Ultrasonography is a noninvasive diagnostic technique in which high-frequency sound waves are passed into internal body struc-tures and the ultrasonic echoes are recorded on an oscilloscope as they strike tissues of different densities. During abdominal ultra-sonography, an image of the abdominal organs and structures is produced on the oscilloscope. This procedure is generally used to indicate the size and configuration of abdominal structures. It is particularly useful in the detection of cholelithiasis, cholecystitis, and appendicitis. Most recently this technique has proven useful in diagnosing acute colonic diverticulitis.
Advantages of abdominal ultrasonography are that it requires no ionizing radiation, there are no noticeable side effects, and it is relatively inexpensive. One disadvantage is that it cannot be used to examine structures that lie behind bony tissue, because bone prevents sound waves from passing to deeper structures. Gas and fluid in the abdomen or air in the lungs also prevent trans-mission of ultrasound.
Endoscopic ultrasonography (EUS) is a specialized enteroscopic procedure that aids in the diagnosis of GI disorders by providing direct imaging of a target area. A small high-frequency ultrasonic transducer is mounted at the tip of the fiberoptic scope so that a transintestinal study can be completed. This procedure gives results with better quality resolution and definition than regular ultra-sound imaging. It helps in staging of a tumor, including size, spread, and whether the tumor is operable. It is useful in evaluat-ing transmural changes in the bowel wall that occur in ulcerative colitis. Intestinal gas, bone, and thick layers of adipose tissue (all of which hamper conventional ultrasonography) are not problems when this technique is used.
The patient fasts for 8 to 12 hours before the test to decrease the amount of gas in the bowel. If gallbladder studies are being per-formed, the patient should eat a fat-free meal the evening before the test. If barium studies are to be performed, the nurse should make sure they are scheduled after this test; otherwise, the bar-ium will interfere with the transmission of the sound waves.