Gastrointestinal tract imaging
Because the gastrointestinal tract is not visualised with routine radiographic techniques, contrast media, which are opaque to radiation, must be added in some way. Imaging of the oesophagus, ventricle and duodenum (upper gastrointestinal tract) has to be done with oral contrast media (barium) and conventional or digital X-ray technique. These examinations are done mainly to detect or rule out ulcerations and malignant diseases. Imaging of the large bowel is done with a barium enema. Barium, which will cover the mucosal lining, is often supplemented with air insufflation. This technique results in a moderate distension of the organ and thus allows a very detailed and precise imaging of both normal and pathological structures.
Alternative investigations of both upper and lower GI tract are done with endoscopic fiberoptic devices. CT can be of some use in validating both upper and lower GI tract. Ordinary sonography has a very limited use and MRI is not indicated with today's technique. NM is used to measure gastric emptying rate and diagnose gastro-oesophageal reflux and oesophagus motility disorders.
Inflammation and ulceration
Ulcerations in stomach (both benign and malignant) and duodenal bulb (benign) is readily imaged. The technique for performing an upper gastrointestinal series are quite complicated indeed, so the pathological area can be missed or interpreted as normal for several reasons. Crohns disease, diverticulitis, intraabdominal abscess etc. are diagnosed with NM imaging with labelled white blood cells.
Nowadays many doctors prefer an endoscopic examination. This is done with a fibreoptic device and allows a direct visualisation of the mucosa. Endoscopy also adds the possibility to perform biopsies of the mucosa and direct sampling to verify Helicobacter pylori which is closely associated with peptic ulcers.
Gastritis/duodenitis can often be diagnosed by barium examnation, but endoscopy is somewhat more specific.
CT can be of value in some instances, especially when lymphoma or a diffuse infiltrating carcinoma (linitis plastica) is suspected. CT also gives an excellent overview of neighbouring structures. Inflammatory changes in the large intestine (colon) are preferably imaged by endoscopy, which is more sensitive than X-ray regarding minor changes.
Tumours and polypoid lesions
Both barium studies and endoscopy of the colon have a high sensitivity to detect malignant tumours. Polyps of significant size are also readly detected. CT is sometimes used, mainly to determine the extent of involvement in adjacent structures.
Transabdominal ultrasound has a low sensitivity to detect tumours in the gastrointestinal tract, mainly because this is a hollow, and often gas-filled, organ.Endoscopy is the best modality regarding the stomach, although some tumours can be missed, and only be detected by X-ray.
PET has a place in tumour staging and detection of recurrences.
Acute GI bleeding
NM imaging with labelled red cells can detect bleeding rates as low as 0.1ml/min and is more sensitive than angiography. Red cell study is most useful in intermittent bleeding.
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