X-rays

X-rays are a form of electromagnetic radiation, which is visible light. The difference is that X-rays have a much shorter wavelength than visible light and each X-ray particle, or photon, has much more energy than a photon partical of visible light. Its short wavelength permits an X-ray to penetrate the body and produce an image on film. Its high energy causes electrons to be dislodged from atoms and molecules when X-rays strike them. This results in ion formation and causes tissue damage and, potentially, cancer. Therefore X-rays are known as ionizing radiation.

When X-rays pass through the body, tissues of different degrees absorb them. Bones are absorbing the most and the air in the lungs and the intestines are absorbing the least. If a bone is in the path of the beam, few X-rays are striking the film, so it looks white. Convers, many X-rays strike the film when air is in the path of the beam, so that it looks black. Regular X-rays produce good pictures of bones and the lungs (chest X-ray), but in order to do some types of  X-ray exams and to use artificial contrast media, you need a special preparation (go to "Preparation for exams").