Pictures By Sound

For millions of years, bats and porpoises have been using ultrasonic echoes to locate their prey. Now physicians and surgeons are learning to use the same technique to hunt for different targets. With pulses of "sound" far too high for human hearing, they are locating tumors that must be cut out, livers that must be treated for cirrhosis, babies' heads that are too big to pass through the mother's pelvic arch, even fast-beating heart-valve leaflets that need to be repaired.

For Pregnant Women. One of the leading U.S. ultrasound diagnosticians, Dr. Joseph H. Holmes, 55, head of the kidney-disease division at the University of Colorado Medical Center in Denver, has been working since 1951 on three basic machines to perform a variety of diagnostic feats. While he grants that ultrasound is still subordinate to X ray in some respects, he is equally convinced that it can do many things that X rays cannot do.

Ultrasound's advantage comes clearest in the case of pregnant women. No one wants to subject them to X rays because of possible harm to mother and foetus. In Denver, Dr. Holmes's colleagues have measured the skull diameter of unborn babies accurately to within one-eighth of an inch in 95 of 100 cases. And there is no evidence that ultrasound, properly used, has any harmful effects even on such sensitive targets as the unborn child, the reproductive system, or the human eye.

Equally important, unlike some of the more complex X-ray methods, ultrasound diagnosis is completely painless and does not require even a local anesthetic. The simpler machines used in many procedures are portable and can be taken to the patient's bedside or to the emergency room. The cost to the hospital is about the same as for X-ray machines, from $3,500 to $15,000, depending on purpose and complexity. Cost to the patient is about the same as for X rays.

Hold That Shot. In the simplest procedures, a pulse generator sends bursts of current to a crystal, which then produces sonic energy at frequencies ranging from one million to as high as 10 million cycles per second. The pulses pass through a transducer, a combined transmitter-receiver the size of a microphone, which may be simply moistened with water and held against a patient's skull. For a pregnant woman, the transducer is held against the abdomen, which is smeared with light oil.

The crystal puts out from 200 to 400 bursts of ultrasound every second. The silent intervals give it time to pick up the echoes, which are then converted into electrical impulses and fed into an oscilloscope. More complex scanners can give the equivalent of a three-dimensional picture. On the oscilloscope screen, the ultrasound echoes make a picture that may look like Lord Cornwallis' breastworks at Yorktown. Additional circuitry can make the oscilloscope hold the picture long enough for the doctor to snap a photograph of it.

How Thick a Liver. What ultrasound registers best is the "interface" where one kind of tissue with a certain amount of resistance meets another with a different resistance. An examining physician can press on a patient's belly to feel how big his liver is, but he cannot get a clear outline of the liver, let alone tell how thick it is. With a simple twist of the dials, the ultrasound scanner will pick up first the near surface of the liver, then the back surface, and measure the distance between them, thus telling the doctor how much the liver is enlarged.

Ultrasound clearly outlines the excess fluid (ascites) in the abdomen of patients with many types of disease. Glasgow's Dr. Ian Donald has perfected his technique to the point where he can distinguish between an abdomen with ascites caused by a benign tumor, and one with ascites caused by cancer.

Brain surgeons are not uniformly enthusiastic about ultrasound and still rely heavily on X rays. But even skeptics concede that, as a first screening procedure, the new technique has the great advantage of simplicity and painlessness. It may spare many patients the heroic procedure of having air injected into the brain cavities (ventriculogra-phy). Some British neurosurgeons report better than 90% accuracy for ultrasound in determining whether a brain tumor or a hemorrhage is present, and if so, where.

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