Introduction to Gastrointestinal ImagingIn recent years, new techniques such as ultrasonography, computerized tomography (CT), and MR imaging have been used widely and have altered the use of plain films of the abdomen in the evaluation of abdominal diseases. Plain films of the abdomen are still used primarily to assess calcifications and intestinal perforation or obstruction. The plain radiograph is commonly used as a preliminary radiograph before other studies such as CT and barium enema. Plain abdominal radiography is routinely employed before intravenous urography (IVU) because stones in the urinary tract can be obscured by iodinated contrast material but may be shown on plain abdominal radiographs.

The abdomen is composed primarily of soft tissue. The density of soft tissue is similar to the density of water, and the difference in density between solid and liquid is not distinguishable on a plain radiograph. The liver is a homogeneous structure located in the right upper quadrant; the hepatic angle delineates the lower margin of the posterior portion of the liver. In the left upper quadrant a similar angular structure, the splenic angle, can be identified by the fat shadow around the spleen.The study has usually been performed to look at the bowel, in particular the bowel gas pattern. Unless there is an obvious abnormality elsewhere that immediately catches your eye, you should first assess the bowel; gaseous distension, constipation, absence of gas, dilatation, and abnormal wall are all important.

Infants and children typically swallow such things as coins, button batteries, and small toys. Conversely, adults usually have problems with food impactions and bones. Some foreign bodies, including ingested foreign bodies, bullets, or surgical clips, may be seen in the abdomen.

Intra-abdominal free gas. This should be excluded in all films in spite of whatever clinical details you have. A large amount of gas seen in the peritoneal cavity indicates postoperative status or bowel perforation. Air bubbles in the peritoneal cavity indicate a perforated viscus, abscess, or necrotic tumor. As little as 1 to 2 mL of free air in the peritoneal space may be identified if the films are appropriately obtained.

Ileus is a disruption of the normal propulsive ability of the gastrointestinal tract. Although ileus originally referred to any lack of digestive propulsion, including bowel obstruction, up-to-date medical usage restricts its meaning to those disruptions caused by the failure of peristalsis, rather than by mechanical obstruction. Intestinal obstruction, is a mechanical or functional obstruction of the intestines which prevents the normal movement of the products of digestion. Either the small bowel or large bowel may be affected. Causes of bowel obstruction include adhesions, hernias, volvulus, endometriosis, inflammatory bowel disease, appendicitis, tumors, diverticulitis, ischemic bowel, tuberculosis, and intussusception. Small bowel obstructions are most often due to adhesions and hernias while large bowel obstructions are most often due to tumors and volvulus.

The diagnosis may be made on plain X-rays; however, CT scan is more accurate. Ultrasound or MRI may help in the diagnosis of children or pregnant women.

Solid organs. Are they enlarged or atrophic? Is there any associated calcification? Are they outlined by gas? Is there any gas within the structure (biliary or portal venous in the liver, gas within the bladder)? Calcifications in the abdomen include calcified arteries, calculi in the urinary or biliary tract, prostatic calculi, pancreatic calcifications (which are usually indicative of chronic pancreatitis, with or without carcinoma), appendicolith, or ectopic gallstone in the small bowel associated with mechanical obstruction from gallstone ileus.

Bone and joint degenerative disease is common, and bony destruction from tumour, scoliosis may be a pointer to the reason the film was shown. Bony structures or calcifications have the highest density (radiopacity) that is seen on plain films. Bony structures comprise the ribs superiorly, the lumbar spine, and the pelvis.

Take your time to look at all of the opacified lumen. Always check the background chest or abdomen, as well as the bones.Look at the lung bases and hernial orifices.Take your time to look at all of the opacified lumen. Always check the background chest or abdomen, as well as the bones.

Luminal contrast examinations of the gastrointestinal tract can be performed with a variety of contrast materials. Barium sulfate suspensions are the preferred material for most examinations. A variety of barium sulfate suspensions 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 materials used less often and primarily to demonstrate perforation of a hollow viscus or to evaluate the status of a surgical anastomosis in the gastrointestinal tract. Barium studies remain a staple of the examination, despite the fact that fewer such examinations take place in routine clinical practice.

The organs that can be examined in the upper gastrointestinal tract include the esophagus, stomach, and duodenum. The esophagus may be evaluated separately or as part of more complete examinations of the upper gastrointestinal tract. The esophagus, stomach, and duodenum are usually examined together as part of the upper gastrointestinal series. A variety of radiographic techniques are used and usually combined to optimize the upper gastrointestinal examination. Techniques include observation of esophageal motility, which may also be recorded on videotape; filming of the organs with varying amounts of barium suspension, gas, or air; and obtaining views of the mucosal surfaces. An upper gastrointestinal examination may be done with a moderately dense barium suspension using the natural amount of air present in the upper gastrointestinal tract; this is usually called a single-contrast upper gastrointestinal series. Another method involves the use of a high-density barium suspension plus gas-producing crystals and is called a double-contrast upper gastrointestinal series.

The esophagus consists mainly of a tubular portion with a bell-shaped termination called the esophageal vestibule. The esophagogastric junction normally lies within or below the esophageal hiatus. When the esophagogastric junction lies above the hiatus, hiatal hernia is present, which is the most common structural abnormality found on the upper gastrointestinal examination. The esophageal mucosal surface has a smooth appearance when distended and shows smooth, thin longitudinal folds when the organ is collapsed. Esophageal peristalsis can be observed by having the patient swallow single volumes of barium suspension.

Double-contrast and mucosal relief films of the esophagus. Multiple radiographic techniques are combined to evaluate the esophagus to optimize the efficacy of the examination.

