Imaging methods

The choice of imaging modality for optimal demonstration of gastrointestinal anatomy is highly dependent on the clinical symptoms and signs. With the advent of newer technology, the role of plain abdominal radiography has diminished, although characteristic gas and soft tissue patterns can be of great importance in the diagnosis of the ‘acute abdomen’.

Double contrast barium examinations are the most sensitive way of examining the gastrointestinal tract, providing information on distribution of the gut, mucosal and muscular detail, and, using dynamic investigations as in the case of the barium swallow, functional information. The diagnostic information gained from the barium examination is dependent on adequate preparation of the patient and attention to technique. The use of shortacting muscle relaxants, such as hyoscine or glucagon, reduces peristalsis, and improves visualization of the mucosa.

Transabdominal ultrasound scanning has a limited application in the gastrointestinal tract due to bowel gas, but is used to identify intra-abdominal collections. It is particularly useful in children, in the diagnosis of pyloric stenosis, appendicitis, and intussusception. Endoscopic ultrasound is a technique which is being increasingly used in the staging of gastrointestinal tumours. It has been used chiefly in the oesophagus, stomach, colon and rectum. It is performed with high frequency (7.5–20 MHz) probes (either radial or linear array in type). The use of such high frequency probes provides information about the bowel wall which cannot be obtained with other techniques. It can also be used to examine and perhaps biopsy those structures in close proximity to the bowel wall such as the pancreas, biliary tract and lymph nodes.