An MIBG scan is a painless diagnostic imaging test that is used to check for two common types of nerve tumors. MIBG stands for metaiodobenzylguanidine, a radioactive compound containing the isotope iodine-123. A small amount of the compound is injected into the bloodstream and given about one day to circulate throughout the body. A specialized type of radiology machine is then used to check for any unusually heavy concentrations of MIBG, which is indicative of a tumor. MIBG scan results help doctors make proper diagnoses and determine the best course of treatment.
Doctors usually perform MIBG scans to look for neuroblastoma or pheochromocytoma tumors, two cancers that are commonly seen in infants and young children. Young patients who have worsening abdominal pains, tremors, and sweating are scheduled for scans if simpler imaging tests and blood work fail to uncover a cause. An adult patient who develops suspicious symptoms may also need an MIBG scan. The procedure is useful because radioactive material tends to collect within tumors while dispersing lightly and uniformly in the rest of the body. When an MIBG scan is performed, the scanner detects gamma rays emitted by the decaying iodine isotope.
Patients are usually instructed to stop taking non-vital medications for a few days before testing to avoid adverse drug reactions. An oral solution of supersaturated potassium iodide, which helps to protect the thyroid gland from harmful radiation, is often prescribed to take before, during, and after an MIBG scan. On the first day of testing, an intravenous needle is used to inject a carefully-measured dosage of MIBG into the hand or foot. No special monitoring is necessary until the following day.
When it is time for the MIBG scan, the patient is asked lie down on a table and remain as still as possible. The scanning machine is situated close above the patient's body and turned on. Several dozen images are collected during testing, which can take between one and three hours to complete. Dietary and medication restrictions are usually lifted immediately following the procedure, and the patient can go home if he or she is healthy enough to do so. It may take a few days for test results to be thoroughly analyzed by a team of radiologists.
There are few risks with MIBG scans, and most patients do not experience discomfort during or after testing. Radiation exposure is low and leftover iodine tracers are completely excreted within a few days through the urine. Patients who do test positive for tumors are treated accordingly with surgery, chemotherapy, and radiation. Follow-up MIBG scans may be suggested after treatment to make sure tumors are responding.