ABDOMINAL
ULTRASONOGRAPHY
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.
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