by a gamma camera. A computer then analyzes the information obtained by the camera, which in turn produces very clear, detailed pictures of the heart. It is also useful in determining the cause of chest pain, and can detect how damaged and narrowed the arteries are from atherosclerosis. It can also be used to determine and evaluate a person’s blood supply, particularly after surgery or a heart attack.
There are actually several different forms of radionuclide imaging. Some of these forms include:
Positron emission tomography (PET). This form of radionuclide imaging uses a special type of detector called a photomultiplier-scintillator detector to find the gamma rays. With positron emission tomography, tracers are also injected into the patient. They are used in diagnosing heart disease to evaluate the flow of blood to the heart and throughout the body, as well as determine whether there is a presence of coronary heart disease. It can also detect whether a person has had a previous heart attack based on damage done to the heart muscle.
Positron emission tomography is often used in conjunction with exercise stress tests to determine how efficiently the blood flows and the heart pumps in response to physical exertion.
A patient undergoing positron emission tomography will be injected with a radioactive substance, which generally takes around an hour to fully be absorbed by the tissues. Once the doctor determines a sufficient amount of time has lapsed, the PET scanner obtains images of various parts of the heart and body. The tracers accumulate in areas that are abnormal, so a high concentration of a tracer on the scan could indicate an area where heart disease is present.
Single Photon Emission Computed Tomography (SPECT). This diagnostic tool uses a tracer as well, and a CAT scan is used to obtain the images of the blood. However, SPECT is focused more on the flow of blood and the amount rather than actual heart disease itself; the tracer is not absorbed by the tissues, rather, it stays within the blood. Heart disease can be detected with a cardiac SPECT, which can help determine the severity of narrowed arteries as well as determine which areas of the body are not getting enough blood. It can also tell whether a person has had a previous heart attack. This test is often done after an exercise stress test and can help predict how likely a person is to die of heart disease.
Multiple Gated Acquisition Scan (MUGA). A MUGA test can measure how much blood is pumped out of the heart with each beat. The red blood cells within the body absorb the radioactive tracer, and from there a scanner portrays the blood cells and then determines the amount of blood pumped. This test is useful in determining whether a person has certain valve disorders.
Although radionuclide imaging utilizes radioactive material in the tracers, they are not considered dangerous to people. In fact, the amount of radioactive material used in the tracers is less than in a traditional x-ray. The tracer is easily flushed out of the system by drinking fluids.