Investigations

CT Colonography

What is a CT colonography?

A CT colonography or virtual colonoscopy is a specialized CT scan of your colon. CT or Computerised Tomography scanning uses X-rays to provide images of anywhere in the body. The CT scanner can produce over 500 images of the internal structure of the body. This digital information can be viewed as 2D or 3D images of the internal organs on a computer. The CT colonography images can be analysed with specialized 3D software to give views as if you were travelling through the colon! The scan will be viewed and reported by an expert radiologist who specialises in the field.  The report is sent to your surgeon who will discuss the findings with you in the clinic.

Do I need any preparation for a CT colonography?

CT scanning can be used in a targeted fashion to look at the colon but it requires slightly different preparation to a standard CT scan.  This is designed to minimise the amount of stool in the bowel so the lining of the colon can be seen clearly.  The radiology department that performs the scan will be in touch to make an appointment.  They may ask various questions including:

  • Do you have kidney disease?
  • Are you diabetic? 
  • Are you allergic to iodine?
  • Are you pregnant?
  • Can you lie flat?
  • Do you weigh more than 125kg?

For 2 days prior to the scan you will need to be on a low residue diet and take an oral preparation called gastrograffin.  All the instructions will be sent to you from the radiology department and if you have any queries please call the department where the scan is being performed.  If you are diabetic there are specific extra instructions to follow so that your blood sugar level remains within reasonable limits.

Usually, you will have had a small plastic tube, a cannula, inserted into a vein in your arm, to allow injection of a dye. This dye, usually based on iodine, helps to provide superior images of the blood vessels and internal organs. The injection may make you feel flushed and give you a metallic taste.

Once you are in the scanning room, you will be asked to lie on a couch, which will move you through the circular scanner.  To obtain better images of the lining of your bowel, a small flexible tube will be inserted into your back passage, which is used to instil the colon with C02 gas.  This gas is absorbed quickly after the procedure but may make you feel a little bloated.  You may also have an injection of a medication, which relaxes the colon (Buscopan).  This might result in blurred vision for a short while, so you cannot drive until this effect has disappeared.  Following the examination you will be allowed home and can eat and drink as normal.