Single Photon Emission Computed Tomography (SPECT)

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Test Overview

Single photon-emission computed tomography scanner.

Single photon-emission computed tomography (SPECT) is a test that uses a special type of camera and a tracer (a radioactive substance in liquid form) to look at organs or bones in the body. During the test, the tracer is put into a vein (intravenous, or IV) in your arm. Sometimes it's taken by mouth or inhaled through the nose.

The tracer moves through your body, where it may collect in the specific organ or tissue. The tracer gives off tiny bits of radiation called gamma rays. The camera records the gamma rays. Then a computer turns the recording into 3-dimensional pictures. SPECT scan pictures show how organs are working.

Other types of scans, such as computed tomography (CT) scans or magnetic resonance imaging (MRI) show more details of the organs themselves. The SPECT picture may be matched with those from a CT scan to get more detailed information about where the tracer is located.

A SPECT scan is often used to evaluate brain, head, and neck problems; to look at blood flow to the heart; to examine bones; and to diagnose problems in other organs such as the gall bladder, liver, spleen, and kidneys.

Why It Is Done

A SPECT scan is done to:

  • Check to see how well treatments are working.
  • Examine bones for signs of cancer and sometimes for fractures or degenerative bone diseases such as osteoporosis.
  • Evaluate brain conditions such as Alzheimer's disease and other types of dementia, Parkinson's, transient ischemic attack (TIA), and stroke.
  • Help diagnose some psychological conditions, including schizophrenia.
  • Help determine brain death.
  • Find out what's causing seizures, including for epilepsy.
  • Find poor blood flow to the heart, which may mean coronary artery disease or other heart conditions.
  • Assess heart attack risk or find damaged heart tissue after a heart attack.
  • Diagnose gall bladder disease.
  • Evaluate the extent of some cancers, especially lymphomas and lung cancer.
  • Help a doctor choose the best treatment for cancer or find out how well cancer treatment is working.
  • Check the liver, kidney, and spleen for cancers.
  • Find tumors in the endocrine system.
  • Find areas of inflammation or infection.

How To Prepare

  • Before you have a SPECT scan, tell your doctor if you:
    • Have diabetes. If you take medicine to control diabetes, you may need to take less than your normal dose. Talk with your doctor about how much medicine you should take.
    • Have had other nuclear scans.
    • Have any allergies, especially to iodine.
    • Take any medicines, supplements, or herbal remedies. You may need to stop taking some medicines or change your dose before this test.
    • Are or might be pregnant.
    • Are breastfeeding. The radioactive tracer used in this test can get into your breast milk. Do not breastfeed your baby for 2 days after this test. During this time, you can give your baby breast milk you stored before the test, or you can give formula. Don't use the breast milk you pump for 2 days after the test. Get rid of it.
    • Have a fear of enclosed spaces.
  • You may not be able to eat or drink for at least 6 hours before some SPECT scans. Ask your doctor when or if you need to fast before the test.
  • Your doctor will also let you know if you should avoid smoking or drinking caffeine or alcohol for 24 hours before this test.
  • You may be asked to sign a consent form.
  • Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done or what the results mean.

How It Is Done

A single photon-emission computed tomography (SPECT) scan is done in a hospital nuclear medicine department or at a special radiology center by a radiologist or nuclear medicine specialist and a technologist. You will lie on a table that is hooked to a large scanner, cameras, and a computer.

During the test

The radioactive tracer is usually given in a vein (IV). You may need to wait as long as an hour for the tracer to move through your body. During this time, you may need to avoid moving and talking.

The SPECT scanner is a large machine that scans your body. It has two cameras that rotate slowly around your body. They will be very close to your body but should not touch you. The scanned pictures are sent to a computer screen so your doctor can see them. Many scans are done to make a series of pictures.

It's very important to lie still while each scan is being done. At some medical centers, a CT scan will be done at the same time.

