Gastrointestinal iodine-131-meta-iodobenzylguanidine activity.

ABSTRACT

Radioactivity in the colon during 131-I-meta-iodobenzylguanidine (MIBG) scintigraphy may obscure or be mistaken for tumor uptake. Fecal excretion of radioactivity was examined in eight patients following therapeutic 131-I-MIBG administration (123-218 mCi, 4.551-8.066 GBq) and was found to be 0.02-1.93% of the administered dose. Semiquantitative grading of colonic activity on scintigraphy was inversely related to fecal excretion. An additional patient with marked colonic activity was studied before and after an enema all visible gut activity was evacuated. We conclude that radioactivity in the colon seen in 131-I-MIBG scintigraphy is due largely to gut excretion of 131-I and is not due to 131-I-MIBG uptake in the autonomic innervation of the gut. Laxatives and enemas are suggested for patients in which such gut radioactivity may lead to difficulties in interpretation.