Nuclear scans are tests that involve the use of harmless radioactive materials (see Radionuclide Scanning). The radioactive materials are ingested as part of a meal or in a drink or are given by vein (intravenously). The small amount of radiation produced by these materials is used to produce images of internal structures. After the materials are in the body, doctors use a special radiation-sensing scanner or camera, called a gamma camera, to show where the materials are in the body. Different types of scans with different nuclear materials are used depending on the purpose of the test and which part of the body needs to be imaged.
A gastric emptying scan is done to determine how quickly the stomach empties. People whose stomach empties slowly have a disorder called gastroparesis, which may cause symptoms such as nausea, vomiting, or a feeling of fullness after eating a small meal.
For this scan, people drink a beverage or eat a meal that contains a small amount of radioactive material. Doctors then use a gamma camera to observe how quickly the material passes out of the stomach. Because this test cannot show whether a blockage or gastroparesis is the cause of delayed stomach emptying, further tests are done if stomach emptying is delayed. This scan can also help doctors monitor how well people are responding to promotility drugs. These drugs, such as metoclopramide and erythromycin, stimulate the movement of contents through the stomach and intestines. The results of this scan can be affected if people are taking opioids for pain or are taking other drugs that alter how contents move through the stomach.
In specialized centers, additional testing to determine how long it takes food to move through the small intestine and the whole gut can be done. The small intestine test takes place over a 2-day period and the whole gut test takes place over a 4-day period. These tests are useful in people who doctors suspect have a movement disorder of the digestive tract such as severe constipation.
A bleeding scan is sometimes done to determine the location of bleeding in the digestive tract.
For this scan, radioactive material is attached to red blood cells or other material that is injected into the bloodstream. The gamma camera can show the part of the digestive tract where the radioactive-labeled cells are leaking out of the intestine, suggesting the location of the bleeding. This scan is useful mainly for people who have brisk bleeding in the digestive tract and who are not good candidates for endoscopy or for people who have bleeding but whose bleeding source has not been found with other diagnostic tests. The bleeding scan works only when there is active bleeding; it cannot show the location if bleeding has stopped.
A Meckel scan is done to identify a small intestine problem called a Meckel diverticulum.
For this test, radioactive material is injected into a vein. The substance is picked up by cells in the wall of the Meckel diverticulum, which can then be seen using a gamma camera.