Virtual Colonoscopy

Virtual Colonoscopy or CT Pneumocolon is an advanced type of x-ray exam that uses computed tomography (CT or “CAT”) scanning to obtain an interior view of the colon (the large intestine) that can ordinarily only be seen with an endoscope inserted into the rectum. This new minimally invasive test provides three-dimensional images that can depict many polyps and other lesions as clearly as when they are directly seen by optical colonoscopy.

Virtual Colonoscopy

What are common uses of a virtual colonoscopy

The major reason for performing this type of scan is to screen for polyps in the large intestine. Polyps are benign growths that arise from the inner lining of the intestine. Some polyps may grow and turn into cancers. The goal of screening is to find these growths in their early stages so that they can be removed before cancer has had a chance to develop.

  • Most Doctors agree that everyone older than 50 years should be screened for polyps.
  • Screening is especially important if you are at increased risk of developing colon cancer. This is the case if you have had polyps in the past, have a family history of colon cancer, or have blood in your stool.
  • The scan is a less invasive option for patients who do not wish to have a colonoscopy, which involves inserting a flexible tube into the colon to view the bowel wall.
  • This study is an excellent alternative for patients who have clinical factors that increase the risk of complications from colonoscopy, such as treatment with a blood thinner or a severe breathing problem.
  • Elderly patients, especially those who are frail or ill, will tolerate CT scanning better than conventional colonoscopy.
  • CT scanning can be helpful when colonoscopy cannot be completed because the bowel is narrowed or obstructed for any reason, such as by a large tumour.
  • If conventional colonoscopy cannot reach the full length of the colon – which occurs up to 10 per cent of the time – CT scanning can be performed on the same day because the colon has already been cleansed.

How should I prepare for a virtual colonoscopy

It is very important to clean out your bowel before your scan so that the radiologist can clearly see any polyps that might be present. You will be given specific preparation instruction and medicines to take before the scan.

Be sure to check with your doctor if you have heart, liver or kidney disease to be certain that the bowel prep will be safe. You may resume your usual diet immediately after the exam.

Women should be certain to inform their Doctor or CT Radiographer if there is any possibility of pregnancy.

What does the equipment look like?

CT Scanner for virtual colonoscopy

The GI Unit at the Hospital of St John & St Elizabeth has become the first private hospital in the UK to install the Toshiba Genesis CT Scanner.

The key features of the new CT scanner are its ability in cardiac scans to achieve the best possible image quality at the lowest radiation dose of any CT scanner available today. The unique Toshiba flared gantry design with a large 78cm aperture, means that even claustrophobic patients are more likely to be able to be scanned, as the patient experience is one of spaciousness. The patient experience is further enhanced as clinicians no longer need to manually handle the patient in to position as much as previously.

How does the procedure work?

Computed tomography (CT) uses a rotating gantry that houses x-ray emitters and detectors to obtain images from hundreds of angles that are then reconstructed by a computer into the two-dimensional pictures you see. Modern scanners use a method called spiral CT, in which the gantry rotates at the same time that the patient is moving through the scanner, so that the x-ray beam follows a spiral path. Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds.

For Virtual Colonoscopy and CT Pneumocolon scans, the computer generates a detailed three-dimensional model of the abdomen and pelvis, which the radiologist can use to view the bowel in a way that simulates traveling down the colon from the endoscopist’s point-of-view. This is why it is often termed virtual colonoscopy.

How is a virtual colonoscopy performed?

You will lie on your side on the scanner table. A very small, flexible tube will be passed two inches into your rectum to allow carbon dioxide to be gently pumped into the colon. The purpose of the gas is to distend the colon a little to eliminate any folds or wrinkles that might obscure any polyps that are there. You will then be asked to roll on your back prior to obtaining the first scan. As the table moves through the scanner, you will be asked to hold your breath for about 15 seconds. A second pass is made through the scanner after you have turned onto your front, to make sure that all sections of the colon are seen. Once the scan is done, the tube is removed and you are free to leave.

What will I experience during the procedure?

