Which two broad categories of contrast media are discussed in the material?

• A. Negative and Positive
• B. Radiopaque and Radiolucent
• C. Ionic and Nonionic
• D. Buffered and Non-buffered

Answer: (A)

Contrast media are categorized by how they alter the image appearance. Negative contrast media produce dark, radiolucent areas on X-ray because they have lower radiodensity than surrounding tissues (examples include air and CO2). Positive contrast media produce bright, radiopaque areas because they have higher radiodensity (most commonly iodinated solutions, used to outline vessels and organs). These two broad categories—negative and positive—are what the material uses to classify contrast agents, since they directly determine what you see on the image. Other terms describe specific properties of particular agents (like radiopaque vs radiolucent as imaging appearances, or ionic vs nonionic, buffered vs non-buffered), but the fundamental split discussed is negative versus positive.