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Understanding the Image – 1
As X-rays
from the source pass through the body, they lose their energy. The loss of
energy, called attenuation, depends on some tissue characteristics.
As a simple
explanation we may say that some tissues are “transparent” to X-rays, some are
“translucent” (partially transparent) and some are “opaque” to X-rays. A
totally opaque material will absorb all the X-rays, allowing none to pass
through.
A
“transparent” tissue between the source and the film implies that more X-rays
strike the film, affecting more silver halide, leading to a black image, an
“opaque” tissue will block a lot of X-rays, less or no silver is affected and
the image is white. Intermediate degrees of transparency give rise to shades
of gray in the image. Remember that an X-ray image on film is seen as a
negative film!
The actual
shades in the image also depend on the initial energy and the ‘quantity’ of
the X-rays as they emerge from the source.
Key Points :
•X-rays are absorbed, or lose their energy to a variable
extent as they
pass through tissues of the body.
•The X-ray film is exposed to a correspondingly variable degree and shows light and dark areas.