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X-rays are used in a variety of ways to detect pathological conditions. The most common use of the diagnostic x-ray is dental, to locate cavities (caries) in teeth. Other areas examined include the digestive, nervous, reproductive, and endocrine system and the chest and bones. Some special diagnostic x-ray techniques are

1. Computed Tomography (CT, CAT). This is a revolutionary technique in radio diagnosis. Machines called CT scanners (also called CAT scanners) beam ionizing x-rays through a patient at multiple angles around a specific section of the body. The absorption of x-rays at these angles as they pass through the body is detected and relayed to a computer that is programmed with the knowledge of the absorption capacities of the different body tissues. The computer then synthesizes all the information it receives from the abdomen, chest, or head on a screen. The ability of CT scanners to detect abnormalities is enhanced by the use of iodine- containing contrast agents, which outline blood vessels. The CT scanners are highly sensitive in detecting disease in bony structures and can actually provide images of internal organs that are impossible to visualize to with ordinary x-ray technique. CT scans also involve the use of contrast dyes and can detect brain tumors, hematomas, spinal cord lesions, and masses in the chest, liver, kidney and pancreas.

2. Contrast Studies. In x-ray film, the natural differences in the density of body tissue (e.g. air in the lung calcium in bone) produce contrasting shadow images on the x-ray film. However, when x-rays pass through two adjacent body parts composed of substance of the same density, for example, the digestive organs in the abdomen, their images cannot be distinguished on the film or on the screen. It is necessary, then, to inject a contrast medium into the structure or fluid to be visualized so that the specific part, organ, tube, or liquid can be visualized as a negative imprint on the dense contrast agent.

The following are artificial contrast materials used in diagnostic radiological studies;

¨ Barium sulfate Barium sulfate is a metallic powder that is mixed in water and used for examination of the upper and lower GI (gastrointestinal) tract.

¨ A barium swallow (upper GI series) involves oral ingestion of barium sulfate so that the esophagus, stomach and duodenum can be visualized.

¨ A small bowel series (small bowel follow-through) traces the passage of barium in a sequential manner as it passes through the small intestine.

¨ A barium enema opacifies the lumen (passageway) of the large intestine using an, enema containing barium sulfate.

A double-contrast study uses both a radiopaque and a radiolucent contrast medium. For example, the walls of the stomach or intestine are coated with barium and the lumen is filled with air. The radiographs show the pattern of mucosal ridges.