X-rays are basically the same thing as visible light rays. Both are wavelike forms of electromagnetic energy carried by particles called photons. The difference between X-rays and visible light rays is the energy level of the individual photons. This is also expressed as the wavelength of the rays.

Our eyes are sensitive to the particular wavelength of visible light, but not to the shorter wavelength of higher energy X-ray waves or the longer wavelength of the lower energy radio waves.

Visible light photons and X-ray photons are both produced by the movement of electrons in atoms. Electrons occupy different energy levels, or orbitals, around an atom's nucleus. When an electron drops to a lower orbital, it needs to release some energy -- it releases the extra energy in the form of a photon. The energy level of the photon depends on how far the electron dropped between orbitals.

When a photon collides with another atom, the atom may absorb the photon's energy by boosting an electron to a higher level. For this to happen, the energy level of the photon has to match the energy difference between the two electron positions. If not, the photon can't shift electrons between orbitals.

The atoms that make up your body tissue absorb visible light photons very well. The energy level of the photon fits with various energy differences between electron positions. Radio waves don't have enough energy to move electrons between orbitals in larger atoms, so they pass through most stuff. X-ray photons also pass through most things, but for the opposite reason: They have too much energy.

They can, however, knock an electron away from an atom altogether. Some of the energy from the X-ray photon works to separate the electron from the atom, and the rest sends the electron flying through space. A larger atom is more likely to absorb an X-ray photon in this way, because larger atoms have greater energy differences between orbitals -- the energy level more closely matches the energy of the photon. Smaller atoms, where the electron orbitals are separated by relatively low jumps in energy, are less likely to absorb X-ray photons.

The soft tissue in your body is composed of smaller atoms, and so does not absorb X-ray photons particularly well. The calcium atoms that make up your bones are much larger, so they are better at absorbing X-ray photons.

Frequently Asked X-Ray Questions

What is an X-Ray?

An x-ray (radiograph) is a painless medical test that helps physicians diagnose and treat medical conditions.  Radiography involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body.  X-rays are the oldest and most frequently used form of medical imaging.

How does the procedure work?

X-rays are pictures made by passing radiant beams through an object and capturing the image on the other side.  Solid objects, like bones, allow less light to pass through and appear white on the picture.  Less solid objects, like organs in the body, allow more light to pass through and appear more gray on a picture.

How should I prepare for the procedure?

Most x-rays require no special preparation.

What will I experience during and after the x-ray procedure?

You may experience discomfort from the cool temperature in the examination room.  You may also find holding still in a particular position and lying on the hard examination table uncomfortable, especially if you are injured.  The technologist will assist you in finding the most comfortable position possible that still ensures x-ray image quality.

Who interprets the results and how do I get them?

A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will share the results with you.