Then, in a heart-stopping moment, he chanced to
pass his hand through the beam. As he looked at the
screen, the flesh of the hand seemingly melted away,
projecting only the outlines of the bones. The hand was
intact, unharmed. But on the screen, only the bones
showed up. With that observation, the science of
medical radiology was born.
A few days later, Roentgen made a photographic image
of his wife’s hand, using the new rays instead of light for
the exposure. Again, only the bones showed, this time
on a permanent record which others could see—and believe.
The discovery of a new form of energy that could
penetrate solid objects and record their structure excited
Roentgen’s scientific contemporaries. But it was the
skeletal hand that captured the imagination of the public
and of physicians, who recognized instantly that this
discovery could change medical practice forever.
A century later, the vastly more sophisticated arts of
medical imaging are still based upon the recognition
that body parts absorb a beam of X rays according to their
density, producing an image which allows identification
of body structures as well as the recognition of abnormalities
reflective of injury and disease conditions.
Take a chest X-ray image, for example. The calcium
density of the spine and ribs blocks the most X rays,
leaving white areas on a film. No X rays penetrate to
expose the film and darken those spots. The water
densities of the stomach and liver are grayish. They block
less of the X-ray beam than bones. It’s easy to see the
contrast between them. The fat density of muscles is
less than that of the water. They look only slightly darker,
but the distinction is there for a trained eye. Finally,
the air spaces in the lungs allow penetration of most
of the X-ray beam, and look almost black on the films.
Allow that the chest X-ray image looks complex
because three dimensions are recorded as two. Muscle
tissue overlies the ribs, which in turn overlie the lung
cavities. The shapes of blood vessels (water density) and
the esophagus, which carries food and liquids to the
stomach, can be seen. Fractures of the ribs, abnormal
curves of the spine, unusual heart silhouettes are readily
visible. Irregular shadows, caused by cancers growing in
the lung, may require a sophisticated viewer to pick