A procedure used to find neuroendocrine tumors, such as neuroblastomas and pheochromocytomas. A small amount of a substance called radioactive metaiodobenzylguanidine is injected into a vein and travels through the bloodstream. Neuroendocrine tumor cells take up the radioactive metaiodobenzylguanidine and are detected by a scanner. Also called iobenguane scan and MIBG scan.