The x-ray and other similar imaging methods used in Crohn's or Colitis can have different benefits and risks in terms of, for example, exposure to radiation, image quality, or the need for anaesthetic.
Abdominal X-rays
Ordinary or plain abdominal X-rays do not show as much detail of the digestive system as some of the other imaging techniques (see below). However, they may be used in an emergency to diagnose bowel obstruction, perforation or megacolon (widening of the colon which may cause perforation).
Barium studies
Barium is a harmless white substance which is not absorbed into the body, but instead forms a temporary coating on the inside of the intestines. Since X-rays can not pass through barium, it is used to provide a clearer outline of the gut on X-ray pictures. Barium is introduced in different ways depending on the part of the gut needing imaging. For the upper part of the digestive system, you will be asked to swallow barium (known as a barium meal). For the small intestine (known as a barium follow through test), you will take barium by mouth and be asked to take a laxative the day before the test. You will also need to fast overnight.
To visualise the colon, a barium enema is used, delivering barium directly into the colon through a short tube placed in the anus. After taking barium, your faeces will turn pale and chalky looking for a few days and may be difficult to flush away. Barium studies have recently become less common for Crohn's or Colitis due to widespread availability of CT and MRI imaging (see below). CT and MRI offer the advantage of greater detail and information beyond the inner lining of the bowel (such as fistula or abscesses).
Chest X-rays
Biologics increase the risk of infections, such as tuberculosis (TB). Before starting biologics you will need to have a chest X-ray to rule out silent TB infection, which might be made worse by treatment. Whilst on biologics, people with Crohn's or Colitis who have travelled for more than a month to countries with high levels of TB should also consider having a chest X-ray.
DEXA (Duel Energy X-Ray Absorptiometry) scans
DEXA scanners use low dose X-rays to measure bone density, usually in the spine or thigh bone. This is a painless test taking around 20 minutes. DEXA can show if bones have become thinner and weaker than normal – a condition known as osteoporosis. People with IBD have an increased risk of developing osteoporosis, particularly if they have been on steroids, or have low calcium levels. Annual DEXA scans are recommended for people taking steroids long- term. For more details, see our information on Bones.
Computerised Tomography (CT) or Computerised Axial Tomography (CAT)
A CT scanner is a special machine that uses a series of X-ray beams to build up a detailed picture of the body. The scanner looks like a giant ring doughnut, and you lie on a moveable bed, which slowly passes through the centre. X-rays are taken at different angles, and the images put together to produce two-dimensional (2-D), or sometimes, three-dimensional (3-D) views of the body.
CT enterography (CTE) is an imaging test combining CT scanning with contrast material to improve the detail of the small intestine. Before the test, in some hospitals, you will need to drink a few glasses of liquid containing the contrast material. In other hospitals, you may only be asked to drink water. Then during the scan, a different type of contrast material will be injected into a vein in your arm. CTE improves the accuracy of diagnosis and allows good imaging of the entire thickness of the bowel wall. Occasionally, enteroclysis is used where a small tube delivers contrast material to where it is needed in the intestine, instead of the fluid being swallowed.
Advantages of CT and CTE include:
- Rapid scan times (about 10 minutes)
- The ability to examine the entire length of the small bowel
- Imaging children without sedation
- Quiet machines
- Widespread availability.
Also, unlike MRI scanners, the CT scanner does not surround your whole body so you should not feel claustrophobic (fear of enclosed spaces).
Disadvantages include exposure to ionizing radiation. It is considered good practice to minimise radiation where possible for people with IBD because they are likely to require many imaging studies, which could lead to a high total dose of radiation to the body.
Magnetic Resonance Imaging (MRI)
MRI scans use strong magnetic fields and radio waves to create images of the inside of the body. MRI scans do not use X-ray radiation. The MRI scanner looks like a long tube or tunnel, and you will be asked to lie on a moveable table, which slides slowly inside this tunnel. MR enterography (MRE) is a special type of MR imaging that is performed with the addition of contrast material to produce better images. You will need to drink contrast material before the scan, and then during the scan a different type of contrast material will be injected into a vein in your arm. MRE improves the accuracy of diagnosis and allows good imaging of the entire thickness of the bowel wall.
The MRI scan can be noisy (due to the electric current in the scanner coils being turned on and off) so you may be provided with ear plugs or headphones to wear.
The scan can take from 15 minutes to over an hour and a half. This means that some people may find it uncomfortable, especially if they suffer from claustrophobia. However, for Crohn's or Colitis investigations, because the abdomen is usually the area being examined, your head may not be completely inside the scanner for the duration of the test. If you feel anxious, you may want to ask for a mild sedative prior to your examination. It is important to lie very still during the scan to stop images becoming blurred, and you will need to follow instructions to hold your breath from time to time.
Advantages of MR and MRE include scans being free of radiation and the ability to explore the entire length of the small bowel. MRI scanners use magnets, which means that they are not suitable for people with electronic devices (such as pacemakers) or who have metal implants (such as artificial joints).
Some people may have an Magnetic Resonance Cholangiopancreatography (MRCP), which provides detailed images of the liver, gall bladder, bile ducts, pancreas and pancreatic ducts. The technique can be used to diagnose Primary Sclerosing Cholangitis.
Ultrasound
Ultrasound is another form of scan helpful in Crohn's or Colitis. Ultrasound scanners work by using high frequency sound waves to create an image. A handheld sensor is moved over the surface of the skin, and this sends out sound wave signals which bounce off internal organs. The scanner then picks up the echoes and converts them into an image. Ultrasound can show up thickening of the bowel wall, fistulas (abnormal channels linking different parts of the bowel), abscesses and strictures.
Advantages of ultrasound include no exposure to radiation, wide availability and being a comfortable procedure for patients. Before the scan, you will need to drink large amounts of liquid and to avoid eating for a few hours. Drinking a contrast agent before the scan can help improve the detection of inflammation.
Endoscopic Ultrasound Scans (EUS), involve using a special type of endoscope with a tiny ultrasound transmitter in the tip. As with a normal endoscope, EUS is inserted through the mouth to examine the upper part of the digestive system or through the anus to examine the colon and ileum. If necessary, your doctor will be able to take samples of cells. For the procedure you will usually be given a sedative or a local anaesthetic spray to numb your throat.
SeHCAT Scan
A SeHCAT scan is used to find out whether diarrhoea is caused by bile acid malabsorption (BAM). When you eat, bile salts (made in the liver and stored in the gall bladder) are released into the small bowel to help digest food. Normally, when bile salts reach the end of the small bowel, they are taken up by the blood. However, if the lower end of the small bowel is inflamed (due to Crohn’s Disease) or has been removed during surgery, bile salts may not be absorbed. Instead, bile salts enter the large bowel (colon) where they draw fluid from the blood, leading to diarrhoea.
The SeHCAT scan involves two separate appointments. At your first appointment, you will be asked to swallow a small capsule containing synthetic bile salts linked to a radioactive tracer. A little later, a scan will be taken using a special camera that identifies radioactivity. At the second appointment, a further scan will be done to measure the amount of synthetic bile salt remaining in your body, showing whether you have problems absorbing bile salts.
Apart from stopping certain drugs that interfere with the test results (Creon, colestyramine and colesevelam), you can eat, drink and take other medications as normal. No sedation is necessary.
There is no need to be concerned about the level of radiation since the radiation dose is low (equivalent to the amount received from natural sources of radiation in about two months), so you will not need to stay away from anyone. However, you may find some airports have sensitive radiation detectors that are triggered by the small amounts of radioactivity, which remain in your body for up to three months after the scan. Therefore, it is recommended you carry your appointment letter to show airport security officers.