Imaging Studies - Diagnostic Evaluation of Digestive and Gastrointestinal Function

IMAGING STUDIES

Imaging studies include x-ray and contrast studies, computed to-mography (CT) scans, magnetic resonance imaging (MRI), and scintigraphy (radionuclide imaging).

Upper Gastrointestinal Tract Study

X-rays can delineate the entire GI tract after the introduction of a contrast agent. A radiopaque liquid (eg, barium sulfate) is com-monly used. The patient ingests this tasteless, odorless, nongran-ular, and completely insoluble (hence, not absorbable) powder in the form of a thick or thin aqueous suspension for the purpose of studying the upper GI tract (upper GI series or barium swallow). The upper GI series enables the examiner to detect or exclude anatomic or functional derangement of the upper GI organs or sphincters. It also aids in the diagnosis of ulcers, varices, tumors, regional enteritis, and malabsorption syndromes. The procedure may be extended to examine the duodenum and small bowel (small bowel follow-through).

The patient swallows barium under direct fluoroscopic exam-ination. As the barium descends into the stomach, the position, patency, and caliber of the esophagus are visualized, enabling the examiner to detect or exclude any anatomic or functional de-rangement of that organ. Fluoroscopic examination next extends to the stomach as its lumen fills with barium, allowing observa-tion of stomach motility, thickness of the gastric wall, the muco-sal pattern, patency of the pyloric valve, and the anatomy of the duodenum. Multiple x-ray films are obtained during the proce-dure, and additional images may be taken at intervals for up to 24 hours to evaluate the rate of gastric emptying. Small bowel x-rays taken while the barium is passing through that area allow for observation of the motility of the small bowel. Obstructions, ileitis, and diverticula can be detected if present.

Variations of the upper GI study include double-contrast stud-ies and enteroclysis. The double-contrast method of examining the upper GI tract involves administration of a thick barium sus-pension to outline the stomach and esophageal wall, after which tablets that release carbon dioxide in the presence of water are given. This technique has the advantage of showing the esophagus and stomach in finer detail, permitting signs of early superficial neoplasms to be noted.

Enteroclysis is a very detailed, double-contrast study of the en-tire small intestine that involves the continuous infusion, through a duodenal tube, of 500 to 1000 mL of a thin barium sulfate sus-pension. Methylcellulose is then infused into the small intestine through the tube. The barium and methylcellulose fill the in-testinal loops and are observed continuously by fluoroscopy and viewed at frequent intervals as they progress through the jejunum and the ileum. This process (even with normal motility) can take up to 6 hours. The procedure aids in the diagnosis of partial small-bowel obstructions or diverticula.

NURSING INTERVENTIONS

The patient may need to maintain a low-residue diet for several days before the test. He or she should receive nothing by mouth after midnight before the test. The physician may prescribe a lax-ative to clean out the intestinal tract. Because smoking can stim-ulate gastric motility, the nurse discourages the patient from smoking on the morning before the examination. In addition, the nurse withholds all medications.

Follow-up care is needed after any of the upper GI procedures to ensure that the patient has completely eliminated the ingested barium. Fluids must be increased to facilitate evacuation of stool and barium. The nurse monitors the patient’s stools until they re-turn to their normal color (the barium will look like clay). A lax-ative or enema may be needed.

Lower Gastrointestinal Tract Study

When barium is instilled rectally to visualize the lower GI tract, the procedure is called a barium enema. The purpose of a barium enema is to detect the presence of polyps, tumors, and other le-sions of the large intestine and to demonstrate any abnormal anatomy or malfunction of the bowel.

The radiopaque substance is instilled rectally in the radiology department during fluoroscopy. If the patient has been prepared adequately and the colon has been evacuated completely, the con-tour of the entire colon, including the cecum and appendix (if patent), is clearly visible and the motility of each portion may be observed readily. The procedure usually takes about 15 to 30 min-utes, during which time x-ray images are taken.

Other means for visualizing the colon include double-contrast studies and a water-soluble contrast study. A double-contrast or air-contrast barium enema involves the instillation of a thicker barium solution, followed by the instillation of air. The patient may feel some cramping or discomfort with this process. This test provides a contrast between the air-filled lumen and the barium-coated mucosa, allowing easier detection of smaller lesions.

If active inflammatory disease, fistulas, or perforation of the colon is suspected, a water-soluble iodinated contrast agent (eg, Gastrografin) can be used. The procedure is the same as for a barium enema; however, the patient must be assessed for allergy to iodine or contrast agent. The contrast agent is eliminated readily after the procedure, so there is no need for postprocedure laxatives. Some diarrhea may occur in a few patients until the contrast agent has been totally eliminated.

NURSING INTERVENTIONS

Preparing the patient includes emptying and cleansing the lower bowel. This often necessitates a low-residue diet 1 to 2 days be-fore the test (the preparation required by different radiology de-partments may vary); a clear liquid diet and a laxative the evening before; nothing by mouth after midnight; and cleansing enemas until returns are clear the following morning. The nurse should make sure that barium enemas are scheduled before any upper GI studies. If the patient has active inflammatory disease of the colon, enemas are contraindicated. Barium enema also is contraindi-cated in patients with signs of perforation or obstruction; instead, a water-soluble contrast study may be performed in these situa-tions. Active GI bleeding may prohibit the use of laxatives and enemas.

