The scan is normally requested by your doctor in cases where there is an acute gastro-intestinal (gut) bleeding and where this bleeding cannot be localised by gastroscopy or colonoscopy. In difficult cases of chronic gastrointestinal bleeding, these scans are sometimes also requested.
A sample of you blood (normally about 5 ml) is withdrawn from a vein in your arm, labelled or tagged with a radioisotope (normally Technetium) and then reinjected in your arm while you are laying under the gamma camera. The procedure to label the red blood cells is performed in a laboratory.
Serial dynamic views are obtained for about 60 min. If no bleeding is demonstrated within the hour, additional serial static images may be necessary until 3h. Sometimes additional views at 24h can be requested by the physician.