MIBG

MIBG, or meta-iodobenzylguanidine, is a radiopharmaceutical analog of norepinephrine used in nuclear medicine. It is taken up by adrenergic nerve endings via the norepinephrine transporter and stored in neurosecretory granules, leading to selective localization in tissues of the sympathetic nervous system. This mechanism enables both diagnostic imaging and targeted radiotherapy in conditions that overlie adrenergic activity.

In diagnostic use, iodine-123 labeled MIBG (123I-MIBG) is employed for planar and SPECT imaging to localize and stage neuroendocrine tumors such as pheochromocytoma, paraganglioma, and neuroblastoma. It can help identify primary tumors, detect metastases, and monitor treatment response. Imaging protocols typically involve delayed imaging after administration to optimize tumor-to-background contrast.

In therapeutic use, iodine-131 labeled MIBG (131I-MIBG) is used for systemic radiotherapy in patients with unresectable or metastatic pheochromocytoma or neuroblastoma when conventional treatment is insufficient. 131I-MIBG delivers targeted radiation to adrenergic tumor cells but carries hematologic toxicity as a primary dose-limiting side effect. Thyroid protection with potassium iodide or Lugol’s solution is advised to block free iodide uptake.

MIBG is also used in cardiology for 123I-MIBG myocardial scintigraphy to assess cardiac sympathetic innervation, which can aid in evaluating heart failure and other cardiac conditions. The technique yields measures such as the heart-to-mediastinum uptake ratio and myocardial washout rate.

Limitations include variable tumor uptake, potential uptake in non-target tissues, and the need for specialized nuclear medicine facilities.