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What Is Cardiac CT?

Cardiac computed tomography (to-MOG-rah-fee), or cardiac CT, is a painless test that uses an x-ray machine to take clear, detailed pictures of the heart. Doctors use this test to look for heart problems.

During a cardiac CT scan, an x-ray machine will move around your body in a circle. The machine will take a picture of each part of your heart. A computer will put the pictures together to make a three-dimensional (3D) picture of the whole heart.

Sometimes an iodine-based dye (contrast dye) is injected into one of your veins during the scan. The contrast dye highlights your coronary (heart) arteries on the x-ray pictures. This type of CT scan is called a coronary CT angiography (an-je-OG-rah-fee), or CTA.

Overview

Doctors use cardiac CT to help detect or evaluate:

  • Coronary heart disease (CHD). In CHD, a waxy substance called plaque (plak) narrows the coronary arteries and limits blood flow to the heart. A coronary CTA can show whether the coronary arteries are narrow or blocked.  
  • Calcium buildup in the walls of the coronary arteries. This type of CT scan is called a coronary calcium scan. Calcium in the coronary arteries may be an early sign of CHD.
  • Problems with the aorta. The aorta is the main artery that carries oxygen-rich blood from the heart to the body. Cardiac CT can detect two serious problems in the aorta:
    • Aneurysm (AN-u-rism). An aneurysm is a diseased area of a blood vessel wall that bulges out. An aneurysm can be life threatening if it bursts.
    • Dissection. A dissection is a split in one or more layers of the artery wall. The split causes bleeding into and along the layers of the artery wall. This condition can cause pain and may be life threatening.
  • A pulmonary embolism (PE). A PE is a sudden blockage in a lung artery, usually due to a blood clot.
  • Problems in the pulmonary veins. The pulmonary veins carry blood from the lungs to the heart. Problems with these veins may lead to an irregular heart rhythm called atrial fibrillation (AF). The pictures that cardiac CT creates of the pulmonary veins can help guide procedures used to treat AF.
  • Problems with heart function and heart valves. In some cases, doctors may recommend cardiac CT instead of echocardiography or cardiac MRI (magnetic resonance imaging) to look for problems with heart function or heart valves.
  • Pericardial disease. This is a disease that occurs in the pericardium, the sac around your heart. Cardiac CT can create clear, detailed pictures of the pericardium.
  • Results of coronary artery bypass grafting (CABG). In CABG, arteries from other areas in your body are used to bypass (that is, go around) narrow coronary arteries. A CT scan can show whether the grafted arteries remain open after the surgery.

Different types of CT scans are used for different purposes. For example, multidetector computed tomography (MDCT) is a fast type of CT scanner. Because the heart is in motion, a fast scanner is able to produce high-quality pictures of the heart. MDCT also might be used to detect calcium in the coronary arteries.

Another type of CT scanner, called electron-beam computed tomography (EBCT), also is used to detect calcium in the coronary arteries.

Outlook

Because an x-ray machine is used, cardiac CT involves radiation. The amount of radiation used is considered small. Depending on the type of CT scan you have, the amount of radiation is similar to the amount you’re naturally exposed to over 1–5 years.

There is a small chance that cardiac CT will cause cancer because of the radiation. The risk is higher in people younger than 40 years old. New cardiac CT methods are available that reduce the amount of radiation used during the test.

Researchers continue to study new and better ways to use cardiac CT.




Other Names for Cardiac CT

  • CAT scan
  • Coronary artery scan
  • Coronary CT angiography
  • CT angiography



What To Expect Before Cardiac CT

Your doctor will tell you how to prepare for the cardiac CT scan. He or she may tell you to avoid caffeine and not eat anything for 4 hours before the scan. You’re usually allowed to drink water before the test.

If you take medicine for diabetes, talk with your doctor about whether you'll need to change how you take it on the day of your cardiac CT scan.

Tell your doctor whether you:

  • Are pregnant or might be pregnant. Even though cardiac CT uses a low radiation dose, the x rays may harm your fetus.
  • Have asthma or kidney problems or are allergic to any medicines, iodine, or shellfish. These problems can increase your chance of having an allergic reaction to the contrast dye that's sometimes used during cardiac CT.

A technician will ask you to remove your clothes above the waist and wear a hospital gown. You also will be asked to remove any jewelry from around your neck or chest.

If you don't have asthma, COPD (chronic obstructive pulmonary disease), or heart failure, your doctor may give you medicine to slow your heart rate. A slower heart rate will help produce better quality pictures. The medicine will be given by mouth or injected into a vein.




What To Expect During Cardiac CT

Cardiac CT is done in a hospital or outpatient office. A doctor who has experience with CT scanning will supervise the test.

The doctor may want to use an iodine-based dye (contrast dye) during the cardiac CT scan. If so, a needle connected to an intravenous (IV) line will be put in a vein in your hand or arm.

The doctor will inject the contrast dye through the IV line during the scan. You may have a warm feeling when this happens. The dye will make your blood vessels visible on the CT scan pictures.

The technician who runs the cardiac CT scanner will clean areas on your chest and apply sticky patches called electrodes. The patches are attached to an EKG (electrocardiogram) machine. The machine records your heart's electrical activity during the scan.

The CT scanner is a large machine that has a hollow, circular tube in the middle. You will lie on your back on a sliding table. The table can move up and down, and it goes inside the tunnel-like machine.

The table will slide slowly into the opening in the machine. Inside the scanner, an x-ray tube moves around your body to take pictures of different parts of your heart. A computer will put the pictures together to make a three-dimensional (3D) picture of the whole heart.

The technician controls the CT scanner from the next room. He or she can see you through a glass window and talk to you through a speaker.

