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Computed Tomography (CT) Scan
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Computed Tomography (CT) Scan
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A CT scan ("cat scan") is an x-ray technique that uses a computer to create cross-sectional (or slice-like) pictures of the heart.

Photo showing the view from the control room during a CT scan.

View from the control room during a CT scan.
How does it work?

The CT scanner is a large X-ray machine that has a short, open-ended tube in the middle (like a very short tunnel). The patient lies on a scanning table, which slides through the middle of the CT scanner. The CT scanner takes many x-ray pictures of thin slices of your heart. A computer then puts these images together to make one detailed picture. In some cases, a contrast dye is injected into the bloodstream to help doctors get a clearer picture.

What should I expect?

If a contrast dye is not going to be used during your CT scan, you should not eat for about 2 hours before the test. If a contrast dye is going to be used, you should not eat for about 4 hours before the test. The contrast dye may cause hot flushing in some patients.

You will be asked to undress and put on a hospital gown. Then, you will lie down on a table, which will be slowly moved through the hollow center of the CT scanner. You will be asked to lie still and to hold your breath briefly as each picture is taken.

After the test, you may go about your normal activities. Some people find that they have a bad reaction to the contrast dye, but this is rare. If this happens, you will be treated at the hospital after your test.

CT scanning is a safe test. Although your exposure to radiation is small, you should not have a CT scan if you are pregnant.

A CT scan

A CT scan does not get a moving picture of the heart. Instead, CT scans are used to see if part of the heart has calcified. This patient has had a heart attack that scarred the heart's main pumping chamber (the left ventricle). The red arrows point to the scarred part of the heart that has since formed a thick, calcified wall at the tip of the left ventricle.

The red arrows in the images point to a large aneurysm of the abdominal aorta seen from the front (left picture) and the side (right picture).

 A CT scan gets a number of images that your doctor can look at one by one. New computer technology now lets technicians stack the images on top of each other to get a 3-D image that can be rotated and viewed from any angle. The red arrows in the images above point to a large aneurysm of the abdominal aorta seen from the front (left picture) and the side (right picture).


Electron Beam Computed Tomography (EBCT or Ultrafast® CT)

An electron beam CT scan. The red arrow is pointing to calcification in the left coronary artery.

An electron beam CT scan is faster than a regular CT scan. The technician can "freeze" an image while the heart is in motion. This lets doctors get a better look at the coronary arteries. The red arrow is pointing to calcification in the left coronary artery.
EBCT is a faster type of CT scanning, which takes an x-ray of the heart in about one-tenth of a second. Ordinary CT scanning can take anywhere from 1 to 10 seconds. EBCT takes pictures so quickly that it can avoid blurred pictures caused by the beating of the heart, a problem with a regular CT scan. This type of scanning can also detect calcium buildup in the arteries of the heart (the coronary arteries). The amount of calcium in the coronary arteries has been found to be a marker for the presence of coronary artery disease.


Multi-Detector Computed Tomography (MDCT)

Ordinary CT scanning can take anywhere from 1 to 10 seconds per slice (or picture), but the faster MDCT scanners have many rows of detectors (up to 64!) that can take multiple X-rays of the heart at the same time. These scanners can also obtain pictures of the entire heart in about 1 ten-second breathhold.

The new MDCT scanners are used routinely to measure the amount of calcium in the coronary arteries—similar to EBCT—but are also now able to take images of the coronary arteries that are nearly comparable to those taken during a cardiac catheterization. For many patients, an MDCT scan of the heart is enough for doctors to determine whether coronary artery disease is present, and patients may not need to have a cardiac catheterization.

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The two MDCT views above show that the left coronary artery (red arrows) and its side branches are normal.

3D MDCT view shows a normal coronary artery (black arrow) and side branches.

This 3D MDCT view is looking down on top of the left ventricle. It shows a normal coronary artery (black arrow) and side branches.


See on other sites:

MedlinePlus
www.nlm.nih.gov/medlineplus/ency/article/003330.htm
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