Brain Nuclear Scan

After injection of a small amount of radioactive material, a special camera records the uptake of the radiotracer within the brain. Normally, the blood-brain barrier—a protective characteristic of blood vessels in the brain that blocks out potentially harmful substances—prevents the radiotracer from being taken up by brain tissues, but if this barrier has been disrupted by disease, the material will concentrate in abnormal regions of the brain. The camera data are translated by computer into two-dimensional images that are recorded on film.

A variation of nuclear scanning, called single-photon emission computed tomography (SPECT), enhances the sensitivity of the test. It utilizes certain radiotracers that emit single gamma rays to evaluate changes in blood flow and other brain abnormalities. Computer methods similar to those employed in CT scanning are then used to produce images of multiple sections of the brain, which are then recorded on film.

Purpose of the Brain Scan

  • To detect and evaluate abnormalities affecting the brain, including tumors, infarction (an area of dead tissue caused by interruption of blood flow), infection, bleeding, or blockage of blood vessels and maps mental development
  • To evaluate epilepsy, headaches, and other neurologic symptoms
  • To aid in the evaluation of dementia, cerebrovascular disease and psychiatric disorders
  • In adults with Down syndrome, to assess levels of amyloid plaques and neurofibrillary tangles — the hallmarks of Alzheimer's disease.

Who Performs Brain Scan

  • A radiologist or a nuclear medicine technician

Special Concerns about Brain Scan

  • In general, CT scans, MRI, and carotid artery duplex scans have replaced brain nuclear scans for the diagnosis of neurological disorders. SPECT is rarely used outside of research purposes today.
  • This test should not be performed in pregnant or breastfeeding women because of possible risks to the fetus or infant.
  • People with allergies to iodine or shellfish may experience a severe allergic reaction if radioactive iodine is used in the test.

Before the Brain Scan

  • Inform your doctor if you have an allergy to iodine or shellfish.
  • You will be asked to rest quietly for 10 to 20 minutes before the procedure is started.
  • Remove all jewelry and metal objects.
  • Empty your bladder before the test.
  • An intravenous (IV) needle or catheter is inserted into a vein in your arm immediately before the test begins.
  • Certain medications, called blocking agents, may be administered orally or by injection before the test to prevent excessive uptake of the radioisotope by specific tissues.

What You Experience

  • After a radiotracer is injected into the IV line, you lie on your back on a table with your head under a large scanning camera.
  • You will be asked to assume different positions—on your back, side, or stomach—while the scanner records the gamma rays emitted by the radiotracer in a timed sequence to follow the material during its first flow through the brain. (For a SPECT exam, you will lie on your back as a special rotating camera records images from multiple angles.)
  • You must remain very still during the scanning process.
  • This procedure takes about 35 to 45 minutes. Another scan is then performed 30 minutes to 2 hours later to identify any abnormal areas in the brain.

Risks and Complications of Brain Scan

  • The trace amount of radioactive material used in this test is not associated with significant risks or complications.
  • In extremely rare cases, patients may be hypersensitive to the radiotracer and may experience an adverse reaction.

After the Brain Scan

  • Drink extra fluids to aid in the excretion of the radioactive material.
  • You are free to leave and resume your normal activities.
  • Blood may collect and clot under the skin (hematoma) at the IV needle insertion site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.

Brain Scan Results

  • A physician will examine the scans for evidence of any brain abnormality.
  • If a definitive diagnosis can be made, appropriate treatment will be initiated.
  • Abnormal results may also necessitate additional tests, such as MRI or MRA of the brain.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 13 Jan 2012

Last Modified: 13 Jan 2012