MIBG scan is a scintigraphic study that uses metaiodobenzylguanidine, noradrenaline analogue ⁹, labelled to iodine-123 or iodine-131. It is indicated in the investigation of phaeochromocytoma. I-131 MIBG, also called I-131 iobenguane, is a theranostic agent used to treat unresectable MIBG-positive tumours.

Indications

MIBG is positive in:

• neuroblastoma

  • olfactory neuroblastoma ¹

• digestive system neuroendocrine tumours ⁴

• carcinoid tumours of the lung ⁴

• paraganglioma

• phaeochromocytoma ⁹

• medullary thyroid carcinoma ⁹

• ganglioneuroma

• ganglioneuroblastoma

Some mild uptake can be physiologic in ⁴:

• liver

• salivary glands

• urinary bladder 

• heart

• gastrointestinal tract

• adrenal glands

• brown fat 

Cardiac imaging studies with MIBG labelled to radio-iodine may be useful in the evaluation of cardiac toxicity from chemotherapy ^5-8.

Procedure

Iodine-123 has 13 hours of half-life and allows imaging up to 48 hours. Iodine-131 is only used when iodine-123 is not available. The higher energy photons emitted by iodine-131 render it inferior to iodine-123 because of higher dose it gives to patients ⁹.

Medications that can interfere with MIBG uptake should be stopped such as tricyclic antidepressants, antihypertensives, and decongestant drugs such as pseudoephedrine, phenylpropanolamine, and phenylephrine ⁹.

To reduce radiation dose to the thyroid gland, 400 mg of oral potassium perchlorate is given at one hour before MIBG injection in adults. In children, 0.1 to 0.2 ml of Lugol's iodine diluted with water or milk is given three times a day starting at 48 hours before the injection ⁹.

Technique

• administer intravenous MIBG slowly over 1 to 2 minutes to prevent adrenergic side effects in case of fast injection ⁹

• images are taken for anterior and posterior abdomen at 10 to 20 minutes per view ⁹

• whole body image is taken to look for metastasis ⁹

• SPECT is helpful for anatomical localisation ⁹

• pelvic images taken at 24 hours after urinary bladder emptying. Sometimes, images may also be taken at 4 or 48 hours ⁹