Bleeding scans use 99mTc-labeled red blood cells, or occasionally 99mTc-labeled colloid, to determine the origin of lower gastrointestinal hemorrhage before surgery or angiography. Active bleeding sites are identified by focal areas of tracer that conform to bowel anatomy, increase with time, and move with peristalsis. Bleeding scans are useful mainly for colonic bleeding in patients with significant hemorrhage and an unprepared bowel, in whom endoscopic visualization is difficult.
Gastric emptying can be measured by having the patient ingest a radiolabeled meal (solid or liquid) and observing its passage out of the stomach with a gamma camera. Because this test cannot differentiate physical obstruction from gastroparesis, further diagnostic studies typically are done if emptying is delayed. The test also is useful in monitoring response to promotility drugs (eg, metoclopramide, erythromycin). The results of this test can be affected by use of opioids or other drugs that alter gastrointestinal motility.
Specialized motility centers can also evaluate small intestine and whole gut transit. The small intestine transit test takes place over a 2-day period and the whole gut transit test takes place over a 4-day period. These tests are useful in patients with suspected motility disorders, severe constipation, or colonic inertia.
A Meckel scan identifies ectopic gastric mucosa (as in a Meckel diverticulum) by using an injection of 99mTc pertechnetate, which is taken up by mucus-secreting cells of the gastric mucosa. Focal uptake outside of the stomach and in the small bowel indicates a Meckel diverticulum.
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