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Single Photon Emission Computed Tomography (SPECT)

Test Overview

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.

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. These may include Alzheimer's disease and other types of dementia, Parkinson's, transient ischemic attack (TIA), and stroke.
  • Help diagnose some psychological conditions, such as 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 gallbladder disease.
  • Evaluate the extent of some cancers, especially lymphomas and lung cancer.
  • Help a doctor choose the best treatment for cancer. Or it can 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

  • 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.
  • Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
  • If you are breastfeeding, you may want to pump enough breast milk before the test to get through 1 to 2 days of feeding. The radioactive tracer used in this test can get into your breast milk and is not good for the baby.
  • Tell your doctor if you get nervous in tight spaces. You may get a medicine to help you relax. If you think you'll get this medicine, be sure you have someone to take you home.
  • 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 avoid drinking caffeine or alcohol for 24 hours before this test.

How It Is Done

A SPECT scan is done in a hospital nuclear medicine department. You will lie on a table that is hooked to a large scanner, cameras, and a computer.

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 to talk to each other at all times through a two-way intercom.

How long the test takes

The test takes 1 to 3 hours.

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

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.

Anytime you're exposed to radiation, there's a small chance of damage to cells or tissue. That's the case even with the low-level radioactive tracer used for this test. But the chance of damage is very low compared with the benefits of the test.

Steps you can take

  • After the test, drink lots of fluids for the next 24 hours to help flush the tracer out of your body.
  • The radioactive tracer used in this test can get into your breast milk. Do not breastfeed your baby for 1 or 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. Discard the breast milk you pump in the 1 or 2 days after the test.
  • Most of the tracer will leave your body through your urine or stool within a day. So be sure to flush the toilet right after you use it, and wash your hands well with soap and water. The amount of radiation in the tracer is very small. This means it isn't a risk for people to be around you after the test.

Results

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.

Heart

SPECT results for heart scans

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)

SPECT results for brain scans

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

SPECT results for bone scans

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

SPECT results for other scans

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.

Credits

Current as of: June 17, 2021

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Howard Schaff MD - Diagnostic Radiology