The definition of "radiopaque" refers to materials that do not allow X-rays to pass through them, which leads to a high degree of absorbance of the radiation. This characteristic results in these materials appearing white or light on X-ray images, as they effectively block the passage of X-rays.
Barium is a fitting example of a radiopaque material. It is commonly used as a contrast agent in medical imaging, particularly in gastrointestinal studies. When ingested, barium enhances the visibility of certain structures in the body, allowing for clearer imaging of the digestive tract because it absorbs X-rays.
Materials that allow X-rays to pass through, such as air, would not qualify as radiopaque, as they are instead described as radiolucent. Similarly, while lead does block X-rays effectively, it is often specifically categorized as a protective material rather than being classified in clinical imaging contexts like barium is. Lastly, while tungsten absorbs various forms of radiation, it is not commonly used in medical imaging for this purpose, making it a less relevant example in this context.