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What is Computed Tomography?

Computed tomography (CT) is a test which generates images of the body from lots of different angles and it provides a clear representation of the different types of tissue.

How does it work?

Computed tomography uses a special X-ray machine to obtain images of the body from different angles. The X-ray tube and detector rotate simultaneously around the table where the patient is positionated. Each rotation generates a very thin cross-section of the area of the body being examined. It can be compared to studying different slices of a single lemon. A computer then reassembles all of these images, one after the other, to obtain a highly detailed, multidimensional internal view of the body.

What is it used for?

Computed tomography is a very useful test because it clearly depicts the different types of tissue, e.g., the lungs, bones, soft tissues and blood vessels. It can be used to diagnose problems such as cardiovascular diseases, infections, traumas, musculoskeletal disorders and cancer. It is also a very practical tool when planning and monitoring a medical or surgical treatment and its outcome.

How is it performed?

Aided by technical personnel, the patient stretches out on the examination table in the computed tomography suite. A cushion can be put in place if required to make the patient’s position more comfortable. Upon starting the test, the table will slowly start to move inside the machine. It should be emphasised that you may or may not notice the machine movement depending on which area of the body is being studied.

In some cases a contrast agent may be used to visualise certain parts of the body in greater detail. A contrast agent is a liquid that is either swallowed, injected or administered as an enema depending on the type of test to be carried out. The healthcare professional will ask the patient to sign an informed consent form and inform them about the test and answer any questions they may have.

How do I prepare for a computed tomography scan?

If the test does not require a contrast agent, then no special preparation is required. If a contrast agent is administered, patients should fast for six hours and drink plenty of water because they need to be well hydrated. There are some very specific types of computed tomography scan which involve other interventions and therefore have different requirements. The healthcare professional will explain them in more detail.

Special situations

Always tell your healthcare professional in the following situations:

  • Pregnancy
  • Breastfeeding
  • Alergic to the contrast agent
  • Diabetes, asthma or heart, kidney or thyroid disease;
  • Claustrophobia. There is no need to worry because it is a very open machine. Either way, the patient’s doctor should be told about the claustrophobia.

Who performs the test?

Radiology technicians. They will guide and assist the patient throughout the test. Although they cannot be present in the computed tomography suite during the test, they can still talk with the patient.

Who interprets the results?

A radiologist, i.e., a doctor who specialises in computed tomography scans and other radiological examinations.

What can I expect to feel during the test?

Patients do not usually feel anything. Even if a contrast agent is required, most patients do not notice anything at all. If you have to drink the contrast agent, then you may notice an aniseed flavour. Some people also feel a little warm after swallowing or receiving an injection of contrast agent. But there is no need to worry, the warmth will disappear in a few minutes. If you notice anything other than the sensations described here, then you should tell the healthcare professional immediately as it could be the sign of an allergic reaction.

Substantiated information by:
Laura OleagaRadiologist — Radiology Department

Published: 20 February 2018
Updated: 20 February 2018

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