X-ray

An X-ray photograph of a person's lungs.

X-radiation is a kind of electromagnetic radiation.

Physics

• X-rays are waves of X-radiation.
• X-rays have a shorter wavelength, and therefore more energy, than ultraviolet radiation.
• They have a much shorter wavelength than visible light (the light that we can see).
• Radiation with shorter wavelengths (more energy) than the X-ray is called Gamma radiation (γ-rays).
• These are all parts of the electromagnetic spectrum.
• The wavelength of X-rays covers a wide range.
• Most X-rays have a wavelength in the range of 0.01 to 10 nanometres.
• This corresponds with frequencies in the range 30 petahertz to 30 exahertz (3×10¹⁶ Hz to 3×10¹⁹ Hz) and energies in the range 100 eV to 100 keV.

Characteristics

X-rays can go through many solid materials. For this reason, taking photograms with X-rays is used in medicine in order to see bones and other things inside the body. Sometimes the term "X-Ray" means these pictures instead of the radiation that makes them.

Clinical use

• X-ray imaging creates pictures of the body in different shades of black and white.
• This is because different tissues absorb different amounts of radiation.
• Calcium in bones absorbs x-rays the most, so bones look white.
• Fat and other soft tissues absorb less and look gray. Air absorbs the least, so lungs look black.
• The most familiar use of x-rays is checking for fractures (broken bones), but x-rays are also used in other ways.
• For example, chest x-rays can spot pneumonia. Mammograms use x-rays to look for breast cancer.
• When you have an x-ray, you may wear a lead apron to protect certain parts of your body.
• The amount of radiation you get from an x-ray is small.
• For example, a chest x-ray gives out a radiation dose similar to the amount of radiation you're naturally exposed to from the environment over 10 days.

X-ray of bimalleolar fracture

CAT scan

Also known as Chest CT, X Ray Computed Tomography (x ray CT), computed axial tomography scan (CAT scan)

A chest CT scan is a more detailed type of chest x ray that takes many detailed pictures of your lungs and the inside of your chest.

Risks

• There is a slight risk of cancer, particularly in growing children, because the test uses radiation.
• Although the amount of radiation from one test is usually less than the amount of radiation you are naturally exposed to over three years, patients should not receive more radiation based imaging than the number that clinical guidelines recommend.
• Diagnostic X-rays (primarily from CT scans due to the large dose used) increase the risk of developmental problems and cancer in those exposed. X-rays are classified as a carcinogen by both the World Health Organization's International Agency for Research on Cancer and the U.S. government.
• It is estimated that 0.4% of current cancers in the United States are due to computed tomography (CT scans) performed in the past and that this may increase to as high as 1.5–2% with 2007 rates of CT usage.

CT chest in pneumonia with abscesses caverns and effusions

Other forms of imaging

The X-ray images do not show skin and muscle, however, because these tissues are transparent enough for the X-rays to pass through them without being absorbed too much. To detect tumors, other imaging devices are used; such as magnetic resonance imaging.

• A computed tomography scanner combines an X-ray machine and computer to construct a three dimensional (3D) picture.
• This has some ability to see other things besides bone.
• X-rays are made by hitting metal with fast-moving electrons.
• They are photons, tiny packets of energy that can move atoms and change chemicals in the body.
• They are ionizing radiation but the things they do depend on the wavelength of the X-rays (or how much energy they have).
• X-rays with smaller energies ("soft" x-rays) cause the photoelectric effect.
• Mid-level energies cause Compton scattering. High-level energies ("hard" X-rays) cause pair production.
• X-rays used for making pictures of people have low to medium energy. Radiation therapy that treats cancer uses Compton scattering and sometimes Pair production.
• There are small amounts of X-rays in the air.
• Like other energy in the air, X-rays can change living cells.
• Exposing the human body to high doses of X-rays for a long time is dangerous.

Related pages

• X-ray crystallography
• Interventional Radiology

References

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