Introduction
This topic covers the imaging methods for the gastrointestinal tract with emphasis on the oesophagus and stomach: plain film, contrast studies (barium swallow, upper GI series), CT, MRI and ultrasound, and the normal radiological anatomy of the oesophagus and stomach.
Imaging methods for the GI tract
- Plain X-ray (scout) is the first imaging modality: bowel gas pattern, calcifications, stool clearance.
- Barium oesophagram: ingestion of opaque contrast that coats the mucosa and forms a cast.
- Upper GI series: the same, with imaging carried out down to the duodenum.
- Barium enema: a rectal tube is used.
- CT: for solid visceral organs (liver, pancreas, spleen). Not as good as barium for bowel problems and not as good as ultrasound for the gallbladder. Abdominopelvic CT is excellent for diagnosing appendicitis, diverticulitis and pancreatitis.
- MRI: gives additional information when CT is ambiguous; imaging of inflammatory bowel diseases such as Crohn's; helps clarify disease processes in solid visceral organs and with gas identification.
- Why ultrasound for the gallbladder? It is a fluid-filled structure; it is adjacent to the liver so it is easy to find; the bile ducts are nicely imaged. HIDA is used in acute cholecystitis.
Contrast media
- Positive contrast: BaSO4 (barium sulphate; inert, non-absorbable).
- Negative contrast: air.
- Water-soluble contrast: Gastrografin.