Physics of Diagnostic X-rays

Learning Objectives

On completion of this lesson, you will be able to learn-
♦ x-rays
♦ properties of X-rays
♦ uses of X-rays
♦ bad effects of X-rays.

Historical Background of X-rays

In 1895, W.K. Rontgen a physicist at the University of Wurzburg in
Germany was studied cathode rays in his laboratory. He was using a fairly
high voltage across a tube covered with black paper that had been
evacuated to a low pressure. When he excited the tube with high voltage,
he noticed that some crystals on a nearby bench glowed and that the ray/
radiation’s causing this fluorescence could pass through solid matter. He
called this radiation X-rays. Rontgen showed that X-rays could expose
film and produce image of objects opaque containers. Such pictures are
possible if the container transmits X-rays more rapidly than the objects
inside. A film exposed by the X-rays shows the shadow cast by the
objects. Within three weeks of Rontgen’s announcement two French
physicians Oudin and Barthelemy obtained X-rays of bones in a hand.
Since then, X-rays become one of the host important tools in medicine.

What is X-ray?

X-ray consists of high-energy photons. Electromagnetic radiation with
wavelengths from about 0.01 to about 10nm falls into the category of Xrays.
X-rays are nothing but electromagnetic waves of very short wave
lengths. X-rays are produced when fast moving electron or a beam of
cathode rays impinge on matter.

Properties of X-rays

1. X-rays are transverse electromagnetic radiation like visible light but of much shorter wavelengths
2. X-rays are uncharged particles since electric or magnetic field does not
deflect them.
3. They produce a photo - chemical action and affect a photographic
4. They cause fluorescence in many substance e.g. Barium, Cadmium
5. They can ionize a gas, through which they pass and also eject electrons
from certain metals on which they fall.
6. They have a destructive effect on living tissue.

There are two types of X-rays -

♦ Lower energy or soft X-rays
♦ Higher energy or hard X-rays.

Uses of X-rays

The uses of X-rays in the diagnostic of various medical problems are so
♦ In surgery, X-rays are used for discovering broken bones and detecting
the presence of foreign bodies, fractures diseased organs etc. inside the
human body.
♦ In therapy, X-rays are used for the detection of cancer, ulcer and other diseases
♦ In industry, X-rays are used in finding out internal cracks or holes in
metal sheets.
♦ X-rays have been employed to investigate the structure of crystal
structure and properties of atoms and arrangement of atoms and
molecules in matter.
♦ X-rays are used for ionizing gas.
♦ X-rays always damage living tissues. Cancer cells are more readily
damaged and killed than are normal cells, so that X-rays can be used to
cure cancer.

Bad Effects of X-rays

X-rays can produce biological effects. The most observed effects are the
reddening of the skin after prolonged exposure. A continuation of
exposure produces ulceration of even complete destruction of the tissues.
Another squeal of excessive irradiation is the induction of cancers of the
skin or of the blood (Leukemia), both of which caused the deaths of many
pioneers in the radiological field.

Diagnostic user of X-rays

Perhaps the most widely used of X-rays effects is that on photographic
material. Photographic film exposed to X-rays and then developed, will be
found to be blackened. Bone can absorb X-rays better than tissues. To
make use of photographic effect into different parts of the body,
radiologists often inject contrast media.

Compounds containing iodine are often injected into the blood stream to
show the arteries and an oily mist containing iodine is sometimes sprayed
into the lungs to make the airways visible radiologists give barium
compounds orally to see parts of the upper gastrointestinal tract and
barium enemas to view the other end of the digestive system.

With current techniques it is even possible to view internal body organs
that are quite transparent to X-rays. Injecting into the organ a fluid opaque
to X-rays does this. The wall of the organ then shows up clearly by

Since gases are poorer absorbers of X-rays than liquid and solids, its is
possible to use air as a contrast medium. When a phemoencephalogram
Photograph is taken air is used to replace some of the fluid in the
ventricles of the brain. In a double contrast study barium and air are used
separately to show the same organ.


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