X-rays are made by using external radiation to produce images of the body, its organs, and other internal structures for diagnostic purposes. X-rays pass through body structures onto specially-treated plates (similar to camera film) or digital media and a "negative" type picture is made (the more solid a structure is, the whiter it appears on the film).

When the body undergoes x-rays, different parts of the body allow varying amounts of the x-ray beams to pass through. The soft tissues in the body (such as blood, skin, fat, and muscle) allow most of the x-ray to pass through and appear dark gray on the film or digital media. A bone or a tumor, which is more dense than the soft tissues, allows few of the x-rays to pass through and appears white on the x-ray. At a break in a bone, the x-ray beam passes through the broken area and appears as a dark line in the white bone.

X-ray technology is used in other types of diagnostic procedures, such as arteriograms, computed tomography (CT) scans, and fluoroscopy.

When medical X-rays are being produced, a thin metallic sheet is placed between the emitter and the target, effectively filtering out the lower energy (soft) X-rays. This is often placed close to the window of the X-ray tube. The resultant X-ray is said to be hard. Soft X-rays overlap the range of extreme ultraviolet. The frequency of hard X-rays is higher than that of soft X-rays, and the wavelength is shorter.

Hard X-rays overlap the range of "long"-wavelength (lower energy) gamma rays, however the distinction between the two terms depends on the source of the radiation, not its wavelength; X-ray photons are generated by energetic electron processes, gamma rays by transitions within atomic nuclei.

Since antigen's discovery that X-rays can identify bony structures, X-rays have been developed for their use in medical imaging. Radiology is a specialized field of medicine. Radiographers employ radiography and other techniques for diagnostic imaging. Indeed, this is probably the most common use of X-ray technology.

X-rays are especially useful in the detection of pathology of the skeletal system, but are also useful for detecting some disease processes in soft tissue. Some notable examples are the very common chest X-ray, which can be used to identify lung diseases such as pneumonia, lung cancer or pulmonary edema, and the abdominal X-ray, which can detect ileus (blockage of the intestine), free air (from visceral perforations) and free fluid (in ascites).

In some cases, the use of X-rays is debatable, such as gallstones (which are rarely radiopaque) or kidney stones (which are often visible, but not always). Also, traditional plain X-rays pose very little use in the imaging of soft tissues such as the brain or muscle. Imaging alternatives for soft tissues are computed axial tomography (CAT or CT scanning), magnetic resonance imaging (MRI) or ultrasound. Since 2005, X-rays are listed as a carcinogen by the U.S. government.

Diagnostic x-rays are safe. But who hasnt wondered about them when undergoing a chest x-ray, mammogram, routine dental x-rays, or an x-ray for a broken bone?

The safety of routine X-rays has been called into question following the unexpected discovery that cells exposed to low doses avoid or delay repairing damaged DNA.

Puzzlingly, cells given higher doses of X-rays were faster and more efficient at patching up any damage. But the German researchers who made the discovery say it is not clear whether the sloppy repairs that follow low level exposure is a good or bad thing.

Kai Rothkamm and Markus Brich, at the University of Saarland in Homburg, acknowledge that unrepaired breaks in DNA could well lead to cells becoming cancerous. But it is equally possible, they say, that the failure to repair low-level DNA damage has evolved as a safety measure.

Other experts state that no scientific data indicate any danger. In fact, there is evidence that low doses may actually reduce the chance of cancer. The question about the amount of radiation you receive is difficult for x-ray technicians and doctors to answer because very few x-ray units have an instrument to measure the radiation to the patient.

You may have heard that even the smallest amount of radiation may cause cancer. Based on this unscientific assumption, the risk of causing a fatal cancer from a chest x-ray is 10 times greater than the risk of dying in a commercial airline flight. Or a CT scan of the kidneys has a greater risk of inducing a fatal cancer than a cigarette smoker has of dying from any cancer. These statements produce unnecessary worry. There is no data to show any risk from diagnostic x-rays.

Lastly, radiation during pregnancy may lead to birth defects. Always tell your radiologist or physician if you suspect you may be pregnant.