Radiography involves the use of x-rays; the term “plain x-rays” is sometimes used to distinguish x-rays used alone from x-rays combined with other techniques (eg, CT). For plain x-rays, an x-ray beam is generated and passed through a patient to a piece of film or a radiation detector, producing an image. Different soft tissues attenuate x-ray photons differently, depending on tissue density; the denser the tissue, the whiter (more radiopaque) the image. The range of densities, from most to least dense, is represented by metal (white, or radiopaque), bone cortex (less white), muscle and fluid (gray), fat (darker gray), and air or gas (black, or radiolucent).

Radiography is usually the most readily available imaging method. Typically, it is the first imaging method indicated to evaluate the extremities, chest, and sometimes the spine and abdomen. These areas contain important structures with densities that may differ from those of adjacent tissues. For example, radiography is a first-line test for detecting the following:

• Fractures: White bone is well seen because it is adjacent to gray soft tissues.
• Pneumonia: Inflammatory exudate that fills the lungs is well seen because it contrasts with adjacent air spaces.
• Intestinal obstruction: Dilated, air-filled loops of intestine are well seen amidst the surrounding soft tissue.

Variations

Contrast studies: When the density of adjacent tissues is similar, a radiopaque contrast agent (see Principles of Radiologic Imaging: Radiographic Contrast Agents and Contrast Reactions) is often added to one tissue or structure to differentiate it from its surroundings. Structures typically requiring a contrast agent include blood vessels (for angiography) and the lumina of the GI, biliary, and GU tracts. Gas may be used to distend the lower GI tract and make it visible. Other imaging tests (eg, CT, MRI) have largely replaced contrast studies because their tomographic images provide better anatomic localization of an abnormality.

Fluoroscopy: A continuous x-ray beam is used to produce images of moving structures or objects. Fluoroscopy is most often used with contrast agents (eg, in swallowing studies or coronary artery catheterization) or during medical procedures to guide placement of a lead, catheter, or needle (eg, in electrophysiologic testing or percutaneous coronary interventions).

Disadvantages

Diagnostic accuracy is limited in many situations. Other imaging tests may provide better image detail, be safer or faster, or have other advantages.

Contrast agents such as barium and gastrografin, if used, have disadvantages (see Principles of Radiologic Imaging: Disadvantages), and IV contrast agents have risks (see Principles of Radiologic Imaging: Radiographic Contrast Agents and Contrast Reactions). Fluoroscopy may involve high doses of radiation.

Last full review/revision July 2008 by Jon A. Jacobson, MD

Content last modified February 2012