While preparations for VC vary, the patient will usually be asked to take laxatives or other oral agents at home the day before the procedure to clear stool from the colon. A suppository is also used to cleanse the rectum of any remaining fecal matter. The patient may also given a solution designed to coat any residual faeces which may not have been cleared by the laxative. This is called 'faecal tagging'. This allows the user (usually a consultant radiologist), viewing the 3D images to effectively subtract the left over faeces, which may otherwise give false positive results.

VC takes place in the radiology department of a hospital or medical center. The examination takes about 10 minutes and does not require sedatives.

During the procedure:

* The patient is placed in a supine position on the examination table
* A thin tube is inserted into the rectum, so that air can be pumped through the tube in order to inflate the colon for better viewing.
* The table moves through the scanner to produce a series of two-dimensional cross-sections along the length of the colon. A computer program puts these images together to create a three-dimensional picture that can be viewed on the video screen.
* The patient is asked to hold his/her breath during the scan to avoid distortion on the images.
* The scan is then repeated with the patient lying in a prone position.

After the examination, the images produced by the scanner must be processed into a 3D image, +/- a fly through (a cine program which allows the user move through the bowel as if performing a normal colonoscopy). A radiologist evaluates the results to identify any abnormalities.

The patient may resume normal activity after the procedure, but if abnormalities are found and the patient needs conventional colonoscopy, it may be performed the same day.