What Is Radionuclide Medical Imaging System?

With radionuclide medical imaging system, a tiny amount of a radio actively labeled substance is injected into the vein. Learn about this procedure!

While conventional radiography and CT scanning produce images that depend on a physical difference among body structures, radionuclide scanning uses a different approach. With radionuclide imaging a tiny amount of a radio actively labeled substance is injected into the vein. Although many people have concerns about the amount of radiation the body receives from this procedure there is actually less radiation than one would get from an x-ray. The substance that is injected into the vein is called a tracer. Tracers are quickly distributed through out the body, even in the heart where they are visible by using a gamma camera. Each image will first be displayed on a screen where it can be studied by a doctor. It is then stored on a computer disk so further analysis can be made.

When a person is going through this procedure several types of radiation recording cameras can record a single image or a series of cross sectional images. When cross sectional images are produced the technique is known as single photon emission computed tomography. This is because the images are computer enhanced which provides a three dimensional image. Radionuclide imaging procedure is especially useful when a doctor is attempting to diagnose a chest pain of unknown cause. It is also used for those who have narrowing of the coronary arteries to learn how the hearts blood supply and functioning is being affected. With this procedure it is possible to assess any improvement in the blood supply flowing to the heart muscle after a bypass surgery or to determine a persons condition after a heart attack.

With radionuclide imaging the blood flow through the heart is analyzed by injecting either thallium-201 or technetium 99m into a vein. The doctor will then obtain images as the patient is allowed to perform various exercise test. The heart muscle will absorb the minute traces of radioactive material showing the doctor any areas that are getting a poor supply of blood. If the patient is unable to exercise they will be given an intravenous injection of adenosine or dipyridamole to stimulate the effects of exercise. When these drugs are given they will divert the blood from the abnormal blood vessels to the normal vessels. The patient will then be allowed to rest for a few hours and a second scan will be done. If coronary artery narrowing is found the doctor can tell which areas have irreversible scarring cause by previous heart attacks.



Thallium-201 is used mainly when an acute heart attack is suspected. This drug is unlike thallium which is know only to accumulate in normal tissues or the drug technetium which will primarily accumulate in abnormal tissues. Using radionuclide imaging doctors have been able to detect certain disorders more quickly than with other techniques since changes in the function of an organ will after occur prior to the structure being affected. In a case of bone infections where increased activity of the bone cells is present this technique will result in larger amounts of the drug being taken up by the diseased bone and showing the changes before they can be detected by x-rays. This is a safe procedure which does not carry the risk of toxicity or allergic reaction that is found in the use of radiopaque dyes.

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