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Perhaps in no other field has there been such an explosion of ultrasound applications as in medicine. Ultrasound has been used in the following applications:

  1. to photograph body organs and bones. Body parts as small as 0.004 in (0.1 mm) may be imaged using ultrasound. Heart examinations may be performed to locate tumors, valve diseases, and accumulation of fluids. Pregnancies may be detected as early as five weeks after conception, and fetal size and development is monitored throughout pregnancy and delivery using ultrasonic imaging.
  2. to measure the rate and direction of blood flow using the principle that the frequency of sound changes as it travels toward an observer, but decreases as it moves away. This phenomenon, known as the Doppler effect, accounts for why the pitch of a train whistle, for example, becomes higher as a train first approaches, then becomes lower as it passes people standing on a station platform. Doctors can determine the direction of blood flow in the body by observing increases or decreases in the frequency of the ultrasonic measurements.
  3. to detect tumors in the body and to distinguish between malignant tumors and healthy tissue. Ultrasound is also employed by oncologists to destroy malignant tumors and inclusions, eliminating the need for surgery. Cancer cells are destroyed using ultrasound to produce microscopic bubbles that collapse and send out intense shock waves (cavitation effect). The same technique is used to destroy gallstones and kidney stones.
  4. to view living cells without damaging them. Ultrasonic microscopes can be used to image cellular structures to within 0.2 microns (two-thousandths of a millimeter). Ultrasonic methods are also used to locate foreign objects in the eye during surgery and in routine eye examinations, and to measure the depth of burns in burn patients. This technique affords an accuracy of 0.05-0.1 in (0.1-0.2 mm).
  5. to relieve muscle strain. Ultrasonic heat has been used to treat arthritis, bursitis, myelitis, neuralgia, malignancy, lumbago, rheumatism, arthritis, sciatica, sinitis, and post-operative pain.
  6. to clean teeth by means of ultrasonic prophylaxis units operating at 25 kHz.

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