Ultrasonography is a painless and harmless imaging
technique that uses sound waves with a frequency that is too high for
humans to hear. Its development started with the British use of "sonar"
to track German submarines during World War I.
During an ultrasound examination, a transducer that both emits the sound
and detects the returning echoes is placed on the body part being studied.
When the emitted sound encounters a border between two tissues that
conduct sound differently, some of the sound waves bounce back to the
transducer creating an echo. The echoes are analyzed by a computer in
the ultrasound machine and transformed into moving pictures of the anatomy
being examined. Sonography
can produce excellent images of blood flow and calculate its speed in
accessible vessels using the Doppler effect. This is the same principle
used by the policeman's radar to catch you speeding.
Sonography is best at examining the female pelvis, especially during
pregnancy, the heart (echocardiography), blood vessels, the gallbladder
and other upper abdominal organs, the breast, and the bladder. Its advantages
include lack of damaging radiation, relatively low cost, and real-time
(moving picture) display. A disvantage is its inability to get around
bone and gas, anyway this exam needs a high skilled operator.
A disvantage of ultrasonography is...