Why It's Done
A chest X-ray is used to help find the cause of symptoms such as cough, shortness of breath, or chest pain. It can detect signs of asthma, pneumonia, a collapsed lung, heart problems (such as an enlarged heart), and broken ribs or lung damage after an injury.
Chest X-rays can reveal small metal objects (such as coins) that might have been swallowed. They can also help confirm that medical tubes have been placed in the right locations in the lungs, heart, blood vessels, or stomach.
Preparation
A chest X-ray doesn't require special preparation. Your child may be asked to remove all clothing and jewelry from the waist up and change into a hospital gown because buttons, zippers, clasps, or jewelry might interfere with the image.
Developing babies are more sensitive to radiation and are at more risk for harm, so if your daughter is pregnant, tell her doctor and the X-ray technician.
Procedure
Although the procedure may take 15 minutes or longer from start to finish, the actual exposure time to radiation is usually less than half a second.
Your child will be asked to enter a special room that will most likely contain a table and a large X-ray machine hanging from the ceiling. Parents are usually able to accompany their child to provide reassurance and support.
A chest X-ray may be performed in a standing, sitting, or lying position. This will depend on the condition of your child and the reason for the X-ray. The technician will position your child, then step behind a wall or to an adjoining room to operate the machine.
Older kids will be asked to hold their breath and remain still for 2-3 seconds while the X-ray is taken; infants may require gentle restraint. Keeping the chest still is important to prevent blurring of the X-ray image. Two X-rays are usually taken, one from the back and one from the side.

If your child is in the hospital and cannot easily be brought to the radiology department, a portable X-ray machine can be brought to your child's bedside. Portable X-rays are often used in emergency departments, intensive care units, or operating rooms. In this case, only one X-ray might be taken, usually from the front.