electromagnetic radiation
Meaning of electromagnetic radiation: Energy traveling as waves of electric and magnetic field, from radio at one end of the range to gamma rays at the other.
Definition of electromagnetic radiation
Electromagnetic radiation is energy that travels through space as linked waves of electric and magnetic field, moving at the speed of light. Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays are all the same phenomenon, differing only in wavelength and therefore in energy. The medical importance of any given type follows almost entirely from that energy.
What is the spectrum?
Longer waves carry less energy per packet; shorter waves carry more. The whole range is continuous, and the familiar names simply mark regions along it.
| Type | Energy | Familiar use |
|---|---|---|
| Radio and microwave | Lowest | Broadcasting, phones, MRI signals, heating food |
| Infrared | Low | Heat lamps, thermal cameras |
| Visible light | Low | Sight, endoscopy, lasers |
| Ultraviolet | Moderate to high | Sterilizing surfaces, skin treatments |
| X-ray and gamma | Highest | Imaging and cancer treatment |
Where is the line that matters?
The critical division falls within the ultraviolet band. Above a certain energy, a single packet can knock an electron off an atom it strikes, which makes the atom chemically reactive and can break DNA. That is ionizing radiation, and x-rays and gamma rays belong to it. Below that threshold the packet can only make molecules vibrate, which is felt as heat. Radio waves, microwaves, infrared and visible light are non-ionizing for this reason, no matter how intense they become. Intensity determines how much heating occurs; energy per packet determines whether damage of the other kind is possible at all.
How is it used in medicine?
Almost every imaging method uses some part of the range. Plain films and computed tomography pass x-rays through the body and record what emerges. Magnetic resonance uses radio waves in a strong magnetic field and involves no ionizing exposure. Infrared reads surface temperature, and visible light carries the image in every endoscope. At the treatment end, radiation therapy uses high energy beams deliberately to break DNA in tumor cells. Ultraviolet has a divided reputation: it damages skin cells and drives most skin cancer, and controlled exposure is also used to treat psoriasis and other skin disease.
Does distance change the risk?
Intensity falls steeply as distance from a source increases, roughly with the square of that distance, so stepping twice as far away cuts exposure to about a quarter. This is why staff step behind a screen or out of the room during an exposure while the beam itself is unchanged. Shielding works on a separate principle, since dense materials such as lead absorb the higher energy waves before they reach tissue.
Also known as
Used in a sentence
Magnetic resonance imaging uses electromagnetic radiation in the radio frequency range rather than x-rays.
Good to know
Only the higher energy end of the spectrum can ionize atoms and break DNA, so intensity alone does not make radio waves, microwaves or visible light capable of that kind of damage.