The vast majority of patients who have this type of scan report a feeling of fullness during the examination as if they need to pass gas when the colon is inflated. Significant pain is uncommon, however, occurring in fewer than 5 percent of patients. A muscle-relaxing drug may be injected intravenously to lessen discomfort, but this is seldom necessary. After the tube is inserted, your privacy will be respected. The scanning procedure itself causes no pain or other symptoms. You will be alone in the examining room during CT, but a CT Radiographer in the adjacent control room is able to see and hear you, and can speak to you at any time. The entire examination can be completed within 15 minutes.

Who interprets the results and how do I get them?

The radiologist will check the scan findings briefly after the exam is completed to be sure that it is of sufficient diagnostic quality. He or she will carefully review the study after you have left, once the computer has finished processing all of the images. A detailed report will be sent shortly thereafter to your Consultant, who in turn will inform you of the findings.

What are the benefits vs. risks?


  • CT examination of the colon is a minimally invasive procedure. It markedly lowers the risk of perforating the colon that may occur with conventional colonoscopy. Most of those examined do not have polyps and can be spared having to undergo a full colonoscopy.
  • CT scanning of the colon provides clearer and more detailed images than does a conventional barium enema x-ray examination.
  • In up to 15% of patients, CT scanning shows abnormalities outside the colon, which would be otherwise missed, because colonoscopy only looks at the interior surfaces. Occasionally these are important discoveries.
  • CT is tolerated well. Sedation and pain-relievers are not needed, so there is no recovery period. You will be free to resume your usual activities immediately after the exam.


  • There is a very small risk that inflating the colon could injure or perforate the bowel. This has been estimated to happen in fewer than one in 2,000 patients.
  • CT scanning does require exposure to x-rays, but the radiation dose is very low, typically 15 per cent less than is needed for a barium enema x-ray examination of the colon.
  • Special care is taken during x-ray examinations to ensure maximum radiation safety. Women should always inform their doctor or the CT Staff if there is any possibility that they are pregnant.

Contact Us Today

To ask a question about a virtual colonoscopy or to book an appointment, contact our specialist team available

Monday – Friday 8am – 6pm and on Saturday from 9am – 1pm. 

Our gastrointestinal specialist’s team have a dedicated and caring approach and will seek to find you the earliest appointment possible with the correct specialist for your needs.

If you are self-paying you don’t need a referral from your GP for an appointment with a Consultant. You can simply refer yourself and book an appointment.

However, if you would like to book a Gastroscopy appointment you will need a referral from your GP.

If you have medical insurance (e.g. Bupa, Axa PPP, Aviva), you will need to contact your insurer for authorisation for any treatment and, in most cases, you will require a referral letter from your GP. If you do not have a GP, then we have an in-house private GP practice that you can use. Alternatively, we can suggest the most appropriate course of action for you to take, given your location and individual circumstance.

Call us on 020 7078 3802 or email us at [email protected]

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GI Clinic

The GI Unit is supported by a multidisciplinary team of medical and surgical consultants. Our expert team treats and supports patients with any gastrointestinal conditions.

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Patient information

Our Hospital is renowned for providing exemplary levels of care across more than 90 services. From orthopaedics, to urology, our private GP practice and Urgent Care Clinic, our services are led by some of London’s leading Consultants. For more information, and to find a service suitable for your care, find out more about the services that we offer.

Make an enquiry

If you have any questions relating to treatment options or pricing information, get in touch with us by filling out one of our contact boxes or giving us a call on 020 7078 3802.

Our Appointments Team have a dedicated and caring approach to finding you the earliest appointment possible with the best specialist.

If you are self-paying you don’t need a referral from your GP for a consultation. You can simply refer yourself* and book an appointment.

If you have health insurance (e.g. Bupa, Axa Health, Aviva), you will need to contact your insurer to get authorisation before any treatment, and in most cases you will also require a referral letter from your GP.

If you are not registered with a GP, we have an in-house private GP practice you can use. Alternatively, we can suggest the most appropriate course of action for you to take, given your location and individual circumstances.

*Please note – for investigations such as X-rays and MRIs, a referral will be required. However, we may be able to arrange this for you through our on-site private GP.

    Make an enquiry

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