In contrast, the ribs appear white because they are bone and do not let the X-rays pass through them as easily to react with the silver on the film, which is washed away during processing. To obtain X-ray images in which an internal organ stands out, a contrast material is introduced into the body. The major drawback to X-ray examinations is that they expose the body to ionizing radiation, which carries certain health risks. Although the amount of radiation exposure from a routine X-ray examination is not enough to be dangerous for most people, there are important exceptions. Even a low dose of X-rays can cause birth defects when a fetus is exposed to them during critical stages of development.
Radiation exposure can also damage the male sperm and female eggs and result in genetic defects.
X-rays and other radiation exposure have a cumulative effect, so receiving frequent examinations over a period of time increases the risk of cancer. Its use is limited by the fact that it delivers a continuous X-ray beam, although at a reduced dose compared to a single conventional radiograph. However, it does have important uses. For example, fluoroscopy aids in the accurate movement of a catheter through the circulatory system during such procedures as cardiac catheterization see chapter 5 and is then used to track the flow of contrast material through the coronary arteries and other vessels or structures of the heart. It is also very important in following oral or rectal contrast agents when studying the gastrointestinal tract.