Q: What is the difference between Indium Scan and Gallium scan in localizing infection?

Answer: The indium scan is a procedure in which WBCs (neutrophils) are removed from the patient, tagged with the radioisotope Indium-111, and then injected back into the patient. The tagged leukocytes subsequently enhance areas of relatively new infection, where live neutrophils are still rapidly and actively localizing.

Gallium scan has advantage over the indium scan because gallium binds to neutrophil membranes, even after neutrophil death. This makes gallium more broadly sensitive, localizing to other sources of fever, such as chronic infections and tumors.