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A radionuclide scan of the kidneys shows a picture of your kidneys while they are at work making urine.A kidney radionuclide scan, also called a kidney scan or renal scan, is a diagnostic imaging test that involves administering a small amount of radionuclide, also called a radioactive tracer, into the body and then imaging the kidneys with a gamma camera. The images obtained can help in the diagnosis and treatment of various kidney diseases and conditions. This test can be useful to evaluate infection, blockages, injury to the kidneys, and some causes of high blood pressure.
A kidney scan requires the use of a radioactive material; therefore, patients who are pregnant or suspect they may be pregnant are cautioned not to have the test unless the benefits outweigh the risks. Women should inform their doctor if they are breast feeding. The doctor will recommend the woman stop breast feeding for a specified period of time, depending on the particular tracer and dose used.
Kidney scans are performed either in a hospital nuclear medicine department or in an outpatient radiology or nuclear medicine facility. The patient is positioned in front of, or under, a gamma camera—a special piece of equipment that detects the radiation emitted from the body and produces an image. An intravenous injection of the radionuclide is administered. Immediately after the injection imaging begins, and, in most studies, the flow of blood to each kidney is evaluated. Serial images of the kidneys are obtained over a specified period of time, depending upon the particular radiopharmaceutical used. Kidney scans may be performed to determine the rate at which the kidneys are filtering a patient’s blood. These studies use a radiopharmaceutical called technetium DTPA (Tc99m DTPA). This radiopharmaceutical also can identify obstruction in the renal collecting system. To establish the function of the renal tubules, the radiopharmaceutical Technetium DMSA (Tc99m DMSA) is used.
A kidney scan ranges from 45 minutes to three hours in length, depending upon the goals of the test, but the test typically takes about an hour to an hour and a half. It is important to understand that kidney scans can reveal an abnormality, but they do not always identify the specific problem. They are very useful in providing information about how the various parts of the kidneys function, which, in turn, can assist in making a diagnosis.
Typically, posterior images are obtained but images are also obtained at oblique angles. If indicated, the patient may be positioned so that mobility of the kidney is demonstrated by sitting up or lying down for the images. If obstruction or renal function is being evaluated, a diuretic (drug to induce urination), such as Lasix, may be injected. If hypertension or renal artery sterosis is being evaluated, Captopril or Enalapril (ACE inhibitors) may be injected.
No special preparation is necessary for a kidney scan. In some instances the patient may be required to drink additional liquids and to empty their bladder before the exam. If another nuclear medicine study was recently performed, the patient may have to wait for a specified period to avoid any interference from residual radioactivity in the body. The patient is instructed to remove metal items from the area to be scanned.
Let your doctor know if you could be pregnant or if you are breast-feeding a baby. The medicine used in this test would expose your baby to radiation.
What happens when the test is performed.
You have an IV (intravenous) line placed into a vein. A slightly radioactive version of a substance called sodium pertechnetate is injected through the IV. This substance helps your kidneys and urine show up on pictures.
A camera that is specially designed to detect radioactivity is placed against your back or abdomen. A number of pictures are taken over time. The camera itself does not expose you to any additional radiation, so the number of pictures is not harmful in any way. The test is usually completed within an hour.
Many people worry when they hear that the medicine used in this test is slightly radioactive. In truth, this test exposes you to a very small amount of radiation-no greater than that of routine xrays.
Moreover, Nuclear medicine procedures are very safe. Unlike some of the dyes that may be used in x-ray studies, radioactive tracers rarely cause side effects. There are no long-lasting effects of the tracers themselves, because they have no functional effects on the body’s tissues. If pharmaceuticals are injected these can temporarily raise or lower blood pressure, or cause one to urinate.
Patients can resume their normal daily activities immediately after the test. Most radioactive tracers are excreted through the urinary system, so drinking fluids after a kidney scan can help flush the tracer out of the body more quickly.
The scan should reveal normal kidney function for the patient’s age and medical status, as well as show normal relative position, size, configuration, and location of the kidneys. Initial blood flow images should reflect that blood circulation to both kidneys is equal. Patients whose images suggest a space-occupying lesion or obstruction may require other imaging procedures, such as CT or ultrasound, to provide more information. Also, if the kidneys appear to be abnormal in size, have an unusual contour, or are unusually positioned, other imaging procedures may be required.