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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.