Gallium 67 Scan - General Uses in Medicine

General Uses in Medicine

In the past, the gallium scan was the gold standard for cancer diagnosis and staging, until it was replaced by positron emission tomography using fludeoxyglucose. Gallium imaging is still used to image inflammation and chronic infections, and it still sometimes locates unsuspected tumors as it is taken up by many kinds of cancer cells in amounts that exceed those of normal tissues. Thus, an increased uptake of gallium-67 may indicate a new or old infection, an inflammatory focus from any cause, or a cancerous tumor.

Ga-67 acts as an iron analogue, binding to any proteins that bind iron. Initially it binds to transferrin. Assuming adequate blood flow, the complex diffuses through loose endothelial junctions of capillaries at sites of inflammation and enters the extracellular fluid.

Leukocytes migrate to sites of inflammation and degranulate, releasing large quantities of iron-binding lactoferrin. Ga-67 has higher affinity for leukocyte lactoferrin than it does for serum transferrin, and so follows the leukocyte concentration. The isotope may thus be used in detecting abscesses that provoke a leukocyte response, including abscesses that are "sterile" (free of bacteria, or of living bacteria).

Ga-67 also attaches to the siderophore molecules of bacteria themselves, and for this reason can be used in leukopenic patients with bacterial infection (here it attaches directly to bacterial proteins, and leukocytes are not needed).

It has been suggested that gallium imaging may become an obsolete technique, with indium leukocyte imaging and technetium antigranulocyte antibodies replacing it as a detection mechanism for infections. For detection of tumors, especially lymphomas, gallium imaging is still in use, but may be replaced by fludeoxyglucose PET imaging in the future.

In infections, the gallium scan has an advantage over indium leukocyte imaging (also called indium-111 white blood cell scan) in imaging osteomyelitis (bone infection) of the spine, lung infections and inflammation, and for chronic infections. In part this is because gallium binds to neutrophil membranes, even after neutrophil death. Indium leukocyte imaging is better for acute infections (where neutrophils are still rapidly and actively localizing to the infection), and also for osteomyelitis that does not involve the spine, and for abdominal and pelvic infections. Both the gallium scan and indium leukocyte imaging may be used to image fever of unknown origin (elevated temperature without an explanation). However, the indium leukocyte scan will image only the 25% of such cases which are caused by acute infections, while gallium will also localize to other sources of fever, such as chronic infections and tumors.