Other imaging studies include radionuclide imaging that can be helpful in diagnosing lower gastrointestinal bleeding.

• Radionuclide imaging is more sensitive than angiography in detecting the source of bleeding; however, it is less specific than either a positive endoscopic or angiographic examination.^[1][2][3][4]
• Rates of bleeding as little as 0.1 to 0.5 mL/min can be detected.
• Radionuclide imaging is indicated prior to angiography in patients in whom the bleeding is intermittent or has a low rate, or in whom bleeding points were not identified using CTA, or colonoscopy.
• Accuracy rates have varied across reports, and range from 24% to 91%.

• Erythrocytes are initially labeled by intravenously injecting 2 mL of a stannous agent.
• Twenty minutes later, 400 MBq of technetium pertechnetate are injected.
• Scans are then performed every 5 minutes for up to an hour.
• Single static images are taken several hours later

• Two different types of nuclear scanning agents are commonly used: technetium (99mTc) sulphur colloid, which has a short half-life, and 99mTc pertechnetate, which has a longer half-life.
• With 99mTc pertechnetate, patients can be scanned several times over a 24-hour period. Therefore the latter agent has become the favored radiotracer to use

• Advantages common to both techniques are that they are noninvasive and have a higher sensitivity than does angiography.

• The main disadvantages are that radionuclide scanning can only localize bleeding to an area of the abdomen, and the resolution does not allow the identification of a specific site in the colon.
• Anaphylactic reaction to the radioisotope

• Radionuclide imaging is not recommended in pregnant or breastfeeding women.