An MIBG scan is a nuclear medicine imaging test that uses a mildly radioactive tracer to find specific types of tumors, particularly neuroblastoma in children and adrenal gland tumors in adults. The tracer, called metaiodobenzylguanidine, mimics a natural stress hormone (norepinephrine) that certain nerve-related cells absorb. Because tumor cells from these tissues eagerly take up the tracer, they light up on the scan, revealing their exact location anywhere in the body.
How the Tracer Works
Your body’s sympathetic nervous system, the network responsible for the “fight or flight” response, uses norepinephrine to send signals between nerve cells. MIBG is a synthetic compound that looks enough like norepinephrine that cells with norepinephrine transporters pull it inside. When the MIBG is tagged with a small amount of radioactive iodine, a specialized camera can detect where it concentrates.
Normal tissues like the heart, salivary glands, and adrenal glands absorb some MIBG naturally. But tumors that originate from the sympathetic nervous system absorb much more of it, creating bright spots on the image. This is what makes the scan so useful: it highlights functioning tumor tissue rather than just showing a lump on a CT or MRI. Over 90% of neuroblastoma cases show strong MIBG uptake, making it one of the most reliable tools for that cancer.
Conditions It Helps Diagnose
The most common reasons for ordering an MIBG scan fall into two categories: pediatric cancers and adult adrenal or nerve-related tumors.
- Neuroblastoma: The most frequent use. Neuroblastoma is the most common solid tumor outside the brain in infants and young children, and MIBG scanning is central to finding the original tumor, checking whether it has spread, and monitoring how well treatment is working.
- Pheochromocytoma and paraganglioma: These are rare tumors of the adrenal glands or nearby nerve tissue that can cause dangerous spikes in blood pressure. Because they can appear in unusual locations or as multiple tumors, a whole-body MIBG scan has a major advantage over CT or MRI, which typically image only one region at a time.
- Other neuroendocrine tumors: MIBG scanning can sometimes help evaluate medullary thyroid cancer, ganglioneuroblastoma, Merkel cell tumors, and multiple endocrine neoplasia syndrome, though its sensitivity varies by tumor type.
Beyond cancer, MIBG scans also have a role in heart and brain conditions. Cardiac MIBG imaging, first approved in Japan in 1992, evaluates how well the heart’s sympathetic nerves are functioning. This is useful in heart failure and cardiomyopathy. It can also help distinguish Parkinson’s disease from other conditions that cause similar movement symptoms, because Parkinson’s specifically damages the sympathetic nerve endings in the heart.
Two Types of Radioactive Iodine
MIBG can be labeled with two different forms of radioactive iodine, and the choice affects image quality and radiation exposure. Iodine-123 (I-123) is used primarily for diagnostic scans. It produces cleaner images, delivers a lower radiation dose, and is the standard choice for routine imaging.
Iodine-131 (I-131) delivers more radiation and is mainly used for therapy, where higher-dose MIBG is injected to destroy tumor cells directly. However, scanning done after an I-131 treatment dose can actually detect more lesions than a standard I-123 diagnostic scan, because the much larger amount of tracer makes smaller deposits of tumor visible. In one comparison, post-therapy I-131 scans found roughly twice as many lesions per study as I-123 scans.
How to Prepare
The most important preparation step is thyroid protection. Because the tracer contains radioactive iodine, some of that iodine can break free and collect in your thyroid gland. To block this, you’ll take a saturated solution of potassium iodide (SSKI) or Lugol’s solution, typically starting one day before the injection and continuing for up to seven days afterward. This floods the thyroid with stable iodine so it won’t absorb the radioactive form. The optimal timing is at least one hour before the tracer injection.
Certain medications interfere with the scan by blocking MIBG uptake into tumor cells, which can cause a false-negative result. The strongest evidence for interference exists for labetalol (a blood pressure medication) and reserpine. Tricyclic antidepressants, certain calcium channel blockers, and the heart rhythm drug amiodarone also have moderate evidence of interference. Decongestants and other drugs that stimulate the sympathetic nervous system, along with serotonin-norepinephrine reuptake inhibitor (SNRI) antidepressants, may also need to be paused. Your care team will give you a specific list and timeline for stopping any of these before the scan.
What Happens During the Scan
The procedure spans two days, though your active time in the imaging suite is relatively brief on each visit.
On day one, the tracer is injected into a vein. The injection is given slowly over one to two minutes. This slow pace matters because a rapid injection can temporarily cause nausea, a rise in blood pressure, sweating, or pallor, especially in patients whose tumors actively release stress hormones. For children with hormone-secreting tumors, blood pressure may be monitored during and after the injection.
You then go home and return 24 hours later for imaging. The delay gives the tracer time to travel through your body and concentrate in target tissues while clearing from areas where it doesn’t belong. During imaging, you lie on a table while a gamma camera moves slowly around your body, capturing pictures from multiple angles. Some facilities use SPECT/CT, which combines the nuclear medicine images with a low-dose CT scan for better anatomical detail.
In some cases, a second set of images is taken at 48 hours. Whether this is needed depends on what the 24-hour images show.
The Experience for Children
Because neuroblastoma is a childhood cancer, many MIBG scans are performed on very young patients. Most children can complete the scan without sedation. The decision to sedate is made on a case-by-case basis, usually depending on the child’s age and ability to hold still. Modern scanners have reduced both scan duration and radiation exposure compared to older equipment, which helps with younger or more anxious patients.
Parents should expect the scan to feel uneventful for the child. The injection may cause brief discomfort, and the imaging session requires lying relatively still, but the procedure itself is painless. The most common side effects reported in larger studies of MIBG (primarily at therapeutic doses, which are much higher than diagnostic doses) are mild nausea and occasional vomiting. At the low doses used for diagnostic scans, side effects are rare.
Why MIBG Scans Are Preferred Over CT or MRI
A CT or MRI scan shows the physical structure of tissues, which means it can identify a mass but can’t always tell whether that mass is an active tumor, scar tissue, or something benign. An MIBG scan shows function: it reveals whether cells are actively taking up norepinephrine-like compounds, which is a hallmark of these specific tumor types.
The whole-body coverage is another key advantage. Pheochromocytomas and paragangliomas can occur in the adrenal glands, along the spine, in the chest, or in the pelvis. Neuroblastoma frequently spreads to bone. A single MIBG scan surveys the entire body in one session, catching tumors or metastases that might be missed if imaging were limited to one region. This combination of specificity (knowing what the tissue is) and comprehensive coverage makes it a cornerstone of diagnosis and follow-up for these cancers.