CT colonography

CT colonography (CTC) is one of my main clinical interests. During the last 5 years, I have focussed on improving the experience for patients whilst maintaining a high quality of imaging.

What is CTC?
CTC is a type of CT scan that specifically examines the large bowel (the colon), looking for growths such as polyps and cancers. Traditionally, the options for examining the large bowel have been colonoscopy (camera test) or a barium enema. CTC involves scanning the abdomen with gas in the colon and then looking at the images in 2D and with special 3D software to obtain the same information as a colonoscopy. The 3D software shows the colon like this:

The added benefit of CTC is that all the organs of the abdomen, such as the liver, kidneys and pancreas, are examined at the same time. It also provides information on the blood vessels, lymph nodes, and any inflammation; colonoscopy cannot provide any of this. However, the one benefit of colonoscopy is that if abnormal tissue is seen, a biopsy can be taken immediately; this is not possible with CTC.

How I have improved CTC in Leicester
During my subspecialty training at Imperial College Healthcare NHS Trust, I helped write a brand new protocol for CTC that removed laxatives (which were the traditional preparation) and incorporated Gastrografin. Since commencing practice as a Consultant in Leicester, I have used my London experience to change the preparation from laxatives to Gastrografin. I have conducted patient satisfaction surveys which indicate that my patients prefer this to the traditional preparation. In addition, I have re-written the protocol which is now much easier for diabetic patients to follow. Much of this work has been presented at an international radiology conference.

What is Gastrografin and what does it do?
This is a contrast agent (xray dye) that has several effects on the bowel. It acts as a very mild laxative (much milder than traditional laxatives such as Kleenprep), and it mixes with the stools to make them appear white on CT scans. This means that it is now much easier to differentiate between polyps (soft tissue growths) and pieces of stool in the colon.

This means that I am able to confidently exclude serious pathology on the CT scan instead of subjecting patients to have a colonoscopy because of a doubt between polyps and stool. Gastrografin is also much milder and more tolerable for patients to take, with less of an adverse effect on bowel opening and diarrhoea. My patients report that they are able to continue their daily activities when they take the Gastrografin the day before the scan.

This video shows you what the pictures of the bowel look like on a CT colonogram with Gastrografin:

What actually happens when I have the CT colonogram?
You will be greeted by the radiographer performing the examination, and asked to change into a hospital gown. A small plastic tube called a cannula will be placed in a vein in your arm; this allows us to give you xray dye (contrast) for the scan. While you are lying on the CT scanner table, a small plastic tube is gently inserted into the back passage and gas gently flows through to inflate the bowel. Medication called Buscopan is given to relax the bowel so that it is less painful. When enough gas is present in the bowel, the first scan is done with you lying on your back. Then the radiographer will ask you to turn onto your front for the second scan. If this isn't possible because of back problems, you can lie on your side. When the second scan is complete, the plastic tube will be removed and you can go to the bathroom to get dressed. You will be asked to wait in the department for 15 minutes to ensure you are feeling well enough to leave the department. I will review the images and issue a report for your doctor.

Should I have a CTC?
If you have experienced any of the following symptoms, you should seek medical advice from your GP and consider the options you have for examining the colon: change in bowel habit to more constipated or looser stools / blood mixed with stools / passing mucus with stools / weight loss. These symptoms may indicate that you need some form of bowel test, and you should discuss the options with your own doctor.

Dr Vikas Shah
Consultant Radiologist
Leicester, UK

Disclaimer: None of the information provided here should be taken as medical advice. You are advised to see you doctor who will assess your symptoms and refer you for the appropriate test. If you require any imaging tests after seeing your doctor, please contact me using any of the methods listed on the Contact page.