The nurse administers an enema or laxative after these tests to facilitate barium removal. Increasing fluid intake also will assist in eliminating the barium. As with any barium study, the nurse monitors the patient for complete elimination of the barium.

Computed Tomography

CT provides cross-sectional images of abdominal organs and struc-tures. Multiple x-ray images are taken from many different angles, digitized in the computer, reconstructed, and then viewed on a computer monitor. Indications for abdominal CT scanning are diseases of the liver, spleen, kidney, pancreas, and pelvic organs. CT is a valuable tool for detecting and localizing many inflammatory conditions in the colon, such as appendicitis, diverticulitis, regional enteritis, and ulcerative colitis. Because the adequacy of detail in the test depends on the presence of fat, this diagnostic tool is not useful for very thin, cachectic patients. The procedure is completely painless, but radiation doses are considerable. Because a scanning time of 5 seconds is required, motion artifacts produced by heart-beat and respiration cannot be avoided, resulting in pictures that are less than clear.

New, continuous-motion (helical or spiral), three-dimensional CT scans have been developed that provide very detailed pictures of the GI organs and vasculature (Yamada, 1999). Colonography can be completed in minutes. It involves inserting a thin, straw-like tube into the colon and inflating the bowel with air to gener-ate a computer image of the intestine. There is little discomfort, and sedation is not needed.

NURSING INTERVENTIONS

The patient should not eat or drink for 6 to 8 hours before the test. The practitioner may prescribe an intravenous or oral contrast agent. Therefore, the nurse should question the patient about con-trast dye allergies. If barium studies are to be performed, it is im-portant to schedule them after CT scanning, so as not to interfere with imaging.

Magnetic Resonance Imaging

MRI is used in gastroenterology to supplement ultrasonography and CT scanning. It is a noninvasive technique that uses mag-netic fields and radio waves to produce an image of the area beingstudied. The use of oral contrast agents to enhance the image has increased the application of this technique for the diagnosis of GI diseases. It is useful in evaluating abdominal soft tissues as well as blood vessels, abscesses, fistulas, neoplasms, and other sources of bleeding.

The physiologic artifacts of heartbeat, respiration, and peri-stalsis may create a less-than-clear image. Newer, fast-imaging MRI techniques help to eliminate these physiologic motion arti-facts. MRI is contraindicated for patients with permanent pace-makers, artificial heart valves and defibrillators, implanted insulin pumps, or implanted transcutaneous electrical nerve stimulation devices, because the magnetic field could cause malfunction. MRI is also contraindicated for patients with internal metal devices (eg, aneurysm clips) or intraocular metallic fragments.

NURSING INTERVENTIONS

The patient should not eat or drink for 6 to 8 hours before the test. Before the test, the patient must remove all jewelry and other metals. The patient lies in a machine that constructs an image based on the magnetic field created between the machine and the structures scanned. The entire procedure takes 30 to 90 minutes.

It is important to warn patients that the close-fitting scanners used in many MRI facilities may induce feelings of claustropho-bia and that the machine will make a knocking sound during the procedure. Open MRIs that are less close-fitting eliminate the claustrophobia that many patients experience.

Scintigraphy

Scintigraphy (radionuclide testing) relies on the use of radioactive isotopes (ie, technetium, iodine, and indium) to reveal displaced anatomic structures, changes in organ size, and the presence of neoplasms or other focal lesions, such as cysts or abscesses.

Scintigraphic scanning is also used to measure the uptake of tagged red blood cells and leukocytes. Tagging of red blood cells and leukocytes by injection of a radionuclide is performed to de-fine areas of inflammation, abscess, blood loss, or neoplasm. A sample of blood is removed, mixed with a radioactive substance, and reinjected into the patient. Abnormal concentrations of blood cells are then detected at 24- and 48-hour intervals.

Gastrointestinal Motility Studies

Radionuclide testing also is used to assess gastric emptying and colonic transit time. For gastric emptying studies, the liquid and solid components of a meal are tagged with radionuclide mark-ers. After the patient ingests the meal, the patient is positioned under a scintiscanner, which measures the rate of passage of the radioactive substance out of the stomach. This is useful in diag-nosing disorders of gastric motility. Radionuclide evaluation of gastric emptying is now preferred over intubation methods be-cause it gives more defined results (Phillips & Wingate, 1998). This procedure is helpful for evaluating any functional cause of gastric emptying, but its most common clinical uses at this time are in the evaluation of diabetic gastroparesis and of the rapid emptying process in the dumping syndrome.

Colonic transit studies are used to evaluate colonic motility in-stances of chronic constipation and obstructive defecation syn-dromes. This is usually an outpatient study. The patient is given a capsule containing 20 radionuclide markers and instructions to follow a regular diet and normal daily activities. Abdominal x-rays are taken every 24 hours until all markers are passed. This process usually takes 4 to 5 days, but in the presence of severe constipa-tion it may take as long as 10 days. People with chronic diarrhea may be evaluated at 8-hour intervals. The amount of time it takes for the radioactive material to move through the colon indicates colonic motility.