Define the term "radiopaque".

The term "radiopaque" refers to substances that prevent x-ray passage. These materials are dense and absorb x-rays effectively, resulting in the appearance of these areas as white or light on radiographic images. Radiopaque substances are often used in medical imaging to highlight structures, such as bones or certain tissues, that should be clearly distinguished from surrounding areas.

For example, barium sulfate is a radiopaque contrast agent frequently used in gastrointestinal studies to provide clearer visualization of internal structures. Understanding the properties of radiopaque materials is crucial for interpreting radiological images and making accurate diagnoses.