X rays are electromagnetic radiation that differentially penetrates
structures within the body and creates images of these structures on
photographic film or a fluorescent screen. These images are called
diagnostic x rays.
Diagnostic x rays are useful in detecting abnormalities within the body.
They are a painless, non-invasive way to help diagnose problems such as
broken bones, tumors, dental decay, and the presence of foreign bodies.
X rays are a form of radiation similar to light rays, except that they are
more energetic than light rays and are invisible to the human eye. They
are created when an electric current is passed through a vacuum tube. X
rays were accidentally discovered in 1895 by German physicist Wilhem
Roentgen (1845-1923), who was later awarded the first Nobel Prize in
physics for his discovery. Roentgen was also a photographer and almost
immediately realized that the shadows created when x rays passed through
the body could be permanently recorded on photographic plates. His first
x-ray picture was of his wife's hand. Within a few years, x rays
became a valued diagnostic tool of physicians world-wide.
X rays pass easily through air and soft tissue of the body. When they
encounter more dense material, such as a tumor, bone, or a metal fragment,
they are stopped. Diagnostic x rays are performed by positioning the part
of the body to be examined between a focused beam of x rays and a plate
containing film. This process is painless. The greater the density of the
material that the x rays pass through, the more rays are absorbed. Thus
bone absorbs more x rays than muscle or fat, and tumors may absorb more x
rays than surrounding tissue. The x rays that pass through the body strike
the photographic plate and interact with silver molecules on the surface
of the film.
Once the film plates have been processed, dense material such as bone
shows up as white, while softer tissue shows up as shades of gray, and
airspaces look black. A radiologist, who is a physician trained to
interpret diagnostic x rays, examines the pictures and reports to the
doctor who ordered the tests. Plain film x rays normally take only a few
minutes to perform and can be done in a hospital, radiological center,
clinic, doctor's or dentist's office, or at bedside with a
portable x-ray machine.
Mammograms are fixed plate x rays that are designed to locate tumors
within the breasts. Dental x rays are designed to locate decay within the
tooth. Sometimes a liquid called contrast material (for example, barium)
is used to help outline internal organs such as the intestines. The
contrast material absorbs x rays, helping to make soft tissue more easily
visible on the x-ray films. Contrast material is commonly used in making x
rays of the digestive system. The contrast liquid can be swallowed or
injected, depending on the part of the body being x rayed. This may cause
some minor discomfort.
Fluoroscopy is a special x-ray technique that produces real-time images on
a television monitor. With fluoroscopy, contrast material is injected into
a blood vessel. The physician can then watch the real-time movement of the
contrast material to determine if there are blockages in circulation.
Fluoroscopy is also used to help guide catheters into place in the heart
during cardiac catheterization or to guide an endoscope during endoscopic
or CT scan works on the same principles as fixed plate x rays, only with
a CT scan, an x ray tube rotates around the individual, taking hundreds of
images that are then compiled by a computer to produce a two-dimensional
cross section of the body. Although many images are taken to produce a CT
scan, the total dose of radiation the individual is exposed to is low.
Other common imaging techniques such as
magnetic resonance imaging
(MRI) and ultrasound do not use x rays.
Fixed plate x rays are extremely common diagnostic tests. A trained x-ray
technologist takes the x ray. The individual is first asked to remove
clothing and jewelry and to wear a hospital gown. The x ray technologist
positions the patient appropriately, so that the part of the body to be x
rayed will be between the x-ray beam and the film plate. Usually the
individual either lies on an adjustable table or stands. Parts of the body
that are especially sensitive to damage by x rays (for example, the
reproductive organs, the thyroid) are shielded with a lead apron. Lead is
very dense and effectively protects the body by stopping all x rays.
It is essential to remain motionless during the x ray, since movement
causes the resulting picture to be blurry. Sometimes patients are asked to
hold their breath briefly during the procedure. Children who are not old
enough follow directions or who cannot stay still may need to be
restrained or given medication to sedate them in order to keep them still
enough to obtain useful results. Sometimes parents can stay with children
during an x ray, unless the mother is pregnant, in which case she must
protect the fetus from x-ray exposure.
If a contrast material is to be used, the individual will be given special
instructions to prepare for the procedure and may be asked to remain
afterwards until recovery is complete. (See Preparation and Aftercare
Although unnecessary exposure to radiation should be avoided, the low
levels of radiation one is exposed to during an x ray does not cause harm
with a few exceptions. Pregnant women should not have x rays unless in
emergencies the benefits highly outweigh the risks. Exposure of the fetus
to x rays, especially during early pregnancy can increase the risk of the
child later developing leukemia. Body parts not being x rayed should be
shielded with a lead apron, especially the testes, ovaries, and thyroid.
No special preparation is needed for fixed plate x rays unless contrast
material is used. When x rays are scheduled that involve the use of
contrast material, the physician will give specific instructions for
preparation. For example, in a lower GI series, the individual may have to
fast and use special
to cleanse the bowel before swallowing the contrast material. Parents can
prepare children for x rays be explaining what will happen and that these
tests are short and painless.
—Also called a contrast medium, this is usually a barium or
iodine dye that is injected into the area under investigation. The dye
makes the interior body parts more visible on an x-ray film.
—Packets of energy that develop when an electric current passes
through a vacuum tube.
—A medical instrument that can be passed into an area of the body
(the bladder or intestine, for example) to allow visual examination of
that area. The endoscope usually has a fiberoptic camera that allows a
greatly magnified image to be shown on a television screen viewed by the
operator. Many endoscopes also allow the operator to retrieve a small
sample (biopsy) of the area being examined, to more closely view the
tissue under a microscope.
Low dose exposure to x rays creates minimal cell damage and minimal risk
when x rays are performed in an accredited facility. There is an increased
risk that a developing fetus will develop leukemia during childhood if
exposed to x-ray radiation; pregnant or potentially pregnant women should
avoid x rays. There is also a
slight risk of an allergic reaction to the contrast material or dye used
in certain x rays.
Some parents are concerned about health consequences of their
child's exposure to x-ray radiation. However, doses of radiation
received in most x rays are quite similar to the environmental
(background) radiation one is exposed to simply by living on Earth.
Although unnecessary x rays should be avoided, in most cases, the benefits
greatly outweigh the potentially small increased risk of exposure.
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The Patient's Guide to Medical Tests, 2nd ed. New York: Houghton
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American College of radiology
1891 Preston White Drive, Reston, Virginia 20191-4397. Telephone (800)
Radiological Society of North America.
820 Jorie Boulevard, Oak Brook, Illinois 60523-2251. Telephone: (800)
Cameron, John R. "Understanding X-rays."
eMedicine.com Consumer Health
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Children's Virtual Hospital. "X-Rays."
Children's Hospital of Iowa/University of Iowa.
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