For a SPECT scan of the brain, you will lie on a bed. You may be asked to read, name letters, or tell a story, depending on whether speech, reasoning, or memory is being tested. During the scan, you may be given earplugs and a blindfold (if you don't need to read during the test) to wear for your comfort.

If you are having a SPECT scan of your heart, electrodes for an electrocardiogram (EKG, ECG) will be put on your body. During the test, you will be alone in the scanner room. The technologist will watch you through a window. You will be able talk to him or her at all times through a two-way intercom.

The test takes 1 to 3 hours. You may need to return for follow-up scans.

After the test

After the test, drink lots of fluids for the next 24 hours to help flush the tracer out of your body.

Be careful with body fluids. Flush toilets and wash hands well right after you use the bathroom. Avoid using a urinal.

How It Feels

You won't feel pain during the test. The table you lie on may be hard, and the room may be cool. It may be difficult to lie still during the test.

You may feel a quick sting or pinch when the IV is put in your arm. The tracer is unlikely to cause any side effects. If you don't feel well during or after the test, tell the person who is doing the test.

You may feel nervous while the SPECT scanner moves around you.

Risks

There is always a slight chance of damage to cells or tissue from radiation, including the low levels of radiation used for this test. But the chance of damage is usually very low compared with the benefits of the test.

Most of the tracer will be flushed from your body within 6 to 24 hours. Allergic reactions to the tracer are very rare.

In rare cases, you may have some soreness or swelling at the IV site where the radioactive tracer was put in. If so, apply a moist, warm compress to your arm.

Results

Single photon-emission computed tomography (SPECT) is a test that uses a special type of camera and a tracer (a radioactive substance in liquid form) to look at organs in the body.

The radiologist may discuss preliminary results of the SPECT scan with you right after the test. Complete results are usually available in 1 to 2 days.

Single photon-emission computed tomography (SPECT) results
Heart:Normal:
  • Left ventricular end diastolic volume <= 70 ML
  • Left ventricular end systolic volume <= 25 ML
  • Left ventricular ejection fraction > 50%
  • Right ventricular ejection fraction >40%
  • Normal cardiac wall motion. No muscle wall thickening.
Abnormal:
  • Abnormal stress and resting images may be a sign of heart attack.
  • Tracer uptake in the heart muscles (myocardium) may be a sign of a thickening of the heart (cardiac hypertrophy).
  • Enlarged left ventricle or other heart chamber disorder is seen.
  • Ventricular septal defects are seen.
Brain (such as epilepsy, dementia, stroke):Normal:
  • Tracer is distributed normally around the brain.
Abnormal:
  • Tracer is not distributed normally around the brain.
  • Abnormal stress images with normal resting images may be a sign of possible stroke.
Bone:Normal:
  • Tracer is spread evenly throughout the bones.
Abnormal:
  • Concentrations of tracer can show areas of cancer, fractures, arthritis, and other bone diseases, such as Paget's disease or osteomyelitis.
Other:Normal:
  • Gallbladder: Normal if organ appears on camera within an hour after you take the tracer.
  • Liver/spleen: Normal if size, shape and position of organs appear normal and consistent.
  • Lung: Normal if tracer spreads evenly throughout the lungs.
Abnormal:
  • Gallbladder: Abnormal if organ isn't visible or if it takes longer than hour to see it.
  • Liver/spleen: Abnormal if any variation is seen in uptake of the tracer.

What Affects the Test

You may not be able to have the test or the results may not be helpful if:

  • You are pregnant. A SPECT scan usually isn't done during pregnancy because the radiation could harm the unborn baby (fetus).
  • You aren't able to lie still for the test.
  • You use sedatives.
  • You take medicines, such as insulin, that change your metabolism.
  • You recently had surgery, a biopsy, chemotherapy, or radiation therapy.

Credits

ByHealthwise Staff

Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine

Adam Husney, MD - Family Medicine

Specialist Medical ReviewerHoward Schaff, MD - Diagnostic Radiology

Current as ofOctober 9, 2017