|  | Healthcare Industry | Hospitals

Define Contrast Medium in X-Rays

Radiographic contrast media are used to enhance the visualization of anatomic structures within the body that usually provide little subject contrast. Because the tissue composition and density of structures such as the alimentary canal, the genitourinary system, blood vessels, and hepatobiliary system are very similar to surrounding tissues, they can be very difficult to visualize on plain-film radiographs. By introducing radiographic contrast media into hollow structures and vessels, the visual contrast is enhanced, allowing examination of the tissues. Positive contrast media has a higher atomic number than soft tissue and creates white areas on the film. Negative contrast media has a lower atomic number than tissue and creates dark areas on the film.

  1. Barium Sulfate

    • Barium sulfate suspension is a positive contrast media, used only for studies of the gastrointestinal tract. For examination of the oropharynx, esophagus, stomach or small intestines, a flavoring agent is added. Barium sulfate can cause serious complications if it escapes the alimentary canal and enters the peritoneal cavity. It may not be used if an alimentary canal perforation is suspected. Because barium is eliminated through the lower intestine, it cannot be used if the patient has a bowel obstruction.

    Iodine Contrast Agents

    • Iodinated contrast agents are used to image soft tissues in the body, including the gastrointestinal tract when barium is contraindicated. Iodine is used as a positive contrast agent to visualize structures such as blood vessels in angiography; the kidneys, ureters and bladder; the thecal sac in myelograms; and the biliary and pancreatic ducts. The primary contraindication to the use of iodinated contrast is an allergy to iodine. Patients are carefully screened to assess the risk of anaphylaxis, prior to using iodinated contrast for exams.

    Negative Contrast Agents

    • Oxygen, air, carbon dioxide and nitrous oxide are used as negative contrast agents. Because carbon dioxide is readily absorbed in the serum, it poses the lowest threat for embolism (air clot) formation. Negative contrast agents are typically used to examine the stomach, large intestine, the urinary bladder and peritoneal sac.

    Double Contrast Studies

    • To visualize mucosal linings of the alimentary canal, a combination of barium and air is commonly used. A thick suspension of barium is ingested into the stomach or administered via an enema into the large intestine. The cavities are then insufflated with air to inflate the canal. This method offers very good visualization of mucosal abnormalities such as polyps and ulcers.

    Methods of Administering Contrast Media

    • Barium may be administered via swallowing, gastric tube or enema administration. Negative contrast agents are administered via swallowing, gastric tube, or enema into the gastrointestinal tract. They may be injected into the pericardial sac or peritoneum. A catheter may be used to administer negative contrast into the urinary bladder. Iodinated contrast may be injected into structures such as vessels, fistulas, salivary and lacrimal ducts. An atomized form of iodine contrast may be administered via ventilation to study the bronchial tree.

Hospitals - Related Articles