Which describes positive contrast media?

• A. Gases and vapors
• B. Liquid and powder substances
• C. Water-based liquids
• D. Iodine-based emulsions

Answer: (B)

Positive contrast media are substances that appear bright on radiographs because they are radiopaque, highlighting hollow organs or luminal spaces by increasing local radiodensity. They commonly come as liquids or powders that are prepared as suspensions or solutions for administration, such as barium suspensions or iodine-containing preparations. This broad, physical-form description fits the concept of positive contrast media well, since it covers the common practical forms used to outline structures. In contrast, gases and vapors are negative contrast because they create darker areas on the image, and water-based liquids by themselves aren’t inherently radiopaque unless doped with a contrast agent. While iodine-based emulsions are indeed positive contrast, the general description of positive media as liquid and powder forms best captures the typical materials used in practice.