How exactly does a virtual colonoscopy work?

Written by: Dr John Martin
Published: | Updated: 28/07/2023
Edited by: Cameron Gibson-Watt

Reaching a certain age means your risk for developing some diseases increases, so regular check-ups are recommended. It is advised that you start having colonoscopies after the age of 50 to check inside the colon for abnormalities.


Nowadays, a virtual colonoscopy is available to patients, which offers a non-invasive and less aggressive alternative to a regular colonoscopy. Dr John Martin, a leading gastroenterologist in London, explains what a virtual colonoscopy is and why it might be right for you.

What is a virtual colonoscopy?

virtual colonoscopy, is a type of CT scan dedicated to examining the colon. It uses X-rays and computers to provide images of the colon from outside the body and is able to show polyps and cancer.


What happens during the virtual colonoscopy procedure?

The preparations for this procedure are similar to that of a colonoscopy. You will need to have a low-fibre diet for a couple of days beforehand. On the day before, it is advised not to eat anything after breakfast, but you can drink.


Gentle laxatives are also given to help clean out the bowels. These are similar to those used for colonoscopy but are normally less aggressive in their action.


During the procedure, a tube is inserted into the rectum and your intestine filled with carbon dioxide. This isn’t normally painful but can be slightly uncomfortable and make your belly feel full. The scan will take place and you’ll be asked to move onto your front and then onto your back to get various images. The procedure will take less than 15 minutes to complete.


Many patients report feeling gassy and bloated afterwards but you’ll be able to return to your normal diet and activities once you leave the hospital.


Why might a doctor recommend a virtual colonoscopy over a colonoscopy with an endoscope?

Often, it’s the patient’s choice to have this procedure as it’s slightly less invasive and faster to perform in comparison to a regular colonoscopy. It also doesn’t require sedation, making it more attractive to patients.


Sometimes, if the patient has an underlying health condition, such as a heart problem, then a doctor may recommend a virtual colonoscopy as the sedation during a regular procedure can add extra risks in some patients.


Does a virtual colonoscopy offer more reliable results than an endoscopic colonoscopy?

Unfortunately it doesn’t. A virtual colonoscopy is similar to a regular colonoscopy for the detection of large polyps but is less reliable in finding small polyps, that are less than 5mm in size. On very rare occasions, these small polyps can be cancerous or become cancerous if not removed.


With a VC, images are also obtained of the surrounding organs such as the kidneys, which means that you can detect other conditions or diseases that may not be causing symptoms. That can be beneficial if a serious condition is spotted but, at times, this can cause anxiety and stimulate investigation of an irrelevant finding that doesn’t pose any threat to the patient.


What are the advantages and disadvantages of a VC?


  • It’s a minimally invasive and less aggressive procedure compared to a regular colonoscopy
  • Laxatives that are given during the preparation period are slightly gentler
  • It’s quicker and slightly more comfortable
  • It’s better for patients with heart or other medical problems
  • You will not need sedation



  • It cannot remove any polyp during testing
  • A colonoscopy may be needed if the results are abnormal
  • You have some exposure to radiation
  • Full preparation is still needed, much like a regular colonoscopy


If you are interested in this procedure, visit Dr John Martin’s profile and book a consultation with him.

By Dr John Martin

Dr John Martin is a highly-experienced gastroenterologist and endoscopist based in London and holds an NHS Consultant post at Imperial College (ICL). He is an expert in colorectal cancer screening, therapeutic and diagnostic colonoscopy and has 25 years' experience of managing all aspects of gastroenterology including abdominal pain or discomfort, reflux disease, diarrhoea and constipation, rectal bleeding, irritable bowel syndrome, Crohn’s disease and ulcerative colitis

Graduated from Cambridge University and King’s College Hospital, London in 1990, Dr Martin completed his gastroenterology training within North West London. In 2002, he was awarded an MD from the University of London in bowel cancer screening and became a consultant at Chelsea and Westminster Hospital before joining Charing Cross Hospital in 2006. Dr Martin refined his skills in colonoscopy to ensure they are always safe, high-quality and comfortable for his patients. 

Dr Martin teaches colonoscopy both within the NHS Trust and also at national screening centres. He is a bowel cancer screening accredited colonoscopist and an examiner for BCSP colonoscopy accreditation. He has authored numerous peer reviewed publications.  

Dr Martin is director of the West London Bowel Cancer Screening Centre; he is the national advisor to Public Health England on endoscopy within the Bowel Cancer screening service and chairs the national advisory committee on quality and safety of endoscopy within screening. He forms an integral part of numerous other professional bodies and has been widely published in peer-reviewed journals. 

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