Moving your body can cause the pictures to blur. You'll be asked to lie still and hold your breath for short moments, while each picture is taken.

A cardiac CT scan usually takes about 15 minutes to complete. However, it can take more than an hour to get ready for the test and for the medicine to slow your heart rate. (For more information, go to "What To Expect Before Cardiac CT.")




What To Expect After Cardiac CT

After the cardiac CT scan is done, you'll be able to return to your normal activities. A doctor who has experience with CT will provide your doctor with the results of your scan. Your doctor will discuss the findings with you.




What Does Cardiac CT Show?

Many x-ray pictures are taken during a cardiac CT scan. A computer puts the pictures together to make a three-dimensional (3D) picture of the whole heart. This picture shows the inside of the heart and the structures that surround the heart.

Cardiac CT

Figure A is an illustration of the outside of the heart. The arrow shows the point of view of the cardiac CT image. The inset image shows the position of the heart in the body. Figure B is a cardiac CT image showing the coronary arteries on the surface of the heart. This is a picture of the whole heart put together by a computer.

Figure A is an illustration of the outside of the heart. The arrow shows the point of view of the cardiac CT image. The inset image shows the position of the heart in the body. Figure B is a cardiac CT image showing the coronary arteries on the surface of the heart. This is a picture of the whole heart put together by a computer.

Doctors use cardiac CT to detect or evaluate:  

  • Coronary heart disease (CHD). In CHD, a waxy substance called plaque narrows the coronary arteries and limits blood flow to the heart. Contrast dye might be used during a cardiac CT scan to show whether the coronary arteries are narrow or blocked. When contrast dye is used, the test is called a coronary CT angiography, or CTA.
  • Calcium buildup in the walls of the coronary arteries. This type of CT scan is called a coronary calcium scan. Calcium in the coronary arteries may be an early sign of CHD.
  • Problems with the aorta. The aorta is the main artery that carries oxygen-rich blood from the heart to the body. Cardiac CT can detect two serious problems in the aorta:
    • Aneurysm (AN-u-rism). An aneurysm is a diseased area of a blood vessel wall that bulges out. An aneurysm can be life threatening if it bursts.
    • Dissection. A dissection is a split in one or more layers of the artery wall. The split causes bleeding into and along the layers of the artery wall. This condition can cause pain and may be life threatening.
  • A pulmonary embolism (PE). A PE is a sudden blockage in a lung artery, usually due to a blood clot.
  • Problems in the pulmonary veins. The pulmonary veins carry blood from the lungs to the heart. Problems with these veins may lead to an irregular heart rhythm called atrial fibrillation (AF). The pictures that cardiac CT creates of the pulmonary veins can help guide procedures used to treat AF.
  • Problems with heart function and heart valves. In some cases, doctors may recommend cardiac CT instead of echocardiography or cardiac MRI (magnetic resonance imaging) to look for problems with heart function or heart valves.
  • Pericardial disease. This is a disease that occurs in the pericardium, the sac around your heart. Cardiac CT can create clear, detailed pictures of the pericardium.
  • Results of coronary artery bypass grafting (CABG). In CABG, arteries from other areas in your body are used to bypass (that is, go around) narrow coronary arteries. A CT scan can help determine whether the grafted arteries remain open after the surgery.

Doctors also might recommend cardiac CT scans before or after other heart procedures, such as cardiac resynchronization therapy. A CT scan can help your doctor pinpoint the areas of the heart or blood vessels where the procedure should be done. The scan also can help your doctor check your heart after the procedure.

Because the heart is in motion, a fast type of CT scanner, called multidetector computed tomography (MDCT), might be used to take high-quality pictures of the heart. MDCT also might be used to detect calcium in the coronary arteries.

Another type of CT scanner, called electron-beam computed tomography (EBCT), also is used to detect calcium in the coronary arteries.




What Are the Risks of Cardiac CT?

Cardiac CT involves radiation, although the amount used is considered small. Depending on the type of CT scan you have, the amount of radiation is similar to the amount you’re naturally exposed to over 1–5 years.

There is a small chance that cardiac CT will cause cancer because of the radiation. The risk is higher for people younger than 40 years old. New cardiac CT methods are available that reduce the amount of radiation used during the test.

Cardiac CT scans are painless. Some people have side effects from the contrast dye that might be used during the scan. An itchy feeling or a rash may appear after the contrast dye is injected. Normally, neither side effect lasts for long, so medicine often isn't needed.

If you do want medicine to relieve the symptoms, your doctor may prescribe an antihistamine. This type of medicine is used to help stop allergic reactions.

Although rare, it is possible to have a serious allergic reaction to the contrast dye. This reaction may cause breathing problems. Doctors use medicine to treat serious allergic reactions.

People who have asthma, COPD (chronic obstructive pulmonary disease), or heart failure may have breathing problems during cardiac CT if they're given beta blockers to slow their heart rates.




Clinical Trials

The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.

NHLBI-supported research has led to many advances in medical knowledge and care. Often, these advances depend on the willingness of volunteers to take part in clinical trials.

Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions. For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.

By taking part in a clinical trial, you may gain access to new treatments before they’re widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don’t directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.

If you volunteer for a clinical trial, the research will be explained to you in detail. You’ll learn about treatments and tests you may receive, and the benefits and risks they may pose. You’ll also be given a chance to ask questions about the research. This process is called informed consent.

If you agree to take part in the trial, you’ll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.

For more information about clinical trials related to cardiac CT, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:

For more information about clinical trials for children, visit the NHLBI’s Children and Clinical Studies Web page.




Links to Other Information About Cardiac CT

NHLBI Resources

Non-NHLBI Resources

Clinical Trials

 
February 29, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.

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