MIBG (131I-m-Iodobenzylguanidine) Scan

Norm of MIBG (131I-m-Iodobenzylguanidine) Scan

The adrenal glands will not be visualized. There is variable physiologic uptake by the bladder, colon, heart, spleen, and uterus.


Usage of MIBG (131I-m-Iodobenzylguanidine) Scan

Location and diagnosis of primary and metastatic pheochromocytoma, adrenal medullary hyperplasia, multiple endocrine neoplasia (MEN), von Hippel-Lindau disease, von Recklinghausen's disease, neuroblastoma, paraganglioma, medullary carcinoma of thyroid, and other neuroendocrine tumors.


Description of MIBG (131I-m-Iodobenzylguanidine) Scan

A MIBG scan is a nuclear medicine scan of the whole body after injection of the radioactive tracer 131I-MIBG for the purpose of detecting areas of increased uptake by hyperactive endocrine tissue or tumor. MIBG is a catecholamine analog, similar to noradrenaline. Various organs and tumors uptake the tracer to varying degrees. A series of scans is conducted at 24 and 48 hours following injection of radioisotope. The isotope is concentrated in hyperactive endocrine tissue, such as pheochromocytoma tissue, and appears on the scan as a “hot spot.”


Professional Considerations of MIBG (131I-m-Iodobenzylguanidine) Scan

Consent form IS required.

Allergic reaction to tracer (itching, hives, rash, tight feeling in the throat, shortness of breath, anaphylaxis).
Previous allergy to MIBG or iodine solution (Lugol's solution or SSKI) or shellfish; pregnancy (because of radioactive iodine crossing the blood-placental barrier); breast-feeding; anuria; dialysis.



  1. See Client and Family Teaching.
  2. Assess client for history of allergy to iodine or shellfish.
  3. A prescribed dose of potassium iodide (SSKI) or Lugol's solution will be started 24 to 48 hours before the injection of the radioisotope to prevent uptake of radioisotope by the thyroid.
  4. Women of childbearing age should have a pregnancy test within 48 hours before the test.
  5. A bowel prep may be prescribed.
  6. Have emergency equipment readily available.
  7. Remove jewelry and metal objects before each scan.
  8. Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.



  1. Position client in lying position and take baseline BP.
  2. Slowly inject radioisotope intravenously, over 1–2 minutes.
  3. Monitor BP during injection and 20 minutes following injection.
  4. A scan may be done 4, 24, 48, and possibly 72 hours following the injection of the isotope. For the scan, the client is positioned supine on the imaging table and the whole body is scanned using a gamma camera.


Postprocedure Care

  1. SSKI or Lugol's solution will be given throughout the test period and will continue for 4–7 days following the injection of MIBG.
  2. Check with institutional policy regarding special instructions for discarding urine for 24 hours following isotope injection.


Client and Family Teaching

  1. Many prescribed and over-the-counter medications can interfere with the results of this test. Be sure to inform physician of any medications that are being taken.
  2. Medications that may need to be discontinued up to 4–6 weeks before the test include labetalol, reserpine, loxapine, tricyclic antidepressants (doxepin, amitriptyline and derivatives, imipramine and derivatives, amoxapine), sympathomimetics (phenylephrine, phenylpropanolamine, pseudoephedrine), calcium channel blockers, SSRI, catecholamine receptor agonists and antagonists, phenothiazines, butyrophenones (i.e., haloperidol), guanethidine, phenoxybenzamine.
  3. Inform the physician if pregnant or breast-feeding, or if young children are in the household.
  4. No fast is required for this test.
  5. You will need to lie still during the procedure. Young children may need to be sedated.
  6. There is no discomfort associated with the scan.
  7. SSKI or Lugol's solution will be taken for 4–7 days, beginning 1–2 days before the injection of the radioisotope. This medication can be diluted in a glass of water or juice.
  8. Despite the use of thyroid blocking medication, the thyroid may be affected for a short period of time. Prolonged feelings of fatigue, temperature irregularities, or changes in heart rate should be reported to the physician.
  9. The scan takes approximately 1–2 hours.


Factors That Affect Results

  1. Many medications can impact the results of this test. Refer to Client and Family Teaching.


Other Data

  1. During the scan, the kidneys may be localized in relation to the adrenal glands by obtaining a correlative image of the kidneys using a renal tracer.
  2. MIBG is excreted by the kidneys. The half-life is 8 days.
  3. Health care professionals working in a nuclear medicine area must follow federal standards set by the Nuclear Regulatory Commission. These standards include precautions for handling the radioactive material and monitoring of potential radiation exposure.