Nuclear medicine imaging uses specific radioactive isotopes (called “radioactive tracers” or simply “radiotracers”) to detect specific suspected conditions. Depending on the test, the patient may inhale or swallow these radiotracers, or they may be injected directly into the patient’s bloodstream. As they move through the body, these radiotracers emit low-dose gamma ray radiation that can be detected and imaged by a special camera.
There are several general types of nuclear imaging:
A bone scan is very sensitive and may identify abnormalities in the bones and joints that may not yet be visible on X-rays.A radiotracer is injected into a vein through a small needle. In some cases an initial scan will be performed immediately after the injection to determine the blood flow pattern to the part of the body being scanned. Following the injection, it takes two to three hours for the radioactive isotope to enter the bones. During that time, the patient will drink several glasses of water or other fluids. After two to three hours, the scan is performed using a gamma camera which detects the amount and location of the radioisotope in the bones. The scan with the gamma camera takes approximately thirty to sixty minutes. The small dose of radiation in a bone scan is similar to that obtained from an X-ray.
A lung scan is ordered if on X-rays or other laboratory examinations reveal abnormal findings in the chest area, and/or to determine whether a patient’s chest pain or shortness of breath is caused blood clots in the arteries of the lungs.
There are two parts to a lung scan. The first part is known as the ventilation scan. For the ventilation scan a mask is placed over your face and you inhale a radioactive aerosol. A scan is then performed with a gamma camera which identifies the distribution of the aerosol in the lungs. The second part of the examination is the perfusion scan. The perfusion scan involves an injection of a radioactive isotope tracer into a vein in the arm using a small needle. Immediately after the injection, scans are done with a gamma camera which show the distribution of the injected radioisotope in the lungs.
A chest X-ray performed within six hours of the lung scan is needed for comparison. Based on lung scan results, additional tests (including pulmonary angiography or a CT scan) may be suggested.
A gallium scan is ordered when an infection, inflammation or tumor is suspected. A tracer dose of a radioisotope gallium-67 citrate is injected into the vein through a small needle. A gamma camera scan is obtained 48-72 hours later. A bone scan may also be ordered to compare with the gallium scan. Based on the results of the gallium scan, other imaging tests may be ordered to further clarify the diagnosis, including a X-ray, CT scan, MRI or an ultrasound examinations. Because gallium accumulates in the bowels, the nuclear medicine technologist may recommend that a patient take laxatives or receive an enema prior to receiving the injection, and/or 48-72 hours after.
An indium-111 WBC scan is used to look for a suspected infection. The scan involves the injection of radioactive white blood cells into the vein through a small needle, followed by a gamma camera scan to confirm or exclude a clinically suspected infection. The radiation dose received during the procedure is similar to that obtained from a chest X-ray.
Other tests, including a bone scan and a sulfur colloid bone marrow scan, may be ordered for comparison with the indium-111 WBC scan. CT, MRI and/or ultrasound examinations may also be recommended, based on the results of the indium-ill WBC scan.