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Ultrasound scans: Using ultra-high frequency sound waves, these painless scans give internal pictures of the body’s organs and can help doctors detect tissue masses, abscesses and fluid. They can also show thickened or inflamed sections of the intestines. A hand-held device rather like a microphone is covered in jelly and then gently moved around the surface of the abdomen to give two-dimensional black and white pictures of our insides on a monitor. Ultrasound scans normally take about 15–20 minutes. Endo-anal ultrasound scans use a probe placed just inside the anus, and are performed when there might be a problem with the sphincter muscle structure – for example, in people suffering with faecal incontinence.

CT scan (computerized tomography): This uses an enormous round machine with a hole in the middle, through which the patient, lying on a table, slowly passes. The CT scanner takes multiple x-rays, which are like ‘slices’ of the patient. A computer then puts these together to recreate a three-dimensional image. You may have an intravenous injection of a special dye to show certain features up better, or you may swallow a contrast liquid or have it injected into the rectum. You normally have to fast for around 4 hours beforehand, and will need to stay still while the scan is performed. It can take 30–40 minutes. Newer machines are becoming much faster and advanced technology has also meant the development of spiral CT and ‘multi-slice’ CT scans, which are quicker.

PET scan (positron emission tomography): This is one of the newest medical scanning techniques. It is often used to analyse the brain and heart, but can also detect tumours. PET scanning measures the uptake by certain body tissues of molecules like oxygen or glucose that are specially labelled with a radioactive substance. This indicates how well the body tissues are functioning. Tumours, for example, have a high energy demand and labelled glucose shows up clearly in a tumour. PET scans give more information about the activity of body tissues rather than their physical form.

MRI scan (magnetic resonance imaging): MRI scans use magnetism (not x-rays) to create three-dimensional, very detailed pictures of the human body. They are very good for looking at solid objects like the bones and liver, though less good at the intestines, which are constantly moving. Patients lie on a table inside a small chamber of the scanner and although you don’t feel anything, you hear a loud series of ‘knocking’ noises. People with claustrophobia may not be comfortable or able to tolerate an MRI scan while awake. Newer ‘open’ MRI scanners may minimize this problem.

Nuclear medicine (white cell) scan: This technique can be useful for locating areas of inflammation in the intestines. A sample of blood is taken and the white cells are given a mildly radioactive ‘marker’ before being injected back into the patient. Because white cells are naturally attracted to areas of inflammation, they show up in concentration when the body is scanned using a gamma camera that picks up the radioactive marker. There are other types of nuclear medicine scan that use different radioactive isotopes.