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X rays are electromagnetic waves that have a shorter wavelength than light and can penetrate the body to form an image on film or a digital screen. X rays are generated by an electrical current that passes through an X-ray tube and produces a beam of ionizing radiation that can pass through the body part being examined. This process creates an image of internal body structures called a radiograph. "X ray" is also the term for the image or for an examination with X rays.
Because soft body structures are less dense, a greater amount of radiation passes through them, and more radiation reaches the film (the film is exposed to larger amounts of X rays). Soft body tissues appear dark on X-ray film. Because bones are more dense than soft tissue, they absorb more of the radiation, and a lesser amount passes through them. Bones leave the film only slightly exposed and appear light or white on the X-ray film.
Why It Is Performed
X rays, formerly known as roentgen rays, are performed on different parts of the body for various diagnostic purposes. A chest X ray may be performed to look for evidence of pneumonia, tumors, or fluid or to evaluate the size of the heart. Chest X rays are usually performed before major surgery as part of screening, but they are no longer given as a part of routine checkups.
X rays of the abdomen are usually done to determine the cause of acute abdominal pain. They also may be helpful for locating a swallowed foreign object, an intestinal obstruction, or a perforation in the digestive tract.
A myelogram is an X ray of the spine that uses a contrast medium injected into the spinal fluid to outline the spinal cord. It is usually done to check for damaged disks in people with lower back pain. An arthrogram is an X ray of the inside of a joint (usually the knee or hip) that uses contrast medium injected into the joint to make the image clearer. Arthrograms are usually done to detect a tear in the cartilage or other joint abnormality. In some X-ray procedures, a contrast medium containing iodine is injected into a vein or artery; in other procedures, a contrast medium such as barium is ingested to help outline internal structures.
Mammography uses special X-ray equipment to help detect breast cancer. Dental X rays may be performed to detect cavities and other problems with the teeth and gums.
How X rays are done
X-ray examinations are generally performed in a radiology department of a hospital or in an outpatient clinic. A woman undergoing a mammogram will be told not to use deodorant, body powders, or lotions under the arms or on the chest before the procedure because these products can interfere with the image. If soft internal structures are being examined (such as the intestines or blood vessels), a contrast medium such as barium or an iodine-based compound may be ingested or injected for better definition of these structures.
The person being examined is positioned against a cassette holding the film, or the person may be asked to hold the cassette holding the film against the body part being studied. A lead shield may be placed over other parts of the body to reduce their exposure to the X rays.
The X-ray unit is aligned over the part of the body to be examined. The technician moves away from the area to activate the X-ray unit and to avoid exposing himself or herself to unnecessary radiation. It is important that the person being examined remain as motionless as possible as the X ray is taken to prevent the images from being blurred. After an X-ray examination, a person can resume normal activities. If a contrast medium was used, it is important that the person consume extra fluids to enhance the prompt excretion of the contrast medium.