A CT virtual colonoscopy is a special scan of the abdomen using Computed Tomography (CT), that produces 3-D images of the bowel. It is done to identify lesions in the bowel such as polyps, tumours or ulceration.
On arrival at reception, a member of staff will give you two forms to read and complete. One will be a consent to have the procedure performed, and the other will be a questionnaire regarding xray dye (Contrast) injected. Prior to the procedure, a nurse or radiographer will show you to the changing room. You will be expected to remove all clothing and a disposable gown will be provided (please wear this with the opening at the back).
For the procedure, you will be required to lie on a narrow table. This table will move in and out of the scanner during the procedure. The procedure usually takes up to 30 minutes.
A small, plastic needle (cannula) will be inserted into a vein In your arm. Through this, a special “xray dye” (contrast) is injected to highlight the bowel for the scan. This injection may produce an unusual sensation, such as a hot, flushing feeling, bladder emptying sensation, or even an unusual taste. All of these sensations wear off as quickly as they arrive.
You may also be given some medication to relax the muscle wall of your bowel, reducing the risk of spasm. This is called Buscopan. It is important that you inform the staff if you are allergic to this kind of medication or if you have neuromuscular diseases, prostate problems, a disorder of the gullet “oesophagus” (Achalasia), or a fast heart rate (tachyarrythmias).
Prior to the injection of contrast, your bowel will need to be inflated. This will require you to initially lie on your right side, where a nurse or doctor will insert a very small tube partially into your rectum. Once in position, you will be lying on your back, then air is manually pumped through this tube in order to inflate the bowel. During inflation, you may experience some abdominal discomfort, very similar to wind-like pain. If the pain becomes extreme, it is important you inform our staff immediately.
An initial scan will then be performed to see if enough of your bowel has been inflated for a quality image. If not, more air will be given. You will then receive the injection of contrast, and another one or two more scans will be performed. During the scans, you will be required to keep very still, whilst holding your breath. The breath hold should be no longer than 10 seconds.
For the final scan, you will be required to lie on your front. A further small amount of air will be given to inflate the lower part of your bowel. The air will be released as soon as all the images have been taken.
Risks / Side Effects
Buscopan is a relatively safe drug which is frequently taken to relieve stomach cramps. Possible side effects include dry mouth, blurred vision, itchiness, drowsiness and increased pulse rate. If you experience any of these they should pass quickly. Rarely it can cause an inability to pass urine. As with any drug there is a very small risk of allergic reaction. As X-ray contrast is administered, there is a small risk of allergic reaction. Mild reactions can be a rash or hives and severe reactions can include difficulty breathing, shock and circulatory disturbance. Severe reactions are rare and life threatening reactions are extremely rare (1 in 170,000).
It is common to feel some abdominal discomfort from the air in the bowel. You may feel some nausea. Risks include:
- Bowel perforation
If severe these may require surgical intervention.
In patients with untreated or unknown glaucoma it may precipitate a red swollen eye. If you experience increasing pain in the eye or deteriorating sight please go to an emergency department.
Before your Scan
The day before your procedure you will be required to have a clear liquid diet and commence taking the medication to prepare your bowel. You will be given three types of medication. “BARIUM”, GASTROGRAFFIN” and “GO-KIT”. These must be taken at the times indicated on the bowel preparation form which will be provided to you. Follow the instructions provided on the form and in the kit starting the day before the test.
The procedure cannot be performed if you have had a biopsy of your bowel (colon) within the last 2 weeks.
The procedure usually takes up to 30 minutes
You may feel the urge to empty your bowel. It is likely you will pass a certain amount of air, and will be taken to the bathroom immediately after the procedure.
Once you have dressed, you will be required to take a seatand wait for 20 minutes before the plastic cannula is removed and any blurred vision has resolved.
You may experience some cramping discomfort for a short time following the procedure