X-ray tests are commonly done to show up bones and certain other tissues.
What are x-rays?
X-rays are a type of high
energy radiation. An x-ray machine can produce short bursts of x-rays.
The rays pass easily through fluids and soft tissues of the body.
However, dense tissue such as bone will block some of the x-rays. The
more dense the tissue, the less x-rays pass through.
How is an x-ray test done?
A film, similar
to a photographic film, is placed behind the part of the body being
x-rayed. The x-ray machine fires a short burst of x-rays through part
of your body. The x-rays hit the film which is then developed. The more
x-rays that hit the film, the blacker it develops. So, dense parts of
the body that block many of the x-rays show up white (such as bones).
Hollow or air filled parts of the body show up black (such as parts of
the lung). Soft tissues such as muscle and body organs show up as
various shades of grey, depending on how dense they are.
The developed film is studied by an x-ray doctor (radiologist) who sends a report to the doctor who requested the test.
An
ordinary x-ray test is painless. You cannot see or feel x-rays. You
should stay still when the x-ray beam is 'fired' as otherwise the
picture may be blurred.
What can ordinary x-rays show?
- Bones, teeth, bone fractures, and other abnormalities of bone.
- Joint spaces and some abnormalities of joints such as osteoarthritis.
- The size and shape of the heart. So, certain heart conditions can be detected.
- Changes in the density of some softer tissues. For example, a lung
tumour is more dense than air-filled lung and will show as a 'shadow'
on a chest x-ray. A breast tumour is more dense than ordinary breast
tissue and shows as a 'shadow' on an x-ray of the breast.
- Collections of fluid - for example in the lung or gut - may show as
grey 'shadows' against the normal black of the air filled chest, or
hollow gut.
- Some other abnormalities in the body.
An ordinary x-ray is a quick, easy and cheap test. It may be
all that is needed to diagnose or assess various problems. However, an
ordinary x-ray has limited use. More sophisticated 'contrast' x-rays,
CT scans, or other imaging techniques may be needed for accurate or
further assessment of certain body parts, particularly of soft tissues
and organs such as the brain or liver.
Are there any risks from x-rays?
There is
very little risk with having one x-ray test. However, with repeated
tests there is a risk that the x-rays may damage some cells in the
body, possibly leading to cancer in the future. The dose of x-ray
radiation is always kept to the minimum needed to get a good picture of
the particular body part being checked. (Also, radiographers who take
the x-ray pictures always wear lead aprons or go behind a protective
screen when the x-rays are fired to avoid repeated exposure to x-rays.)
Pregnant women,
if possible, should not have an x-ray test as there is a small risk
that x-rays may cause an abnormality to the unborn child. This is why
women are asked before having an x-ray if they are, or might be,
pregnant.
© EMIS and PiP 2008 Updated: 19 Feb 2008
