Computer tomography (CT)

A CT scan is an x-ray technique that uses an x-ray generator and a computer to show cross-sectional (or slice-like) pictures of the heart.

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 multiple rays of the patient’s heart, and a computer summarises them to produce detailed sliced pictures. In some cases, a contrast dye is injected into the blood to get a better picture.

Different types of CT

There are several different types of CT scanners, for example Electron-Beam CT (EBCT or ultrafast CT) and Multi-Detector CT, which differ from each other by the number of images that are made simultaneously and by the speed.

EBCT is a fast type of CT scanning that takes an x-ray of the heart in about a tenth of a second. Ordinary CT scanning can take from 1 to 30 seconds. EBCT takes pictures so quickly that it can avoid blurred images caused by the heart beating, which is a problem with a regular CT scan. This type of scanning can also detect calcium build-up in the arteries of the heart (the coronary arteries). The amount of calcium in the coronary arteries can indicate the presence of coronary artery disease.

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 10 seconds, while the patient holds their breath. The new MDCT scanners are used routinely to measure the amount of calcium in the coronary arteries—similar to EBCT—but they are now able to take images of the coronary arteries that are almost comparable with those taken during a cardiac catheterisation procedure. For many patients, a MDCT scan of the heart is enough for doctors to establish whether coronary artery disease is present, and patients might not need to have a cardiac catheterisation procedure.


If a contrast dye is going to be used during the CT scan, the patient is requested not to eat for about 4 hours before the test. Then, he or she will lie down on a scanning table, which will be slowly moved through the hollow centre of the CT scanner. The patient will be asked to lie still and to hold his or her breath briefly as each picture is taken. After the test, the patient can return to normal activities. Adverse reactions to contrast dye are rare, but it can cause nausea or allergic reactions that have to be treated medically. Some patients will experience application of the contrast agent as a warm flush.


The main indications for making a CT in patients with congenital heart disease are:

Cardiac pathologies

  • Coronary vessels
  • Complex heart diseases, evaluation after surgery and pacemaker

Extra-cardiac pathology


  • With a heart pacemaker
  • With metal devices 
  • Unstable patients with the need for a quick imaging procedure

Value of the test and restrictions

CT scanning is a safe test. Pregnant women should not be scanned because of the radiation. When contrast dye is needed, the thyroid and renal function have to be considered.

Author(s): Montse Mireles
Last updated: 2008-09-24