The stomach has a complex shape that varies considerably depending on the degree of distention. When the stomach is collapsed, the rugal folds are seen prominently and may mimic focal or diffuse gastric disorders. With gastric distention, the rugal folds are flattened and the mucosal surface of the stomach is seen more effectively. A fine reticulated mucosal pattern of the stomach called the areae gastricae may be appreciated, especially when high-density barium suspensions are used. Barium studies of the upper gastrointestinal tract evaluate gastric function poorly; radionuclide gastric emptying studies are more effective for this purpose.

The radiographic examination of the small bowel evaluates the mesenteric portion of the organ, which consists of the jejunum and ileum. The following three methods can be used to examine the small intestine: peroralsmall bowel series, enteroclysis, and various retrograde techniques. The peroral small-bowel series is most commonly used and is often done immediately following an upper gastrointestinal series. The patient ingests 16 to 24 ounces of an appropriate barium suspension and serial films of the abdomen are obtained in a timely order. In addition, smaller films with pressure on the abdomen (i.e., compression) are used to separate and visualize all of the loops of the small bowel; the entire small bowel, including the terminal ileum, is filmed in this fashion. Depending on the degree of distention, the mucosal folds (valvulae conniventes) may have a feathery appearance or may be transversely oriented across the intestinal lumen with more complete distention. The mucosal folds are more numerous in the jejunum and gradually decrease in number and size in the ileum.

Enteroclysis is an intubated examination of the small intestine and can be done by several techniques. The small intestine is intubated by a nasal or oral route with a small-bore enteric tube, which is directed with fluoroscopic guidance into the distal duodenum or proximal jejunum . In the single-contrast method, a dilute barium suspension is used and allowed to flow into the small bowel by gravity. Other techniques include the use of a dense and more viscous barium suspension along with water, air, or a methylcellulose solution to produce a double-contrast effect. Compared to the peroral small-bowel examination, the enteroclysis techniques permit better control of small-bowel distention and more exact visualization of small-bowel loops. Retrograde examination of the small bowel involves filling of the organ from the opposite direction. A variety of techniques are used depending on the patient's anatomy. Reflux of the small intestine through the ileocecal valve can be done as part of a barium enema. If the patient has an ileostomy, various devices can be introduced into the ostomy site and a barium suspension instilled directly.

The large intestine consists of the rectum, sigmoid colon, descending colon, splenic flexure, transverse colon, hepatic flexure, ascending colon, and cecum. The length of the colon varies considerably among adults depending mainly on the length and redundancy of the sigmoid colon and the colic flexures. The colon varies in caliber depending on the location and degree of luminal distention. The mucosal surface has a smooth appearance and the colonic contour is indented by the haustra, which are less numerous in the descending portion of the colon.

The radiographic examination of the large bowel evaluates the entire organ from the rectum to the cecum. Reflux of barium suspension into the ileum and the appendix, if present, occurs commonly. As with the upper gastrointestinal examinations, the colon can be evaluated by the following techniques: single-contrast barium enema or doublecontrast barium enema. Both examinations require insertion of a rectal tip for installation of the examining materials. The single-contrast barium enema is performed using a lowdensity barium suspension that flows into the colon through the rectal tip.

The double-contrast barium enema is performed with a special rectal tip that allows installation and removal of a dense, viscous barium suspension and also installation of air. The double-contrast effect is produced by the combined use of the barium suspension and the air. As with the single-contrast method, all segments of the colon are examined with the patient in various positions, and both large and small films are obtained.

Endoscopy is now usually used in preference to the barium meal for the investigation of upper gastrointestinal symptoms as it is more sensitive for detecting mucosa) lesions and biopsies can be taken. In particular the barium meal is poor at detecting active ulceration when the mucosa is deformed from previous ulceration or gastric surgery. The barium meal is reserved for patients who are unable to tolerate endoscopy, when endoscopy is incomplete or confusing, or when morphological changes that are easier to appreciate with a barium meal are suspected, such as a modest lower oesophageal stricture or linitis plastica. 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. Also, endoscopy does not assess functional abnormalities of these organs. The major advantage of endoscopy compared to barium examination of the upper gastrointestinal tract is a better demonstration of milder inflammatory processes, such as small peptic ulcers and erosions. Endoscopy of the mesenteric portions of the small intestine has become possible in recent years. A variety of enteroscopes are available to examine the jejunum and ileum; however, complete endoscopic visualization of the entire mesenteric small intestine remains difficult. Enteroscopy can be used to evaluate patients with diffuse small-bowel disease, especially if biopsy is needed, and those with unexplained gastrointestinal bleeding.

Colonoscopy is both a diagnostic and therapeutic modality. Inflammatory and neoplastic diseases of the colon are evaluated accurately. Biopsies can be obtained when needed.Using various techniques, the majority of colonic polyps can be removed through the colonoscope. When compared to the barium enema, colonoscopy is associated with more complications, including colonic perforation, and a higher cost and mortality.

CT imaging of the chest and abdomen can portray the various 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 detected with CT imaging. 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 staging, especially of distant metastases, and for evaluation of recurrence following surgery. Recurrent masses appearing after surgery may also be biopsied percutaneously.

Abdominal ultrasound has had an increasing impact on evaluation of the hollow organs of the gastrointestinal tract, although their location and gas interfering with transmission of sound remain technical problems. An ultrasound can be used to assess for inflammatory disorders, such as acute appendicitis. Endoluminal ultrasound using blind probes or those attached to an endoscope have been used in the upper gastrointestinal tract and the colorectum to stage malignancy.

Endoscopic ultrasound (EUS) is useful for local tumour staging and for determining the precise location tumor within the stomach wall.

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 being used to evaluate and stage malignancies, especially of the esophagus and rectum, and also to assess inflammatory and obstructive bowel disease.