Gastrointestinal Tract: Examination Techniques

Luminal Contrast Studies

Luminal contrast examinations of the gastrointestinal tract can be performed with a variety of contrast materials. Barium sul-fate suspensions are the preferred material for most examina-tions. A variety of barium products are available commercially, and many are formulated for specific examinations depending on their density and viscosity. Water-soluble contrast agents, which contain organically bound iodine, are used less often, primarily to demonstrate perforation of a hollow viscus or to evaluate the status of a surgical anastomosis in the gastrointesti-nal tract. The details and various options available for luminal contrast examination depend on the organ(s) being evaluated and are further elaborated in the normal imaging section.

Computed Tomographic Imaging

CT imaging of the chest and abdomen can portray the var-ious hollow organs of the gastrointestinal tract. Mucosal disease, such as ulcers, and small neoplasms will not be shown with this imaging modality. Larger gastrointestinal neoplasms, thickening of the walls of the hollow organs, and extrinsic processes can be easily detected. Also, with the use of luminal distention and intravenous contrast material, a vari-ety of gastrointestinal disorders are more readily evaluated.

A major role of CT scanning, especially in the esophagus and colon, is staging malignancy of these organs. In the colon, for example, CT examination is used for initial stag-ing, especially for distant metastases, and for evaluation of re-currence following surgery. Recurrent masses appearing after surgery may also be biopsied percutaneously. CT colonogra-phy (CTC) is yet another expanding application for colon cancer screening and detection of polyps and malignancies of the large bowel.

Magnetic Resonance Imaging

Magnetic resonance (MR) imaging is the newest modality developed for cross-sectional imaging of the body and nearly all organ systems can be evaluated with this technique. MR imaging of the hollow organs of the gastrointestinal tract is increasingly being used to evaluate a wide assortment of gas-trointestinal tract disorders. As with CT imaging, mild mu-cosal diseases and small focal lesions are not well detected with this technique; however, malignancies can be similarly evaluated and staged.

Also, with the use of luminal distention and intravenous agents of various types, assessment of obstructive and inflam-matory bowel disease has shown dramatic results. Small-bowel obstruction and Crohn disease in particular have become common indications for use of MR imaging. With the newer technologies, both CT and MR imaging offer multiple options for viewing the gastrointestinal tract, including multiplanar viewing and 2-D and 3-D reconstructions. Dynamic MR im-aging has also emerged with application in several areas, such as assessment of pelvic floor dysfunction in women.

Endoscopy

Upper gastrointestinal endoscopy visualizes the mucosal surfaces of the esophagus, stomach, and duodenum. The pharynx and often the distal portion of the duodenum are not evaluated with this technique. Also, endoscopy does not assess functional abnormalities of these organs, such as pharyngeal dysfunction and esophageal motility disor-ders. The major advantages of endoscopy compared to barium examination of the upper gastrointestinal tract are a better demonstration of milder inflammatory processes, such as erosions and small peptic ulcers, and its therapeu-tic potential.

Endoscopy of the mesenteric portions of the small in-testine has shown dramatic advancements in recent years. A variety of endoscopic methods are now available to ex-amine much if not all of the jejunum and ileum; these in-clude push enteroscopy and double-balloon enteroscopy, both of which offer therapeutic options. Capsule endo-scopy, in which the patient ingests a pill-sized device con-taining a photo detector and radio transmitter, takes two images per second, which are transmitted to an external detector and viewed on a computer; this new technology has been shown to be superior to barium small-bowel ex-amination in detecting early Crohn disease, small erosions and polyps, and vascular lesions, such as arteriovenous malformations (AVMs).

Colonoscopy is both a diagnostic and therapeutic modal-ity. Inflammatory and neoplastic diseases of the colon are evaluated accurately. Biopsies can be obtained when needed, and the majority of colonic polyps can be removed through the colonoscope. Despite a steep decline in the use of the bar-ium enema, colonoscopy requires conscious sedation, is more costly, and is associated with more complications, in-cluding a small mortality rate. CTC is considered a safer al-ternative to colonoscopy, but is not as effective in detecting smaller polyps and offers no therapeutic choices.

Abdominal Ultrasound

Abdominal ultrasound has had an increasing impact on evaluation of the hollow organs of the gastrointestinal tract, although in the United States, this modality is used mainly to examine the solid organs of the abdomen and the biliary tract, including the gallbladder. The location of the hollow organs and the presence of gas interference remain technical problems; however, inflammatory disorders can be evaluated, such as acute appendicitis, especially in pedi-atric patients. Endoluminal ultrasound using blind probes or those attached to an endoscope has been used in the upper gastrointestinal tract and the colorectum to detect and stage malignancy; other indications include fine-needle aspiration (FNA) of pancreatic masses through the gastro-duodenal wall.