Medical imaging helps doctors see injuries and disease directly, so they don't have to rely on external exams or exploratory surgeries. Several tomography techniques have spread widely. In each case, a patient lies on a bed inside a doughnut-shaped machine. Hardware takes images of numerous two-dimensional slices of the person's body, and a computer assembles them into a three-dimensional picture.

Computed tomography (CT), which creates images with x-rays, is good at showing sharp contrasts in bone and tissue density, indicating broken bones, blood clots and kidney stones. Early machines of the 1970s required five minutes to render a slice 10 millimeters across; today resolution is one millimeter, and a slice takes only one second. If machine cost and speed improve only a bit further, CT could also take over most standard x-ray procedures, says C. Carl Jaffe, professor of internal medicine at Yale University.

This article was originally published with the title Seeing Inside.

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