What are X-rays and how do they work? X-rays are a form of electromagnetic radiation, but they have a higher energy than light waves and can pass through the body. The amount of the X-ray energy that passes through the body depends on the density of the bones or bodily tissues. The more dense the body part, the more the X-ray is absorbed



(and therefore less passes through). Using X-ray sensitive photographic film, you can see pictures of the body. The X-rays turn the film black, so the more X-rays are absorbed, the whiter the area will appear on the film. Bones, for instance, will appear very white, whereas the lungs, which are much less dense, appear much blacker.

Like regular photos, motion can cause the image to be blurred. You will need to be still while taking X-rays. For chest X-rays, you will need to hold your breath.

What are X-rays used for? In general, there are three types of diagnostic uses for X-rays: (1) Normal X-ray tests; (2) Computed Tomography (CT) scanning; and (3) Fluoroscopy. In addition, X-rays may be used medically for therapeutic reasons, as a treatment for cancer.

  • Normal X-ray tests: In this method, a single snapshot is taken. This is ideal for finding a major physical change like a broken bone, but is not good for examining many internal organs, such as the brain, heart, or liver.
  • CT scanning: This method uses a computer to take more precise pictures, including 3-D imaging. Rather than one composite image, the CT comprises multiple “slices” to give more detail than normal X-ray tests.
  • Fluoroscopy: Using X-rays, often with a contrast material to enhance the imaging, this test records the images like a movie on a TV screen. This technique is commonly used for examining for coronary artery (heart) disease, i.e. cardiac catheterization.

What are the risks of X-rays? Most of the radiation we encounter comes from elsewhere in the universe, such as the sun (so-called cosmic or background radiation). Published data reveal that the radiation from medical tests accounts for 14% of the yearly total radiation exposure. Although the amount of radiation absorbed is small, there is a slightly increased risk of cancer from medical X-rays. This risk is cumulative, however, so that the more X-rays one has, the higher the risk. The amount of radiation we absorb depends upon the type of X-ray test and the body part. Fluoroscopy and CT involve higher levels of radiation dose.

In the US, the radiation from medical X-rays has been estimated to increase a person’s lifetime risk of getting cancer by 0.9%. To put this in perspective, a 4-hour long airplane flight will expose a person to about the same amount of radiation as from a simple chest X-ray, or the same amount from “background” radiation that we are exposed to everyday over 10 days.

Getting a simple chest X-ray, X-ray of a broken arm, or dental X-ray adds less than 1 in a million to your lifetime risk of cancer (equal to a few days to a few weeks of background radiation). A mammogram adds between 1 in 100,000 and 1 in 10,000 (or a few months to a year of background radiation). A chest or abdominal CT, fluoroscopy, or barium enema X-ray adds between 1 in 10,000 and 1 in 1,000 to your lifetime risk (equivalent to a few years of background radiation). These risks are all very small additions to the 1 in 3 to 1 in 2 risk of developing cancer during our lifetime (National Cancer Institute. SEER Cancer Statistics Review 1975-2006).

How does an X-ray cause cancer? Simply put, when the X-ray energy is absorbed by the body, it causes electrons to leave the cell’s atoms, leaving behind “free radicals” that cause damage to DNA. Usually damaged cells repair themselves perfectly, or die, but in very rare occasions, the repair has mistakes, leading to cancerous growth.

What are the benefits of X-rays? All three forms of medical X-rays have benefit for diagnosis and treatment. For example, the benefit of diagnosing and mending a broken leg far outweigh the few extra days worth of radiation. Detecting and treating a cancer earlier hopefully provides for more cures than the radiation from the X-ray causes.

How do I minimize the risks?

  • Avoid unnecessary X-ray procedures.
  • If you are pregnant, or could be pregnant, tell your doctor because X-rays pose higher risks to unborn babies.
  • If you need an X-ray, tell your doctor if you have had a recent similar X-ray.
  • If you have had any of the higher dose X-rays (such as a CT scan or barium meal or enema), discuss this with your doctor.

Where can I learn more?

American College of Radiology
National Institutes of Health
X-ray risk calculator