What is radiation?

What do the sun, nuclear reactors, microwave ovens, radio antennas, X-ray machines, and power lines all have in common?

They all produce radiation.

Radiation occurs when energy emitted by one body travels in a straight line through a material or through space.

Ionizing and non-ionizing radiation

Radiation can be either ionizing or non-ionizing.

Non-ionizing radiation is lower energy radiation that comes from the lower part of the electromagnetic spectrum.

[Radiation symbol]
Radiation provides various benefits for healthcare, but it must be used correctly.

It is called non-ionizing because it does not have enough energy to completely remove an electron from an atom or molecule.

Examples of non-ionizing radiation include visible light, infrared light, microwave radiation, radio waves, and longwave, or low frequency, radiation.

Ionizing radiation has enough energy to carry out ionization, which means it can detach electrons from atoms or molecules. Ionizing radiation comes from both subatomic particles and the shorter wavelength portion of the electromagnetic spectrum.

Examples include ultraviolet (UV) radiation, X-rays, and gamma rays from the electromagnetic spectrum and subatomic particles such as alpha particles, beta particles, and neutrons. Subatomic particles are usually emitted as an atom decays and loses protons, neutrons, electrons, or their antiparticles.

In short, the “radiation” that one thinks about with CT scans and X-rays are ionized radiation.

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Is radiation dangerous?

High levels of radiation can be dangerous for people, but low levels of radiation are all around, and do not affect human health.

Some kinds of radiation are more dangerous than others. Ionizing radiation is more hazardous than non-ionizing radiation.

The more ionizing radiation people are exposed to, the more dangerous it is.

How is radiation used in medical imaging?

In healthcare, radiology is used to diagnose diseases using imaging technologies based on radiation. In this section we will look at some of the common techniques.

Projectional radiography provides an image of a body part. Techniques include X-rays, fluoroscopy, computed tomography (CT) scans, ultrasound and magnetic resonance imaging (MRI).


X-ray radiation is directed through a part of the body, which absorbs some of the radiation. Hard tissue such as bone absorbs more radiation than soft tissue such as muscle. The X-rays that are not absorbed pass through the body and expose photographic film on the other side of the body, creating a shadow effect. Different parts of the body will need different X-ray strengths. This type of X-ray is commonly used for the chest, in mammography and by dentists.


Fluoroscopy uses X-rays and a contrast material, usually iodine or barium, to get a moving image of what is happening inside the body. Examples are angiography, for viewing the cardiovascular system, and gastrointestinal fluoroscopy, which enables physicians to see the gastrointestinal tract.

CT scan

A CT scan uses X-rays and computers to show slices of soft and hard tissues. Contrast agents are often used. CT scans give a 3D reconstruction of a part of the body. Uses of CT scans include looking for a bleed in the brain, and checking for appendicitis in the abdomen, among many others.


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