CT SCAN

Computed Tomography (CT) is a sensitive diagnostic tool that uses X-rays to take a series of two-dimensional cross-sectional images ('slices') around an axis. It has been in widespread use since the 1970s and is used to image many diseases and injuries.

Using X-rays does carry a small risk. However, to put this into context, a CT scan will deliver approximately the same amount of radiation you would absorb from your normal surroundings in about three years. Another way of looking at this is to say that the benefits of having a scan outweigh the risks associated with it.

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TEST PREPARATION

If you’ve never had an CT scan you might not know what to expect and this brief guide is designed to answer the questions that might be in your mind.

  • It’s important that you tell us before the scan if you:
  • are diabetic and taking metformin.
  • have any allergies or asthma.
  • have impaired renal function.
  • are pregnant or are breast-feeding
  • We will make sure that it's appropriate for you to have a CT scan. We'll ask you some basic questions when you book and you'll be required to complete a questionnaire before your appointment.
  • If we’re scanning your abdomen or pelvis, we might ask you to drink a certain amount water or contrast agent. You will be given details if this is necessary.
  • It might be necessary for you to stop eating or drinking for a specified time before your scan. You will be given the details if this is necessary.
  • Please wear loose, comfortable clothing and leave jewellery and watches at home if possible.
  • Please let us know if you have any disabilities so that we can ensure we are able to offer you the highest quality service.
  • If you’ve been given a prescription (order) for this exam, please be sure to bring it with you on the day of your appointment.
  • Once you’ve checked in at reception a member of the radiography team will meet you, explain the procedure, go through your safety questionnaire with you and ask you to sign a consent form. You'll have the opportunity to ask any questions about the scanning process.
  • We will ask you to change into an examination gown. We will provide somewhere to store your personal possessions.
  • We might need to give you an injection (known as a contrast medium) to increase the amount of information we can get from the scan. Depending on the area we're scanning, we might ask you to drink the contrast medium instead of injecting it. In this case, you might have to wait up to an hour before you can be scanned.
  • You need to let the technologist know if you've ever reacted to an injection given for a kidney X-ray (IVP or IVU) or a previous CT scan.
  • The technologist operating the scanner will be able to see and hear you throughout the procedure.
  • We’ll ask you to lie down on the scanner bed and we'll make sure you're comfortable so you can stay as still as possible. We might have to ask you to hold your breath or not to swallow when the scanner is taking the images.
  • Most scan sessions last between 15 and 30 minutes.
  • There are no restrictions on normal activity, you can eat and drink normally, drive and return to work immediately after the scan.
  • If we’ve given you a contrast medium injection there is a very small risk of an allergic reaction so we’ll ask you to stay with us for half an hour after the scan.
  • A radiologist will examine the images shortly after your visit and send a report to your doctor or consultant, normally within a few days.
  • For ethical and professional reasons, we cannot discuss results with you. Only your doctor or consultant can do this

MORE FACTS ABOUT CT SCAN

A CT (computerised tomography) scanner is a special kind of X-ray machine. Instead of producing an image (radiograph) from a single direction, the X-ray source is rotated around the patient - acquiring a cross-sectional image (tomogram) from many angles.
The X-rays from the beams are detected after they've passed through the body and their strength is measured. Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have been absorbed by denser tissue such as bone will be weaker.
A computer can use this information to work out the relative density of the tissues examined. The computer processes the results, displaying them as a two-dimensional picture shown on a monitor.

Using X-rays does carry a small risk. To put this into context, a CT scan will deliver approximately the same amount of radiation you would absorb from your normal surroundings in about three years. Another way of looking at this is to say that the benefits of having a scan outweigh the risks associated with it.

For an abdominal CT you may be asked to drink a liquid to outline the bowel before commencing the examination or you may need a small injection of contrast medium to assist the examination.

During the scan you'll lie on a bed, with the body part under examination placed in opening of the scanner.

The bed then moves slowly backwards and forwards to allow the scanner to take pictures of your body, although it won't actually touch you. The length of the examination depends on the number of pictures and the different angles taken.