sábado, 17 de noviembre de 2012

Single Photon Emission Computed Tomography (SPECT)

Single Photon Emission Computed Tomography (SPECT)

Single Photon Emission Computed Tomography (SPECT)
  • Updated:Nov 6,2012
What is a cardiac SPECT scan?A SPECT scan of the heart is a noninvasive nuclear imaging test. It uses radioactive tracers that are injected into the blood to produce pictures of your heart. Doctors use SPECT to diagnose coronary artery disease and find out if a heart attack has occurred. SPECT can show how well blood is flowing to the heart and how well the heart is working.

Quick facts
  • SPECT scans use radioactive material called tracers. The tracers mix with your blood and are taken up by living heart muscle.
  • A special “gamma” camera picks up signals from the tracer as it moves around your chest. The tracer’s signals are converted into images by a computer.  
  • The pictures will help your doctor see if your heart is getting enough blood or if blood flow is reduced because of narrowed arteries.
  • A SPECT scan can be used to examine blood flow in your heart at rest and during exercise (called a nuclear stress test). If you can’t exercise, you’ll get a medicine to increase the blood flow in your heart as if you were exercising (called a chemical or pharmacologic stress).
  • SPECT scans can also give information about how well your heart is pumping.
Why do people have cardiac SPECT scans?SPECT scans show areas of your heart that have low blood flow at rest or during exercise. This information helps your doctor find out:
  • If you have coronary artery disease
  • If you’ve had a heart attack and areas of scar tissue exist.
  • How well bypass surgery or other cardiac procedures are working
  • If you are having a heart attack and need more immediate tests such as a cardiac catheterization or percutaneous coronary intervention (PCI)
  • If you are at risk of having a heart attack
How does a SPECT scan work?A radioactive tracer is injected into your bloodstream. Inside your body, the tracer produces a type of energy called gamma rays. A gamma camera picks up signals from the tracer, and a computer converts them into pictures of blood flow through your heart. Images of thin slices made all the way through the heart can be produced from all different directions and angles. These images are examined for the location of the tracer. Computer graphics can be used to create a 3-dimensional image of your heart from the thin-slice images.

On the pictures, areas of your heart that have good blood flow will be light, and areas with poor blood flow will be dark. Many SPECT scans produce colored images. The different colors represent different amounts of tracer uptake.
SPECT scans can be done while you rest and during an exercise stress test (called a nuclear stress test). The stress test gives your doctor a better idea of how well your heart handles work. If you can’t exercise, you may get a medicine to increase the blood flow in your heart as if you were exercising. This is called a chemical or pharmacologic stress test.
  • If the test is normal during both exercise and rest, blood flow through the coronary arteries is normal.
  • The test may show normal blood flow (perfusion) at rest but not after exercise. This may be due to a blockage in one or more coronary (heart) arteries. A blockage can create a “perfusion defect” or an area where little to no uptake of tracer can be seen.
  • The test may be abnormal during both exercise and rest. In this case, the tracer won’t be visible in an area. This means that not enough blood is flowing to that area of the heart at any time. 
  • Lack of tracer often means that the cells in that area are dead from a prior heart attack. (They have become scar tissue.)
    By using specific radioactive tracers designed for this test, SPECT scans can also show how well your heart’s left ventricle (lower pumping chamber) is working.
Note:  SPECT is a noninvasive nuclear imaging test.  It uses radioactive tracers that are injected into the blood to produce pictures of the heart.  The pictures will help your doctor see if your heart is getting enough blood.

What are the risks of cardiac SPECT?Cardiac SPECT is safe for most people. The amount of radiation is small, and your body will get rid of it through your kidneys in about 24 to 72 hours.
If you’re pregnant or think you might be pregnant, or if you’re a nursing mother, tell your doctor before you have this test. It could harm your baby.

How do I prepare for cardiac SPECT?
  • Tell your doctor about any medicines you take, including over-the-counter medicines, herbs and vitamins. The doctor may ask you not to take them before the test. Don’t stop taking your medicine until your doctor tells you to.
  • Your doctor may also ask you not to have certain foods, such as caffeine-containing drinks, for 24 hours before your test. The test may have to be postponed or cancelled if you’ve had caffeine. 
  • Don’t eat, and drink only water for 4 to 6 hours before your test.
  • Wear comfortable, loose-fitting clothing and comfortable shoes if you will have an exercise stress test.
What happens during cardiac SPECT?A doctor and nuclear medicine technologist usually perform the scan in a hospital or clinic using special equipment.
  • The technician will place small metal disks (electrodes) on your chest, arms and legs. The disks have wires that hook to a machine that records your electrocardiogram (ECG). The ECG keeps track of your heartbeat during the test and can be used to signal the camera when to take a picture.
  • You’ll wear a cuff around your arm to track your blood pressure.
  • The technician will put an intravenous line (IV) in your arm. The tracer will be injected through the IV. 
  • For a resting scan, you’ll lie on a table and a gamma camera will move around your chest and convert the tracer’s signals into pictures. 
  • For a nuclear stress test, you’ll either walk on a treadmill or ride on a stationary bicycle. Then you’ll again lie on the table for more pictures. If you can’t exercise, you’ll receive a medicine (chemical stress) through the IV to increase the blood flow in your heart similar to what occurs during physical activity. These medicines may include adenosine, dipyridamole (Persantine) or dobutamine.The tests may take between 2 and 2 1/2 hours.
What happens after my SPECT imaging test?
  • You can usually go back to your normal activities right away.
  • Drink plenty of water for the next couple of days. This will help flush the radioactive material from your body.
  • Make an appointment with your doctor to discuss the test results and next steps.
How can I learn more about cardiac SPECT?Talk with your doctor. Here are some good questions to ask:
  • Why are you doing this test rather than a different one?
  • What do I need to do to get ready for this test?
  • When will I get the results of my test?
  • Will I need to have more tests after this?
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